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GNAT Reference Manual
GNAT, The GNU Ada Compiler
GCC version 4.8.3
AdaCore
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This manual contains useful information in writing programs using the GNAT compiler. It includes information on implementation dependent characteristics of GNAT, including all the information required by Annex M of the Ada language standard.
GNAT implements Ada 95 and Ada 2005, and it may also be invoked in Ada 83 compatibility mode. By default, GNAT assumes Ada 2005, but you can override with a compiler switch to explicitly specify the language version. (Please refer to Compiling Different Versions of Ada in GNAT User’s Guide, for details on these switches.) Throughout this manual, references to “Ada” without a year suffix apply to both the Ada 95 and Ada 2005 versions of the language.
Ada is designed to be highly portable. In general, a program will have the same effect even when compiled by different compilers on different platforms. However, since Ada is designed to be used in a wide variety of applications, it also contains a number of system dependent features to be used in interfacing to the external world.
Note: Any program that makes use of implementation-dependent features may be non-portable. You should follow good programming practice and isolate and clearly document any sections of your program that make use of these features in a non-portable manner.
• What This Reference Manual Contains: | ||
• Conventions: | ||
• Related Information: |
Next: Conventions, Previous: Index, Up: About This Guide [Contents][Index]
This reference manual contains the following chapters:
Specialized Needs Annexes, describes the GNAT implementation of all of the specialized needs annexes.
This reference manual assumes a basic familiarity with the Ada 95 language, as described in the International Standard ANSI/ISO/IEC-8652:1995, January 1995. It does not require knowledge of the new features introduced by Ada 2005, (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1 and Amendment 1). Both reference manuals are included in the GNAT documentation package.
Next: Related Information, Previous: What This Reference Manual Contains, Up: About This Guide [Contents][Index]
Following are examples of the typographical and graphic conventions used in this guide:
Functions
, utility program names
, standard names
,
and classes
.
Option flags
Variables
, environment variables
, and metasyntactic
variables.
and then shown this way.
Commands that are entered by the user are preceded in this manual by the characters ‘$ ’ (dollar sign followed by space). If your system uses this sequence as a prompt, then the commands will appear exactly as you see them in the manual. If your system uses some other prompt, then the command will appear with the ‘$’ replaced by whatever prompt character you are using.
Next: Pragma Abort_Defer, Previous: Conventions, Up: About This Guide [Contents][Index]
See the following documents for further information on GNAT:
Next: Implementation Defined Attributes, Previous: About This Guide, Up: Top [Contents][Index]
Ada defines a set of pragmas that can be used to supply additional information to the compiler. These language defined pragmas are implemented in GNAT and work as described in the Ada Reference Manual.
In addition, Ada allows implementations to define additional pragmas whose meaning is defined by the implementation. GNAT provides a number of these implementation-defined pragmas, which can be used to extend and enhance the functionality of the compiler. This section of the GNAT Reference Manual describes these additional pragmas.
Note that any program using these pragmas might not be portable to other compilers (although GNAT implements this set of pragmas on all platforms). Therefore if portability to other compilers is an important consideration, the use of these pragmas should be minimized.
Next: Pragma Ada_83, Previous: Related Information, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Abort_Defer;
This pragma must appear at the start of the statement sequence of a
handled sequence of statements (right after the begin
). It has
the effect of deferring aborts for the sequence of statements (but not
for the declarations or handlers, if any, associated with this statement
sequence).
Next: Pragma Ada_95, Previous: Pragma Abort_Defer, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ada_83;
A configuration pragma that establishes Ada 83 mode for the unit to
which it applies, regardless of the mode set by the command line
switches. In Ada 83 mode, GNAT attempts to be as compatible with
the syntax and semantics of Ada 83, as defined in the original Ada
83 Reference Manual as possible. In particular, the keywords added by Ada 95
and Ada 2005 are not recognized, optional package bodies are allowed,
and generics may name types with unknown discriminants without using
the (<>)
notation. In addition, some but not all of the additional
restrictions of Ada 83 are enforced.
Ada 83 mode is intended for two purposes. Firstly, it allows existing Ada 83 code to be compiled and adapted to GNAT with less effort. Secondly, it aids in keeping code backwards compatible with Ada 83. However, there is no guarantee that code that is processed correctly by GNAT in Ada 83 mode will in fact compile and execute with an Ada 83 compiler, since GNAT does not enforce all the additional checks required by Ada 83.
Next: Pragma Ada_05, Previous: Pragma Ada_83, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ada_95;
A configuration pragma that establishes Ada 95 mode for the unit to which
it applies, regardless of the mode set by the command line switches.
This mode is set automatically for the Ada
and System
packages and their children, so you need not specify it in these
contexts. This pragma is useful when writing a reusable component that
itself uses Ada 95 features, but which is intended to be usable from
either Ada 83 or Ada 95 programs.
Next: Pragma Ada_2005, Previous: Pragma Ada_95, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ada_05;
A configuration pragma that establishes Ada 2005 mode for the unit to which it applies, regardless of the mode set by the command line switches. This pragma is useful when writing a reusable component that itself uses Ada 2005 features, but which is intended to be usable from either Ada 83 or Ada 95 programs.
Next: Pragma Ada_12, Previous: Pragma Ada_05, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ada_2005;
This configuration pragma is a synonym for pragma Ada_05 and has the same syntax and effect.
Next: Pragma Ada_2012, Previous: Pragma Ada_2005, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ada_12;
A configuration pragma that establishes Ada 2012 mode for the unit to which
it applies, regardless of the mode set by the command line switches.
This mode is set automatically for the Ada
and System
packages and their children, so you need not specify it in these
contexts. This pragma is useful when writing a reusable component that
itself uses Ada 2012 features, but which is intended to be usable from
Ada 83, Ada 95, or Ada 2005 programs.
Next: Pragma Annotate, Previous: Pragma Ada_12, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ada_2012;
This configuration pragma is a synonym for pragma Ada_12 and has the same syntax and effect.
Next: Pragma Assert, Previous: Pragma Ada_2012, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Annotate (IDENTIFIER [,IDENTIFIER {, ARG}]); ARG ::= NAME | EXPRESSION
This pragma is used to annotate programs. identifier identifies
the type of annotation. GNAT verifies that it is an identifier, but does
not otherwise analyze it. The second optional identifier is also left
unanalyzed, and by convention is used to control the action of the tool to
which the annotation is addressed. The remaining arg arguments
can be either string literals or more generally expressions.
String literals are assumed to be either of type
Standard.String
or else Wide_String
or Wide_Wide_String
depending on the character literals they contain.
All other kinds of arguments are analyzed as expressions, and must be
unambiguous.
The analyzed pragma is retained in the tree, but not otherwise processed by any part of the GNAT compiler, except to generate corresponding note lines in the generated ALI file. For the format of these note lines, see the compiler source file lib-writ.ads. This pragma is intended for use by external tools, including ASIS. The use of pragma Annotate does not affect the compilation process in any way. This pragma may be used as a configuration pragma.
Next: Pragma Assertion_Policy, Previous: Pragma Annotate, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Assert ( boolean_EXPRESSION [, string_EXPRESSION]);
The effect of this pragma depends on whether the corresponding command line switch is set to activate assertions. The pragma expands into code equivalent to the following:
if assertions-enabled then if not boolean_EXPRESSION then System.Assertions.Raise_Assert_Failure (string_EXPRESSION); end if; end if;
The string argument, if given, is the message that will be associated with the exception occurrence if the exception is raised. If no second argument is given, the default message is ‘file:nnn’, where file is the name of the source file containing the assert, and nnn is the line number of the assert. A pragma is not a statement, so if a statement sequence contains nothing but a pragma assert, then a null statement is required in addition, as in:
… if J > 3 then pragma Assert (K > 3, "Bad value for K"); null; end if;
Note that, as with the if
statement to which it is equivalent, the
type of the expression is either Standard.Boolean
, or any type derived
from this standard type.
If assertions are disabled (switch -gnata not used), then there is no run-time effect (and in particular, any side effects from the expression will not occur at run time). (The expression is still analyzed at compile time, and may cause types to be frozen if they are mentioned here for the first time).
If assertions are enabled, then the given expression is tested, and if
it is False
then System.Assertions.Raise_Assert_Failure
is called
which results in the raising of Assert_Failure
with the given message.
You should generally avoid side effects in the expression arguments of this pragma, because these side effects will turn on and off with the setting of the assertions mode, resulting in assertions that have an effect on the program. However, the expressions are analyzed for semantic correctness whether or not assertions are enabled, so turning assertions on and off cannot affect the legality of a program.
Note that the implementation defined policy DISABLE
, given in a
pragma Assertion_Policy, can be used to suppress this semantic analysis.
Note: this is a standard language-defined pragma in versions of Ada from 2005 on. In GNAT, it is implemented in all versions of Ada, and the DISABLE policy is an implementation-defined addition.
Next: Pragma Assume_No_Invalid_Values, Previous: Pragma Assert, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Assertion_Policy (CHECK | DISABLE | IGNORE);
This is a standard Ada 2005 pragma that is available as an implementation-defined pragma in earlier versions of Ada.
If the argument is CHECK
, then assertions are enabled.
If the argument is IGNORE
, then assertions are ignored.
This pragma overrides the effect of the -gnata switch on the
command line.
Assertions are of three kinds:
Assert
.
The implementation defined policy DISABLE
is like
IGNORE
except that it completely disables semantic
checking of the argument to pragma Assert
. This may
be useful when the pragma argument references subprograms
in a with’ed package which is replaced by a dummy package
for the final build.
Note: this is a standard language-defined pragma in versions of Ada from 2005 on. In GNAT, it is implemented in all versions of Ada, and the DISABLE policy is an implementation-defined addition.
Next: Pragma Ast_Entry, Previous: Pragma Assertion_Policy, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Assume_No_Invalid_Values (On | Off);
This is a configuration pragma that controls the assumptions made by the compiler about the occurrence of invalid representations (invalid values) in the code.
The default behavior (corresponding to an Off argument for this pragma), is to assume that values may in general be invalid unless the compiler can prove they are valid. Consider the following example:
V1 : Integer range 1 .. 10; V2 : Integer range 11 .. 20; ... for J in V2 .. V1 loop ... end loop;
if V1 and V2 have valid values, then the loop is known at compile
time not to execute since the lower bound must be greater than the
upper bound. However in default mode, no such assumption is made,
and the loop may execute. If Assume_No_Invalid_Values (On)
is given, the compiler will assume that any occurrence of a variable
other than in an explicit 'Valid
test always has a valid
value, and the loop above will be optimized away.
The use of Assume_No_Invalid_Values (On)
is appropriate if
you know your code is free of uninitialized variables and other
possible sources of invalid representations, and may result in
more efficient code. A program that accesses an invalid representation
with this pragma in effect is erroneous, so no guarantees can be made
about its behavior.
It is peculiar though permissible to use this pragma in conjunction with validity checking (-gnatVa). In such cases, accessing invalid values will generally give an exception, though formally the program is erroneous so there are no guarantees that this will always be the case, and it is recommended that these two options not be used together.
Next: Pragma Attribute_Definition, Previous: Pragma Assume_No_Invalid_Values, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma AST_Entry (entry_IDENTIFIER);
This pragma is implemented only in the OpenVMS implementation of GNAT. The
argument is the simple name of a single entry; at most one AST_Entry
pragma is allowed for any given entry. This pragma must be used in
conjunction with the AST_Entry
attribute, and is only allowed after
the entry declaration and in the same task type specification or single task
as the entry to which it applies. This pragma specifies that the given entry
may be used to handle an OpenVMS asynchronous system trap (AST
)
resulting from an OpenVMS system service call. The pragma does not affect
normal use of the entry. For further details on this pragma, see the
DEC Ada Language Reference Manual, section 9.12a.
Next: Pragma C_Pass_By_Copy, Previous: Pragma Ast_Entry, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Attribute_Definition ([Attribute =>] ATTRIBUTE_DESIGNATOR, [Entity =>] LOCAL_NAME, [Expression =>] EXPRESSION | NAME);
If Attribute
is a known attribute name, this pragma is equivalent to
the attribute definition clause:
for Entity'Attribute use Expression;
If Attribute
is not a recognized attribute name, the pragma is
ignored, and a warning is emitted. This allows source
code to be written that takes advantage of some new attribute, while remaining
compilable with earlier compilers.
Next: Pragma Check, Previous: Pragma Attribute_Definition, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma C_Pass_By_Copy ([Max_Size =>] static_integer_EXPRESSION);
Normally the default mechanism for passing C convention records to C
convention subprograms is to pass them by reference, as suggested by RM
B.3(69). Use the configuration pragma C_Pass_By_Copy
to change
this default, by requiring that record formal parameters be passed by
copy if all of the following conditions are met:
Max_Size
.
Convention C
.
If these conditions are met the argument is passed by copy, i.e. in a manner consistent with what C expects if the corresponding formal in the C prototype is a struct (rather than a pointer to a struct).
You can also pass records by copy by specifying the convention
C_Pass_By_Copy
for the record type, or by using the extended
Import
and Export
pragmas, which allow specification of
passing mechanisms on a parameter by parameter basis.
Next: Pragma Check_Float_Overflow, Previous: Pragma C_Pass_By_Copy, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Check ( [Name =>] Identifier, [Check =>] Boolean_EXPRESSION [, [Message =>] string_EXPRESSION] );
This pragma is similar to the predefined pragma Assert
except that an
extra identifier argument is present. In conjunction with pragma
Check_Policy
, this can be used to define groups of assertions that can
be independently controlled. The identifier Assertion
is special, it
refers to the normal set of pragma Assert
statements. The identifiers
Precondition
and Postcondition
correspond to the pragmas of these
names, so these three names would normally not be used directly in a pragma
Check
.
Checks introduced by this pragma are normally deactivated by default. They can
be activated either by the command line option -gnata, which turns on
all checks, or individually controlled using pragma Check_Policy
.
Next: Pragma Check_Name, Previous: Pragma Check, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Check_Float_Overflow;
In Ada, the predefined floating-point types (Short_Float
,
Float
, Long_Float
, Long_Long_Float
) are
defined to be unconstrained. This means that even though each
has a well-defined base range, an operation that delivers a result
outside this base range is not required to raise an exception.
This implementation permission accommodates the notion
of infinities in IEEE floating-point, and corresponds to the
efficient execution mode on most machines. GNAT will not raise
overflow exceptions on these machines; instead it will generate
infinities and NaN’s as defined in the IEEE standard.
Generating infinities, although efficient, is not always desirable. Often the preferable approach is to check for overflow, even at the (perhaps considerable) expense of run-time performance. This can be accomplished by defining your own constrained floating-point subtypes – i.e., by supplying explicit range constraints – and indeed such a subtype can have the same base range as its base type. For example:
subtype My_Float is Float range Float'Range;
Here My_Float
has the same range as
Float
but is constrained, so operations on
My_Float
values will be checked for overflow
against this range.
This style will achieve the desired goal, but
it is often more convenient to be able to simply use
the standard predefined floating-point types as long
as overflow checking could be guaranteed.
The Check_Float_Overflow
configuration pragma achieves this effect. If a unit is compiled
subject to this configuration pragma, then all operations
on predefined floating-point types will be treated as
though those types were constrained, and overflow checks
will be generated. The Constraint_Error
exception is raised if the result is out of range.
This mode can also be set by use of the compiler switch -gnateF.
Next: Pragma Check_Policy, Previous: Pragma Check_Float_Overflow, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Check_Name (check_name_IDENTIFIER);
This is a configuration pragma that defines a new implementation defined check name (unless IDENTIFIER matches one of the predefined check names, in which case the pragma has no effect). Check names are global to a partition, so if two or more configuration pragmas are present in a partition mentioning the same name, only one new check name is introduced.
An implementation defined check name introduced with this pragma may
be used in only three contexts: pragma Suppress
,
pragma Unsuppress
,
and as the prefix of a Check_Name'Enabled
attribute reference. For
any of these three cases, the check name must be visible. A check
name is visible if it is in the configuration pragmas applying to
the current unit, or if it appears at the start of any unit that
is part of the dependency set of the current unit (e.g., units that
are mentioned in with
clauses).
Next: Pragma Comment, Previous: Pragma Check_Name, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Check_Policy ([Name =>] Identifier, [Policy =>] POLICY_IDENTIFIER); POLICY_IDENTIFIER ::= ON | OFF | CHECK | DISABLE | IGNORE
This pragma is similar to the predefined pragma Assertion_Policy
,
except that it controls sets of named assertions introduced using the
Check
pragmas. It can be used as a configuration pragma or (unlike
Assertion_Policy
) can be used within a declarative part, in which case
it controls the status to the end of the corresponding construct (in a manner
identical to pragma Suppress)
.
The identifier given as the first argument corresponds to a name used in
associated Check
pragmas. For example, if the pragma:
pragma Check_Policy (Critical_Error, OFF);
is given, then subsequent Check
pragmas whose first argument is also
Critical_Error
will be disabled. The special identifier Assertion
controls the behavior of normal assertions (thus a pragma
Check_Policy
with this identifier is similar to the normal
Assertion_Policy
pragma except that it can appear within a
declarative part).
The special identifiers Precondition
and Postcondition
control
the status of preconditions and postconditions given as pragmas.
If a Precondition
pragma
is encountered, it is ignored if turned off by a Check_Policy
specifying
that Precondition
checks are Off
or Ignored
. Similarly use
of the name Postcondition
controls whether Postcondition
pragmas
are recognized. Note that preconditions and postconditions given as aspects
are controlled differently, either by the Assertion_Policy
pragma or
by the Check_Policy
pragma with identifier Assertion
.
The check policy is OFF
to turn off corresponding checks, and ON
to turn on corresponding checks. The default for a set of checks for which no
Check_Policy
is given is OFF
unless the compiler switch
-gnata is given, which turns on all checks by default.
The check policy settings CHECK
and IGNORE
are also recognized
as synonyms for ON
and OFF
. These synonyms are provided for
compatibility with the standard Assertion_Policy
pragma.
The implementation defined policy DISABLE
is like
OFF
except that it completely disables semantic
checking of the argument to the corresponding class of
pragmas. This may be useful when the pragma arguments reference
subprograms in a with’ed package which is replaced by a dummy package
for the final build.
Next: Pragma Common_Object, Previous: Pragma Check_Policy, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Comment (static_string_EXPRESSION);
This is almost identical in effect to pragma Ident
. It allows the
placement of a comment into the object file and hence into the
executable file if the operating system permits such usage. The
difference is that Comment
, unlike Ident
, has
no limitations on placement of the pragma (it can be placed
anywhere in the main source unit), and if more than one pragma
is used, all comments are retained.
Next: Pragma Compile_Time_Error, Previous: Pragma Comment, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Common_Object ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Size =>] EXTERNAL_SYMBOL] ); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION
This pragma enables the shared use of variables stored in overlaid
linker areas corresponding to the use of COMMON
in Fortran. The single
object LOCAL_NAME is assigned to the area designated by
the External argument.
You may define a record to correspond to a series
of fields. The Size argument
is syntax checked in GNAT, but otherwise ignored.
Common_Object
is not supported on all platforms. If no
support is available, then the code generator will issue a message
indicating that the necessary attribute for implementation of this
pragma is not available.
Next: Pragma Compile_Time_Warning, Previous: Pragma Common_Object, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Compile_Time_Error (boolean_EXPRESSION, static_string_EXPRESSION);
This pragma can be used to generate additional compile time error messages. It is particularly useful in generics, where errors can be issued for specific problematic instantiations. The first parameter is a boolean expression. The pragma is effective only if the value of this expression is known at compile time, and has the value True. The set of expressions whose values are known at compile time includes all static boolean expressions, and also other values which the compiler can determine at compile time (e.g., the size of a record type set by an explicit size representation clause, or the value of a variable which was initialized to a constant and is known not to have been modified). If these conditions are met, an error message is generated using the value given as the second argument. This string value may contain embedded ASCII.LF characters to break the message into multiple lines.
Next: Pragma Compiler_Unit, Previous: Pragma Compile_Time_Error, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Compile_Time_Warning (boolean_EXPRESSION, static_string_EXPRESSION);
Same as pragma Compile_Time_Error, except a warning is issued instead of an error message. Note that if this pragma is used in a package that is with’ed by a client, the client will get the warning even though it is issued by a with’ed package (normally warnings in with’ed units are suppressed, but this is a special exception to that rule).
One typical use is within a generic where compile time known characteristics of formal parameters are tested, and warnings given appropriately. Another use with a first parameter of True is to warn a client about use of a package, for example that it is not fully implemented.
Next: Pragma Complete_Representation, Previous: Pragma Compile_Time_Warning, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Compiler_Unit;
This pragma is intended only for internal use in the GNAT run-time library. It indicates that the unit is used as part of the compiler build. The effect is to disallow constructs (raise with message, conditional expressions etc) that would cause trouble when bootstrapping using an older version of GNAT. For the exact list of restrictions, see the compiler sources and references to Is_Compiler_Unit.
Next: Pragma Complex_Representation, Previous: Pragma Compiler_Unit, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Complete_Representation;
This pragma must appear immediately within a record representation clause. Typical placements are before the first component clause or after the last component clause. The effect is to give an error message if any component is missing a component clause. This pragma may be used to ensure that a record representation clause is complete, and that this invariant is maintained if fields are added to the record in the future.
Next: Pragma Component_Alignment, Previous: Pragma Complete_Representation, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Complex_Representation ([Entity =>] LOCAL_NAME);
The Entity argument must be the name of a record type which has two fields of the same floating-point type. The effect of this pragma is to force gcc to use the special internal complex representation form for this record, which may be more efficient. Note that this may result in the code for this type not conforming to standard ABI (application binary interface) requirements for the handling of record types. For example, in some environments, there is a requirement for passing records by pointer, and the use of this pragma may result in passing this type in floating-point registers.
Next: Pragma Contract_Case, Previous: Pragma Complex_Representation, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Component_Alignment ( [Form =>] ALIGNMENT_CHOICE [, [Name =>] type_LOCAL_NAME]); ALIGNMENT_CHOICE ::= Component_Size | Component_Size_4 | Storage_Unit | Default
Specifies the alignment of components in array or record types. The meaning of the Form argument is as follows:
Component_Size
Aligns scalar components and subcomponents of the array or record type on boundaries appropriate to their inherent size (naturally aligned). For example, 1-byte components are aligned on byte boundaries, 2-byte integer components are aligned on 2-byte boundaries, 4-byte integer components are aligned on 4-byte boundaries and so on. These alignment rules correspond to the normal rules for C compilers on all machines except the VAX.
Component_Size_4
Naturally aligns components with a size of four or fewer bytes. Components that are larger than 4 bytes are placed on the next 4-byte boundary.
Storage_Unit
Specifies that array or record components are byte aligned, i.e.
aligned on boundaries determined by the value of the constant
System.Storage_Unit
.
Default
Specifies that array or record components are aligned on default
boundaries, appropriate to the underlying hardware or operating system or
both. For OpenVMS VAX systems, the Default
choice is the same as
the Storage_Unit
choice (byte alignment). For all other systems,
the Default
choice is the same as Component_Size
(natural
alignment).
If the Name
parameter is present, type_LOCAL_NAME must
refer to a local record or array type, and the specified alignment
choice applies to the specified type. The use of
Component_Alignment
together with a pragma Pack
causes the
Component_Alignment
pragma to be ignored. The use of
Component_Alignment
together with a record representation clause
is only effective for fields not specified by the representation clause.
If the Name
parameter is absent, the pragma can be used as either
a configuration pragma, in which case it applies to one or more units in
accordance with the normal rules for configuration pragmas, or it can be
used within a declarative part, in which case it applies to types that
are declared within this declarative part, or within any nested scope
within this declarative part. In either case it specifies the alignment
to be applied to any record or array type which has otherwise standard
representation.
If the alignment for a record or array type is not specified (using
pragma Pack
, pragma Component_Alignment
, or a record rep
clause), the GNAT uses the default alignment as described previously.
Next: Pragma Convention_Identifier, Previous: Pragma Component_Alignment, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Contract_Case ( [Name =>] static_string_Expression ,[Mode =>] (Nominal | Robustness) [, Requires => Boolean_Expression] [, Ensures => Boolean_Expression]);
The Contract_Case
pragma allows defining fine-grain specifications
that can complement or replace the contract given by a precondition and a
postcondition. Additionally, the Contract_Case
pragma can be used
by testing and formal verification tools. The compiler checks its validity and,
depending on the assertion policy at the point of declaration of the pragma,
it may insert a check in the executable. For code generation, the contract
case
pragma Contract_Case ( Name => ... Mode => ... Requires => R, Ensures => E);
is equivalent to
pragma Postcondition (not R'Old or else E);
which is also equivalent to (in Ada 2012)
pragma Postcondition (if R'Old then E);
expressing that, whenever condition R
is satisfied on entry to the
subprogram, condition E
should be fulfilled on exit to the subprogram.
A precondition P
and postcondition Q
can also be
expressed as contract cases:
pragma Contract_Case ( Name => "Replace precondition", Mode => Nominal, Requires => not P, Ensures => False); pragma Contract_Case ( Name => "Replace postcondition", Mode => Nominal, Requires => P, Ensures => Q);
Contract_Case
pragmas may only appear immediately following the
(separate) declaration of a subprogram in a package declaration, inside
a package spec unit. Only other pragmas may intervene (that is appear
between the subprogram declaration and a contract case).
The compiler checks that boolean expressions given in Requires
and
Ensures
are valid, where the rules for Requires
are the
same as the rule for an expression in Precondition
and the rules
for Ensures
are the same as the rule for an expression in
Postcondition
. In particular, attributes 'Old
and
'Result
can only be used within the Ensures
expression. The following is an example of use within a package spec:
package Math_Functions is ... function Sqrt (Arg : Float) return Float; pragma Contract_Case (Name => "Small argument", Mode => Nominal, Requires => Arg < 100, Ensures => Sqrt'Result < 10); ... end Math_Functions;
The meaning of a contract case is that, whenever the associated subprogram is
executed in a context where Requires
holds, then Ensures
should hold when the subprogram returns. Mode Nominal
indicates
that the input context should also satisfy the precondition of the
subprogram, and the output context should also satisfy its
postcondition. More Robustness
indicates that the precondition and
postcondition of the subprogram should be ignored for this contract case,
which is mostly useful when testing such a contract using a testing tool
that understands contract cases.
Next: Pragma CPP_Class, Previous: Pragma Contract_Case, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Convention_Identifier ( [Name =>] IDENTIFIER, [Convention =>] convention_IDENTIFIER);
This pragma provides a mechanism for supplying synonyms for existing
convention identifiers. The Name
identifier can subsequently
be used as a synonym for the given convention in other pragmas (including
for example pragma Import
or another Convention_Identifier
pragma). As an example of the use of this, suppose you had legacy code
which used Fortran77 as the identifier for Fortran. Then the pragma:
pragma Convention_Identifier (Fortran77, Fortran);
would allow the use of the convention identifier Fortran77
in
subsequent code, avoiding the need to modify the sources. As another
example, you could use this to parameterize convention requirements
according to systems. Suppose you needed to use Stdcall
on
windows systems, and C
on some other system, then you could
define a convention identifier Library
and use a single
Convention_Identifier
pragma to specify which convention
would be used system-wide.
Next: Pragma CPP_Constructor, Previous: Pragma Convention_Identifier, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma CPP_Class ([Entity =>] LOCAL_NAME);
The argument denotes an entity in the current declarative region that is declared as a record type. It indicates that the type corresponds to an externally declared C++ class type, and is to be laid out the same way that C++ would lay out the type. If the C++ class has virtual primitives then the record must be declared as a tagged record type.
Types for which CPP_Class
is specified do not have assignment or
equality operators defined (such operations can be imported or declared
as subprograms as required). Initialization is allowed only by constructor
functions (see pragma CPP_Constructor
). Such types are implicitly
limited if not explicitly declared as limited or derived from a limited
type, and an error is issued in that case.
See Interfacing to C++ for related information.
Note: Pragma CPP_Class
is currently obsolete. It is supported
for backward compatibility but its functionality is available
using pragma Import
with Convention
= CPP
.
Next: Pragma CPP_Virtual, Previous: Pragma CPP_Class, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma CPP_Constructor ([Entity =>] LOCAL_NAME [, [External_Name =>] static_string_EXPRESSION ] [, [Link_Name =>] static_string_EXPRESSION ]);
This pragma identifies an imported function (imported in the usual way
with pragma Import
) as corresponding to a C++ constructor. If
External_Name
and Link_Name
are not specified then the
Entity
argument is a name that must have been previously mentioned
in a pragma Import
with Convention
= CPP
. Such name
must be of one of the following forms:
function Fname return T
function Fname return T'Class
function Fname (…) return T
function Fname (…) return T'Class
where T is a limited record type imported from C++ with pragma
Import
and Convention
= CPP
.
The first two forms import the default constructor, used when an object of type T is created on the Ada side with no explicit constructor. The latter two forms cover all the non-default constructors of the type. See the GNAT User’s Guide for details.
If no constructors are imported, it is impossible to create any objects on the Ada side and the type is implicitly declared abstract.
Pragma CPP_Constructor
is intended primarily for automatic generation
using an automatic binding generator tool (such as the -fdump-ada-spec
GCC switch).
See Interfacing to C++ for more related information.
Note: The use of functions returning class-wide types for constructors is currently obsolete. They are supported for backward compatibility. The use of functions returning the type T leave the Ada sources more clear because the imported C++ constructors always return an object of type T; that is, they never return an object whose type is a descendant of type T.
Next: Pragma CPP_Vtable, Previous: Pragma CPP_Constructor, Up: Implementation Defined Pragmas [Contents][Index]
This pragma is now obsolete has has no effect because GNAT generates the same object layout than the G++ compiler.
See Interfacing to C++ for related information.
Next: Pragma CPU, Previous: Pragma CPP_Virtual, Up: Implementation Defined Pragmas [Contents][Index]
This pragma is now obsolete has has no effect because GNAT generates the same object layout than the G++ compiler.
See Interfacing to C++ for related information.
Next: Pragma Debug, Previous: Pragma CPP_Vtable, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma CPU (EXPRESSSION);
This pragma is standard in Ada 2012, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Debug_Policy, Previous: Pragma CPU, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON); PROCEDURE_CALL_WITHOUT_SEMICOLON ::= PROCEDURE_NAME | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
The procedure call argument has the syntactic form of an expression, meeting the syntactic requirements for pragmas.
If debug pragmas are not enabled or if the condition is present and evaluates
to False, this pragma has no effect. If debug pragmas are enabled, the
semantics of the pragma is exactly equivalent to the procedure call statement
corresponding to the argument with a terminating semicolon. Pragmas are
permitted in sequences of declarations, so you can use pragma Debug
to
intersperse calls to debug procedures in the middle of declarations. Debug
pragmas can be enabled either by use of the command line switch -gnata
or by use of the configuration pragma Debug_Policy
.
Next: Pragma Default_Storage_Pool, Previous: Pragma Debug, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Debug_Policy (CHECK | DISABLE | IGNORE);
If the argument is CHECK
, then pragma DEBUG
is enabled.
If the argument is IGNORE
, then pragma DEBUG
is ignored.
This pragma overrides the effect of the -gnata switch on the
command line.
The implementation defined policy DISABLE
is like
IGNORE
except that it completely disables semantic
checking of the argument to pragma Debug
. This may
be useful when the pragma argument references subprograms
in a with’ed package which is replaced by a dummy package
for the final build.
Next: Pragma Detect_Blocking, Previous: Pragma Debug_Policy, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Default_Storage_Pool (storage_pool_NAME | null);
This pragma is standard in Ada 2012, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Dispatching_Domain, Previous: Pragma Default_Storage_Pool, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Detect_Blocking;
This is a standard pragma in Ada 2005, that is available in all earlier versions of Ada as an implementation-defined pragma.
This is a configuration pragma that forces the detection of potentially blocking operations within a protected operation, and to raise Program_Error if that happens.
Next: Pragma Elaboration_Checks, Previous: Pragma Detect_Blocking, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Dispatching_Domain (EXPRESSION);
This pragma is standard in Ada 2012, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Eliminate, Previous: Pragma Dispatching_Domain, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Elaboration_Checks (Dynamic | Static);
This is a configuration pragma that provides control over the
elaboration model used by the compilation affected by the
pragma. If the parameter is Dynamic
,
then the dynamic elaboration
model described in the Ada Reference Manual is used, as though
the -gnatE switch had been specified on the command
line. If the parameter is Static
, then the default GNAT static
model is used. This configuration pragma overrides the setting
of the command line. For full details on the elaboration models
used by the GNAT compiler, see Elaboration Order Handling in GNAT in GNAT User’s Guide.
Next: Pragma Export_Exception, Previous: Pragma Elaboration_Checks, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Eliminate ([Entity =>] DEFINING_DESIGNATOR, [Source_Location =>] STRING_LITERAL);
The string literal given for the source location is a string which specifies the line number of the occurrence of the entity, using the syntax for SOURCE_TRACE given below:
SOURCE_TRACE ::= SOURCE_REFERENCE [LBRACKET SOURCE_TRACE RBRACKET] LBRACKET ::= [ RBRACKET ::= ] SOURCE_REFERENCE ::= FILE_NAME : LINE_NUMBER LINE_NUMBER ::= DIGIT {DIGIT}
Spaces around the colon in a Source_Reference
are optional.
The DEFINING_DESIGNATOR
matches the defining designator used in an
explicit subprogram declaration, where the entity
name in this
designator appears on the source line specified by the source location.
The source trace that is given as the Source_Location
shall obey the
following rules. The FILE_NAME
is the short name (with no directory
information) of an Ada source file, given using exactly the required syntax
for the underlying file system (e.g. case is important if the underlying
operating system is case sensitive). LINE_NUMBER
gives the line
number of the occurrence of the entity
as a decimal literal without an exponent or point. If an entity
is not
declared in a generic instantiation (this includes generic subprogram
instances), the source trace includes only one source reference. If an entity
is declared inside a generic instantiation, its source trace (when parsing
from left to right) starts with the source location of the declaration of the
entity in the generic unit and ends with the source location of the
instantiation (it is given in square brackets). This approach is recursively
used in case of nested instantiations: the rightmost (nested most deeply in
square brackets) element of the source trace is the location of the outermost
instantiation, the next to left element is the location of the next (first
nested) instantiation in the code of the corresponding generic unit, and so
on, and the leftmost element (that is out of any square brackets) is the
location of the declaration of the entity to eliminate in a generic unit.
Note that the Source_Location
argument specifies which of a set of
similarly named entities is being eliminated, dealing both with overloading,
and also appearence of the same entity name in different scopes.
This pragma indicates that the given entity is not used in the program to be compiled and built. The effect of the pragma is to allow the compiler to eliminate the code or data associated with the named entity. Any reference to an eliminated entity causes a compile-time or link-time error.
The intention of pragma Eliminate
is to allow a program to be compiled
in a system-independent manner, with unused entities eliminated, without
needing to modify the source text. Normally the required set of
Eliminate
pragmas is constructed automatically using the gnatelim tool.
Any source file change that removes, splits, or
adds lines may make the set of Eliminate pragmas invalid because their
Source_Location
argument values may get out of date.
Pragma Eliminate
may be used where the referenced entity is a dispatching
operation. In this case all the subprograms to which the given operation can
dispatch are considered to be unused (are never called as a result of a direct
or a dispatching call).
Next: Pragma Export_Function, Previous: Pragma Eliminate, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Export_Exception ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Form =>] Ada | VMS] [, [Code =>] static_integer_EXPRESSION]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION
This pragma is implemented only in the OpenVMS implementation of GNAT. It causes the specified exception to be propagated outside of the Ada program, so that it can be handled by programs written in other OpenVMS languages. This pragma establishes an external name for an Ada exception and makes the name available to the OpenVMS Linker as a global symbol. For further details on this pragma, see the DEC Ada Language Reference Manual, section 13.9a3.2.
Next: Pragma Export_Object, Previous: Pragma Export_Exception, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Export_Function ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Parameter_Types =>] PARAMETER_TYPES] [, [Result_Type =>] result_SUBTYPE_MARK] [, [Mechanism =>] MECHANISM] [, [Result_Mechanism =>] MECHANISM_NAME]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION | "" PARAMETER_TYPES ::= null | TYPE_DESIGNATOR {, TYPE_DESIGNATOR} TYPE_DESIGNATOR ::= subtype_NAME | subtype_Name ' Access MECHANISM ::= MECHANISM_NAME | (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION}) MECHANISM_ASSOCIATION ::= [formal_parameter_NAME =>] MECHANISM_NAME MECHANISM_NAME ::= Value | Reference | Descriptor [([Class =>] CLASS_NAME)] | Short_Descriptor [([Class =>] CLASS_NAME)] CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
Use this pragma to make a function externally callable and optionally
provide information on mechanisms to be used for passing parameter and
result values. We recommend, for the purposes of improving portability,
this pragma always be used in conjunction with a separate pragma
Export
, which must precede the pragma Export_Function
.
GNAT does not require a separate pragma Export
, but if none is
present, Convention Ada
is assumed, which is usually
not what is wanted, so it is usually appropriate to use this
pragma in conjunction with a Export
or Convention
pragma that specifies the desired foreign convention.
Pragma Export_Function
(and Export
, if present) must appear in the same declarative
region as the function to which they apply.
internal_name must uniquely designate the function to which the
pragma applies. If more than one function name exists of this name in
the declarative part you must use the Parameter_Types
and
Result_Type
parameters is mandatory to achieve the required
unique designation. subtype_marks in these parameters must
exactly match the subtypes in the corresponding function specification,
using positional notation to match parameters with subtype marks.
The form with an 'Access
attribute can be used to match an
anonymous access parameter.
Passing by descriptor is supported only on the OpenVMS ports of GNAT. The default behavior for Export_Function is to accept either 64bit or 32bit descriptors unless short_descriptor is specified, then only 32bit descriptors are accepted.
Special treatment is given if the EXTERNAL is an explicit null string or a static string expressions that evaluates to the null string. In this case, no external name is generated. This form still allows the specification of parameter mechanisms.
Next: Pragma Export_Procedure, Previous: Pragma Export_Function, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Export_Object [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Size =>] EXTERNAL_SYMBOL] EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION
This pragma designates an object as exported, and apart from the
extended rules for external symbols, is identical in effect to the use of
the normal Export
pragma applied to an object. You may use a
separate Export pragma (and you probably should from the point of view
of portability), but it is not required. Size is syntax checked,
but otherwise ignored by GNAT.
Next: Pragma Export_Value, Previous: Pragma Export_Object, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Export_Procedure ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Parameter_Types =>] PARAMETER_TYPES] [, [Mechanism =>] MECHANISM]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION | "" PARAMETER_TYPES ::= null | TYPE_DESIGNATOR {, TYPE_DESIGNATOR} TYPE_DESIGNATOR ::= subtype_NAME | subtype_Name ' Access MECHANISM ::= MECHANISM_NAME | (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION}) MECHANISM_ASSOCIATION ::= [formal_parameter_NAME =>] MECHANISM_NAME MECHANISM_NAME ::= Value | Reference | Descriptor [([Class =>] CLASS_NAME)] | Short_Descriptor [([Class =>] CLASS_NAME)] CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
This pragma is identical to Export_Function
except that it
applies to a procedure rather than a function and the parameters
Result_Type
and Result_Mechanism
are not permitted.
GNAT does not require a separate pragma Export
, but if none is
present, Convention Ada
is assumed, which is usually
not what is wanted, so it is usually appropriate to use this
pragma in conjunction with a Export
or Convention
pragma that specifies the desired foreign convention.
Passing by descriptor is supported only on the OpenVMS ports of GNAT. The default behavior for Export_Procedure is to accept either 64bit or 32bit descriptors unless short_descriptor is specified, then only 32bit descriptors are accepted.
Special treatment is given if the EXTERNAL is an explicit null string or a static string expressions that evaluates to the null string. In this case, no external name is generated. This form still allows the specification of parameter mechanisms.
Next: Pragma Export_Valued_Procedure, Previous: Pragma Export_Procedure, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Export_Value ( [Value =>] static_integer_EXPRESSION, [Link_Name =>] static_string_EXPRESSION);
This pragma serves to export a static integer value for external use. The first argument specifies the value to be exported. The Link_Name argument specifies the symbolic name to be associated with the integer value. This pragma is useful for defining a named static value in Ada that can be referenced in assembly language units to be linked with the application. This pragma is currently supported only for the AAMP target and is ignored for other targets.
Next: Pragma Extend_System, Previous: Pragma Export_Value, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Export_Valued_Procedure ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Parameter_Types =>] PARAMETER_TYPES] [, [Mechanism =>] MECHANISM]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION | "" PARAMETER_TYPES ::= null | TYPE_DESIGNATOR {, TYPE_DESIGNATOR} TYPE_DESIGNATOR ::= subtype_NAME | subtype_Name ' Access MECHANISM ::= MECHANISM_NAME | (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION}) MECHANISM_ASSOCIATION ::= [formal_parameter_NAME =>] MECHANISM_NAME MECHANISM_NAME ::= Value | Reference | Descriptor [([Class =>] CLASS_NAME)] | Short_Descriptor [([Class =>] CLASS_NAME)] CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
This pragma is identical to Export_Procedure
except that the
first parameter of LOCAL_NAME, which must be present, must be of
mode OUT
, and externally the subprogram is treated as a function
with this parameter as the result of the function. GNAT provides for
this capability to allow the use of OUT
and IN OUT
parameters in interfacing to external functions (which are not permitted
in Ada functions).
GNAT does not require a separate pragma Export
, but if none is
present, Convention Ada
is assumed, which is almost certainly
not what is wanted since the whole point of this pragma is to interface
with foreign language functions, so it is usually appropriate to use this
pragma in conjunction with a Export
or Convention
pragma that specifies the desired foreign convention.
Passing by descriptor is supported only on the OpenVMS ports of GNAT. The default behavior for Export_Valued_Procedure is to accept either 64bit or 32bit descriptors unless short_descriptor is specified, then only 32bit descriptors are accepted.
Special treatment is given if the EXTERNAL is an explicit null string or a static string expressions that evaluates to the null string. In this case, no external name is generated. This form still allows the specification of parameter mechanisms.
Next: Pragma Extensions_Allowed, Previous: Pragma Export_Valued_Procedure, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Extend_System ([Name =>] IDENTIFIER);
This pragma is used to provide backwards compatibility with other
implementations that extend the facilities of package System
. In
GNAT, System
contains only the definitions that are present in
the Ada RM. However, other implementations, notably the DEC Ada 83
implementation, provide many extensions to package System
.
For each such implementation accommodated by this pragma, GNAT provides a
package Aux_xxx
, e.g. Aux_DEC
for the DEC Ada 83
implementation, which provides the required additional definitions. You
can use this package in two ways. You can with
it in the normal
way and access entities either by selection or using a use
clause. In this case no special processing is required.
However, if existing code contains references such as
System.xxx
where xxx is an entity in the extended
definitions provided in package System
, you may use this pragma
to extend visibility in System
in a non-standard way that
provides greater compatibility with the existing code. Pragma
Extend_System
is a configuration pragma whose single argument is
the name of the package containing the extended definition
(e.g. Aux_DEC
for the DEC Ada case). A unit compiled under
control of this pragma will be processed using special visibility
processing that looks in package System.Aux_xxx
where
Aux_xxx
is the pragma argument for any entity referenced in
package System
, but not found in package System
.
You can use this pragma either to access a predefined System
extension supplied with the compiler, for example Aux_DEC
or
you can construct your own extension unit following the above
definition. Note that such a package is a child of System
and thus is considered part of the implementation. To compile
it you will have to use the appropriate switch for compiling
system units.
See About This Guide in GNAT User’s Guide,
for details.
Next: Pragma External, Previous: Pragma Extend_System, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Extensions_Allowed (On | Off);
This configuration pragma enables or disables the implementation extension mode (the use of Off as a parameter cancels the effect of the -gnatX command switch).
In extension mode, the latest version of the Ada language is implemented (currently Ada 2012), and in addition a small number of GNAT specific extensions are recognized as follows:
The Constrained
attribute is permitted for objects of
generic types. The result indicates if the corresponding actual
is constrained.
Next: Pragma External_Name_Casing, Previous: Pragma Extensions_Allowed, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma External ( [ Convention =>] convention_IDENTIFIER, [ Entity =>] LOCAL_NAME [, [External_Name =>] static_string_EXPRESSION ] [, [Link_Name =>] static_string_EXPRESSION ]);
This pragma is identical in syntax and semantics to pragma
Export
as defined in the Ada Reference Manual. It is
provided for compatibility with some Ada 83 compilers that
used this pragma for exactly the same purposes as pragma
Export
before the latter was standardized.
Next: Pragma Fast_Math, Previous: Pragma External, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma External_Name_Casing ( Uppercase | Lowercase [, Uppercase | Lowercase | As_Is]);
This pragma provides control over the casing of external names associated with Import and Export pragmas. There are two cases to consider:
Implicit external names are derived from identifiers. The most common case arises when a standard Ada Import or Export pragma is used with only two arguments, as in:
pragma Import (C, C_Routine);
Since Ada is a case-insensitive language, the spelling of the identifier in
the Ada source program does not provide any information on the desired
casing of the external name, and so a convention is needed. In GNAT the
default treatment is that such names are converted to all lower case
letters. This corresponds to the normal C style in many environments.
The first argument of pragma External_Name_Casing
can be used to
control this treatment. If Uppercase
is specified, then the name
will be forced to all uppercase letters. If Lowercase
is specified,
then the normal default of all lower case letters will be used.
This same implicit treatment is also used in the case of extended DEC Ada 83 compatible Import and Export pragmas where an external name is explicitly specified using an identifier rather than a string.
Explicit external names are given as string literals. The most common case arises when a standard Ada Import or Export pragma is used with three arguments, as in:
pragma Import (C, C_Routine, "C_routine");
In this case, the string literal normally provides the exact casing required
for the external name. The second argument of pragma
External_Name_Casing
may be used to modify this behavior.
If Uppercase
is specified, then the name
will be forced to all uppercase letters. If Lowercase
is specified,
then the name will be forced to all lowercase letters. A specification of
As_Is
provides the normal default behavior in which the casing is
taken from the string provided.
This pragma may appear anywhere that a pragma is valid. In particular, it can be used as a configuration pragma in the gnat.adc file, in which case it applies to all subsequent compilations, or it can be used as a program unit pragma, in which case it only applies to the current unit, or it can be used more locally to control individual Import/Export pragmas.
It is primarily intended for use with OpenVMS systems, where many compilers convert all symbols to upper case by default. For interfacing to such compilers (e.g. the DEC C compiler), it may be convenient to use the pragma:
pragma External_Name_Casing (Uppercase, Uppercase);
to enforce the upper casing of all external symbols.
Next: Pragma Favor_Top_Level, Previous: Pragma External_Name_Casing, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Fast_Math;
This is a configuration pragma which activates a mode in which speed is considered more important for floating-point operations than absolutely accurate adherence to the requirements of the standard. Currently the following operations are affected:
The normal simple formula for complex multiplication can result in intermediate
overflows for numbers near the end of the range. The Ada standard requires that
this situation be detected and corrected by scaling, but in Fast_Math mode such
cases will simply result in overflow. Note that to take advantage of this you
must instantiate your own version of Ada.Numerics.Generic_Complex_Types
under control of the pragma, rather than use the preinstantiated versions.
Next: Pragma Finalize_Storage_Only, Previous: Pragma Fast_Math, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Favor_Top_Level (type_NAME);
The named type must be an access-to-subprogram type. This pragma is an efficiency hint to the compiler, regarding the use of ’Access or ’Unrestricted_Access on nested (non-library-level) subprograms. The pragma means that nested subprograms are not used with this type, or are rare, so that the generated code should be efficient in the top-level case. When this pragma is used, dynamically generated trampolines may be used on some targets for nested subprograms. See also the No_Implicit_Dynamic_Code restriction.
Next: Pragma Float_Representation, Previous: Pragma Favor_Top_Level, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
This pragma allows the compiler not to emit a Finalize call for objects defined at the library level. This is mostly useful for types where finalization is only used to deal with storage reclamation since in most environments it is not necessary to reclaim memory just before terminating execution, hence the name.
Next: Pragma Ident, Previous: Pragma Finalize_Storage_Only, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Float_Representation (FLOAT_REP[, float_type_LOCAL_NAME]); FLOAT_REP ::= VAX_Float | IEEE_Float
In the one argument form, this pragma is a configuration pragma which
allows control over the internal representation chosen for the predefined
floating point types declared in the packages Standard
and
System
. On all systems other than OpenVMS, the argument must
be IEEE_Float
and the pragma has no effect. On OpenVMS, the
argument may be VAX_Float
to specify the use of the VAX float
format for the floating-point types in Standard. This requires that
the standard runtime libraries be recompiled.
The two argument form specifies the representation to be used for
the specified floating-point type. On all systems other than OpenVMS,
the argument must
be IEEE_Float
and the pragma has no effect. On OpenVMS, the
argument may be VAX_Float
to specify the use of the VAX float
format, as follows:
Next: Pragma Implementation_Defined, Previous: Pragma Float_Representation, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ident (static_string_EXPRESSION);
This pragma provides a string identification in the generated object file,
if the system supports the concept of this kind of identification string.
This pragma is allowed only in the outermost declarative part or
declarative items of a compilation unit. If more than one Ident
pragma is given, only the last one processed is effective.
On OpenVMS systems, the effect of the pragma is identical to the effect of
the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
maximum allowed length is 31 characters, so if it is important to
maintain compatibility with this compiler, you should obey this length
limit.
Next: Pragma Implemented, Previous: Pragma Ident, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Implementation_Defined (local_NAME);
This pragma marks a previously declared entioty as implementation-defined. For an overloaded entity, applies to the most recent homonym.
pragma Implementation_Defined;
The form with no arguments appears anywhere within a scope, most typically a package spec, and indicates that all entities that are defined within the package spec are Implementation_Defined.
This pragma is used within the GNAT runtime library to identify implementation-defined entities introduced in language-defined units, for the purpose of implementing the No_Implementation_Identifiers restriction.
Next: Pragma Implicit_Packing, Previous: Pragma Implementation_Defined, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Implemented (procedure_LOCAL_NAME, implementation_kind); implementation_kind ::= By_Entry | By_Protected_Procedure | By_Any
This is an Ada 2012 representation pragma which applies to protected, task and synchronized interface primitives. The use of pragma Implemented provides a way to impose a static requirement on the overriding operation by adhering to one of the three implementation kinds: entry, protected procedure or any of the above. This pragma is available in all earlier versions of Ada as an implementation-defined pragma.
type Synch_Iface is synchronized interface; procedure Prim_Op (Obj : in out Iface) is abstract; pragma Implemented (Prim_Op, By_Protected_Procedure); protected type Prot_1 is new Synch_Iface with procedure Prim_Op; -- Legal end Prot_1; protected type Prot_2 is new Synch_Iface with entry Prim_Op; -- Illegal end Prot_2; task type Task_Typ is new Synch_Iface with entry Prim_Op; -- Illegal end Task_Typ;
When applied to the procedure_or_entry_NAME of a requeue statement, pragma Implemented determines the runtime behavior of the requeue. Implementation kind By_Entry guarantees that the action of requeueing will proceed from an entry to another entry. Implementation kind By_Protected_Procedure transforms the requeue into a dispatching call, thus eliminating the chance of blocking. Kind By_Any shares the behavior of By_Entry and By_Protected_Procedure depending on the target’s overriding subprogram kind.
Next: Pragma Import_Exception, Previous: Pragma Implemented, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Implicit_Packing;
This is a configuration pragma that requests implicit packing for packed arrays for which a size clause is given but no explicit pragma Pack or specification of Component_Size is present. It also applies to records where no record representation clause is present. Consider this example:
type R is array (0 .. 7) of Boolean; for R'Size use 8;
In accordance with the recommendation in the RM (RM 13.3(53)), a Size clause does not change the layout of a composite object. So the Size clause in the above example is normally rejected, since the default layout of the array uses 8-bit components, and thus the array requires a minimum of 64 bits.
If this declaration is compiled in a region of code covered by an occurrence of the configuration pragma Implicit_Packing, then the Size clause in this and similar examples will cause implicit packing and thus be accepted. For this implicit packing to occur, the type in question must be an array of small components whose size is known at compile time, and the Size clause must specify the exact size that corresponds to the length of the array multiplied by the size in bits of the component type.
Similarly, the following example shows the use in the record case
type r is record a, b, c, d, e, f, g, h : boolean; chr : character; end record; for r'size use 16;
Without a pragma Pack, each Boolean field requires 8 bits, so the minimum size is 72 bits, but with a pragma Pack, 16 bits would be sufficient. The use of pragma Implicit_Packing allows this record declaration to compile without an explicit pragma Pack.
Next: Pragma Import_Function, Previous: Pragma Implicit_Packing, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Import_Exception ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Form =>] Ada | VMS] [, [Code =>] static_integer_EXPRESSION]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION
This pragma is implemented only in the OpenVMS implementation of GNAT. It allows OpenVMS conditions (for example, from OpenVMS system services or other OpenVMS languages) to be propagated to Ada programs as Ada exceptions. The pragma specifies that the exception associated with an exception declaration in an Ada program be defined externally (in non-Ada code). For further details on this pragma, see the DEC Ada Language Reference Manual, section 13.9a.3.1.
Next: Pragma Import_Object, Previous: Pragma Import_Exception, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Import_Function ( [Internal =>] LOCAL_NAME, [, [External =>] EXTERNAL_SYMBOL] [, [Parameter_Types =>] PARAMETER_TYPES] [, [Result_Type =>] SUBTYPE_MARK] [, [Mechanism =>] MECHANISM] [, [Result_Mechanism =>] MECHANISM_NAME] [, [First_Optional_Parameter =>] IDENTIFIER]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION PARAMETER_TYPES ::= null | TYPE_DESIGNATOR {, TYPE_DESIGNATOR} TYPE_DESIGNATOR ::= subtype_NAME | subtype_Name ' Access MECHANISM ::= MECHANISM_NAME | (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION}) MECHANISM_ASSOCIATION ::= [formal_parameter_NAME =>] MECHANISM_NAME MECHANISM_NAME ::= Value | Reference | Descriptor [([Class =>] CLASS_NAME)] | Short_Descriptor [([Class =>] CLASS_NAME)] CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
This pragma is used in conjunction with a pragma Import
to
specify additional information for an imported function. The pragma
Import
(or equivalent pragma Interface
) must precede the
Import_Function
pragma and both must appear in the same
declarative part as the function specification.
The Internal argument must uniquely designate
the function to which the
pragma applies. If more than one function name exists of this name in
the declarative part you must use the Parameter_Types
and
Result_Type parameters to achieve the required unique
designation. Subtype marks in these parameters must exactly match the
subtypes in the corresponding function specification, using positional
notation to match parameters with subtype marks.
The form with an 'Access
attribute can be used to match an
anonymous access parameter.
You may optionally use the Mechanism and Result_Mechanism parameters to specify passing mechanisms for the parameters and result. If you specify a single mechanism name, it applies to all parameters. Otherwise you may specify a mechanism on a parameter by parameter basis using either positional or named notation. If the mechanism is not specified, the default mechanism is used.
Passing by descriptor is supported only on the OpenVMS ports of GNAT. The default behavior for Import_Function is to pass a 64bit descriptor unless short_descriptor is specified, then a 32bit descriptor is passed.
First_Optional_Parameter
applies only to OpenVMS ports of GNAT.
It specifies that the designated parameter and all following parameters
are optional, meaning that they are not passed at the generated code
level (this is distinct from the notion of optional parameters in Ada
where the parameters are passed anyway with the designated optional
parameters). All optional parameters must be of mode IN
and have
default parameter values that are either known at compile time
expressions, or uses of the 'Null_Parameter
attribute.
Next: Pragma Import_Procedure, Previous: Pragma Import_Function, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Import_Object [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Size =>] EXTERNAL_SYMBOL]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION
This pragma designates an object as imported, and apart from the
extended rules for external symbols, is identical in effect to the use of
the normal Import
pragma applied to an object. Unlike the
subprogram case, you need not use a separate Import
pragma,
although you may do so (and probably should do so from a portability
point of view). size is syntax checked, but otherwise ignored by
GNAT.
Next: Pragma Import_Valued_Procedure, Previous: Pragma Import_Object, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Import_Procedure ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Parameter_Types =>] PARAMETER_TYPES] [, [Mechanism =>] MECHANISM] [, [First_Optional_Parameter =>] IDENTIFIER]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION PARAMETER_TYPES ::= null | TYPE_DESIGNATOR {, TYPE_DESIGNATOR} TYPE_DESIGNATOR ::= subtype_NAME | subtype_Name ' Access MECHANISM ::= MECHANISM_NAME | (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION}) MECHANISM_ASSOCIATION ::= [formal_parameter_NAME =>] MECHANISM_NAME MECHANISM_NAME ::= Value | Reference | Descriptor [([Class =>] CLASS_NAME)] | Short_Descriptor [([Class =>] CLASS_NAME)] CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
This pragma is identical to Import_Function
except that it
applies to a procedure rather than a function and the parameters
Result_Type
and Result_Mechanism
are not permitted.
Next: Pragma Independent, Previous: Pragma Import_Procedure, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Import_Valued_Procedure ( [Internal =>] LOCAL_NAME [, [External =>] EXTERNAL_SYMBOL] [, [Parameter_Types =>] PARAMETER_TYPES] [, [Mechanism =>] MECHANISM] [, [First_Optional_Parameter =>] IDENTIFIER]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION PARAMETER_TYPES ::= null | TYPE_DESIGNATOR {, TYPE_DESIGNATOR} TYPE_DESIGNATOR ::= subtype_NAME | subtype_Name ' Access MECHANISM ::= MECHANISM_NAME | (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION}) MECHANISM_ASSOCIATION ::= [formal_parameter_NAME =>] MECHANISM_NAME MECHANISM_NAME ::= Value | Reference | Descriptor [([Class =>] CLASS_NAME)] | Short_Descriptor [([Class =>] CLASS_NAME)] CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
This pragma is identical to Import_Procedure
except that the
first parameter of LOCAL_NAME, which must be present, must be of
mode OUT
, and externally the subprogram is treated as a function
with this parameter as the result of the function. The purpose of this
capability is to allow the use of OUT
and IN OUT
parameters in interfacing to external functions (which are not permitted
in Ada functions). You may optionally use the Mechanism
parameters to specify passing mechanisms for the parameters.
If you specify a single mechanism name, it applies to all parameters.
Otherwise you may specify a mechanism on a parameter by parameter
basis using either positional or named notation. If the mechanism is not
specified, the default mechanism is used.
Note that it is important to use this pragma in conjunction with a separate pragma Import that specifies the desired convention, since otherwise the default convention is Ada, which is almost certainly not what is required.
Next: Pragma Independent_Components, Previous: Pragma Import_Valued_Procedure, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Independent (Local_NAME);
This pragma is standard in Ada 2012 mode (which also provides an aspect of the same name). It is also available as an implementation-defined pragma in all earlier versions. It specifies that the designated object or all objects of the designated type must be independently addressable. This means that separate tasks can safely manipulate such objects. For example, if two components of a record are independent, then two separate tasks may access these two components. This may place constraints on the representation of the object (for instance prohibiting tight packing).
Next: Pragma Initialize_Scalars, Previous: Pragma Independent, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Independent_Components (Local_NAME);
This pragma is standard in Ada 2012 mode (which also provides an aspect of the same name). It is also available as an implementation-defined pragma in all earlier versions. It specifies that the components of the designated object, or the components of each object of the designated type, must be independently addressable. This means that separate tasks can safely manipulate separate components in the composite object. This may place constraints on the representation of the object (for instance prohibiting tight packing).
Next: Pragma Inline_Always, Previous: Pragma Independent_Components, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Initialize_Scalars;
This pragma is similar to Normalize_Scalars
conceptually but has
two important differences. First, there is no requirement for the pragma
to be used uniformly in all units of a partition, in particular, it is fine
to use this just for some or all of the application units of a partition,
without needing to recompile the run-time library.
In the case where some units are compiled with the pragma, and some without, then a declaration of a variable where the type is defined in package Standard or is locally declared will always be subject to initialization, as will any declaration of a scalar variable. For composite variables, whether the variable is initialized may also depend on whether the package in which the type of the variable is declared is compiled with the pragma.
The other important difference is that you can control the value used for initializing scalar objects. At bind time, you can select several options for initialization. You can initialize with invalid values (similar to Normalize_Scalars, though for Initialize_Scalars it is not always possible to determine the invalid values in complex cases like signed component fields with non-standard sizes). You can also initialize with high or low values, or with a specified bit pattern. See the GNAT User’s Guide for binder options for specifying these cases.
This means that you can compile a program, and then without having to recompile the program, you can run it with different values being used for initializing otherwise uninitialized values, to test if your program behavior depends on the choice. Of course the behavior should not change, and if it does, then most likely you have an erroneous reference to an uninitialized value.
It is even possible to change the value at execution time eliminating even the need to rebind with a different switch using an environment variable. See the GNAT User’s Guide for details.
Note that pragma Initialize_Scalars
is particularly useful in
conjunction with the enhanced validity checking that is now provided
in GNAT, which checks for invalid values under more conditions.
Using this feature (see description of the -gnatV flag in the
GNAT User’s Guide) in conjunction with
pragma Initialize_Scalars
provides a powerful new tool to assist in the detection of problems
caused by uninitialized variables.
Note: the use of Initialize_Scalars
has a fairly extensive
effect on the generated code. This may cause your code to be
substantially larger. It may also cause an increase in the amount
of stack required, so it is probably a good idea to turn on stack
checking (see description of stack checking in the GNAT
User’s Guide) when using this pragma.
Next: Pragma Inline_Generic, Previous: Pragma Initialize_Scalars, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Inline_Always (NAME [, NAME]);
Similar to pragma Inline
except that inlining is not subject to
the use of option -gnatn or -gnatN and the inlining
happens regardless of whether these options are used.
Next: Pragma Interface, Previous: Pragma Inline_Always, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Inline_Generic (generic_package_NAME);
This is implemented for compatibility with DEC Ada 83 and is recognized, but otherwise ignored, by GNAT. All generic instantiations are inlined by default when using GNAT.
Next: Pragma Interface_Name, Previous: Pragma Inline_Generic, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Interface ( [Convention =>] convention_identifier, [Entity =>] local_NAME [, [External_Name =>] static_string_expression] [, [Link_Name =>] static_string_expression]);
This pragma is identical in syntax and semantics to
the standard Ada pragma Import
. It is provided for compatibility
with Ada 83. The definition is upwards compatible both with pragma
Interface
as defined in the Ada 83 Reference Manual, and also
with some extended implementations of this pragma in certain Ada 83
implementations. The only difference between pragma Interface
and pragma Import
is that there is special circuitry to allow
both pragmas to appear for the same subprogram entity (normally it
is illegal to have multiple Import
pragmas. This is useful in
maintaining Ada 83/Ada 95 compatibility and is compatible with other
Ada 83 compilers.
Next: Pragma Interrupt_Handler, Previous: Pragma Interface, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Interface_Name ( [Entity =>] LOCAL_NAME [, [External_Name =>] static_string_EXPRESSION] [, [Link_Name =>] static_string_EXPRESSION]);
This pragma provides an alternative way of specifying the interface name for an interfaced subprogram, and is provided for compatibility with Ada 83 compilers that use the pragma for this purpose. You must provide at least one of External_Name or Link_Name.
Next: Pragma Interrupt_State, Previous: Pragma Interface_Name, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Interrupt_Handler (procedure_LOCAL_NAME);
This program unit pragma is supported for parameterless protected procedures
as described in Annex C of the Ada Reference Manual. On the AAMP target
the pragma can also be specified for nonprotected parameterless procedures
that are declared at the library level (which includes procedures
declared at the top level of a library package). In the case of AAMP,
when this pragma is applied to a nonprotected procedure, the instruction
IERET
is generated for returns from the procedure, enabling
maskable interrupts, in place of the normal return instruction.
Next: Pragma Invariant, Previous: Pragma Interrupt_Handler, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Interrupt_State ([Name =>] value, [State =>] SYSTEM | RUNTIME | USER);
Normally certain interrupts are reserved to the implementation. Any attempt
to attach an interrupt causes Program_Error to be raised, as described in
RM C.3.2(22). A typical example is the SIGINT
interrupt used in
many systems for an Ctrl-C interrupt. Normally this interrupt is
reserved to the implementation, so that Ctrl-C can be used to
interrupt execution. Additionally, signals such as SIGSEGV
,
SIGABRT
, SIGFPE
and SIGILL
are often mapped to specific
Ada exceptions, or used to implement run-time functions such as the
abort
statement and stack overflow checking.
Pragma Interrupt_State
provides a general mechanism for overriding
such uses of interrupts. It subsumes the functionality of pragma
Unreserve_All_Interrupts
. Pragma Interrupt_State
is not
available on Windows or VMS. On all other platforms than VxWorks,
it applies to signals; on VxWorks, it applies to vectored hardware interrupts
and may be used to mark interrupts required by the board support package
as reserved.
Interrupts can be in one of three states:
The interrupt is reserved (no Ada handler can be installed), and the Ada run-time may not install a handler. As a result you are guaranteed standard system default action if this interrupt is raised.
The interrupt is reserved (no Ada handler can be installed). The run time is allowed to install a handler for internal control purposes, but is not required to do so.
The interrupt is unreserved. The user may install a handler to provide some other action.
These states are the allowed values of the State
parameter of the
pragma. The Name
parameter is a value of the type
Ada.Interrupts.Interrupt_ID
. Typically, it is a name declared in
Ada.Interrupts.Names
.
This is a configuration pragma, and the binder will check that there are no inconsistencies between different units in a partition in how a given interrupt is specified. It may appear anywhere a pragma is legal.
The effect is to move the interrupt to the specified state.
By declaring interrupts to be SYSTEM, you guarantee the standard system action, such as a core dump.
By declaring interrupts to be USER, you guarantee that you can install a handler.
Note that certain signals on many operating systems cannot be caught and
handled by applications. In such cases, the pragma is ignored. See the
operating system documentation, or the value of the array Reserved
declared in the spec of package System.OS_Interface
.
Overriding the default state of signals used by the Ada runtime may interfere
with an application’s runtime behavior in the cases of the synchronous signals,
and in the case of the signal used to implement the abort
statement.
Next: Pragma Keep_Names, Previous: Pragma Interrupt_State, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Invariant ([Entity =>] private_type_LOCAL_NAME, [Check =>] EXPRESSION [,[Message =>] String_Expression]);
This pragma provides exactly the same capabilities as the Type_Invariant aspect defined in AI05-0146-1, and in the Ada 2012 Reference Manual. The Type_Invariant aspect is fully implemented in Ada 2012 mode, but since it requires the use of the aspect syntax, which is not available except in 2012 mode, it is not possible to use the Type_Invariant aspect in earlier versions of Ada. However the Invariant pragma may be used in any version of Ada. Also note that the aspect Invariant is a synonym in GNAT for the aspect Type_Invariant, but there is no pragma Type_Invariant.
The pragma must appear within the visible part of the package specification, after the type to which its Entity argument appears. As with the Invariant aspect, the Check expression is not analyzed until the end of the visible part of the package, so it may contain forward references. The Message argument, if present, provides the exception message used if the invariant is violated. If no Message parameter is provided, a default message that identifies the line on which the pragma appears is used.
It is permissible to have multiple Invariants for the same type entity, in which case they are and’ed together. It is permissible to use this pragma in Ada 2012 mode, but you cannot have both an invariant aspect and an invariant pragma for the same entity.
For further details on the use of this pragma, see the Ada 2012 documentation of the Type_Invariant aspect.
Next: Pragma License, Previous: Pragma Invariant, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME);
The LOCAL_NAME argument
must refer to an enumeration first subtype
in the current declarative part. The effect is to retain the enumeration
literal names for use by Image
and Value
even if a global
Discard_Names
pragma applies. This is useful when you want to
generally suppress enumeration literal names and for example you therefore
use a Discard_Names
pragma in the gnat.adc file, but you
want to retain the names for specific enumeration types.
Next: Pragma Link_With, Previous: Pragma Keep_Names, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
This pragma is provided to allow automated checking for appropriate license
conditions with respect to the standard and modified GPL. A pragma
License
, which is a configuration pragma that typically appears at
the start of a source file or in a separate gnat.adc file, specifies
the licensing conditions of a unit as follows:
with
’ed by a restricted unit.
with
units
which are licensed under the modified GPL (this is the whole point of the
modified GPL).
Normally a unit with no License
pragma is considered to have an
unknown license, and no checking is done. However, standard GNAT headers
are recognized, and license information is derived from them as follows.
If the string “GNU General Public License” is found, then the unit is assumed to have GPL license, unless the string “As a special exception” follows, in which case the license is assumed to be modified GPL.
If one of the strings “This specification is adapted from the Ada Semantic Interface” or “This specification is derived from the Ada Reference Manual” is found then the unit is assumed to be unrestricted.
These default actions means that a program with a restricted license pragma
will automatically get warnings if a GPL unit is inappropriately
with
’ed. For example, the program:
with Sem_Ch3; with GNAT.Sockets; procedure Secret_Stuff is … end Secret_Stuff
if compiled with pragma License
(Restricted
) in a
gnat.adc file will generate the warning:
1. with Sem_Ch3; | >>> license of withed unit "Sem_Ch3" is incompatible 2. with GNAT.Sockets; 3. procedure Secret_Stuff is
Here we get a warning on Sem_Ch3
since it is part of the GNAT
compiler and is licensed under the
GPL, but no warning for GNAT.Sockets
which is part of the GNAT
run time, and is therefore licensed under the modified GPL.
Next: Pragma Linker_Alias, Previous: Pragma License, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Link_With (static_string_EXPRESSION {,static_string_EXPRESSION});
This pragma is provided for compatibility with certain Ada 83 compilers.
It has exactly the same effect as pragma Linker_Options
except
that spaces occurring within one of the string expressions are treated
as separators. For example, in the following case:
pragma Link_With ("-labc -ldef");
results in passing the strings -labc
and -ldef
as two
separate arguments to the linker. In addition pragma Link_With allows
multiple arguments, with the same effect as successive pragmas.
Next: Pragma Linker_Constructor, Previous: Pragma Link_With, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Linker_Alias ( [Entity =>] LOCAL_NAME, [Target =>] static_string_EXPRESSION);
LOCAL_NAME must refer to an object that is declared at the library
level. This pragma establishes the given entity as a linker alias for the
given target. It is equivalent to __attribute__((alias))
in GNU C
and causes LOCAL_NAME to be emitted as an alias for the symbol
static_string_EXPRESSION in the object file, that is to say no space
is reserved for LOCAL_NAME by the assembler and it will be resolved
to the same address as static_string_EXPRESSION by the linker.
The actual linker name for the target must be used (e.g. the fully
encoded name with qualification in Ada, or the mangled name in C++),
or it must be declared using the C convention with pragma Import
or pragma Export
.
Not all target machines support this pragma. On some of them it is accepted
only if pragma Weak_External
has been applied to LOCAL_NAME.
-- Example of the use of pragma Linker_Alias package p is i : Integer := 1; pragma Export (C, i); new_name_for_i : Integer; pragma Linker_Alias (new_name_for_i, "i"); end p;
Next: Pragma Linker_Destructor, Previous: Pragma Linker_Alias, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Linker_Constructor (procedure_LOCAL_NAME);
procedure_LOCAL_NAME must refer to a parameterless procedure that
is declared at the library level. A procedure to which this pragma is
applied will be treated as an initialization routine by the linker.
It is equivalent to __attribute__((constructor))
in GNU C and
causes procedure_LOCAL_NAME to be invoked before the entry point
of the executable is called (or immediately after the shared library is
loaded if the procedure is linked in a shared library), in particular
before the Ada run-time environment is set up.
Because of these specific contexts, the set of operations such a procedure can perform is very limited and the type of objects it can manipulate is essentially restricted to the elementary types. In particular, it must only contain code to which pragma Restrictions (No_Elaboration_Code) applies.
This pragma is used by GNAT to implement auto-initialization of shared Stand Alone Libraries, which provides a related capability without the restrictions listed above. Where possible, the use of Stand Alone Libraries is preferable to the use of this pragma.
Next: Pragma Linker_Section, Previous: Pragma Linker_Constructor, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Linker_Destructor (procedure_LOCAL_NAME);
procedure_LOCAL_NAME must refer to a parameterless procedure that
is declared at the library level. A procedure to which this pragma is
applied will be treated as a finalization routine by the linker.
It is equivalent to __attribute__((destructor))
in GNU C and
causes procedure_LOCAL_NAME to be invoked after the entry point
of the executable has exited (or immediately before the shared library
is unloaded if the procedure is linked in a shared library), in particular
after the Ada run-time environment is shut down.
See pragma Linker_Constructor
for the set of restrictions that apply
because of these specific contexts.
Next: Pragma Long_Float, Previous: Pragma Linker_Destructor, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Linker_Section ( [Entity =>] LOCAL_NAME, [Section =>] static_string_EXPRESSION);
LOCAL_NAME must refer to an object that is declared at the library
level. This pragma specifies the name of the linker section for the given
entity. It is equivalent to __attribute__((section))
in GNU C and
causes LOCAL_NAME to be placed in the static_string_EXPRESSION
section of the executable (assuming the linker doesn’t rename the section).
The compiler normally places library-level objects in standard sections
depending on their type: procedures and functions generally go in the
.text
section, initialized variables in the .data
section
and uninitialized variables in the .bss
section.
Other, special sections may exist on given target machines to map special hardware, for example I/O ports or flash memory. This pragma is a means to defer the final layout of the executable to the linker, thus fully working at the symbolic level with the compiler.
Some file formats do not support arbitrary sections so not all target
machines support this pragma. The use of this pragma may cause a program
execution to be erroneous if it is used to place an entity into an
inappropriate section (e.g. a modified variable into the .text
section). See also pragma Persistent_BSS
.
-- Example of the use of pragma Linker_Section package IO_Card is Port_A : Integer; pragma Volatile (Port_A); pragma Linker_Section (Port_A, ".bss.port_a"); Port_B : Integer; pragma Volatile (Port_B); pragma Linker_Section (Port_B, ".bss.port_b"); end IO_Card;
Next: Pragma Loop_Optimize, Previous: Pragma Linker_Section, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Long_Float (FLOAT_FORMAT); FLOAT_FORMAT ::= D_Float | G_Float
This pragma is implemented only in the OpenVMS implementation of GNAT.
It allows control over the internal representation chosen for the predefined
type Long_Float
and for floating point type representations with
digits
specified in the range 7 through 15.
For further details on this pragma, see the
DEC Ada Language Reference Manual, section 3.5.7b. Note that to use
this pragma, the standard runtime libraries must be recompiled.
Next: Pragma Machine_Attribute, Previous: Pragma Long_Float, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Loop_Optimize (OPTIMIZATION_HINT {, OPTIMIZATION_HINT}); OPTIMIZATION_HINT ::= No_Unroll | Unroll | No_Vector | Vector
This pragma must appear immediately within a loop statement. It allows the programmer to specify optimization hints for the enclosing loop. The hints are not mutually exclusive and can be freely mixed, but not all combinations will yield a sensible outcome.
There are four supported optimization hints for a loop:
The loop must not be unrolled. This is a strong hint: the compiler will not unroll a loop marked with this hint.
The loop should be unrolled. This is a weak hint: the compiler will try to apply unrolling to this loop preferably to other optimizations, notably vectorization, but there is no guarantee that the loop will be unrolled.
The loop must not be vectorized. This is a strong hint: the compiler will not vectorize a loop marked with this hint.
The loop should be vectorized. This is a weak hint: the compiler will try to apply vectorization to this loop preferably to other optimizations, notably unrolling, but there is no guarantee that the loop will be vectorized.
These hints do not void the need to pass the appropriate switches to the compiler in order to enable the relevant optimizations, that is to say -funroll-loops for unrolling and -ftree-vectorize for vectorization.
Next: Pragma Main, Previous: Pragma Loop_Optimize, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Machine_Attribute ( [Entity =>] LOCAL_NAME, [Attribute_Name =>] static_string_EXPRESSION [, [Info =>] static_EXPRESSION] );
Machine-dependent attributes can be specified for types and/or
declarations. This pragma is semantically equivalent to
__attribute__((attribute_name))
(if info is not
specified) or __attribute__((attribute_name(info)))
in GNU C, where attribute_name
is recognized by the
compiler middle-end or the TARGET_ATTRIBUTE_TABLE
machine
specific macro. A string literal for the optional parameter info
is transformed into an identifier, which may make this pragma unusable
for some attributes. See Defining target-specific
uses of __attribute__
in GNU Compiler Collection (GCC)
Internals, further information.
Next: Pragma Main_Storage, Previous: Pragma Machine_Attribute, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Main (MAIN_OPTION [, MAIN_OPTION]); MAIN_OPTION ::= [Stack_Size =>] static_integer_EXPRESSION | [Task_Stack_Size_Default =>] static_integer_EXPRESSION | [Time_Slicing_Enabled =>] static_boolean_EXPRESSION
This pragma is provided for compatibility with OpenVMS VAX Systems. It has no effect in GNAT, other than being syntax checked.
Next: Pragma No_Body, Previous: Pragma Main, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Main_Storage (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]); MAIN_STORAGE_OPTION ::= [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION | [TOP_GUARD =>] static_SIMPLE_EXPRESSION
This pragma is provided for compatibility with OpenVMS VAX Systems. It has no effect in GNAT, other than being syntax checked. Note that the pragma also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
Next: Pragma No_Inline, Previous: Pragma Main_Storage, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma No_Body;
There are a number of cases in which a package spec does not require a body, and in fact a body is not permitted. GNAT will not permit the spec to be compiled if there is a body around. The pragma No_Body allows you to provide a body file, even in a case where no body is allowed. The body file must contain only comments and a single No_Body pragma. This is recognized by the compiler as indicating that no body is logically present.
This is particularly useful during maintenance when a package is modified in such a way that a body needed before is no longer needed. The provision of a dummy body with a No_Body pragma ensures that there is no interference from earlier versions of the package body.
Next: Pragma No_Return, Previous: Pragma No_Body, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma No_Inline (NAME [, NAME]);
This pragma suppresses inlining for the callable entity or the instances of
the generic subprogram designated by NAME, including inlining that
results from the use of pragma Inline
. This pragma is always active,
in particular it is not subject to the use of option -gnatn or
-gnatN. It is illegal to specify both pragma No_Inline
and
pragma Inline_Always
for the same NAME.
Next: Pragma No_Strict_Aliasing, Previous: Pragma No_Inline, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma No_Return (procedure_LOCAL_NAME {, procedure_LOCAL_NAME});
Each procedure_LOCAL_NAME argument must refer to one or more procedure
declarations in the current declarative part. A procedure to which this
pragma is applied may not contain any explicit return
statements.
In addition, if the procedure contains any implicit returns from falling
off the end of a statement sequence, then execution of that implicit
return will cause Program_Error to be raised.
One use of this pragma is to identify procedures whose only purpose is to raise an exception. Another use of this pragma is to suppress incorrect warnings about missing returns in functions, where the last statement of a function statement sequence is a call to such a procedure.
Note that in Ada 2005 mode, this pragma is part of the language. It is available in all earlier versions of Ada as an implementation-defined pragma.
Next: Pragma Normalize_Scalars, Previous: Pragma No_Return, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma No_Strict_Aliasing [([Entity =>] type_LOCAL_NAME)];
type_LOCAL_NAME must refer to an access type declaration in the current declarative part. The effect is to inhibit strict aliasing optimization for the given type. The form with no arguments is a configuration pragma which applies to all access types declared in units to which the pragma applies. For a detailed description of the strict aliasing optimization, and the situations in which it must be suppressed, see Optimization and Strict Aliasing in GNAT User’s Guide.
This pragma currently has no effects on access to unconstrained array types.
Next: Pragma Obsolescent, Previous: Pragma No_Strict_Aliasing, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Normalize_Scalars;
This is a language defined pragma which is fully implemented in GNAT. The effect is to cause all scalar objects that are not otherwise initialized to be initialized. The initial values are implementation dependent and are as follows:
Standard.Character
Objects whose root type is Standard.Character are initialized to Character’Last unless the subtype range excludes NUL (in which case NUL is used). This choice will always generate an invalid value if one exists.
Standard.Wide_Character
Objects whose root type is Standard.Wide_Character are initialized to Wide_Character’Last unless the subtype range excludes NUL (in which case NUL is used). This choice will always generate an invalid value if one exists.
Standard.Wide_Wide_Character
Objects whose root type is Standard.Wide_Wide_Character are initialized to the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in which case NUL is used). This choice will always generate an invalid value if one exists.
Integer types
Objects of an integer type are treated differently depending on whether negative values are present in the subtype. If no negative values are present, then all one bits is used as the initial value except in the special case where zero is excluded from the subtype, in which case all zero bits are used. This choice will always generate an invalid value if one exists.
For subtypes with negative values present, the largest negative number is used, except in the unusual case where this largest negative number is in the subtype, and the largest positive number is not, in which case the largest positive value is used. This choice will always generate an invalid value if one exists.
Floating-Point Types
Objects of all floating-point types are initialized to all 1-bits. For standard IEEE format, this corresponds to a NaN (not a number) which is indeed an invalid value.
Fixed-Point Types
Objects of all fixed-point types are treated as described above for integers, with the rules applying to the underlying integer value used to represent the fixed-point value.
Modular types
Objects of a modular type are initialized to all one bits, except in the special case where zero is excluded from the subtype, in which case all zero bits are used. This choice will always generate an invalid value if one exists.
Enumeration types
Objects of an enumeration type are initialized to all one-bits, i.e. to
the value 2 ** typ'Size - 1
unless the subtype excludes the literal
whose Pos value is zero, in which case a code of zero is used. This choice
will always generate an invalid value if one exists.
Next: Pragma Optimize_Alignment, Previous: Pragma Normalize_Scalars, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Obsolescent; pragma Obsolescent ( [Message =>] static_string_EXPRESSION [,[Version =>] Ada_05]]); pragma Obsolescent ( [Entity =>] NAME [,[Message =>] static_string_EXPRESSION [,[Version =>] Ada_05]] );
This pragma can occur immediately following a declaration of an entity, including the case of a record component. If no Entity argument is present, then this declaration is the one to which the pragma applies. If an Entity parameter is present, it must either match the name of the entity in this declaration, or alternatively, the pragma can immediately follow an enumeration type declaration, where the Entity argument names one of the enumeration literals.
This pragma is used to indicate that the named entity is considered obsolescent and should not be used. Typically this is used when an API must be modified by eventually removing or modifying existing subprograms or other entities. The pragma can be used at an intermediate stage when the entity is still present, but will be removed later.
The effect of this pragma is to output a warning message on a reference to an entity thus marked that the subprogram is obsolescent if the appropriate warning option in the compiler is activated. If the Message parameter is present, then a second warning message is given containing this text. In addition, a reference to the entity is considered to be a violation of pragma Restrictions (No_Obsolescent_Features).
This pragma can also be used as a program unit pragma for a package,
in which case the entity name is the name of the package, and the
pragma indicates that the entire package is considered
obsolescent. In this case a client with
’ing such a package
violates the restriction, and the with
statement is
flagged with warnings if the warning option is set.
If the Version parameter is present (which must be exactly the identifier Ada_05, no other argument is allowed), then the indication of obsolescence applies only when compiling in Ada 2005 mode. This is primarily intended for dealing with the situations in the predefined library where subprograms or packages have become defined as obsolescent in Ada 2005 (e.g. in Ada.Characters.Handling), but may be used anywhere.
The following examples show typical uses of this pragma:
package p is pragma Obsolescent (p, Message => "use pp instead of p"); end p; package q is procedure q2; pragma Obsolescent ("use q2new instead"); type R is new integer; pragma Obsolescent (Entity => R, Message => "use RR in Ada 2005", Version => Ada_05); type M is record F1 : Integer; F2 : Integer; pragma Obsolescent; F3 : Integer; end record; type E is (a, bc, 'd', quack); pragma Obsolescent (Entity => bc) pragma Obsolescent (Entity => 'd') function "+" (a, b : character) return character; pragma Obsolescent (Entity => "+"); end;
Note that, as for all pragmas, if you use a pragma argument identifier, then all subsequent parameters must also use a pragma argument identifier. So if you specify "Entity =>" for the Entity argument, and a Message argument is present, it must be preceded by "Message =>".
Next: Pragma Ordered, Previous: Pragma Obsolescent, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Optimize_Alignment (TIME | SPACE | OFF);
This is a configuration pragma which affects the choice of default alignments for types where no alignment is explicitly specified. There is a time/space trade-off in the selection of these values. Large alignments result in more efficient code, at the expense of larger data space, since sizes have to be increased to match these alignments. Smaller alignments save space, but the access code is slower. The normal choice of default alignments (which is what you get if you do not use this pragma, or if you use an argument of OFF), tries to balance these two requirements.
Specifying SPACE causes smaller default alignments to be chosen in two cases. First any packed record is given an alignment of 1. Second, if a size is given for the type, then the alignment is chosen to avoid increasing this size. For example, consider:
type R is record X : Integer; Y : Character; end record; for R'Size use 5*8;
In the default mode, this type gets an alignment of 4, so that access to the
Integer field X are efficient. But this means that objects of the type end up
with a size of 8 bytes. This is a valid choice, since sizes of objects are
allowed to be bigger than the size of the type, but it can waste space if for
example fields of type R appear in an enclosing record. If the above type is
compiled in Optimize_Alignment (Space)
mode, the alignment is set to 1.
However, there is one case in which SPACE is ignored. If a variable length record (that is a discriminated record with a component which is an array whose length depends on a discriminant), has a pragma Pack, then it is not in general possible to set the alignment of such a record to one, so the pragma is ignored in this case (with a warning).
Specifying TIME causes larger default alignments to be chosen in the case of small types with sizes that are not a power of 2. For example, consider:
type R is record A : Character; B : Character; C : Boolean; end record; pragma Pack (R); for R'Size use 17;
The default alignment for this record is normally 1, but if this type is
compiled in Optimize_Alignment (Time)
mode, then the alignment is set
to 4, which wastes space for objects of the type, since they are now 4 bytes
long, but results in more efficient access when the whole record is referenced.
As noted above, this is a configuration pragma, and there is a requirement that all units in a partition be compiled with a consistent setting of the optimization setting. This would normally be achieved by use of a configuration pragma file containing the appropriate setting. The exception to this rule is that units with an explicit configuration pragma in the same file as the source unit are excluded from the consistency check, as are all predefined units. The latter are compiled by default in pragma Optimize_Alignment (Off) mode if no pragma appears at the start of the file.
Next: Pragma Overflow_Mode, Previous: Pragma Optimize_Alignment, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Ordered (enumeration_first_subtype_LOCAL_NAME);
Most enumeration types are from a conceptual point of view unordered. For example, consider:
type Color is (Red, Blue, Green, Yellow);
By Ada semantics Blue > Red
and Green > Blue
,
but really these relations make no sense; the enumeration type merely
specifies a set of possible colors, and the order is unimportant.
For unordered enumeration types, it is generally a good idea if clients avoid comparisons (other than equality or inequality) and explicit ranges. (A client is a unit where the type is referenced, other than the unit where the type is declared, its body, and its subunits.) For example, if code buried in some client says:
if Current_Color < Yellow then ... if Current_Color in Blue .. Green then ...
then the client code is relying on the order, which is undesirable.
It makes the code hard to read and creates maintenance difficulties if
entries have to be added to the enumeration type. Instead,
the code in the client should list the possibilities, or an
appropriate subtype should be declared in the unit that declares
the original enumeration type. E.g., the following subtype could
be declared along with the type Color
:
subtype RBG is Color range Red .. Green;
and then the client could write:
if Current_Color in RBG then ... if Current_Color = Blue or Current_Color = Green then ...
However, some enumeration types are legitimately ordered from a conceptual point of view. For example, if you declare:
type Day is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
then the ordering imposed by the language is reasonable, and clients can depend on it, writing for example:
if D in Mon .. Fri then ... if D < Wed then ...
The pragma Ordered is provided to mark enumeration types that are conceptually ordered, alerting the reader that clients may depend on the ordering. GNAT provides a pragma to mark enumerations as ordered rather than one to mark them as unordered, since in our experience, the great majority of enumeration types are conceptually unordered.
The types Boolean
, Character
, Wide_Character
,
and Wide_Wide_Character
are considered to be ordered types, so each is declared with a
pragma Ordered
in package Standard
.
Normally pragma Ordered
serves only as documentation and a guide for
coding standards, but GNAT provides a warning switch -gnatw.u that
requests warnings for inappropriate uses (comparisons and explicit
subranges) for unordered types. If this switch is used, then any
enumeration type not marked with pragma Ordered
will be considered
as unordered, and will generate warnings for inappropriate uses.
For additional information please refer to the description of the -gnatw.u switch in the GNAT User’s Guide.
Next: Pragma Partition_Elaboration_Policy, Previous: Pragma Ordered, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Overflow_Mode ( [General =>] MODE [,[Assertions =>] MODE]); MODE ::= STRICT | MINIMIZED | ELIMINATED
This pragma sets the current overflow mode to the given setting. For details
of the meaning of these modes, please refer to the
“Overflow Check Handling in GNAT” appendix in the
GNAT User’s Guide. If only the General
parameter is present,
the given mode applies to all expressions. If both parameters are present,
the General
mode applies to expressions outside assertions, and
the Eliminated
mode applies to expressions within assertions.
The case of the MODE
parameter is ignored,
so MINIMIZED
, Minimized
and
minimized
all have the same effect.
The Overflow_Mode
pragma has the same scoping and placement
rules as pragma Suppress
, so it can occur either as a
configuration pragma, specifying a default for the whole
program, or in a declarative scope, where it applies to the
remaining declarations and statements in that scope.
The pragma Suppress (Overflow_Check)
suppresses
overflow checking, but does not affect the overflow mode.
The pragma Unsuppress (Overflow_Check)
unsuppresses (enables)
overflow checking, but does not affect the overflow mode.
Next: Pragma Passive, Previous: Pragma Overflow_Mode, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Partition_Elaboration_Policy (POLICY_IDENTIFIER); POLICY_IDENTIFIER ::= Concurrent | Sequential
This pragma is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Persistent_BSS, Previous: Pragma Partition_Elaboration_Policy, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Passive [(Semaphore | No)];
Syntax checked, but otherwise ignored by GNAT. This is recognized for
compatibility with DEC Ada 83 implementations, where it is used within a
task definition to request that a task be made passive. If the argument
Semaphore
is present, or the argument is omitted, then DEC Ada 83
treats the pragma as an assertion that the containing task is passive
and that optimization of context switch with this task is permitted and
desired. If the argument No
is present, the task must not be
optimized. GNAT does not attempt to optimize any tasks in this manner
(since protected objects are available in place of passive tasks).
Next: Pragma Polling, Previous: Pragma Passive, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Persistent_BSS [(LOCAL_NAME)]
This pragma allows selected objects to be placed in the .persistent_bss
section. On some targets the linker and loader provide for special
treatment of this section, allowing a program to be reloaded without
affecting the contents of this data (hence the name persistent).
There are two forms of usage. If an argument is given, it must be the local name of a library level object, with no explicit initialization and whose type is potentially persistent. If no argument is given, then the pragma is a configuration pragma, and applies to all library level objects with no explicit initialization of potentially persistent types.
A potentially persistent type is a scalar type, or a non-tagged, non-discriminated record, all of whose components have no explicit initialization and are themselves of a potentially persistent type, or an array, all of whose constraints are static, and whose component type is potentially persistent.
If this pragma is used on a target where this feature is not supported,
then the pragma will be ignored. See also pragma Linker_Section
.
Next: Pragma Postcondition, Previous: Pragma Persistent_BSS, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Polling (ON | OFF);
This pragma controls the generation of polling code. This is normally off.
If pragma Polling (ON)
is used then periodic calls are generated to
the routine Ada.Exceptions.Poll
. This routine is a separate unit in the
runtime library, and can be found in file a-excpol.adb.
Pragma Polling
can appear as a configuration pragma (for example it
can be placed in the gnat.adc file) to enable polling globally, or it
can be used in the statement or declaration sequence to control polling
more locally.
A call to the polling routine is generated at the start of every loop and
at the start of every subprogram call. This guarantees that the Poll
routine is called frequently, and places an upper bound (determined by
the complexity of the code) on the period between two Poll
calls.
The primary purpose of the polling interface is to enable asynchronous
aborts on targets that cannot otherwise support it (for example Windows
NT), but it may be used for any other purpose requiring periodic polling.
The standard version is null, and can be replaced by a user program. This
will require re-compilation of the Ada.Exceptions
package that can
be found in files a-except.ads and a-except.adb.
A standard alternative unit (in file 4wexcpol.adb in the standard GNAT
distribution) is used to enable the asynchronous abort capability on
targets that do not normally support the capability. The version of
Poll
in this file makes a call to the appropriate runtime routine
to test for an abort condition.
Note that polling can also be enabled by use of the -gnatP switch. See Switches for gcc in GNAT User’s Guide, for details.
Next: Pragma Preelaborable_Initialization, Previous: Pragma Polling, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Postcondition ( [Check =>] Boolean_Expression [,[Message =>] String_Expression]);
The Postcondition
pragma allows specification of automatic
postcondition checks for subprograms. These checks are similar to
assertions, but are automatically inserted just prior to the return
statements of the subprogram with which they are associated (including
implicit returns at the end of procedure bodies and associated
exception handlers).
In addition, the boolean expression which is the condition which must be true may contain references to function’Result in the case of a function to refer to the returned value.
Postcondition
pragmas may appear either immediately following the
(separate) declaration of a subprogram, or at the start of the
declarations of a subprogram body. Only other pragmas may intervene
(that is appear between the subprogram declaration and its
postconditions, or appear before the postcondition in the
declaration sequence in a subprogram body). In the case of a
postcondition appearing after a subprogram declaration, the
formal arguments of the subprogram are visible, and can be
referenced in the postcondition expressions.
The postconditions are collected and automatically tested just
before any return (implicit or explicit) in the subprogram body.
A postcondition is only recognized if postconditions are active
at the time the pragma is encountered. The compiler switch gnata
turns on all postconditions by default, and pragma Check_Policy
with an identifier of Postcondition
can also be used to
control whether postconditions are active.
The general approach is that postconditions are placed in the spec if they represent functional aspects which make sense to the client. For example we might have:
function Direction return Integer; pragma Postcondition (Direction'Result = +1 or else Direction'Result = -1);
which serves to document that the result must be +1 or -1, and will test that this is the case at run time if postcondition checking is active.
Postconditions within the subprogram body can be used to check that some internal aspect of the implementation, not visible to the client, is operating as expected. For instance if a square root routine keeps an internal counter of the number of times it is called, then we might have the following postcondition:
Sqrt_Calls : Natural := 0; function Sqrt (Arg : Float) return Float is pragma Postcondition (Sqrt_Calls = Sqrt_Calls'Old + 1); ... end Sqrt
As this example, shows, the use of the Old
attribute
is often useful in postconditions to refer to the state on
entry to the subprogram.
Note that postconditions are only checked on normal returns from the subprogram. If an abnormal return results from raising an exception, then the postconditions are not checked.
If a postcondition fails, then the exception
System.Assertions.Assert_Failure
is raised. If
a message argument was supplied, then the given string
will be used as the exception message. If no message
argument was supplied, then the default message has
the form "Postcondition failed at file:line". The
exception is raised in the context of the subprogram
body, so it is possible to catch postcondition failures
within the subprogram body itself.
Within a package spec, normal visibility rules in Ada would prevent forward references within a postcondition pragma to functions defined later in the same package. This would introduce undesirable ordering constraints. To avoid this problem, all postcondition pragmas are analyzed at the end of the package spec, allowing forward references.
The following example shows that this even allows mutually recursive postconditions as in:
package Parity_Functions is function Odd (X : Natural) return Boolean; pragma Postcondition (Odd'Result = (x = 1 or else (x /= 0 and then Even (X - 1)))); function Even (X : Natural) return Boolean; pragma Postcondition (Even'Result = (x = 0 or else (x /= 1 and then Odd (X - 1)))); end Parity_Functions;
There are no restrictions on the complexity or form of
conditions used within Postcondition
pragmas.
The following example shows that it is even possible
to verify performance behavior.
package Sort is Performance : constant Float; -- Performance constant set by implementation -- to match target architecture behavior. procedure Treesort (Arg : String); -- Sorts characters of argument using N*logN sort pragma Postcondition (Float (Clock - Clock'Old) <= Float (Arg'Length) * log (Float (Arg'Length)) * Performance); end Sort;
Note: postcondition pragmas associated with subprograms that are marked as Inline_Always, or those marked as Inline with front-end inlining (-gnatN option set) are accepted and legality-checked by the compiler, but are ignored at run-time even if postcondition checking is enabled.
Next: Pragma Priority_Specific_Dispatching, Previous: Pragma Postcondition, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Preelaborable_Initialization (DIRECT_NAME);
This pragma is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Precondition, Previous: Pragma Preelaborable_Initialization, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Priority_Specific_Dispatching ( POLICY_IDENTIFIER, first_priority_EXPRESSION, last_priority_EXPRESSION) POLICY_IDENTIFIER ::= EDF_Across_Priorities | FIFO_Within_Priorities | Non_Preemptive_Within_Priorities | Round_Robin_Within_Priorities
This pragma is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Profile (Ravenscar), Previous: Pragma Priority_Specific_Dispatching, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Precondition ( [Check =>] Boolean_Expression [,[Message =>] String_Expression]);
The Precondition
pragma is similar to Postcondition
except that the corresponding checks take place immediately upon
entry to the subprogram, and if a precondition fails, the exception
is raised in the context of the caller, and the attribute ’Result
cannot be used within the precondition expression.
Otherwise, the placement and visibility rules are identical to those described for postconditions. The following is an example of use within a package spec:
package Math_Functions is ... function Sqrt (Arg : Float) return Float; pragma Precondition (Arg >= 0.0) ... end Math_Functions;
Precondition
pragmas may appear either immediately following the
(separate) declaration of a subprogram, or at the start of the
declarations of a subprogram body. Only other pragmas may intervene
(that is appear between the subprogram declaration and its
postconditions, or appear before the postcondition in the
declaration sequence in a subprogram body).
Note: postcondition pragmas associated with subprograms that are marked as Inline_Always, or those marked as Inline with front-end inlining (-gnatN option set) are accepted and legality-checked by the compiler, but are ignored at run-time even if postcondition checking is enabled.
Next: Pragma Profile (Restricted), Previous: Pragma Precondition, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Profile (Ravenscar | Restricted);
This pragma is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. This is a configuration pragma that establishes the following set of configuration pragmas:
Task_Dispatching_Policy (FIFO_Within_Priorities)
[RM D.2.2] Tasks are dispatched following a preemptive priority-ordered scheduling policy.
Locking_Policy (Ceiling_Locking)
[RM D.3] While tasks and interrupts execute a protected action, they inherit the ceiling priority of the corresponding protected object.
plus the following set of restrictions:
Max_Entry_Queue_Length => 1
No task can be queued on a protected entry.
Max_Protected_Entries => 1
Max_Task_Entries => 0
No rendezvous statements are allowed.
No_Abort_Statements
No_Dynamic_Attachment
No_Dynamic_Priorities
No_Implicit_Heap_Allocations
No_Local_Protected_Objects
No_Local_Timing_Events
No_Protected_Type_Allocators
No_Relative_Delay
No_Requeue_Statements
No_Select_Statements
No_Specific_Termination_Handlers
No_Task_Allocators
No_Task_Hierarchy
No_Task_Termination
Simple_Barriers
The Ravenscar profile also includes the following restrictions that specify that there are no semantic dependences on the corresponding predefined packages:
No_Dependence => Ada.Asynchronous_Task_Control
No_Dependence => Ada.Calendar
No_Dependence => Ada.Execution_Time.Group_Budget
No_Dependence => Ada.Execution_Time.Timers
No_Dependence => Ada.Task_Attributes
No_Dependence => System.Multiprocessors.Dispatching_Domains
This set of configuration pragmas and restrictions correspond to the definition of the “Ravenscar Profile” for limited tasking, devised and published by the International Real-Time Ada Workshop, 1997, and whose most recent description is available at http://www-users.cs.york.ac.uk/~burns/ravenscar.ps.
The original definition of the profile was revised at subsequent IRTAW meetings. It has been included in the ISO Guide for the Use of the Ada Programming Language in High Integrity Systems, and has been approved by ISO/IEC/SC22/WG9 for inclusion in the next revision of the standard. The formal definition given by the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and AI-305) available at http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ais/ai-00249.txt and http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ais/ai-00305.txt.
The above set is a superset of the restrictions provided by pragma
Profile (Restricted)
, it includes six additional restrictions
(Simple_Barriers
, No_Select_Statements
,
No_Calendar
, No_Implicit_Heap_Allocations
,
No_Relative_Delay
and No_Task_Termination
). This means
that pragma Profile (Ravenscar)
, like the pragma
Profile (Restricted)
,
automatically causes the use of a simplified,
more efficient version of the tasking run-time system.
Next: Pragma Profile (Rational), Previous: Pragma Profile (Ravenscar), Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Profile (Restricted);
This is an implementation-defined version of the standard pragma defined in Ada 2005. It is available in all versions of Ada. It is a configuration pragma that establishes the following set of restrictions:
This set of restrictions causes the automatic selection of a simplified version of the run time that provides improved performance for the limited set of tasking functionality permitted by this set of restrictions.
Next: Pragma Psect_Object, Previous: Pragma Profile (Restricted), Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Profile (Rational);
The Rational profile is intended to facilitate porting legacy code that compiles with the Rational APEX compiler, even when the code includes non- conforming Ada constructs. The profile enables the following three pragmas:
Next: Pragma Pure_Function, Previous: Pragma Profile (Rational), Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Psect_Object ( [Internal =>] LOCAL_NAME, [, [External =>] EXTERNAL_SYMBOL] [, [Size =>] EXTERNAL_SYMBOL]); EXTERNAL_SYMBOL ::= IDENTIFIER | static_string_EXPRESSION
This pragma is identical in effect to pragma Common_Object
.
Next: Pragma Relative_Deadline, Previous: Pragma Psect_Object, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
This pragma appears in the same declarative part as a function
declaration (or a set of function declarations if more than one
overloaded declaration exists, in which case the pragma applies
to all entities). It specifies that the function Entity
is
to be considered pure for the purposes of code generation. This means
that the compiler can assume that there are no side effects, and
in particular that two calls with identical arguments produce the
same result. It also means that the function can be used in an
address clause.
Note that, quite deliberately, there are no static checks to try
to ensure that this promise is met, so Pure_Function
can be used
with functions that are conceptually pure, even if they do modify
global variables. For example, a square root function that is
instrumented to count the number of times it is called is still
conceptually pure, and can still be optimized, even though it
modifies a global variable (the count). Memo functions are another
example (where a table of previous calls is kept and consulted to
avoid re-computation).
Note also that the normal rules excluding optimization of subprograms in pure units (when parameter types are descended from System.Address, or when the full view of a parameter type is limited), do not apply for the Pure_Function case. If you explicitly specify Pure_Function, the compiler may optimize away calls with identical arguments, and if that results in unexpected behavior, the proper action is not to use the pragma for subprograms that are not (conceptually) pure.
Note: Most functions in a Pure
package are automatically pure, and
there is no need to use pragma Pure_Function
for such functions. One
exception is any function that has at least one formal of type
System.Address
or a type derived from it. Such functions are not
considered pure by default, since the compiler assumes that the
Address
parameter may be functioning as a pointer and that the
referenced data may change even if the address value does not.
Similarly, imported functions are not considered to be pure by default,
since there is no way of checking that they are in fact pure. The use
of pragma Pure_Function
for such a function will override these default
assumption, and cause the compiler to treat a designated subprogram as pure
in these cases.
Note: If pragma Pure_Function
is applied to a renamed function, it
applies to the underlying renamed function. This can be used to
disambiguate cases of overloading where some but not all functions
in a set of overloaded functions are to be designated as pure.
If pragma Pure_Function
is applied to a library level function, the
function is also considered pure from an optimization point of view, but the
unit is not a Pure unit in the categorization sense. So for example, a function
thus marked is free to with
non-pure units.
Next: Pragma Remote_Access_Type, Previous: Pragma Pure_Function, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Relative_Deadline (time_span_EXPRESSSION);
This pragma is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. See Ada 2012 Reference Manual for details.
Next: Pragma Restriction_Warnings, Previous: Pragma Relative_Deadline, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Remote_Access_Type ([Entity =>] formal_access_type_LOCAL_NAME);
This pragma appears in the formal part of a generic declaration. It specifies an exception to the RM rule from E.2.2(17/2), which forbids the use of a remote access to class-wide type as actual for a formal access type.
When this pragma applies to a formal access type Entity
, that
type is treated as a remote access to class-wide type in the generic.
It must be a formal general access type, and its designated type must
be the class-wide type of a formal tagged limited private type from the
same generic declaration.
In the generic unit, the formal type is subject to all restrictions pertaining to remote access to class-wide types. At instantiation, the actual type must be a remote access to class-wide type.
Next: Pragma Shared, Previous: Pragma Remote_Access_Type, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Restriction_Warnings (restriction_IDENTIFIER {, restriction_IDENTIFIER});
This pragma allows a series of restriction identifiers to be
specified (the list of allowed identifiers is the same as for
pragma Restrictions
). For each of these identifiers
the compiler checks for violations of the restriction, but
generates a warning message rather than an error message
if the restriction is violated.
Next: Pragma Short_Circuit_And_Or, Previous: Pragma Restriction_Warnings, Up: Implementation Defined Pragmas [Contents][Index]
This pragma is provided for compatibility with Ada 83. The syntax and semantics are identical to pragma Atomic.
Next: Pragma Short_Descriptors, Previous: Pragma Shared, Up: Implementation Defined Pragmas [Contents][Index]
This configuration pragma causes any occurrence of the AND operator applied to operands of type Standard.Boolean to be short-circuited (i.e. the AND operator is treated as if it were AND THEN). Or is similarly treated as OR ELSE. This may be useful in the context of certification protocols requiring the use of short-circuited logical operators. If this configuration pragma occurs locally within the file being compiled, it applies only to the file being compiled. There is no requirement that all units in a partition use this option.
Next: Pragma Simple_Storage_Pool_Type, Previous: Pragma Short_Circuit_And_Or, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Short_Descriptors
In VMS versions of the compiler, this configuration pragma causes all occurrences of the mechanism types Descriptor[_xxx] to be treated as Short_Descriptor[_xxx]. This is helpful in porting legacy applications from a 32-bit environment to a 64-bit environment. This pragma is ignored for non-VMS versions.
Next: Pragma Source_File_Name, Previous: Pragma Short_Descriptors, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Simple_Storage_Pool_Type (type_LOCAL_NAME);
A type can be established as a “simple storage pool type” by applying
the representation pragma Simple_Storage_Pool_Type
to the type.
A type named in the pragma must be a library-level immutably limited record
type or limited tagged type declared immediately within a package declaration.
The type can also be a limited private type whose full type is allowed as
a simple storage pool type.
For a simple storage pool type SSP, nonabstract primitive subprograms
Allocate
, Deallocate
, and Storage_Size
can be declared that
are subtype conformant with the following subprogram declarations:
procedure Allocate (Pool : in out SSP; Storage_Address : out System.Address; Size_In_Storage_Elements : System.Storage_Elements.Storage_Count; Alignment : System.Storage_Elements.Storage_Count); procedure Deallocate (Pool : in out SSP; Storage_Address : System.Address; Size_In_Storage_Elements : System.Storage_Elements.Storage_Count; Alignment : System.Storage_Elements.Storage_Count); function Storage_Size (Pool : SSP) return System.Storage_Elements.Storage_Count;
Procedure Allocate
must be declared, whereas Deallocate
and
Storage_Size
are optional. If Deallocate
is not declared, then
applying an unchecked deallocation has no effect other than to set its actual
parameter to null. If Storage_Size
is not declared, then the
Storage_Size
attribute applied to an access type associated with
a pool object of type SSP returns zero. Additional operations can be declared
for a simple storage pool type (such as for supporting a mark/release
storage-management discipline).
An object of a simple storage pool type can be associated with an access
type by specifying the attribute Simple_Storage_Pool
. For example:
My_Pool : My_Simple_Storage_Pool_Type; type Acc is access My_Data_Type; for Acc'Simple_Storage_Pool use My_Pool;
See attribute Simple_Storage_Pool
for further details.
Next: Pragma Source_File_Name_Project, Previous: Pragma Simple_Storage_Pool_Type, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Source_File_Name ( [Unit_Name =>] unit_NAME, Spec_File_Name => STRING_LITERAL, [Index => INTEGER_LITERAL]); pragma Source_File_Name ( [Unit_Name =>] unit_NAME, Body_File_Name => STRING_LITERAL, [Index => INTEGER_LITERAL]);
Use this to override the normal naming convention. It is a configuration pragma, and so has the usual applicability of configuration pragmas (i.e. it applies to either an entire partition, or to all units in a compilation, or to a single unit, depending on how it is used. unit_name is mapped to file_name_literal. The identifier for the second argument is required, and indicates whether this is the file name for the spec or for the body.
The optional Index argument should be used when a file contains multiple
units, and when you do not want to use gnatchop
to separate then
into multiple files (which is the recommended procedure to limit the
number of recompilations that are needed when some sources change).
For instance, if the source file source.ada contains
package B is ... end B; with B; procedure A is begin .. end A;
you could use the following configuration pragmas:
pragma Source_File_Name (B, Spec_File_Name => "source.ada", Index => 1); pragma Source_File_Name (A, Body_File_Name => "source.ada", Index => 2);
Note that the gnatname
utility can also be used to generate those
configuration pragmas.
Another form of the Source_File_Name
pragma allows
the specification of patterns defining alternative file naming schemes
to apply to all files.
pragma Source_File_Name ( [Spec_File_Name =>] STRING_LITERAL [,[Casing =>] CASING_SPEC] [,[Dot_Replacement =>] STRING_LITERAL]); pragma Source_File_Name ( [Body_File_Name =>] STRING_LITERAL [,[Casing =>] CASING_SPEC] [,[Dot_Replacement =>] STRING_LITERAL]); pragma Source_File_Name ( [Subunit_File_Name =>] STRING_LITERAL [,[Casing =>] CASING_SPEC] [,[Dot_Replacement =>] STRING_LITERAL]); CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
The first argument is a pattern that contains a single asterisk indicating the point at which the unit name is to be inserted in the pattern string to form the file name. The second argument is optional. If present it specifies the casing of the unit name in the resulting file name string. The default is lower case. Finally the third argument allows for systematic replacement of any dots in the unit name by the specified string literal.
Note that Source_File_Name pragmas should not be used if you are using project files. The reason for this rule is that the project manager is not aware of these pragmas, and so other tools that use the projet file would not be aware of the intended naming conventions. If you are using project files, file naming is controlled by Source_File_Name_Project pragmas, which are usually supplied automatically by the project manager. A pragma Source_File_Name cannot appear after a Pragma Source_File_Name_Project.
For more details on the use of the Source_File_Name
pragma,
See Using Other File Names in GNAT User’s Guide,
and Alternative File Naming Schemes in GNAT
User’s Guide.
Next: Pragma Source_Reference, Previous: Pragma Source_File_Name, Up: Implementation Defined Pragmas [Contents][Index]
This pragma has the same syntax and semantics as pragma Source_File_Name. It is only allowed as a stand alone configuration pragma. It cannot appear after a Pragma Source_File_Name, and most importantly, once pragma Source_File_Name_Project appears, no further Source_File_Name pragmas are allowed.
The intention is that Source_File_Name_Project pragmas are always generated by the Project Manager in a manner consistent with the naming specified in a project file, and when naming is controlled in this manner, it is not permissible to attempt to modify this naming scheme using Source_File_Name or Source_File_Name_Project pragmas (which would not be known to the project manager).
Next: Pragma Static_Elaboration_Desired, Previous: Pragma Source_File_Name_Project, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
This pragma must appear as the first line of a source file.
integer_literal is the logical line number of the line following
the pragma line (for use in error messages and debugging
information). string_literal is a static string constant that
specifies the file name to be used in error messages and debugging
information. This is most notably used for the output of gnatchop
with the -r switch, to make sure that the original unchopped
source file is the one referred to.
The second argument must be a string literal, it cannot be a static string expression other than a string literal. This is because its value is needed for error messages issued by all phases of the compiler.
Next: Pragma Stream_Convert, Previous: Pragma Source_Reference, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Static_Elaboration_Desired;
This pragma is used to indicate that the compiler should attempt to initialize statically the objects declared in the library unit to which the pragma applies, when these objects are initialized (explicitly or implicitly) by an aggregate. In the absence of this pragma, aggregates in object declarations are expanded into assignments and loops, even when the aggregate components are static constants. When the aggregate is present the compiler builds a static expression that requires no run-time code, so that the initialized object can be placed in read-only data space. If the components are not static, or the aggregate has more that 100 components, the compiler emits a warning that the pragma cannot be obeyed. (See also the restriction No_Implicit_Loops, which supports static construction of larger aggregates with static components that include an others choice.)
Next: Pragma Style_Checks, Previous: Pragma Static_Elaboration_Desired, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Stream_Convert ( [Entity =>] type_LOCAL_NAME, [Read =>] function_NAME, [Write =>] function_NAME);
This pragma provides an efficient way of providing stream functions for types defined in packages. Not only is it simpler to use than declaring the necessary functions with attribute representation clauses, but more significantly, it allows the declaration to made in such a way that the stream packages are not loaded unless they are needed. The use of the Stream_Convert pragma adds no overhead at all, unless the stream attributes are actually used on the designated type.
The first argument specifies the type for which stream functions are provided. The second parameter provides a function used to read values of this type. It must name a function whose argument type may be any subtype, and whose returned type must be the type given as the first argument to the pragma.
The meaning of the Read parameter is that if a stream attribute directly or indirectly specifies reading of the type given as the first parameter, then a value of the type given as the argument to the Read function is read from the stream, and then the Read function is used to convert this to the required target type.
Similarly the Write parameter specifies how to treat write attributes that directly or indirectly apply to the type given as the first parameter. It must have an input parameter of the type specified by the first parameter, and the return type must be the same as the input type of the Read function. The effect is to first call the Write function to convert to the given stream type, and then write the result type to the stream.
The Read and Write functions must not be overloaded subprograms. If necessary renamings can be supplied to meet this requirement. The usage of this attribute is best illustrated by a simple example, taken from the GNAT implementation of package Ada.Strings.Unbounded:
function To_Unbounded (S : String) return Unbounded_String renames To_Unbounded_String; pragma Stream_Convert (Unbounded_String, To_Unbounded, To_String);
The specifications of the referenced functions, as given in the Ada Reference Manual are:
function To_Unbounded_String (Source : String) return Unbounded_String; function To_String (Source : Unbounded_String) return String;
The effect is that if the value of an unbounded string is written to a stream,
then the representation of the item in the stream is in the same format that
would be used for Standard.String'Output
, and this same representation
is expected when a value of this type is read from the stream. Note that the
value written always includes the bounds, even for Unbounded_String’Write,
since Unbounded_String is not an array type.
Next: Pragma Subtitle, Previous: Pragma Stream_Convert, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Style_Checks (string_LITERAL | ALL_CHECKS | On | Off [, LOCAL_NAME]);
This pragma is used in conjunction with compiler switches to control the built in style checking provided by GNAT. The compiler switches, if set, provide an initial setting for the switches, and this pragma may be used to modify these settings, or the settings may be provided entirely by the use of the pragma. This pragma can be used anywhere that a pragma is legal, including use as a configuration pragma (including use in the gnat.adc file).
The form with a string literal specifies which style options are to be
activated. These are additive, so they apply in addition to any previously
set style check options. The codes for the options are the same as those
used in the -gnaty switch to gcc
or gnatmake
.
For example the following two methods can be used to enable
layout checking:
pragma Style_Checks ("l");
gcc -c -gnatyl …
The form ALL_CHECKS activates all standard checks (its use is equivalent
to the use of the gnaty
switch with no options. See About This Guide in GNAT User’s Guide, for details.)
Note: the behavior is slightly different in GNAT mode (-gnatg used). In this case, ALL_CHECKS implies the standard set of GNAT mode style check options (i.e. equivalent to -gnatyg).
The forms with Off
and On
can be used to temporarily disable style checks
as shown in the following example:
pragma Style_Checks ("k"); -- requires keywords in lower case pragma Style_Checks (Off); -- turn off style checks NULL; -- this will not generate an error message pragma Style_Checks (On); -- turn style checks back on NULL; -- this will generate an error message
Finally the two argument form is allowed only if the first argument is
On
or Off
. The effect is to turn of semantic style checks
for the specified entity, as shown in the following example:
pragma Style_Checks ("r"); -- require consistency of identifier casing Arg : Integer; Rf1 : Integer := ARG; -- incorrect, wrong case pragma Style_Checks (Off, Arg); Rf2 : Integer := ARG; -- OK, no error
Next: Pragma Suppress, Previous: Pragma Style_Checks, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Subtitle ([Subtitle =>] STRING_LITERAL);
This pragma is recognized for compatibility with other Ada compilers but is ignored by GNAT.
Next: Pragma Suppress_All, Previous: Pragma Subtitle, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Suppress (Identifier [, [On =>] Name]);
This is a standard pragma, and supports all the check names required in
the RM. It is included here because GNAT recognizes one additional check
name: Alignment_Check
which can be used to suppress alignment checks
on addresses used in address clauses. Such checks can also be suppressed
by suppressing range checks, but the specific use of Alignment_Check
allows suppression of alignment checks without suppressing other range checks.
Note that pragma Suppress gives the compiler permission to omit checks, but does not require the compiler to omit checks. The compiler will generate checks if they are essentially free, even when they are suppressed. In particular, if the compiler can prove that a certain check will necessarily fail, it will generate code to do an unconditional “raise”, even if checks are suppressed. The compiler warns in this case.
Of course, run-time checks are omitted whenever the compiler can prove that they will not fail, whether or not checks are suppressed.
Next: Pragma Suppress_Exception_Locations, Previous: Pragma Suppress, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Suppress_All;
This pragma can appear anywhere within a unit.
The effect is to apply Suppress (All_Checks)
to the unit
in which it appears. This pragma is implemented for compatibility with DEC
Ada 83 usage where it appears at the end of a unit, and for compatibility
with Rational Ada, where it appears as a program unit pragma.
The use of the standard Ada pragma Suppress (All_Checks)
as a normal configuration pragma is the preferred usage in GNAT.
Next: Pragma Suppress_Initialization, Previous: Pragma Suppress_All, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Suppress_Exception_Locations;
In normal mode, a raise statement for an exception by default generates
an exception message giving the file name and line number for the location
of the raise. This is useful for debugging and logging purposes, but this
entails extra space for the strings for the messages. The configuration
pragma Suppress_Exception_Locations
can be used to suppress the
generation of these strings, with the result that space is saved, but the
exception message for such raises is null. This configuration pragma may
appear in a global configuration pragma file, or in a specific unit as
usual. It is not required that this pragma be used consistently within
a partition, so it is fine to have some units within a partition compiled
with this pragma and others compiled in normal mode without it.
Next: Pragma Task_Info, Previous: Pragma Suppress_Exception_Locations, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Suppress_Initialization ([Entity =>] subtype_Name);
Here subtype_Name is the name introduced by a type declaration or subtype declaration. This pragma suppresses any implicit or explicit initialization for all variables of the given type or subtype, including initialization resulting from the use of pragmas Normalize_Scalars or Initialize_Scalars.
This is considered a representation item, so it cannot be given after the type is frozen. It applies to all subsequent object declarations, and also any allocator that creates objects of the type.
If the pragma is given for the first subtype, then it is considered to apply to the base type and all its subtypes. If the pragma is given for other than a first subtype, then it applies only to the given subtype. The pragma may not be given after the type is frozen.
Next: Pragma Task_Name, Previous: Pragma Suppress_Initialization, Up: Implementation Defined Pragmas [Contents][Index]
Syntax
pragma Task_Info (EXPRESSION);
This pragma appears within a task definition (like pragma
Priority
) and applies to the task in which it appears. The
argument must be of type System.Task_Info.Task_Info_Type
.
The Task_Info
pragma provides system dependent control over
aspects of tasking implementation, for example, the ability to map
tasks to specific processors. For details on the facilities available
for the version of GNAT that you are using, see the documentation
in the spec of package System.Task_Info in the runtime
library.
Next: Pragma Task_Storage, Previous: Pragma Task_Info, Up: Implementation Defined Pragmas [Contents][Index]
Syntax
pragma Task_Name (string_EXPRESSION);
This pragma appears within a task definition (like pragma
Priority
) and applies to the task in which it appears. The
argument must be of type String, and provides a name to be used for
the task instance when the task is created. Note that this expression
is not required to be static, and in particular, it can contain
references to task discriminants. This facility can be used to
provide different names for different tasks as they are created,
as illustrated in the example below.
The task name is recorded internally in the run-time structures
and is accessible to tools like the debugger. In addition the
routine Ada.Task_Identification.Image
will return this
string, with a unique task address appended.
-- Example of the use of pragma Task_Name with Ada.Task_Identification; use Ada.Task_Identification; with Text_IO; use Text_IO; procedure t3 is type Astring is access String; task type Task_Typ (Name : access String) is pragma Task_Name (Name.all); end Task_Typ; task body Task_Typ is Nam : constant String := Image (Current_Task); begin Put_Line ("-->" & Nam (1 .. 14) & "<--"); end Task_Typ; type Ptr_Task is access Task_Typ; Task_Var : Ptr_Task; begin Task_Var := new Task_Typ (new String'("This is task 1")); Task_Var := new Task_Typ (new String'("This is task 2")); end;
Next: Pragma Test_Case, Previous: Pragma Task_Name, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Task_Storage ( [Task_Type =>] LOCAL_NAME, [Top_Guard =>] static_integer_EXPRESSION);
This pragma specifies the length of the guard area for tasks. The guard
area is an additional storage area allocated to a task. A value of zero
means that either no guard area is created or a minimal guard area is
created, depending on the target. This pragma can appear anywhere a
Storage_Size
attribute definition clause is allowed for a task
type.
Next: Pragma Thread_Local_Storage, Previous: Pragma Task_Storage, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Test_Case ( [Name =>] static_string_Expression ,[Mode =>] (Nominal | Robustness) [, Requires => Boolean_Expression] [, Ensures => Boolean_Expression]);
The Test_Case
pragma allows defining fine-grain specifications
for use by testing tools. Its syntax is similar to the syntax of the
Contract_Case
pragma, which is used for both testing and
formal verification.
The compiler checks the validity of the Test_Case
pragma, but its
presence does not lead to any modification of the code generated by the
compiler, contrary to the treatment of the Contract_Case
pragma.
Test_Case
pragmas may only appear immediately following the
(separate) declaration of a subprogram in a package declaration, inside
a package spec unit. Only other pragmas may intervene (that is appear
between the subprogram declaration and a test case).
The compiler checks that boolean expressions given in Requires
and
Ensures
are valid, where the rules for Requires
are the
same as the rule for an expression in Precondition
and the rules
for Ensures
are the same as the rule for an expression in
Postcondition
. In particular, attributes 'Old
and
'Result
can only be used within the Ensures
expression. The following is an example of use within a package spec:
package Math_Functions is ... function Sqrt (Arg : Float) return Float; pragma Test_Case (Name => "Test 1", Mode => Nominal, Requires => Arg < 10000, Ensures => Sqrt'Result < 10); ... end Math_Functions;
The meaning of a test case is that there is at least one context where
Requires
holds such that, if the associated subprogram is executed in
that context, then Ensures
holds when the subprogram returns.
Mode Nominal
indicates that the input context should also satisfy the
precondition of the subprogram, and the output context should also satisfy its
postcondition. More Robustness
indicates that the precondition and
postcondition of the subprogram should be ignored for this test case.
Next: Pragma Time_Slice, Previous: Pragma Test_Case, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Thread_Local_Storage ([Entity =>] LOCAL_NAME);
This pragma specifies that the specified entity, which must be
a variable declared in a library level package, is to be marked as
"Thread Local Storage" (TLS
). On systems supporting this (which
include Solaris, GNU/Linux and VxWorks 6), this causes each thread
(and hence each Ada task) to see a distinct copy of the variable.
The variable may not have default initialization, and if there is
an explicit initialization, it must be either null
for an
access variable, or a static expression for a scalar variable.
This provides a low level mechanism similar to that provided by
the Ada.Task_Attributes
package, but much more efficient
and is also useful in writing interface code that will interact
with foreign threads.
If this pragma is used on a system where TLS
is not supported,
then an error message will be generated and the program will be rejected.
Next: Pragma Title, Previous: Pragma Thread_Local_Storage, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Time_Slice (static_duration_EXPRESSION);
For implementations of GNAT on operating systems where it is possible to supply a time slice value, this pragma may be used for this purpose. It is ignored if it is used in a system that does not allow this control, or if it appears in other than the main program unit. Note that the effect of this pragma is identical to the effect of the DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
Next: Pragma Unchecked_Union, Previous: Pragma Time_Slice, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Title (TITLING_OPTION [, TITLING OPTION]); TITLING_OPTION ::= [Title =>] STRING_LITERAL, | [Subtitle =>] STRING_LITERAL
Syntax checked but otherwise ignored by GNAT. This is a listing control pragma used in DEC Ada 83 implementations to provide a title and/or subtitle for the program listing. The program listing generated by GNAT does not have titles or subtitles.
Unlike other pragmas, the full flexibility of named notation is allowed for this pragma, i.e. the parameters may be given in any order if named notation is used, and named and positional notation can be mixed following the normal rules for procedure calls in Ada.
Next: Pragma Unimplemented_Unit, Previous: Pragma Title, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unchecked_Union (first_subtype_LOCAL_NAME);
This pragma is used to specify a representation of a record type that is equivalent to a C union. It was introduced as a GNAT implementation defined pragma in the GNAT Ada 95 mode. Ada 2005 includes an extended version of this pragma, making it language defined, and GNAT fully implements this extended version in all language modes (Ada 83, Ada 95, and Ada 2005). For full details, consult the Ada 2012 Reference Manual, section B.3.3.
Next: Pragma Universal_Aliasing, Previous: Pragma Unchecked_Union, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unimplemented_Unit;
If this pragma occurs in a unit that is processed by the compiler, GNAT aborts with the message ‘xxx not implemented’, where xxx is the name of the current compilation unit. This pragma is intended to allow the compiler to handle unimplemented library units in a clean manner.
The abort only happens if code is being generated. Thus you can use specs of unimplemented packages in syntax or semantic checking mode.
Next: Pragma Universal_Data, Previous: Pragma Unimplemented_Unit, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Universal_Aliasing [([Entity =>] type_LOCAL_NAME)];
type_LOCAL_NAME must refer to a type declaration in the current declarative part. The effect is to inhibit strict type-based aliasing optimization for the given type. In other words, the effect is as though access types designating this type were subject to pragma No_Strict_Aliasing. For a detailed description of the strict aliasing optimization, and the situations in which it must be suppressed, See Optimization and Strict Aliasing in GNAT User’s Guide.
Next: Pragma Unmodified, Previous: Pragma Universal_Aliasing, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Universal_Data [(library_unit_Name)];
This pragma is supported only for the AAMP target and is ignored for other targets. The pragma specifies that all library-level objects (Counter 0 data) associated with the library unit are to be accessed and updated using universal addressing (24-bit addresses for AAMP5) rather than the default of 16-bit Data Environment (DENV) addressing. Use of this pragma will generally result in less efficient code for references to global data associated with the library unit, but allows such data to be located anywhere in memory. This pragma is a library unit pragma, but can also be used as a configuration pragma (including use in the gnat.adc file). The functionality of this pragma is also available by applying the -univ switch on the compilations of units where universal addressing of the data is desired.
Next: Pragma Unreferenced, Previous: Pragma Universal_Data, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unmodified (LOCAL_NAME {, LOCAL_NAME});
This pragma signals that the assignable entities (variables,
out
parameters, in out
parameters) whose names are listed are
deliberately not assigned in the current source unit. This
suppresses warnings about the
entities being referenced but not assigned, and in addition a warning will be
generated if one of these entities is in fact assigned in the
same unit as the pragma (or in the corresponding body, or one
of its subunits).
This is particularly useful for clearly signaling that a particular parameter is not modified, even though the spec suggests that it might be.
Next: Pragma Unreferenced_Objects, Previous: Pragma Unmodified, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unreferenced (LOCAL_NAME {, LOCAL_NAME}); pragma Unreferenced (library_unit_NAME {, library_unit_NAME});
This pragma signals that the entities whose names are listed are deliberately not referenced in the current source unit. This suppresses warnings about the entities being unreferenced, and in addition a warning will be generated if one of these entities is in fact subsequently referenced in the same unit as the pragma (or in the corresponding body, or one of its subunits).
This is particularly useful for clearly signaling that a particular parameter is not referenced in some particular subprogram implementation and that this is deliberate. It can also be useful in the case of objects declared only for their initialization or finalization side effects.
If LOCAL_NAME
identifies more than one matching homonym in the
current scope, then the entity most recently declared is the one to which
the pragma applies. Note that in the case of accept formals, the pragma
Unreferenced may appear immediately after the keyword do
which
allows the indication of whether or not accept formals are referenced
or not to be given individually for each accept statement.
The left hand side of an assignment does not count as a reference for the purpose of this pragma. Thus it is fine to assign to an entity for which pragma Unreferenced is given.
Note that if a warning is desired for all calls to a given subprogram, regardless of whether they occur in the same unit as the subprogram declaration, then this pragma should not be used (calls from another unit would not be flagged); pragma Obsolescent can be used instead for this purpose, see See Pragma Obsolescent.
The second form of pragma Unreferenced
is used within a context
clause. In this case the arguments must be unit names of units previously
mentioned in with
clauses (similar to the usage of pragma
Elaborate_All
. The effect is to suppress warnings about unreferenced
units and unreferenced entities within these units.
Next: Pragma Unreserve_All_Interrupts, Previous: Pragma Unreferenced, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unreferenced_Objects (local_subtype_NAME {, local_subtype_NAME});
This pragma signals that for the types or subtypes whose names are listed, objects which are declared with one of these types or subtypes may not be referenced, and if no references appear, no warnings are given.
This is particularly useful for objects which are declared solely for their initialization and finalization effect. Such variables are sometimes referred to as RAII variables (Resource Acquisition Is Initialization). Using this pragma on the relevant type (most typically a limited controlled type), the compiler will automatically suppress unwanted warnings about these variables not being referenced.
Next: Pragma Unsuppress, Previous: Pragma Unreferenced_Objects, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unreserve_All_Interrupts;
Normally certain interrupts are reserved to the implementation. Any attempt
to attach an interrupt causes Program_Error to be raised, as described in
RM C.3.2(22). A typical example is the SIGINT
interrupt used in
many systems for a Ctrl-C interrupt. Normally this interrupt is
reserved to the implementation, so that Ctrl-C can be used to
interrupt execution.
If the pragma Unreserve_All_Interrupts
appears anywhere in any unit in
a program, then all such interrupts are unreserved. This allows the
program to handle these interrupts, but disables their standard
functions. For example, if this pragma is used, then pressing
Ctrl-C will not automatically interrupt execution. However,
a program can then handle the SIGINT
interrupt as it chooses.
For a full list of the interrupts handled in a specific implementation,
see the source code for the spec of Ada.Interrupts.Names
in
file a-intnam.ads. This is a target dependent file that contains the
list of interrupts recognized for a given target. The documentation in
this file also specifies what interrupts are affected by the use of
the Unreserve_All_Interrupts
pragma.
For a more general facility for controlling what interrupts can be
handled, see pragma Interrupt_State
, which subsumes the functionality
of the Unreserve_All_Interrupts
pragma.
Next: Pragma Use_VADS_Size, Previous: Pragma Unreserve_All_Interrupts, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
This pragma undoes the effect of a previous pragma Suppress
. If
there is no corresponding pragma Suppress
in effect, it has no
effect. The range of the effect is the same as for pragma
Suppress
. The meaning of the arguments is identical to that used
in pragma Suppress
.
One important application is to ensure that checks are on in cases where code depends on the checks for its correct functioning, so that the code will compile correctly even if the compiler switches are set to suppress checks.
This pragma is standard in Ada 2005. It is available in all earlier versions of Ada as an implementation-defined pragma.
Next: Pragma Validity_Checks, Previous: Pragma Unsuppress, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Use_VADS_Size;
This is a configuration pragma. In a unit to which it applies, any use of the ’Size attribute is automatically interpreted as a use of the ’VADS_Size attribute. Note that this may result in incorrect semantic processing of valid Ada 95 or Ada 2005 programs. This is intended to aid in the handling of existing code which depends on the interpretation of Size as implemented in the VADS compiler. See description of the VADS_Size attribute for further details.
Next: Pragma Volatile, Previous: Pragma Use_VADS_Size, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
This pragma is used in conjunction with compiler switches to control the built-in validity checking provided by GNAT. The compiler switches, if set provide an initial setting for the switches, and this pragma may be used to modify these settings, or the settings may be provided entirely by the use of the pragma. This pragma can be used anywhere that a pragma is legal, including use as a configuration pragma (including use in the gnat.adc file).
The form with a string literal specifies which validity options are to be
activated. The validity checks are first set to include only the default
reference manual settings, and then a string of letters in the string
specifies the exact set of options required. The form of this string
is exactly as described for the -gnatVx compiler switch (see the
GNAT User’s Guide for details). For example the following two
methods can be used to enable validity checking for mode in
and
in out
subprogram parameters:
pragma Validity_Checks ("im");
gcc -c -gnatVim …
The form ALL_CHECKS activates all standard checks (its use is equivalent
to the use of the gnatva
switch.
The forms with Off
and On
can be used to temporarily disable validity checks
as shown in the following example:
pragma Validity_Checks ("c"); -- validity checks for copies pragma Validity_Checks (Off); -- turn off validity checks A := B; -- B will not be validity checked pragma Validity_Checks (On); -- turn validity checks back on A := C; -- C will be validity checked
Next: Pragma Warnings, Previous: Pragma Validity_Checks, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Volatile (LOCAL_NAME);
This pragma is defined by the Ada Reference Manual, and the GNAT implementation is fully conformant with this definition. The reason it is mentioned in this section is that a pragma of the same name was supplied in some Ada 83 compilers, including DEC Ada 83. The Ada 95 / Ada 2005 implementation of pragma Volatile is upwards compatible with the implementation in DEC Ada 83.
Next: Pragma Weak_External, Previous: Pragma Volatile, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Warnings (On | Off); pragma Warnings (On | Off, LOCAL_NAME); pragma Warnings (static_string_EXPRESSION); pragma Warnings (On | Off, static_string_EXPRESSION);
Normally warnings are enabled, with the output being controlled by
the command line switch. Warnings (Off
) turns off generation of
warnings until a Warnings (On
) is encountered or the end of the
current unit. If generation of warnings is turned off using this
pragma, then no warning messages are output, regardless of the
setting of the command line switches.
The form with a single argument may be used as a configuration pragma.
If the LOCAL_NAME parameter is present, warnings are suppressed for
the specified entity. This suppression is effective from the point where
it occurs till the end of the extended scope of the variable (similar to
the scope of Suppress
).
The form with a single static_string_EXPRESSION argument provides more precise control over which warnings are active. The string is a list of letters specifying which warnings are to be activated and which deactivated. The code for these letters is the same as the string used in the command line switch controlling warnings. For a brief summary, use the gnatmake command with no arguments, which will generate usage information containing the list of warnings switches supported. For full details see Warning Message Control in GNAT User’s Guide.
The warnings controlled by the ‘-gnatw’ switch are generated by the front end of the compiler. The ‘GCC’ back end can provide additional warnings and they are controlled by the ‘-W’ switch. The form with a single static_string_EXPRESSION argument also works for the latters, but the string must be a single full ‘-W’ switch in this case. The above reference lists a few examples of these additional warnings.
The specified warnings will be in effect until the end of the program or another pragma Warnings is encountered. The effect of the pragma is cumulative. Initially the set of warnings is the standard default set as possibly modified by compiler switches. Then each pragma Warning modifies this set of warnings as specified. This form of the pragma may also be used as a configuration pragma.
The fourth form, with an On|Off
parameter and a string, is used to
control individual messages, based on their text. The string argument
is a pattern that is used to match against the text of individual
warning messages (not including the initial "warning: " tag).
The pattern may contain asterisks, which match zero or more characters in
the message. For example, you can use
pragma Warnings (Off, "*bits of*unused")
to suppress the warning
message warning: 960 bits of "a" unused
. No other regular
expression notations are permitted. All characters other than asterisk in
these three specific cases are treated as literal characters in the match.
The above use of patterns to match the message applies only to warning messages generated by the front end. This form of the pragma with a string argument can also be used to control back end warnings controlled by a "-Wxxx" switch. Such warnings can be identified by the appearence of a string of the form "[-Wxxx]" in the message which identifies the "-W" switch that controls the message. By using the text of the "-W" switch in the pragma, such back end warnings can be turned on and off.
There are two ways to use the pragma in this form. The OFF form can be used as a configuration pragma. The effect is to suppress all warnings (if any) that match the pattern string throughout the compilation (or match the -W switch in the back end case).
The second usage is to suppress a warning locally, and in this case, two pragmas must appear in sequence:
pragma Warnings (Off, Pattern); … code where given warning is to be suppressed pragma Warnings (On, Pattern);
In this usage, the pattern string must match in the Off and On pragmas, and at least one matching warning must be suppressed.
Note: to write a string that will match any warning, use the string
"***"
. It will not work to use a single asterisk or two asterisks
since this looks like an operator name. This form with three asterisks
is similar in effect to specifying pragma Warnings (Off)
except that a
matching pragma Warnings (On, "***")
will be required. This can be
helpful in avoiding forgetting to turn warnings back on.
Note: the debug flag -gnatd.i (/NOWARNINGS_PRAGMAS
in VMS) can be
used to cause the compiler to entirely ignore all WARNINGS pragmas. This can
be useful in checking whether obsolete pragmas in existing programs are hiding
real problems.
Note: pragma Warnings does not affect the processing of style messages. See separate entry for pragma Style_Checks for control of style messages.
Next: Pragma Wide_Character_Encoding, Previous: Pragma Warnings, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Weak_External ([Entity =>] LOCAL_NAME);
LOCAL_NAME must refer to an object that is declared at the library
level. This pragma specifies that the given entity should be marked as a
weak symbol for the linker. It is equivalent to __attribute__((weak))
in GNU C and causes LOCAL_NAME to be emitted as a weak symbol instead
of a regular symbol, that is to say a symbol that does not have to be
resolved by the linker if used in conjunction with a pragma Import.
When a weak symbol is not resolved by the linker, its address is set to zero. This is useful in writing interfaces to external modules that may or may not be linked in the final executable, for example depending on configuration settings.
If a program references at run time an entity to which this pragma has been applied, and the corresponding symbol was not resolved at link time, then the execution of the program is erroneous. It is not erroneous to take the Address of such an entity, for example to guard potential references, as shown in the example below.
Some file formats do not support weak symbols so not all target machines support this pragma.
-- Example of the use of pragma Weak_External package External_Module is key : Integer; pragma Import (C, key); pragma Weak_External (key); function Present return boolean; end External_Module; with System; use System; package body External_Module is function Present return boolean is begin return key'Address /= System.Null_Address; end Present; end External_Module;
Next: Abort_Signal, Previous: Pragma Weak_External, Up: Implementation Defined Pragmas [Contents][Index]
Syntax:
pragma Wide_Character_Encoding (IDENTIFIER | CHARACTER_LITERAL);
This pragma specifies the wide character encoding to be used in program source text appearing subsequently. It is a configuration pragma, but may also be used at any point that a pragma is allowed, and it is permissible to have more than one such pragma in a file, allowing multiple encodings to appear within the same file.
The argument can be an identifier or a character literal. In the identifier
case, it is one of HEX
, UPPER
, SHIFT_JIS
,
EUC
, UTF8
, or BRACKETS
. In the character literal
case it is correspondingly one of the characters ‘h’, ‘u’,
‘s’, ‘e’, ‘8’, or ‘b’.
Note that when the pragma is used within a file, it affects only the encoding within that file, and does not affect withed units, specs, or subunits.
Next: Standard and Implementation Defined Restrictions, Previous: Implementation Defined Pragmas, Up: Top [Contents][Index]
Ada defines (throughout the Ada reference manual, summarized in Annex K), a set of attributes that provide useful additional functionality in all areas of the language. These language defined attributes are implemented in GNAT and work as described in the Ada Reference Manual.
In addition, Ada allows implementations to define additional attributes whose meaning is defined by the implementation. GNAT provides a number of these implementation-dependent attributes which can be used to extend and enhance the functionality of the compiler. This section of the GNAT reference manual describes these additional attributes.
Note that any program using these attributes may not be portable to other compilers (although GNAT implements this set of attributes on all platforms). Therefore if portability to other compilers is an important consideration, you should minimize the use of these attributes.
• Abort_Signal: | ||
• Address_Size: | ||
• Asm_Input: | ||
• Asm_Output: | ||
• AST_Entry: | ||
• Bit: | ||
• Bit_Position: | ||
• Compiler_Version: | ||
• Code_Address: | ||
• Default_Bit_Order: | ||
• Descriptor_Size: | ||
• Elaborated: | ||
• Elab_Body: | ||
• Elab_Spec: | ||
• Elab_Subp_Body: | ||
• Emax: | ||
• Enabled: | ||
• Enum_Rep: | ||
• Enum_Val: | ||
• Epsilon: | ||
• Fixed_Value: | ||
• Has_Access_Values: | ||
• Has_Discriminants: | ||
• Img: | ||
• Integer_Value: | ||
• Invalid_Value: | ||
• Large: | ||
• Machine_Size: | ||
• Mantissa: | ||
• Max_Interrupt_Priority: | ||
• Max_Priority: | ||
• Maximum_Alignment: | ||
• Mechanism_Code: | ||
• Null_Parameter: | ||
• Object_Size: | ||
• Passed_By_Reference: | ||
• Pool_Address: | ||
• Range_Length: | ||
• Ref: | ||
• Result: | ||
• Safe_Emax: | ||
• Safe_Large: | ||
• Scalar_Storage_Order: | ||
• Simple_Storage_Pool: | ||
• Small: | ||
• Storage_Unit: | ||
• Stub_Type: | ||
• System_Allocator_Alignment: | ||
• Target_Name: | ||
• Tick: | ||
• To_Address: | ||
• Type_Class: | ||
• UET_Address: | ||
• Unconstrained_Array: | ||
• Universal_Literal_String: | ||
• Unrestricted_Access: | ||
• Valid_Scalars: | ||
• VADS_Size: | ||
• Value_Size: | ||
• Wchar_T_Size: | ||
• Word_Size: |
Next: Address_Size, Previous: Pragma Wide_Character_Encoding, Up: Implementation Defined Attributes [Contents][Index]
Standard'Abort_Signal
(Standard
is the only allowed
prefix) provides the entity for the special exception used to signal
task abort or asynchronous transfer of control. Normally this attribute
should only be used in the tasking runtime (it is highly peculiar, and
completely outside the normal semantics of Ada, for a user program to
intercept the abort exception).
Next: Asm_Input, Previous: Abort_Signal, Up: Implementation Defined Attributes [Contents][Index]
Standard'Address_Size
(Standard
is the only allowed
prefix) is a static constant giving the number of bits in an
Address
. It is the same value as System.Address’Size,
but has the advantage of being static, while a direct
reference to System.Address’Size is non-static because Address
is a private type.
Next: Asm_Output, Previous: Address_Size, Up: Implementation Defined Attributes [Contents][Index]
The Asm_Input
attribute denotes a function that takes two
parameters. The first is a string, the second is an expression of the
type designated by the prefix. The first (string) argument is required
to be a static expression, and is the constraint for the parameter,
(e.g. what kind of register is required). The second argument is the
value to be used as the input argument. The possible values for the
constant are the same as those used in the RTL, and are dependent on
the configuration file used to built the GCC back end.
Machine Code Insertions
Next: AST_Entry, Previous: Asm_Input, Up: Implementation Defined Attributes [Contents][Index]
The Asm_Output
attribute denotes a function that takes two
parameters. The first is a string, the second is the name of a variable
of the type designated by the attribute prefix. The first (string)
argument is required to be a static expression and designates the
constraint for the parameter (e.g. what kind of register is
required). The second argument is the variable to be updated with the
result. The possible values for constraint are the same as those used in
the RTL, and are dependent on the configuration file used to build the
GCC back end. If there are no output operands, then this argument may
either be omitted, or explicitly given as No_Output_Operands
.
Machine Code Insertions
Next: Bit, Previous: Asm_Output, Up: Implementation Defined Attributes [Contents][Index]
This attribute is implemented only in OpenVMS versions of GNAT. Applied to
the name of an entry, it yields a value of the predefined type AST_Handler
(declared in the predefined package System, as extended by the use of
pragma Extend_System (Aux_DEC)
). This value enables the given entry to
be called when an AST occurs. For further details, refer to the DEC Ada
Language Reference Manual, section 9.12a.
Next: Bit_Position, Previous: AST_Entry, Up: Implementation Defined Attributes [Contents][Index]
obj'Bit
, where obj is any object, yields the bit
offset within the storage unit (byte) that contains the first bit of
storage allocated for the object. The value of this attribute is of the
type Universal_Integer
, and is always a non-negative number not
exceeding the value of System.Storage_Unit
.
For an object that is a variable or a constant allocated in a register, the value is zero. (The use of this attribute does not force the allocation of a variable to memory).
For an object that is a formal parameter, this attribute applies to either the matching actual parameter or to a copy of the matching actual parameter.
For an access object the value is zero. Note that
obj.all'Bit
is subject to an Access_Check
for the
designated object. Similarly for a record component
X.C'Bit
is subject to a discriminant check and
X(I).Bit
and X(I1..I2)'Bit
are subject to index checks.
This attribute is designed to be compatible with the DEC Ada 83 definition
and implementation of the Bit
attribute.
Next: Compiler_Version, Previous: Bit, Up: Implementation Defined Attributes [Contents][Index]
R.C'Bit_Position
, where R is a record object and C is one
of the fields of the record type, yields the bit
offset within the record contains the first bit of
storage allocated for the object. The value of this attribute is of the
type Universal_Integer
. The value depends only on the field
C and is independent of the alignment of
the containing record R.
Next: Code_Address, Previous: Bit_Position, Up: Implementation Defined Attributes [Contents][Index]
Standard'Compiler_Version
(Standard
is the only allowed
prefix) yields a static string identifying the version of the compiler
being used to compile the unit containing the attribute reference. A
typical result would be something like "GNAT version (20090221)".
Next: Default_Bit_Order, Previous: Compiler_Version, Up: Implementation Defined Attributes [Contents][Index]
The 'Address
attribute may be applied to subprograms in Ada 95 and Ada 2005, but the
intended effect seems to be to provide
an address value which can be used to call the subprogram by means of
an address clause as in the following example:
procedure K is … procedure L; for L'Address use K'Address; pragma Import (Ada, L);
A call to L
is then expected to result in a call to K
.
In Ada 83, where there were no access-to-subprogram values, this was
a common work-around for getting the effect of an indirect call.
GNAT implements the above use of Address
and the technique
illustrated by the example code works correctly.
However, for some purposes, it is useful to have the address of the start
of the generated code for the subprogram. On some architectures, this is
not necessarily the same as the Address
value described above.
For example, the Address
value may reference a subprogram
descriptor rather than the subprogram itself.
The 'Code_Address
attribute, which can only be applied to
subprogram entities, always returns the address of the start of the
generated code of the specified subprogram, which may or may not be
the same value as is returned by the corresponding 'Address
attribute.
Next: Descriptor_Size, Previous: Code_Address, Up: Implementation Defined Attributes [Contents][Index]
Standard'Default_Bit_Order
(Standard
is the only
permissible prefix), provides the value System.Default_Bit_Order
as a Pos
value (0 for High_Order_First
, 1 for
Low_Order_First
). This is used to construct the definition of
Default_Bit_Order
in package System
.
Next: Elaborated, Previous: Default_Bit_Order, Up: Implementation Defined Attributes [Contents][Index]
Non-static attribute Descriptor_Size
returns the size in bits of the
descriptor allocated for a type. The result is non-zero only for unconstrained
array types and the returned value is of type universal integer. In GNAT, an
array descriptor contains bounds information and is located immediately before
the first element of the array.
type Unconstr_Array is array (Positive range <>) of Boolean; Put_Line ("Descriptor size = " & Unconstr_Array'Descriptor_Size'Img);
The attribute takes into account any additional padding due to type alignment.
In the example above, the descriptor contains two values of type
Positive
representing the low and high bound. Since Positive
has
a size of 31 bits and an alignment of 4, the descriptor size is 2 *
Positive'Size + 2
or 64 bits.
Next: Elab_Body, Previous: Descriptor_Size, Up: Implementation Defined Attributes [Contents][Index]
The prefix of the 'Elaborated
attribute must be a unit name. The
value is a Boolean which indicates whether or not the given unit has been
elaborated. This attribute is primarily intended for internal use by the
generated code for dynamic elaboration checking, but it can also be used
in user programs. The value will always be True once elaboration of all
units has been completed. An exception is for units which need no
elaboration, the value is always False for such units.
Next: Elab_Spec, Previous: Elaborated, Up: Implementation Defined Attributes [Contents][Index]
This attribute can only be applied to a program unit name. It returns the entity for the corresponding elaboration procedure for elaborating the body of the referenced unit. This is used in the main generated elaboration procedure by the binder and is not normally used in any other context. However, there may be specialized situations in which it is useful to be able to call this elaboration procedure from Ada code, e.g. if it is necessary to do selective re-elaboration to fix some error.
Next: Elab_Subp_Body, Previous: Elab_Body, Up: Implementation Defined Attributes [Contents][Index]
This attribute can only be applied to a program unit name. It returns the entity for the corresponding elaboration procedure for elaborating the spec of the referenced unit. This is used in the main generated elaboration procedure by the binder and is not normally used in any other context. However, there may be specialized situations in which it is useful to be able to call this elaboration procedure from Ada code, e.g. if it is necessary to do selective re-elaboration to fix some error.
Next: Emax, Previous: Elab_Spec, Up: Implementation Defined Attributes [Contents][Index]
This attribute can only be applied to a library level subprogram name and is only allowed in CodePeer mode. It returns the entity for the corresponding elaboration procedure for elaborating the body of the referenced subprogram unit. This is used in the main generated elaboration procedure by the binder in CodePeer mode only and is unrecognized otherwise.
Next: Enabled, Previous: Elab_Subp_Body, Up: Implementation Defined Attributes [Contents][Index]
The Emax
attribute is provided for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute.
Next: Enum_Rep, Previous: Emax, Up: Implementation Defined Attributes [Contents][Index]
The Enabled
attribute allows an application program to check at compile
time to see if the designated check is currently enabled. The prefix is a
simple identifier, referencing any predefined check name (other than
All_Checks
) or a check name introduced by pragma Check_Name. If
no argument is given for the attribute, the check is for the general state
of the check, if an argument is given, then it is an entity name, and the
check indicates whether an Suppress
or Unsuppress
has been
given naming the entity (if not, then the argument is ignored).
Note that instantiations inherit the check status at the point of the
instantiation, so a useful idiom is to have a library package that
introduces a check name with pragma Check_Name
, and then contains
generic packages or subprograms which use the Enabled
attribute
to see if the check is enabled. A user of this package can then issue
a pragma Suppress
or pragma Unsuppress
before instantiating
the package or subprogram, controlling whether the check will be present.
Next: Enum_Val, Previous: Enabled, Up: Implementation Defined Attributes [Contents][Index]
For every enumeration subtype S, S'Enum_Rep
denotes a
function with the following spec:
function S'Enum_Rep (Arg : S'Base) return Universal_Integer;
It is also allowable to apply Enum_Rep
directly to an object of an
enumeration type or to a non-overloaded enumeration
literal. In this case S'Enum_Rep
is equivalent to
typ'Enum_Rep(S)
where typ is the type of the
enumeration literal or object.
The function returns the representation value for the given enumeration
value. This will be equal to value of the Pos
attribute in the
absence of an enumeration representation clause. This is a static
attribute (i.e. the result is static if the argument is static).
S'Enum_Rep
can also be used with integer types and objects,
in which case it simply returns the integer value. The reason for this
is to allow it to be used for (<>)
discrete formal arguments in
a generic unit that can be instantiated with either enumeration types
or integer types. Note that if Enum_Rep
is used on a modular
type whose upper bound exceeds the upper bound of the largest signed
integer type, and the argument is a variable, so that the universal
integer calculation is done at run time, then the call to Enum_Rep
may raise Constraint_Error
.
Next: Epsilon, Previous: Enum_Rep, Up: Implementation Defined Attributes [Contents][Index]
For every enumeration subtype S, S'Enum_Val
denotes a
function with the following spec:
function S'Enum_Val (Arg : Universal_Integer) return S’Base;
The function returns the enumeration value whose representation matches the
argument, or raises Constraint_Error if no enumeration literal of the type
has the matching value.
This will be equal to value of the Val
attribute in the
absence of an enumeration representation clause. This is a static
attribute (i.e. the result is static if the argument is static).
Next: Fixed_Value, Previous: Enum_Val, Up: Implementation Defined Attributes [Contents][Index]
The Epsilon
attribute is provided for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute.
Next: Has_Access_Values, Previous: Epsilon, Up: Implementation Defined Attributes [Contents][Index]
For every fixed-point type S, S'Fixed_Value
denotes a
function with the following specification:
function S'Fixed_Value (Arg : Universal_Integer) return S;
The value returned is the fixed-point value V such that
V = Arg * S'Small
The effect is thus similar to first converting the argument to the integer type used to represent S, and then doing an unchecked conversion to the fixed-point type. The difference is that there are full range checks, to ensure that the result is in range. This attribute is primarily intended for use in implementation of the input-output functions for fixed-point values.
Next: Has_Discriminants, Previous: Fixed_Value, Up: Implementation Defined Attributes [Contents][Index]
The prefix of the Has_Access_Values
attribute is a type. The result
is a Boolean value which is True if the is an access type, or is a composite
type with a component (at any nesting depth) that is an access type, and is
False otherwise.
The intended use of this attribute is in conjunction with generic
definitions. If the attribute is applied to a generic private type, it
indicates whether or not the corresponding actual type has access values.
Next: Img, Previous: Has_Access_Values, Up: Implementation Defined Attributes [Contents][Index]
The prefix of the Has_Discriminants
attribute is a type. The result
is a Boolean value which is True if the type has discriminants, and False
otherwise. The intended use of this attribute is in conjunction with generic
definitions. If the attribute is applied to a generic private type, it
indicates whether or not the corresponding actual type has discriminants.
Next: Integer_Value, Previous: Has_Discriminants, Up: Implementation Defined Attributes [Contents][Index]
The Img
attribute differs from Image
in that it may be
applied to objects as well as types, in which case it gives the
Image
for the subtype of the object. This is convenient for
debugging:
Put_Line ("X = " & X'Img);
has the same meaning as the more verbose:
Put_Line ("X = " & T'Image (X));
where T is the (sub)type of the object X
.
Next: Invalid_Value, Previous: Img, Up: Implementation Defined Attributes [Contents][Index]
For every integer type S, S'Integer_Value
denotes a
function with the following spec:
function S'Integer_Value (Arg : Universal_Fixed) return S;
The value returned is the integer value V, such that
Arg = V * T'Small
where T is the type of Arg
.
The effect is thus similar to first doing an unchecked conversion from
the fixed-point type to its corresponding implementation type, and then
converting the result to the target integer type. The difference is
that there are full range checks, to ensure that the result is in range.
This attribute is primarily intended for use in implementation of the
standard input-output functions for fixed-point values.
Next: Large, Previous: Integer_Value, Up: Implementation Defined Attributes [Contents][Index]
For every scalar type S, S’Invalid_Value returns an undefined value of the type. If possible this value is an invalid representation for the type. The value returned is identical to the value used to initialize an otherwise uninitialized value of the type if pragma Initialize_Scalars is used, including the ability to modify the value with the binder -Sxx flag and relevant environment variables at run time.
Next: Machine_Size, Previous: Invalid_Value, Up: Implementation Defined Attributes [Contents][Index]
The Large
attribute is provided for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute.
Next: Mantissa, Previous: Large, Up: Implementation Defined Attributes [Contents][Index]
This attribute is identical to the Object_Size
attribute. It is
provided for compatibility with the DEC Ada 83 attribute of this name.
Next: Max_Interrupt_Priority, Previous: Machine_Size, Up: Implementation Defined Attributes [Contents][Index]
The Mantissa
attribute is provided for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute.
Next: Max_Priority, Previous: Mantissa, Up: Implementation Defined Attributes [Contents][Index]
Standard'Max_Interrupt_Priority
(Standard
is the only
permissible prefix), provides the same value as
System.Max_Interrupt_Priority
.
Next: Maximum_Alignment, Previous: Max_Interrupt_Priority, Up: Implementation Defined Attributes [Contents][Index]
Standard'Max_Priority
(Standard
is the only permissible
prefix) provides the same value as System.Max_Priority
.
Next: Mechanism_Code, Previous: Max_Priority, Up: Implementation Defined Attributes [Contents][Index]
Standard'Maximum_Alignment
(Standard
is the only
permissible prefix) provides the maximum useful alignment value for the
target. This is a static value that can be used to specify the alignment
for an object, guaranteeing that it is properly aligned in all
cases.
Next: Null_Parameter, Previous: Maximum_Alignment, Up: Implementation Defined Attributes [Contents][Index]
function'Mechanism_Code
yields an integer code for the
mechanism used for the result of function, and
subprogram'Mechanism_Code (n)
yields the mechanism
used for formal parameter number n (a static integer value with 1
meaning the first parameter) of subprogram. The code returned is:
by copy (value)
by reference
by descriptor (default descriptor class)
by descriptor (UBS: unaligned bit string)
by descriptor (UBSB: aligned bit string with arbitrary bounds)
by descriptor (UBA: unaligned bit array)
by descriptor (S: string, also scalar access type parameter)
by descriptor (SB: string with arbitrary bounds)
by descriptor (A: contiguous array)
by descriptor (NCA: non-contiguous array)
Values from 3 through 10 are only relevant to Digital OpenVMS implementations.
Next: Object_Size, Previous: Mechanism_Code, Up: Implementation Defined Attributes [Contents][Index]
A reference T'Null_Parameter
denotes an imaginary object of
type or subtype T allocated at machine address zero. The attribute
is allowed only as the default expression of a formal parameter, or as
an actual expression of a subprogram call. In either case, the
subprogram must be imported.
The identity of the object is represented by the address zero in the argument list, independent of the passing mechanism (explicit or default).
This capability is needed to specify that a zero address should be
passed for a record or other composite object passed by reference.
There is no way of indicating this without the Null_Parameter
attribute.
Next: Passed_By_Reference, Previous: Null_Parameter, Up: Implementation Defined Attributes [Contents][Index]
The size of an object is not necessarily the same as the size of the type
of an object. This is because by default object sizes are increased to be
a multiple of the alignment of the object. For example,
Natural'Size
is
31, but by default objects of type Natural
will have a size of 32 bits.
Similarly, a record containing an integer and a character:
type Rec is record I : Integer; C : Character; end record;
will have a size of 40 (that is Rec'Size
will be 40). The
alignment will be 4, because of the
integer field, and so the default size of record objects for this type
will be 64 (8 bytes).
Next: Pool_Address, Previous: Object_Size, Up: Implementation Defined Attributes [Contents][Index]
type'Passed_By_Reference
for any subtype type returns
a value of type Boolean
value that is True
if the type is
normally passed by reference and False
if the type is normally
passed by copy in calls. For scalar types, the result is always False
and is static. For non-scalar types, the result is non-static.
Next: Range_Length, Previous: Passed_By_Reference, Up: Implementation Defined Attributes [Contents][Index]
X'Pool_Address
for any object X returns the address
of X within its storage pool. This is the same as
X'Address
, except that for an unconstrained array whose
bounds are allocated just before the first component,
X'Pool_Address
returns the address of those bounds,
whereas X'Address
returns the address of the first
component.
Here, we are interpreting “storage pool” broadly to mean “wherever
the object is allocated”, which could be a user-defined storage pool,
the global heap, on the stack, or in a static memory area. For an
object created by new
, Ptr.all'Pool_Address
is
what is passed to Allocate
and returned from Deallocate
.
Next: Ref, Previous: Pool_Address, Up: Implementation Defined Attributes [Contents][Index]
type'Range_Length
for any discrete type type yields
the number of values represented by the subtype (zero for a null
range). The result is static for static subtypes. Range_Length
applied to the index subtype of a one dimensional array always gives the
same result as Range
applied to the array itself.
Next: Result, Previous: Range_Length, Up: Implementation Defined Attributes [Contents][Index]
The System.Address'Ref
(System.Address
is the only permissible prefix)
denotes a function identical to
System.Storage_Elements.To_Address
except that
it is a static attribute. See To_Address for more details.
Next: Safe_Emax, Previous: Ref, Up: Implementation Defined Attributes [Contents][Index]
function'Result
can only be used with in a Postcondition pragma
for a function. The prefix must be the name of the corresponding function. This
is used to refer to the result of the function in the postcondition expression.
For a further discussion of the use of this attribute and examples of its use,
see the description of pragma Postcondition.
Next: Safe_Large, Previous: Result, Up: Implementation Defined Attributes [Contents][Index]
The Safe_Emax
attribute is provided for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute.
Next: Scalar_Storage_Order, Previous: Safe_Emax, Up: Implementation Defined Attributes [Contents][Index]
The Safe_Large
attribute is provided for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute.
Next: Simple_Storage_Pool, Previous: Safe_Large, Up: Implementation Defined Attributes [Contents][Index]
For every array or record type S, the representation attribute
Scalar_Storage_Order
denotes the order in which storage elements
that make up scalar components are ordered within S:
-- Component type definitions subtype Yr_Type is Natural range 0 .. 127; subtype Mo_Type is Natural range 1 .. 12; subtype Da_Type is Natural range 1 .. 31; -- Record declaration type Date is record Years_Since_1980 : Yr_Type; Month : Mo_Type; Day_Of_Month : Da_Type; end record; -- Record representation clause for Date use record Years_Since_1980 at 0 range 0 .. 6; Month at 0 range 7 .. 10; Day_Of_Month at 0 range 11 .. 15; end record; -- Attribute definition clauses for Date'Bit_Order use System.High_Order_First; for Date'Scalar_Storage_Order use System.High_Order_First; -- If Scalar_Storage_Order is specified, it must be consistent with -- Bit_Order, so it's best to always define the latter explicitly if -- the former is used.
Other properties are
as for standard representation attribute Bit_Order
, as defined by
Ada RM 13.5.3(4). The default is System.Default_Bit_Order
.
For a record type S, if S'Scalar_Storage_Order
is
specified explicitly, it shall be equal to S'Bit_Order
. Note:
this means that if a Scalar_Storage_Order
attribute definition
clause is not confirming, then the type’s Bit_Order
shall be
specified explicitly and set to the same value.
For a record extension, the derived type shall have the same scalar storage order as the parent type.
If a component of S has itself a record or array type, then it shall also
have a Scalar_Storage_Order
attribute definition clause. In addition,
if the component does not start on a byte boundary, then the scalar storage
order specified for S and for the nested component type shall be identical.
No component of a type that has a Scalar_Storage_Order
attribute
definition may be aliased.
A confirming Scalar_Storage_Order
attribute definition clause (i.e.
with a value equal to System.Default_Bit_Order
) has no effect.
If the opposite storage order is specified, then whenever the value of a scalar component of an object of type S is read, the storage elements of the enclosing machine scalar are first reversed (before retrieving the component value, possibly applying some shift and mask operatings on the enclosing machine scalar), and the opposite operation is done for writes.
In that case, the restrictions set forth in 13.5.1(10.3/2) for scalar components are relaxed. Instead, the following rules apply:
(position + first_bit / storage_element_size) ..
(position + (last_bit + storage_element_size - 1) /
storage_element_size)
position + first_bit / storage_element_size
and covering
storage elements at least up to position + (last_bit +
storage_element_size - 1) / storage_element_size
Next: Small, Previous: Scalar_Storage_Order, Up: Implementation Defined Attributes [Contents][Index]
For every nonformal, nonderived access-to-object type Acc, the
representation attribute Simple_Storage_Pool
may be specified
via an attribute_definition_clause (or by specifying the equivalent aspect):
My_Pool : My_Simple_Storage_Pool_Type; type Acc is access My_Data_Type; for Acc'Simple_Storage_Pool use My_Pool;
The name given in an attribute_definition_clause for the
Simple_Storage_Pool
attribute shall denote a variable of
a “simple storage pool type” (see pragma Simple_Storage_Pool_Type
).
The use of this attribute is only allowed for a prefix denoting a type for which it has been specified. The type of the attribute is the type of the variable specified as the simple storage pool of the access type, and the attribute denotes that variable.
It is illegal to specify both Storage_Pool
and Simple_Storage_Pool
for the same access type.
If the Simple_Storage_Pool
attribute has been specified for an access
type, then applying the Storage_Pool
attribute to the type is flagged
with a warning and its evaluation raises the exception Program_Error
.
If the Simple_Storage_Pool attribute has been specified for an access
type S, then the evaluation of the attribute S'Storage_Size
returns the result of calling Storage_Size (S'Simple_Storage_Pool)
,
which is intended to indicate the number of storage elements reserved for
the simple storage pool. If the Storage_Size function has not been defined
for the simple storage pool type, then this attribute returns zero.
If an access type S has a specified simple storage pool of type
SSP, then the evaluation of an allocator for that access type calls
the primitive Allocate
procedure for type SSP, passing
S'Simple_Storage_Pool
as the pool parameter. The detailed
semantics of such allocators is the same as those defined for allocators
in section 13.11 of the Ada Reference Manual, with the term
“simple storage pool” substituted for “storage pool”.
If an access type S has a specified simple storage pool of type
SSP, then a call to an instance of the Ada.Unchecked_Deallocation
for that access type invokes the primitive Deallocate
procedure
for type SSP, passing S'Simple_Storage_Pool
as the pool
parameter. The detailed semantics of such unchecked deallocations is the same
as defined in section 13.11.2 of the Ada Reference Manual, except that the
term “simple storage pool” is substituted for “storage pool”.
Next: Storage_Unit, Previous: Simple_Storage_Pool, Up: Implementation Defined Attributes [Contents][Index]
The Small
attribute is defined in Ada 95 (and Ada 2005) only for
fixed-point types.
GNAT also allows this attribute to be applied to floating-point types
for compatibility with Ada 83. See
the Ada 83 reference manual for an exact description of the semantics of
this attribute when applied to floating-point types.
Next: Stub_Type, Previous: Small, Up: Implementation Defined Attributes [Contents][Index]
Standard'Storage_Unit
(Standard
is the only permissible
prefix) provides the same value as System.Storage_Unit
.
Next: System_Allocator_Alignment, Previous: Storage_Unit, Up: Implementation Defined Attributes [Contents][Index]
The GNAT implementation of remote access-to-classwide types is organized as described in AARM section E.4 (20.t): a value of an RACW type (designating a remote object) is represented as a normal access value, pointing to a "stub" object which in turn contains the necessary information to contact the designated remote object. A call on any dispatching operation of such a stub object does the remote call, if necessary, using the information in the stub object to locate the target partition, etc.
For a prefix T
that denotes a remote access-to-classwide type,
T'Stub_Type
denotes the type of the corresponding stub objects.
By construction, the layout of T'Stub_Type
is identical to that of
type RACW_Stub_Type
declared in the internal implementation-defined
unit System.Partition_Interface
. Use of this attribute will create
an implicit dependency on this unit.
Next: Target_Name, Previous: Stub_Type, Up: Implementation Defined Attributes [Contents][Index]
Standard'System_Allocator_Alignment
(Standard
is the only
permissible prefix) provides the observable guaranted to be honored by
the system allocator (malloc). This is a static value that can be used
in user storage pools based on malloc either to reject allocation
with alignment too large or to enable a realignment circuitry if the
alignment request is larger than this value.
Next: Tick, Previous: System_Allocator_Alignment, Up: Implementation Defined Attributes [Contents][Index]
Standard'Target_Name
(Standard
is the only permissible
prefix) provides a static string value that identifies the target
for the current compilation. For GCC implementations, this is the
standard gcc target name without the terminating slash (for
example, GNAT 5.0 on windows yields "i586-pc-mingw32msv").
Next: To_Address, Previous: Target_Name, Up: Implementation Defined Attributes [Contents][Index]
Standard'Tick
(Standard
is the only permissible prefix)
provides the same value as System.Tick
,
Next: Type_Class, Previous: Tick, Up: Implementation Defined Attributes [Contents][Index]
The System'To_Address
(System
is the only permissible prefix)
denotes a function identical to
System.Storage_Elements.To_Address
except that
it is a static attribute. This means that if its argument is
a static expression, then the result of the attribute is a
static expression. The result is that such an expression can be
used in contexts (e.g. preelaborable packages) which require a
static expression and where the function call could not be used
(since the function call is always non-static, even if its
argument is static).
Next: UET_Address, Previous: To_Address, Up: Implementation Defined Attributes [Contents][Index]
type'Type_Class
for any type or subtype type yields
the value of the type class for the full type of type. If
type is a generic formal type, the value is the value for the
corresponding actual subtype. The value of this attribute is of type
System.Aux_DEC.Type_Class
, which has the following definition:
type Type_Class is (Type_Class_Enumeration, Type_Class_Integer, Type_Class_Fixed_Point, Type_Class_Floating_Point, Type_Class_Array, Type_Class_Record, Type_Class_Access, Type_Class_Task, Type_Class_Address);
Protected types yield the value Type_Class_Task
, which thus
applies to all concurrent types. This attribute is designed to
be compatible with the DEC Ada 83 attribute of the same name.
Next: Unconstrained_Array, Previous: Type_Class, Up: Implementation Defined Attributes [Contents][Index]
The UET_Address
attribute can only be used for a prefix which
denotes a library package. It yields the address of the unit exception
table when zero cost exception handling is used. This attribute is
intended only for use within the GNAT implementation. See the unit
Ada.Exceptions
in files a-except.ads and a-except.adb
for details on how this attribute is used in the implementation.
Next: Universal_Literal_String, Previous: UET_Address, Up: Implementation Defined Attributes [Contents][Index]
The Unconstrained_Array
attribute can be used with a prefix that
denotes any type or subtype. It is a static attribute that yields
True
if the prefix designates an unconstrained array,
and False
otherwise. In a generic instance, the result is
still static, and yields the result of applying this test to the
generic actual.
Next: Unrestricted_Access, Previous: Unconstrained_Array, Up: Implementation Defined Attributes [Contents][Index]
The prefix of Universal_Literal_String
must be a named
number. The static result is the string consisting of the characters of
the number as defined in the original source. This allows the user
program to access the actual text of named numbers without intermediate
conversions and without the need to enclose the strings in quotes (which
would preclude their use as numbers).
For example, the following program prints the first 50 digits of pi:
with Text_IO; use Text_IO; with Ada.Numerics; procedure Pi is begin Put (Ada.Numerics.Pi'Universal_Literal_String); end;
Next: Valid_Scalars, Previous: Universal_Literal_String, Up: Implementation Defined Attributes [Contents][Index]
The Unrestricted_Access
attribute is similar to Access
except that all accessibility and aliased view checks are omitted. This
is a user-beware attribute. It is similar to
Address
, for which it is a desirable replacement where the value
desired is an access type. In other words, its effect is identical to
first applying the Address
attribute and then doing an unchecked
conversion to a desired access type. In GNAT, but not necessarily in
other implementations, the use of static chains for inner level
subprograms means that Unrestricted_Access
applied to a
subprogram yields a value that can be called as long as the subprogram
is in scope (normal Ada accessibility rules restrict this usage).
It is possible to use Unrestricted_Access
for any type, but care
must be exercised if it is used to create pointers to unconstrained
objects. In this case, the resulting pointer has the same scope as the
context of the attribute, and may not be returned to some enclosing
scope. For instance, a function cannot use Unrestricted_Access
to create a unconstrained pointer and then return that value to the
caller.
Next: VADS_Size, Previous: Unrestricted_Access, Up: Implementation Defined Attributes [Contents][Index]
The 'Valid_Scalars
attribute is intended to make it easier to
check the validity of scalar subcomponents of composite objects. It
is defined for any prefix X
that denotes an object.
The value of this attribute is of the predefined type Boolean.
X'Valid_Scalars
yields True if and only if evaluation of
P'Valid
yields True for every scalar part P of X or if X has
no scalar parts. It is not specified in what order the scalar parts
are checked, nor whether any more are checked after any one of them
is determined to be invalid. If the prefix X
is of a class-wide
type T'Class
(where T
is the associated specific type),
or if the prefix X
is of a specific tagged type T
, then
only the scalar parts of components of T
are traversed; in other
words, components of extensions of T
are not traversed even if
T'Class (X)'Tag /= T'Tag
. The compiler will issue a warning if it can
be determined at compile time that the prefix of the attribute has no
scalar parts (e.g., if the prefix is of an access type, an interface type,
an undiscriminated task type, or an undiscriminated protected type).
Next: Value_Size, Previous: Valid_Scalars, Up: Implementation Defined Attributes [Contents][Index]
The 'VADS_Size
attribute is intended to make it easier to port
legacy code which relies on the semantics of 'Size
as implemented
by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
same semantic interpretation. In particular, 'VADS_Size
applied
to a predefined or other primitive type with no Size clause yields the
Object_Size (for example, Natural'Size
is 32 rather than 31 on
typical machines). In addition 'VADS_Size
applied to an object
gives the result that would be obtained by applying the attribute to
the corresponding type.
Next: Wchar_T_Size, Previous: VADS_Size, Up: Implementation Defined Attributes [Contents][Index]
type'Value_Size
is the number of bits required to represent
a value of the given subtype. It is the same as type'Size
,
but, unlike Size
, may be set for non-first subtypes.
Next: Word_Size, Previous: Value_Size, Up: Implementation Defined Attributes [Contents][Index]
Standard'Wchar_T_Size
(Standard
is the only permissible
prefix) provides the size in bits of the C wchar_t
type
primarily for constructing the definition of this type in
package Interfaces.C
.
Next: Partition-Wide Restrictions, Previous: Wchar_T_Size, Up: Implementation Defined Attributes [Contents][Index]
Standard'Word_Size
(Standard
is the only permissible
prefix) provides the value System.Word_Size
.
Next: Implementation Advice, Previous: Implementation Defined Attributes, Up: Top [Contents][Index]
All RM defined Restriction identifiers are implemented:
GNAT implements additional restriction identifiers. All restrictions, whether language defined or GNAT-specific, are listed in the following.
• Partition-Wide Restrictions: | ||
• Program Unit Level Restrictions: |
Next: Program Unit Level Restrictions, Previous: Word_Size, Up: Standard and Implementation Defined Restrictions [Contents][Index]
There are two separate lists of restriction identifiers. The first set requires consistency throughout a partition (in other words, if the restriction identifier is used for any compilation unit in the partition, then all compilation units in the partition must obey the restriction).
Next: Max_Asynchronous_Select_Nesting, Previous: Program Unit Level Restrictions, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures that, except for storage occupied by objects created by allocators and not deallocated via unchecked deallocation, any storage reserved at run time for an object is immediately reclaimed when the object no longer exists.
Next: Max_Entry_Queue_Length, Previous: Immediate_Reclamation, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies the maximum dynamic nesting level of asynchronous selects. Violations of this restriction with a value of zero are detected at compile time. Violations of this restriction with values other than zero cause Storage_Error to be raised.
Next: Max_Protected_Entries, Previous: Max_Asynchronous_Select_Nesting, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction is a declaration that any protected entry compiled in the scope of the restriction has at most the specified number of tasks waiting on the entry at any one time, and so no queue is required. Note that this restriction is checked at run time. Violation of this restriction results in the raising of Program_Error exception at the point of the call.
Next: Max_Select_Alternatives, Previous: Max_Entry_Queue_Length, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies the maximum number of entries per protected type. The bounds of every entry family of a protected unit shall be static, or shall be defined by a discriminant of a subtype whose corresponding bound is static.
Next: Max_Storage_At_Blocking, Previous: Max_Protected_Entries, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies the maximum number of alternatives in a selective accept.
Next: Max_Task_Entries, Previous: Max_Select_Alternatives, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies the maximum portion (in storage elements) of a task’s Storage_Size that can be retained by a blocked task. A violation of this restriction causes Storage_Error to be raised.
Next: Max_Tasks, Previous: Max_Storage_At_Blocking, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies the maximum number of entries per task. The bounds of every entry family of a task unit shall be static, or shall be defined by a discriminant of a subtype whose corresponding bound is static.
Next: No_Abort_Statements, Previous: Max_Task_Entries, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies the maximum number of task that may be created, not counting the creation of the environment task. Violations of this restriction with a value of zero are detected at compile time. Violations of this restriction with values other than zero cause Storage_Error to be raised.
Next: No_Access_Parameter_Allocators, Previous: Max_Tasks, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] There are no abort_statements, and there are no calls to Task_Identification.Abort_Task.
Next: No_Access_Subprograms, Previous: No_Abort_Statements, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of an allocator as the actual parameter to an access parameter.
Next: No_Allocators, Previous: No_Access_Parameter_Allocators, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no declarations of access-to-subprogram types.
Next: No_Anonymous_Allocators, Previous: No_Access_Subprograms, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of an allocator.
Next: No_Calendar, Previous: No_Allocators, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of an allocator of anonymous access type.
Next: No_Coextensions, Previous: No_Anonymous_Allocators, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that there is no implicit or
explicit dependence on the package Ada.Calendar
.
Next: No_Default_Initialization, Previous: No_Calendar, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no coextensions. See 3.10.2.
Next: No_Delay, Previous: No_Coextensions, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction prohibits any instance of default initialization of variables. The binder implements a consistency rule which prevents any unit compiled without the restriction from with’ing a unit with the restriction (this allows the generation of initialization procedures to be skipped, since you can be sure that no call is ever generated to an initialization procedure in a unit with the restriction active). If used in conjunction with Initialize_Scalars or Normalize_Scalars, the effect is to prohibit all cases of variables declared without a specific initializer (including the case of OUT scalar parameters).
Next: No_Dependence, Previous: No_Default_Initialization, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no delay statements and no dependences on package Calendar.
Next: No_Direct_Boolean_Operators, Previous: No_Delay, Up: Partition-Wide Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that there are no dependence on a library unit.
Next: No_Dispatch, Previous: No_Dependence, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures that no logical (and/or/xor) are used on operands of type Boolean (or any type derived from Boolean). This is intended for use in safety critical programs where the certification protocol requires the use of short-circuit (and then, or else) forms for all composite boolean operations.
Next: No_Dispatching_Calls, Previous: No_Direct_Boolean_Operators, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no
occurrences of T'Class
, for any (tagged) subtype T
.
Next: No_Dynamic_Attachment, Previous: No_Dispatch, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that the code generated by the
compiler involves no dispatching calls. The use of this restriction allows the
safe use of record extensions, classwide membership tests and other classwide
features not involving implicit dispatching. This restriction ensures that
the code contains no indirect calls through a dispatching mechanism. Note that
this includes internally-generated calls created by the compiler, for example
in the implementation of class-wide objects assignments. The
membership test is allowed in the presence of this restriction, because its
implementation requires no dispatching.
This restriction is comparable to the official Ada restriction
No_Dispatch
except that it is a bit less restrictive in that it allows
all classwide constructs that do not imply dispatching.
The following example indicates constructs that violate this restriction.
package Pkg is type T is tagged record Data : Natural; end record; procedure P (X : T); type DT is new T with record More_Data : Natural; end record; procedure Q (X : DT); end Pkg; with Pkg; use Pkg; procedure Example is procedure Test (O : T'Class) is N : Natural := O'Size;-- Error: Dispatching call C : T'Class := O; -- Error: implicit Dispatching Call begin if O in DT'Class then -- OK : Membership test Q (DT (O)); -- OK : Type conversion plus direct call else P (O); -- Error: Dispatching call end if; end Test; Obj : DT; begin P (Obj); -- OK : Direct call P (T (Obj)); -- OK : Type conversion plus direct call P (T'Class (Obj)); -- Error: Dispatching call Test (Obj); -- OK : Type conversion if Obj in T'Class then -- OK : Membership test null; end if; end Example;
Next: No_Dynamic_Priorities, Previous: No_Dispatching_Calls, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures that there is no call to any of the operations defined in package Ada.Interrupts (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler, Detach_Handler, and Reference).
Next: No_Entry_Calls_In_Elaboration_Code, Previous: No_Dynamic_Attachment, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
Next: No_Enumeration_Maps, Previous: No_Dynamic_Priorities, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that no task or protected entry calls are made during elaboration code. As a result of the use of this restriction, the compiler can assume that no code past an accept statement in a task can be executed at elaboration time.
Next: No_Exception_Handlers, Previous: No_Entry_Calls_In_Elaboration_Code, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that no operations requiring enumeration maps are used (that is Image and Value attributes applied to enumeration types).
Next: No_Exception_Propagation, Previous: No_Enumeration_Maps, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that there are no explicit exception handlers. It also indicates that no exception propagation will be provided. In this mode, exceptions may be raised but will result in an immediate call to the last chance handler, a routine that the user must define with the following profile:
procedure Last_Chance_Handler (Source_Location : System.Address; Line : Integer); pragma Export (C, Last_Chance_Handler, "__gnat_last_chance_handler");
The parameter is a C null-terminated string representing a message to be associated with the exception (typically the source location of the raise statement generated by the compiler). The Line parameter when nonzero represents the line number in the source program where the raise occurs.
Next: No_Exception_Registration, Previous: No_Exception_Handlers, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction guarantees that exceptions are never propagated to an outer subprogram scope. The only case in which an exception may be raised is when the handler is statically in the same subprogram, so that the effect of a raise is essentially like a goto statement. Any other raise statement (implicit or explicit) will be considered unhandled. Exception handlers are allowed, but may not contain an exception occurrence identifier (exception choice). In addition, use of the package GNAT.Current_Exception is not permitted, and reraise statements (raise with no operand) are not permitted.
Next: No_Exceptions, Previous: No_Exception_Propagation, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that no stream operations for types Exception_Id or Exception_Occurrence are used. This also makes it impossible to pass exceptions to or from a partition with this restriction in a distributed environment. If this exception is active, then the generated code is simplified by omitting the otherwise-required global registration of exceptions when they are declared.
Next: No_Finalization, Previous: No_Exception_Registration, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no raise statements and no exception handlers.
Next: No_Fixed_Point, Previous: No_Exceptions, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction disables the language features described in chapter 7.6 of the Ada 2005 RM as well as all form of code generation performed by the compiler to support these features. The following types are no longer considered controlled when this restriction is in effect:
Ada.Finalization.Controlled
Ada.Finalization.Limited_Controlled
Controlled
or Limited_Controlled
The compiler no longer generates code to initialize, finalize or adjust an object or a nested component, either declared on the stack or on the heap. The deallocation of a controlled object no longer finalizes its contents.
Next: No_Floating_Point, Previous: No_Finalization, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of fixed point types and operations.
Next: No_Implicit_Conditionals, Previous: No_Fixed_Point, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of floating point types and operations.
Next: No_Implicit_Dynamic_Code, Previous: No_Floating_Point, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures that the generated code does not contain any implicit conditionals, either by modifying the generated code where possible, or by rejecting any construct that would otherwise generate an implicit conditional. Note that this check does not include run time constraint checks, which on some targets may generate implicit conditionals as well. To control the latter, constraint checks can be suppressed in the normal manner. Constructs generating implicit conditionals include comparisons of composite objects and the Max/Min attributes.
Next: No_Implicit_Heap_Allocations, Previous: No_Implicit_Conditionals, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction prevents the compiler from building “trampolines”.
This is a structure that is built on the stack and contains dynamic
code to be executed at run time. On some targets, a trampoline is
built for the following features: Access
,
Unrestricted_Access
, or Address
of a nested subprogram;
nested task bodies; primitive operations of nested tagged types.
Trampolines do not work on machines that prevent execution of stack
data. For example, on windows systems, enabling DEP (data execution
protection) will cause trampolines to raise an exception.
Trampolines are also quite slow at run time.
On many targets, trampolines have been largely eliminated. Look at the
version of system.ads for your target — if it has
Always_Compatible_Rep equal to False, then trampolines are largely
eliminated. In particular, a trampoline is built for the following
features: Address
of a nested subprogram;
Access
or Unrestricted_Access
of a nested subprogram,
but only if pragma Favor_Top_Level applies, or the access type has a
foreign-language convention; primitive operations of nested tagged
types.
Next: No_Implicit_Loops, Previous: No_Implicit_Dynamic_Code, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] No constructs are allowed to cause implicit heap allocation.
Next: No_Initialize_Scalars, Previous: No_Implicit_Heap_Allocations, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures that the generated code does not contain any
implicit for
loops, either by modifying
the generated code where possible,
or by rejecting any construct that would otherwise generate an implicit
for
loop. If this restriction is active, it is possible to build
large array aggregates with all static components without generating an
intermediate temporary, and without generating a loop to initialize individual
components. Otherwise, a loop is created for arrays larger than about 5000
scalar components.
Next: No_IO, Previous: No_Implicit_Loops, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures that no unit in the partition is compiled with pragma Initialize_Scalars. This allows the generation of more efficient code, and in particular eliminates dummy null initialization routines that are otherwise generated for some record and array types.
Next: No_Local_Allocators, Previous: No_Initialize_Scalars, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no dependences on any of the library units Sequential_IO, Direct_IO, Text_IO, Wide_Text_IO, Wide_Wide_Text_IO, or Stream_IO.
Next: No_Local_Protected_Objects, Previous: No_IO, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of an allocator in subprograms, generic subprograms, tasks, and entry bodies.
Next: No_Local_Timing_Events, Previous: No_Local_Allocators, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures at compile time that protected objects are only declared at the library level.
Next: No_Nested_Finalization, Previous: No_Local_Protected_Objects, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] All objects of type Ada.Timing_Events.Timing_Event are declared at the library level.
Next: No_Protected_Type_Allocators, Previous: No_Local_Timing_Events, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] All objects requiring finalization are declared at the library level.
Next: No_Protected_Types, Previous: No_Nested_Finalization, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures at compile time that there are no allocator expressions that attempt to allocate protected objects.
Next: No_Recursion, Previous: No_Protected_Type_Allocators, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no declarations of protected types or protected objects.
Next: No_Reentrancy, Previous: No_Protected_Types, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] A program execution is erroneous if a subprogram is invoked as part of its execution.
Next: No_Relative_Delay, Previous: No_Recursion, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] A program execution is erroneous if a subprogram is executed by two tasks at the same time.
Next: No_Requeue_Statements, Previous: No_Reentrancy, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures at compile time that there are no delay
relative statements and prevents expressions such as delay 1.23;
from
appearing in source code.
Next: No_Secondary_Stack, Previous: No_Relative_Delay, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures at compile time that no requeue statements
are permitted and prevents keyword requeue
from being used in source
code.
Next: No_Select_Statements, Previous: No_Requeue_Statements, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that the generated code does not contain any reference to the secondary stack. The secondary stack is used to implement functions returning unconstrained objects (arrays or records) on some targets.
Next: No_Specific_Termination_Handlers, Previous: No_Secondary_Stack, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures at compile time no select statements of any
kind are permitted, that is the keyword select
may not appear.
Next: No_Specification_of_Aspect, Previous: No_Select_Statements, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] There are no calls to Ada.Task_Termination.Set_Specific_Handler or to Ada.Task_Termination.Specific_Handler.
Next: No_Standard_Allocators_After_Elaboration, Previous: No_Specific_Termination_Handlers, Up: Partition-Wide Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that no aspect specification, attribute definition clause, or pragma is given for a given aspect.
Next: No_Standard_Storage_Pools, Previous: No_Specification_of_Aspect, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Specifies that an allocator using a standard storage pool should never be evaluated at run time after the elaboration of the library items of the partition has completed. Otherwise, Storage_Error is raised.
Next: No_Stream_Optimizations, Previous: No_Standard_Allocators_After_Elaboration, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that no access types use the standard default storage pool. Any access type declared must have an explicit Storage_Pool attribute defined specifying a user-defined storage pool.
Next: No_Streams, Previous: No_Standard_Storage_Pools, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction affects the performance of stream operations on types
String
, Wide_String
and Wide_Wide_String
. By default, the
compiler uses block reads and writes when manipulating String
objects
due to their supperior performance. When this restriction is in effect, the
compiler performs all IO operations on a per-character basis.
Next: No_Task_Allocators, Previous: No_Stream_Optimizations, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile/bind time that there are no
stream objects created and no use of stream attributes.
This restriction does not forbid dependences on the package
Ada.Streams
. So it is permissible to with
Ada.Streams
(or another package that does so itself)
as long as no actual stream objects are created and no
stream attributes are used.
Note that the use of restriction allows optimization of tagged types, since they do not need to worry about dispatching stream operations. To take maximum advantage of this space-saving optimization, any unit declaring a tagged type should be compiled with the restriction, though this is not required.
Next: No_Task_Attributes_Package, Previous: No_Streams, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] There are no allocators for task types or types containing task subcomponents.
Next: No_Task_Hierarchy, Previous: No_Task_Allocators, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that there are no implicit or
explicit dependencies on the package Ada.Task_Attributes
.
Next: No_Task_Termination, Previous: No_Task_Attributes_Package, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] All (non-environment) tasks depend directly on the environment task of the partition.
Next: No_Tasking, Previous: No_Task_Hierarchy, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] Tasks which terminate are erroneous.
Next: No_Terminate_Alternatives, Previous: No_Task_Termination, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction prevents the declaration of tasks or task types
throughout the partition. It is similar in effect to the use of
Max_Tasks => 0
except that violations are caught at compile time
and cause an error message to be output either by the compiler or
binder.
Next: No_Unchecked_Access, Previous: No_Tasking, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] There are no selective accepts with terminate alternatives.
Next: Simple_Barriers, Previous: No_Terminate_Alternatives, Up: Partition-Wide Restrictions [Contents][Index]
[RM H.4] This restriction ensures at compile time that there are no occurrences of the Unchecked_Access attribute.
Next: Static_Priorities, Previous: No_Unchecked_Access, Up: Partition-Wide Restrictions [Contents][Index]
[RM D.7] This restriction ensures at compile time that barriers in entry declarations for protected types are restricted to either static boolean expressions or references to simple boolean variables defined in the private part of the protected type. No other form of entry barriers is permitted.
Next: Static_Storage_Size, Previous: Simple_Barriers, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that all priority expressions
are static, and that there are no dependences on the package
Ada.Dynamic_Priorities
.
Next: No_Elaboration_Code, Previous: Static_Priorities, Up: Partition-Wide Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that any expression appearing in a Storage_Size pragma or attribute definition clause is static.
Next: Immediate_Reclamation, Previous: Partition-Wide Restrictions, Up: Standard and Implementation Defined Restrictions [Contents][Index]
The second set of restriction identifiers does not require partition-wide consistency. The restriction may be enforced for a single compilation unit without any effect on any of the other compilation units in the partition.
Next: No_Entry_Queue, Previous: Static_Storage_Size, Up: Program Unit Level Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that no elaboration code is
generated. Note that this is not the same condition as is enforced
by pragma Preelaborate
. There are cases in which pragma
Preelaborate
still permits code to be generated (e.g. code
to initialize a large array to all zeroes), and there are cases of units
which do not meet the requirements for pragma Preelaborate
,
but for which no elaboration code is generated. Generally, it is
the case that preelaborable units will meet the restrictions, with
the exception of large aggregates initialized with an others_clause,
and exception declarations (which generate calls to a run-time
registry procedure). This restriction is enforced on
a unit by unit basis, it need not be obeyed consistently
throughout a partition.
In the case of aggregates with others, if the aggregate has a dynamic
size, there is no way to eliminate the elaboration code (such dynamic
bounds would be incompatible with Preelaborate
in any case). If
the bounds are static, then use of this restriction actually modifies
the code choice of the compiler to avoid generating a loop, and instead
generate the aggregate statically if possible, no matter how many times
the data for the others clause must be repeatedly generated.
It is not possible to precisely document the constructs which are compatible with this restriction, since, unlike most other restrictions, this is not a restriction on the source code, but a restriction on the generated object code. For example, if the source contains a declaration:
Val : constant Integer := X;
where X is not a static constant, it may be possible, depending on complex optimization circuitry, for the compiler to figure out the value of X at compile time, in which case this initialization can be done by the loader, and requires no initialization code. It is not possible to document the precise conditions under which the optimizer can figure this out.
Note that this the implementation of this restriction requires full code generation. If it is used in conjunction with "semantics only" checking, then some cases of violations may be missed.
Next: No_Implementation_Aspect_Specifications, Previous: No_Elaboration_Code, Up: Program Unit Level Restrictions [Contents][Index]
[GNAT] This restriction is a declaration that any protected entry compiled in the scope of the restriction has at most one task waiting on the entry at any one time, and so no queue is required. This restriction is not checked at compile time. A program execution is erroneous if an attempt is made to queue a second task on such an entry.
Next: No_Implementation_Attributes, Previous: No_Entry_Queue, Up: Program Unit Level Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that no GNAT-defined aspects are present. With this restriction, the only aspects that can be used are those defined in the Ada Reference Manual.
Next: No_Implementation_Identifiers, Previous: No_Implementation_Aspect_Specifications, Up: Program Unit Level Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that no GNAT-defined attributes are present. With this restriction, the only attributes that can be used are those defined in the Ada Reference Manual.
Next: No_Implementation_Pragmas, Previous: No_Implementation_Attributes, Up: Program Unit Level Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that no implementation-defined identifiers (marked with pragma Implementation_Defined) occur within language-defined packages.
Next: No_Implementation_Restrictions, Previous: No_Implementation_Identifiers, Up: Program Unit Level Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that no GNAT-defined pragmas are present. With this restriction, the only pragmas that can be used are those defined in the Ada Reference Manual.
Next: No_Implementation_Units, Previous: No_Implementation_Pragmas, Up: Program Unit Level Restrictions [Contents][Index]
[GNAT] This restriction checks at compile time that no GNAT-defined restriction
identifiers (other than No_Implementation_Restrictions
itself)
are present. With this restriction, the only other restriction identifiers
that can be used are those defined in the Ada Reference Manual.
Next: No_Implicit_Aliasing, Previous: No_Implementation_Restrictions, Up: Program Unit Level Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that there is no mention in the context clause of any implementation-defined descendants of packages Ada, Interfaces, or System.
Next: No_Obsolescent_Features, Previous: No_Implementation_Units, Up: Program Unit Level Restrictions [Contents][Index]
[GNAT] This restriction, which is not required to be partition-wide consistent, requires an explicit aliased keyword for an object to which ’Access, ’Unchecked_Access, or ’Address is applied, and forbids entirely the use of the ’Unrestricted_Access attribute for objects. Note: the reason that Unrestricted_Access is forbidden is that it would require the prefix to be aliased, and in such cases, it can always be replaced by the standard attribute Unchecked_Access which is preferable.
Next: No_Wide_Characters, Previous: No_Implicit_Aliasing, Up: Program Unit Level Restrictions [Contents][Index]
[RM 13.12.1] This restriction checks at compile time that no obsolescent features are used, as defined in Annex J of the Ada Reference Manual.
Next: SPARK, Previous: No_Obsolescent_Features, Up: Program Unit Level Restrictions [Contents][Index]
[GNAT] This restriction ensures at compile time that no uses of the types
Wide_Character
or Wide_String
or corresponding wide
wide types
appear, and that no wide or wide wide string or character literals
appear in the program (that is literals representing characters not in
type Character
).
Next: Standard I/O Packages, Previous: No_Wide_Characters, Up: Program Unit Level Restrictions [Contents][Index]
[GNAT] This restriction checks at compile time that some constructs forbidden in SPARK are not present. The SPARK version used as a reference is the same as the Ada mode for the unit, so a unit compiled in Ada 95 mode with SPARK restrictions will be checked for constructs forbidden in SPARK 95. Error messages related to SPARK restriction have the form:
violation of restriction "SPARK" at <file> <error message>
This is not a replacement for the semantic checks performed by the SPARK Examiner tool, as the compiler only deals currently with code, not at all with SPARK annotations and does not guarantee catching all cases of constructs forbidden by SPARK.
Thus it may well be the case that code which
passes the compiler in SPARK mode is rejected by the SPARK Examiner,
e.g. due to the different visibility rules of the Examiner based on
SPARK inherit
annotations.
This restriction can be useful in providing an initial filter for code developed using SPARK, or in examining legacy code to see how far it is from meeting SPARK restrictions.
Next: Implementation Defined Characteristics, Previous: Standard and Implementation Defined Restrictions, Up: Top [Contents][Index]
The main text of the Ada Reference Manual describes the required behavior of all Ada compilers, and the GNAT compiler conforms to these requirements.
In addition, there are sections throughout the Ada Reference Manual headed by the phrase “Implementation advice”. These sections are not normative, i.e., they do not specify requirements that all compilers must follow. Rather they provide advice on generally desirable behavior. You may wonder why they are not requirements. The most typical answer is that they describe behavior that seems generally desirable, but cannot be provided on all systems, or which may be undesirable on some systems.
As far as practical, GNAT follows the implementation advice sections in the Ada Reference Manual. This chapter contains a table giving the reference manual section number, paragraph number and several keywords for each advice. Each entry consists of the text of the advice followed by the GNAT interpretation of this advice. Most often, this simply says “followed”, which means that GNAT follows the advice. However, in a number of cases, GNAT deliberately deviates from this advice, in which case the text describes what GNAT does and why.
If an implementation detects the use of an unsupported Specialized Needs
Annex feature at run time, it should raise |
Not relevant. All specialized needs annex features are either supported, or diagnosed at compile time.
If an implementation wishes to provide implementation-defined extensions to the functionality of a language-defined library unit, it should normally do so by adding children to the library unit. |
Followed.
If an implementation detects a bounded error or erroneous
execution, it should raise |
Followed in all cases in which the implementation detects a bounded error or erroneous execution. Not all such situations are detected at runtime.
Normally, implementation-defined pragmas should have no semantic effect for error-free programs; that is, if the implementation-defined pragmas are removed from a working program, the program should still be legal, and should still have the same semantics. |
The following implementation defined pragmas are exceptions to this rule:
Abort_Defer
Affects semantics
Ada_83
Affects legality
Assert
Affects semantics
CPP_Class
Affects semantics
CPP_Constructor
Affects semantics
Debug
Affects semantics
Interface_Name
Affects semantics
Machine_Attribute
Affects semantics
Unimplemented_Unit
Affects legality
Unchecked_Union
Affects semantics
In each of the above cases, it is essential to the purpose of the pragma that this advice not be followed. For details see the separate section on implementation defined pragmas.
Normally, an implementation should not define pragmas that can make an illegal program legal, except as follows: |
A pragma used to complete a declaration, such as a pragma |
A pragma used to configure the environment by adding, removing, or
replacing |
See response to paragraph 16 of this same section.
If an implementation supports a mode with alternative interpretations
for |
Not all wide character modes follow this advice, in particular the JIS and IEC modes reflect standard usage in Japan, and in these encoding, the upper half of the Latin-1 set is not part of the wide-character subset, since the most significant bit is used for wide character encoding. However, this only applies to the external forms. Internally there is no such restriction.
An implementation should support |
Long_Integer
is supported. Other standard integer types are supported
so this advice is not fully followed. These types
are supported for convenient interface to C, and so that all hardware
types of the machine are easily available.
An implementation for a two’s complement machine should support
modular types with a binary modulus up to |
Followed.
For the evaluation of a call on |
Followed.
An implementation should support |
Short_Float
and Long_Long_Float
are also provided. The
former provides improved compatibility with other implementations
supporting this type. The latter corresponds to the highest precision
floating-point type supported by the hardware. On most machines, this
will be the same as Long_Float
, but on some machines, it will
correspond to the IEEE extended form. The notable case is all ia32
(x86) implementations, where Long_Long_Float
corresponds to
the 80-bit extended precision format supported in hardware on this
processor. Note that the 128-bit format on SPARC is not supported,
since this is a software rather than a hardware format.
An implementation should normally represent multidimensional arrays in
row-major order, consistent with the notation used for multidimensional
array aggregates (see 4.3.3). However, if a pragma |
Followed.
Whenever possible in an implementation, the value of |
Followed. (Duration'Small
= 10**(-9)).
The time base for |
Followed.
In an implementation, a type declared in a pre-elaborated package should have the same representation in every elaboration of a given version of the package, whether the elaborations occur in distinct executions of the same program, or in executions of distinct programs or partitions that include the given version. |
Followed, except in the case of tagged types. Tagged types involve implicit pointers to a local copy of a dispatch table, and these pointers have representations which thus depend on a particular elaboration of the package. It is not easy to see how it would be possible to follow this advice without severely impacting efficiency of execution.
|
Followed. For each exception that doesn’t have a specified
Exception_Message
, the compiler generates one containing the location
of the raise statement. This location has the form “file:line”, where
file is the short file name (without path information) and line is the line
number in the file. Note that in the case of the Zero Cost Exception
mechanism, these messages become redundant with the Exception_Information that
contains a full backtrace of the calling sequence, so they are disabled.
To disable explicitly the generation of the source location message, use the
Pragma Discard_Names
.
The implementation should minimize the code executed for checks that have been suppressed. |
Followed.
The recommended level of support for all representation items is qualified as follows: |
An implementation need not support representation items containing non-static expressions, except that an implementation should support a representation item for a given entity if each non-static expression in the representation item is a name that statically denotes a constant declared before the entity. |
Followed. In fact, GNAT goes beyond the recommended level of support by allowing nonstatic expressions in some representation clauses even without the need to declare constants initialized with the values of such expressions. For example:
X : Integer; Y : Float; for Y'Address use X'Address;>>
An implementation need not support a specification for the |
Followed. Size Clauses are not permitted on non-static components, as described above.
An aliased component, or a component whose type is by-reference, should always be allocated at an addressable location. |
Followed.
If a type is packed, then the implementation should try to minimize storage allocated to objects of the type, possibly at the expense of speed of accessing components, subject to reasonable complexity in addressing calculations. |
The recommended level of support pragma For a packed record type, the components should be packed as tightly as
possible subject to the Sizes of the component subtypes, and subject to
any |
Followed. Tight packing of arrays is supported for all component sizes up to 64-bits. If the array component size is 1 (that is to say, if the component is a boolean type or an enumeration type with two values) then values of the type are implicitly initialized to zero. This happens both for objects of the packed type, and for objects that have a subcomponent of the packed type.
An implementation should support Address clauses for imported subprograms. |
For an array X, |
Followed.
The recommended level of support for the
|
Followed. A valid address will be produced even if none of those conditions have been met. If necessary, the object is forced into memory to ensure the address is valid.
An implementation should support |
Followed.
Objects (including subcomponents) that are aliased or of a by-reference type should be allocated on storage element boundaries. |
Followed.
If the |
Followed.
The recommended level of support for the An implementation should support specified Alignments that are factors and multiples of the number of storage elements per word, subject to the following: |
Followed.
An implementation need not support specified |
Followed.
An implementation need not support specified |
Followed.
The recommended level of support for the Same as above, for subtypes, but in addition: |
Followed.
For stand-alone library-level objects of statically constrained
subtypes, the implementation should support all |
Followed.
The recommended level of support for the A |
Followed.
If the Aliased objects (including components). |
Followed.
|
Followed. But note that this can be overridden by use of the implementation pragma Implicit_Packing in the case of packed arrays.
The recommended level of support for the |
The |
Followed.
For a subtype implemented with levels of indirection, the |
Followed.
The recommended level of support for the |
An implementation need not support specified |
Followed.
An implementation should support specified |
Followed.
The recommended level of support for enumeration representation clauses is: An implementation need not support enumeration representation clauses
for boolean types, but should at minimum support the internal codes in
the range |
Followed.
The recommended level of support for
An implementation should support storage places that can be extracted with a load, mask, shift sequence of machine code, and set with a load, shift, mask, store sequence, given the available machine instructions and run-time model. |
Followed.
A storage place should be supported if its size is equal to the
|
Followed.
If the default bit ordering applies to the declaration of a given type,
then for a component whose subtype’s |
Followed.
An implementation may reserve a storage place for the tag field of a tagged type, and disallow other components from overlapping that place. |
Followed. The storage place for the tag field is the beginning of the tagged record, and its size is Address’Size. GNAT will reject an explicit component clause for the tag field.
An implementation need not support a |
Followed. The above advice on record representation clauses is followed, and all mentioned features are implemented.
If a component is represented using some form of pointer (such as an offset) to the actual data of the component, and this data is contiguous with the rest of the object, then the storage place attributes should reflect the place of the actual data, not the pointer. If a component is allocated discontinuously from the rest of the object, then a warning should be generated upon reference to one of its storage place attributes. |
Followed. There are no such components in GNAT.
The recommended level of support for the non-default bit ordering is: |
If |
Followed. Word size does not equal storage size in this implementation. Thus non-default bit ordering is not supported.
|
Followed.
Operations in |
Followed. Address arithmetic is modular arithmetic that wraps around. No
operation raises Program_Error
, since all operations make sense.
The |
Followed.
The implementation should not generate unnecessary run-time checks to ensure that the representation of S is a representation of the target type. It should take advantage of the permission to return by reference when possible. Restrictions on unchecked conversions should be avoided unless required by the target environment. |
Followed. There are no restrictions on unchecked conversion. A warning is generated if the source and target types do not have the same size since the semantics in this case may be target dependent.
The recommended level of support for unchecked conversions is: |
Unchecked conversions should be supported and should be reversible in the cases where this clause defines the result. To enable meaningful use of unchecked conversion, a contiguous representation should be used for elementary subtypes, for statically constrained array subtypes whose component subtype is one of the subtypes described in this paragraph, and for record subtypes without discriminants whose component subtypes are described in this paragraph. |
Followed.
An implementation should document any cases in which it dynamically allocates heap storage for a purpose other than the evaluation of an allocator. |
Followed, the only other points at which heap storage is dynamically allocated are as follows:
A default (implementation-provided) storage pool for an access-to-constant type should not have overhead to support deallocation of individual objects. |
Followed.
A storage pool for an anonymous access type should be created at the point of an allocator for the type, and be reclaimed when the designated object becomes inaccessible. |
Followed.
For a standard storage pool, |
Followed.
If a stream element is the same size as a storage element, then the
normal in-memory representation should be used by |
Followed. By default, GNAT uses the interpretation suggested by AI-195,
which specifies using the size of the first subtype.
However, such an implementation is based on direct binary
representations and is therefore target- and endianness-dependent.
To address this issue, GNAT also supplies an alternate implementation
of the stream attributes Read
and Write
,
which uses the target-independent XDR standard representation
for scalar types.
The XDR implementation is provided as an alternative body of the
System.Stream_Attributes
package, in the file
s-stratt-xdr.adb in the GNAT library.
There is no s-stratt-xdr.ads file.
In order to install the XDR implementation, do the following:
System.Stream_Attributes
package with the XDR implementation.
For example on a Unix platform issue the commands:
$ mv s-stratt.adb s-stratt-default.adb $ mv s-stratt-xdr.adb s-stratt.adb
If an implementation provides additional named predefined integer types, then the names should end with ‘Integer’ as in ‘Long_Integer’. If an implementation provides additional named predefined floating point types, then the names should end with ‘Float’ as in ‘Long_Float’. |
Followed.
Ada.Characters.Handling
If an implementation provides a localized definition of |
Followed. GNAT provides no such localized definitions.
Bounded string objects should not be implemented by implicit pointers and dynamic allocation. |
Followed. No implicit pointers or dynamic allocation are used.
Any storage associated with an object of type |
Followed.
If the generator period is sufficiently long in relation to the number
of distinct initiator values, then each possible value of
|
Followed. The generator period is sufficiently long for the first condition here to hold true.
Get_Immediate
The |
Followed on all targets except VxWorks. For VxWorks, there is no way to
provide this functionality that does not result in the input buffer being
flushed before the Get_Immediate
call. A special unit
Interfaces.Vxworks.IO
is provided that contains routines to enable
this functionality.
Export
If an implementation supports pragma |
Followed.
Automatic elaboration of pre-elaborated packages should be
provided when pragma |
Followed when the main program is in Ada. If the main program is in a
foreign language, then
adainit
must be called to elaborate pre-elaborated
packages.
For each supported convention L other than |
Followed.
Interfaces
For each implementation-defined convention identifier, there should be a
child package of package Interfaces with the corresponding name. This
package should contain any declarations that would be useful for
interfacing to the language (implementation) represented by the
convention. Any declarations useful for interfacing to any language on
the given hardware architecture should be provided directly in
|
Followed. An additional package not defined
in the Ada Reference Manual is Interfaces.CPP
, used
for interfacing to C++.
An implementation supporting an interface to C, COBOL, or Fortran should provide the corresponding package or packages described in the following clauses. |
Followed. GNAT provides all the packages described in this section.
An implementation should support the following interface correspondences between Ada and C. |
Followed.
An Ada procedure corresponds to a void-returning C function. |
Followed.
An Ada function corresponds to a non-void C function. |
Followed.
An Ada |
Followed.
An Ada |
Followed.
An Ada access T parameter, or an Ada |
Followed.
An Ada parameter of a record type T, of any mode, is passed as a
|
Followed. This convention may be overridden by the use of the C_Pass_By_Copy pragma, or Convention, or by explicitly specifying the mechanism for a given call using an extended import or export pragma.
An Ada parameter of an array type with component type T, of any
mode, is passed as a |
Followed.
An Ada parameter of an access-to-subprogram type is passed as a pointer to a C function whose prototype corresponds to the designated subprogram’s specification. |
Followed.
An Ada implementation should support the following interface correspondences between Ada and COBOL. |
Followed.
An Ada access T parameter is passed as a ‘BY REFERENCE’ data item of the COBOL type corresponding to T. |
Followed.
An Ada in scalar parameter is passed as a ‘BY CONTENT’ data item of the corresponding COBOL type. |
Followed.
Any other Ada parameter is passed as a ‘BY REFERENCE’ data item of the COBOL type corresponding to the Ada parameter type; for scalars, a local copy is used if necessary to ensure by-copy semantics. |
Followed.
An Ada implementation should support the following interface correspondences between Ada and Fortran: |
Followed.
An Ada procedure corresponds to a Fortran subroutine. |
Followed.
An Ada function corresponds to a Fortran function. |
Followed.
An Ada parameter of an elementary, array, or record type T is passed as a T argument to a Fortran procedure, where T is the Fortran type corresponding to the Ada type T, and where the INTENT attribute of the corresponding dummy argument matches the Ada formal parameter mode; the Fortran implementation’s parameter passing conventions are used. For elementary types, a local copy is used if necessary to ensure by-copy semantics. |
Followed.
An Ada parameter of an access-to-subprogram type is passed as a reference to a Fortran procedure whose interface corresponds to the designated subprogram’s specification. |
Followed.
The machine code or intrinsic support should allow access to all operations normally available to assembly language programmers for the target environment, including privileged instructions, if any. |
Followed.
The interfacing pragmas (see Annex B) should support interface to
assembler; the default assembler should be associated with the
convention identifier |
Followed.
If an entity is exported to assembly language, then the implementation should allocate it at an addressable location, and should ensure that it is retained by the linking process, even if not otherwise referenced from the Ada code. The implementation should assume that any call to a machine code or assembler subprogram is allowed to read or update every object that is specified as exported. |
Followed.
The implementation should ensure that little or no overhead is associated with calling intrinsic and machine-code subprograms. |
Followed for both intrinsics and machine-code subprograms.
It is recommended that intrinsic subprograms be provided for convenient access to any machine operations that provide special capabilities or efficiency and that are not otherwise available through the language constructs. |
Followed. A full set of machine operation intrinsic subprograms is provided.
Atomic read-modify-write operations—e.g., test and set, compare and swap, decrement and test, enqueue/dequeue. |
Followed on any target supporting such operations.
Standard numeric functions—e.g., sin, log. |
Followed on any target supporting such operations.
String manipulation operations—e.g., translate and test. |
Followed on any target supporting such operations.
Vector operations—e.g., compare vector against thresholds. |
Followed on any target supporting such operations.
Direct operations on I/O ports. |
Followed on any target supporting such operations.
If the |
Followed. The underlying system does not allow for finer-grain control of interrupt blocking.
Whenever possible, the implementation should allow interrupt handlers to be called directly by the hardware. |
Followed on any target where the underlying operating system permits such direct calls.
Whenever practical, violations of any implementation-defined restrictions should be detected before run time. |
Followed. Compile time warnings are given when possible.
Interrupts
If implementation-defined forms of interrupt handler procedures are
supported, such as protected procedures with parameters, then for each
such form of a handler, a type analogous to |
Followed.
It is recommended that pre-elaborated packages be implemented in such a way that there should be little or no code executed at run time for the elaboration of entities not already covered by the Implementation Requirements. |
Followed. Executable code is generated in some cases, e.g. loops to initialize large arrays.
Discard_Names
If the pragma applies to an entity, then the implementation should reduce the amount of storage used for storing names associated with that entity. |
Followed.
Some implementations are targeted to domains in which memory use at run time must be completely deterministic. For such implementations, it is recommended that the storage for task attributes will be pre-allocated statically and not from the heap. This can be accomplished by either placing restrictions on the number and the size of the task’s attributes, or by using the pre-allocated storage for the first N attribute objects, and the heap for the others. In the latter case, N should be documented. |
Not followed. This implementation is not targeted to such a domain.
The implementation should use names that end with ‘_Locking’ for locking policies defined by the implementation. |
Followed. Two implementation-defined locking policies are defined,
whose names (Inheritance_Locking
and
Concurrent_Readers_Locking
) follow this suggestion.
Names that end with ‘_Queuing’ should be used for all implementation-defined queuing policies. |
Followed. No such implementation-defined queuing policies exist.
Even though the |
Followed.
On a multi-processor, the delay associated with aborting a task on another processor should be bounded; the implementation should use periodic polling, if necessary, to achieve this. |
Followed.
When feasible, the implementation should take advantage of the specified restrictions to produce a more efficient implementation. |
GNAT currently takes advantage of these restrictions by providing an optimized
run time when the Ravenscar profile and the GNAT restricted run time set
of restrictions are specified. See pragma Profile (Ravenscar)
and
pragma Profile (Restricted)
for more details.
When appropriate, implementations should provide configuration
mechanisms to change the value of |
Such configuration mechanisms are not appropriate to this implementation and are thus not supported.
It is recommended that |
Followed.
It is recommended that the best time base which exists in
the underlying system be available to the application through
|
Followed.
Whenever possible, the PCS on the called partition should allow for multiple tasks to call the RPC-receiver with different messages and should allow them to block until the corresponding subprogram body returns. |
Followed by GLADE, a separately supplied PCS that can be used with GNAT.
The |
Followed by GLADE, a separately supplied PCS that can be used with GNAT.
If COBOL (respectively, C) is widely supported in the target
environment, implementations supporting the Information Systems Annex
should provide the child package |
Followed.
Packed decimal should be used as the internal representation for objects of subtype S when S’Machine_Radix = 10. |
Not followed. GNAT ignores S’Machine_Radix and always uses binary representations.
If Fortran (respectively, C) is widely supported in the target
environment, implementations supporting the Numerics Annex
should provide the child package |
Followed.
Because the usual mathematical meaning of multiplication of a complex operand and a real operand is that of the scaling of both components of the former by the latter, an implementation should not perform this operation by first promoting the real operand to complex type and then performing a full complex multiplication. In systems that, in the future, support an Ada binding to IEC 559:1989, the latter technique will not generate the required result when one of the components of the complex operand is infinite. (Explicit multiplication of the infinite component by the zero component obtained during promotion yields a NaN that propagates into the final result.) Analogous advice applies in the case of multiplication of a complex operand and a pure-imaginary operand, and in the case of division of a complex operand by a real or pure-imaginary operand. |
Not followed.
Similarly, because the usual mathematical meaning of addition of a
complex operand and a real operand is that the imaginary operand remains
unchanged, an implementation should not perform this operation by first
promoting the real operand to complex type and then performing a full
complex addition. In implementations in which the |
Not followed.
Implementations in which |
Followed.
Implementations in which |
Followed.
The versions of the forward trigonometric functions without a
|
Followed.
The version of the |
Followed.
If the partition elaboration policy is |
Not followed.
Next: Intrinsic Subprograms, Previous: Implementation Advice, Up: Top [Contents][Index]
In addition to the implementation dependent pragmas and attributes, and the implementation advice, there are a number of other Ada features that are potentially implementation dependent and are designated as implementation-defined. These are mentioned throughout the Ada Reference Manual, and are summarized in Annex M.
A requirement for conforming Ada compilers is that they provide documentation describing how the implementation deals with each of these issues. In this chapter, you will find each point in Annex M listed followed by a description in italic font of how GNAT handles the implementation dependence.
You can use this chapter as a guide to minimizing implementation dependent features in your programs if portability to other compilers and other operating systems is an important consideration. The numbers in each section below correspond to the paragraph number in the Ada Reference Manual.
2. Whether or not each recommendation given in Implementation Advice is followed. See 1.1.2(37). |
3. Capacity limitations of the implementation. See 1.1.3(3). |
The complexity of programs that can be processed is limited only by the total amount of available virtual memory, and disk space for the generated object files.
4. Variations from the standard that are impractical to avoid given the implementation’s execution environment. See 1.1.3(6). |
There are no variations from the standard.
5. Which |
Any code_statement
can potentially cause external interactions.
6. The coded representation for the text of an Ada program. See 2.1(4). |
See separate section on source representation.
7. The control functions allowed in comments. See 2.1(14). |
See separate section on source representation.
8. The representation for an end of line. See 2.2(2). |
See separate section on source representation.
9. Maximum supported line length and lexical element length. See 2.2(15). |
The maximum line length is 255 characters and the maximum length of a lexical element is also 255 characters. This is the default setting if not overridden by the use of compiler switch -gnaty (which sets the maximum to 79) or -gnatyMnn which allows the maximum line length to be specified to be any value up to 32767. The maximum length of a lexical element is the same as the maximum line length.
10. Implementation defined pragmas. See 2.8(14). |
See Implementation Defined Pragmas.
11. Effect of pragma |
Pragma Optimize
, if given with a Time
or Space
parameter, checks that the optimization flag is set, and aborts if it is
not.
12. The sequence of characters of the value returned by
|
The sequence of characters is as defined by the wide character encoding method used for the source. See section on source representation for further details.
13. The predefined integer types declared in
|
Short_Short_Integer
8 bit signed
Short_Integer
(Short) 16 bit signed
Integer
32 bit signed
Long_Integer
64 bit signed (on most 64 bit targets, depending on the C definition of long). 32 bit signed (all other targets)
Long_Long_Integer
64 bit signed
14. Any nonstandard integer types and the operators defined for them. See 3.5.4(26). |
There are no nonstandard integer types.
15. Any nonstandard real types and the operators defined for them. See 3.5.6(8). |
There are no nonstandard real types.
16. What combinations of requested decimal precision and range are supported for floating point types. See 3.5.7(7). |
The precision and range is as defined by the IEEE standard.
17. The predefined floating point types declared in
|
Short_Float
32 bit IEEE short
Float
(Short) 32 bit IEEE short
Long_Float
64 bit IEEE long
Long_Long_Float
64 bit IEEE long (80 bit IEEE long on x86 processors)
18. The small of an ordinary fixed point type. See 3.5.9(8). |
Fine_Delta
is 2**(-63)
19. What combinations of small, range, and digits are supported for fixed point types. See 3.5.9(10). |
Any combinations are permitted that do not result in a small less than
Fine_Delta
and do not result in a mantissa larger than 63 bits.
If the mantissa is larger than 53 bits on machines where Long_Long_Float
is 64 bits (true of all architectures except ia32), then the output from
Text_IO is accurate to only 53 bits, rather than the full mantissa. This
is because floating-point conversions are used to convert fixed point.
20. The result of |
Block numbers of the form Bnnn
, where nnn is a
decimal integer are allocated.
21. Implementation-defined attributes. See 4.1.4(12). |
See Implementation Defined Attributes.
22. Any implementation-defined time types. See 9.6(6). |
There are no implementation-defined time types.
23. The time base associated with relative delays. |
See 9.6(20). The time base used is that provided by the C library
function gettimeofday
.
24. The time base of the type |
The time base used is that provided by the C library function
gettimeofday
.
25. The time zone used for package |
The time zone used by package Calendar
is the current system time zone
setting for local time, as accessed by the C library function
localtime
.
26. Any limit on |
There are no such limits.
27. Whether or not two non-overlapping parts of a composite
object are independently addressable, in the case where packing, record
layout, or |
Separate components are independently addressable if they do not share overlapping storage units.
28. The representation for a compilation. See 10.1(2). |
A compilation is represented by a sequence of files presented to the
compiler in a single invocation of the gcc
command.
29. Any restrictions on compilations that contain multiple compilation_units. See 10.1(4). |
No single file can contain more than one compilation unit, but any sequence of files can be presented to the compiler as a single compilation.
30. The mechanisms for creating an environment and for adding and replacing compilation units. See 10.1.4(3). |
See separate section on compilation model.
31. The manner of explicitly assigning library units to a partition. See 10.2(2). |
If a unit contains an Ada main program, then the Ada units for the partition are determined by recursive application of the rules in the Ada Reference Manual section 10.2(2-6). In other words, the Ada units will be those that are needed by the main program, and then this definition of need is applied recursively to those units, and the partition contains the transitive closure determined by this relationship. In short, all the necessary units are included, with no need to explicitly specify the list. If additional units are required, e.g. by foreign language units, then all units must be mentioned in the context clause of one of the needed Ada units.
If the partition contains no main program, or if the main program is in a language other than Ada, then GNAT provides the binder options -z and -n respectively, and in this case a list of units can be explicitly supplied to the binder for inclusion in the partition (all units needed by these units will also be included automatically). For full details on the use of these options, refer to The GNAT Make Program gnatmake in GNAT User’s Guide.
32. The implementation-defined means, if any, of specifying which compilation units are needed by a given compilation unit. See 10.2(2). |
The units needed by a given compilation unit are as defined in the Ada Reference Manual section 10.2(2-6). There are no implementation-defined pragmas or other implementation-defined means for specifying needed units.
33. The manner of designating the main subprogram of a partition. See 10.2(7). |
The main program is designated by providing the name of the corresponding ALI file as the input parameter to the binder.
34. The order of elaboration of |
The first constraint on ordering is that it meets the requirements of Chapter 10 of the Ada Reference Manual. This still leaves some implementation dependent choices, which are resolved by first elaborating bodies as early as possible (i.e., in preference to specs where there is a choice), and second by evaluating the immediate with clauses of a unit to determine the probably best choice, and third by elaborating in alphabetical order of unit names where a choice still remains.
35. Parameter passing and function return for the main subprogram. See 10.2(21). |
The main program has no parameters. It may be a procedure, or a function
returning an integer type. In the latter case, the returned integer
value is the return code of the program (overriding any value that
may have been set by a call to Ada.Command_Line.Set_Exit_Status
).
36. The mechanisms for building and running partitions. See 10.2(24). |
GNAT itself supports programs with only a single partition. The GNATDIST tool provided with the GLADE package (which also includes an implementation of the PCS) provides a completely flexible method for building and running programs consisting of multiple partitions. See the separate GLADE manual for details.
37. The details of program execution, including program termination. See 10.2(25). |
See separate section on compilation model.
38. The semantics of any non-active partitions supported by the implementation. See 10.2(28). |
Passive partitions are supported on targets where shared memory is provided by the operating system. See the GLADE reference manual for further details.
39. The information returned by |
Exception message returns the null string unless a specific message has been passed by the program.
40. The result of |
Blocks have implementation defined names of the form Bnnn
where nnn is an integer.
41. The information returned by
|
Exception_Information
returns a string in the following format:
Exception_Name: nnnnn Message: mmmmm PID: ppp Call stack traceback locations: 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
where
nnnn
is the fully qualified name of the exception in all upper
case letters. This line is always present.
mmmm
is the message (this line present only if message is non-null)
ppp
is the Process Id value as a decimal integer (this line is
present only if the Process Id is nonzero). Currently we are
not making use of this field.
The line terminator sequence at the end of each line, including
the last line is a single LF
character (16#0A#
).
42. Implementation-defined check names. See 11.5(27). |
The implementation defined check name Alignment_Check controls checking of address clause values for proper alignment (that is, the address supplied must be consistent with the alignment of the type).
In addition, a user program can add implementation-defined check names by means of the pragma Check_Name.
43. The interpretation of each aspect of representation. See 13.1(20). |
See separate section on data representations.
44. Any restrictions placed upon representation items. See 13.1(20). |
See separate section on data representations.
45. The meaning of |
Size for an indefinite subtype is the maximum possible size, except that for the case of a subprogram parameter, the size of the parameter object is the actual size.
46. The default external representation for a type tag. See 13.3(75). |
The default external representation for a type tag is the fully expanded name of the type in upper case letters.
47. What determines whether a compilation unit is the same in two different partitions. See 13.3(76). |
A compilation unit is the same in two different partitions if and only if it derives from the same source file.
48. Implementation-defined components. See 13.5.1(15). |
The only implementation defined component is the tag for a tagged type, which contains a pointer to the dispatching table.
49. If |
Word_Size
(32) is not the same as Storage_Unit
(8) for this
implementation, so no non-default bit ordering is supported. The default
bit ordering corresponds to the natural endianness of the target architecture.
50. The contents of the visible part of package |
See the definition of these packages in files system.ads and s-stoele.ads.
51. The contents of the visible part of package
|
See the definition and documentation in file s-maccod.ads.
52. The effect of unchecked conversion. See 13.9(11). |
Unchecked conversion between types of the same size results in an uninterpreted transmission of the bits from one type to the other. If the types are of unequal sizes, then in the case of discrete types, a shorter source is first zero or sign extended as necessary, and a shorter target is simply truncated on the left. For all non-discrete types, the source is first copied if necessary to ensure that the alignment requirements of the target are met, then a pointer is constructed to the source value, and the result is obtained by dereferencing this pointer after converting it to be a pointer to the target type. Unchecked conversions where the target subtype is an unconstrained array are not permitted. If the target alignment is greater than the source alignment, then a copy of the result is made with appropriate alignment
53. The semantics of operations on invalid representations. See 13.9.2(10-11). |
For assignments and other operations where the use of invalid values cannot result in erroneous behavior, the compiler ignores the possibility of invalid values. An exception is raised at the point where an invalid value would result in erroneous behavior. For example executing:
procedure invalidvals is X : Integer := -1; Y : Natural range 1 .. 10; for Y'Address use X'Address; Z : Natural range 1 .. 10; A : array (Natural range 1 .. 10) of Integer; begin Z := Y; -- no exception A (Z) := 3; -- exception raised; end;
As indicated, an exception is raised on the array assignment, but not on the simple assignment of the invalid negative value from Y to Z.
53. The manner of choosing a storage pool for an access type
when |
There are 3 different standard pools used by the compiler when
Storage_Pool
is not specified depending whether the type is local
to a subprogram or defined at the library level and whether
Storage_Size
is specified or not. See documentation in the runtime
library units System.Pool_Global
, System.Pool_Size
and
System.Pool_Local
in files s-poosiz.ads,
s-pooglo.ads and s-pooloc.ads for full details on the
default pools used.
54. Whether or not the implementation provides user-accessible names for the standard pool type(s). See 13.11(17). |
See documentation in the sources of the run time mentioned in paragraph
53 . All these pools are accessible by means of with
’ing
these units.
55. The meaning of |
Storage_Size
is measured in storage units, and refers to the
total space available for an access type collection, or to the primary
stack space for a task.
56. Implementation-defined aspects of storage pools. See 13.11(22). |
See documentation in the sources of the run time mentioned in paragraph 53 for details on GNAT-defined aspects of storage pools.
57. The set of restrictions allowed in a pragma
|
See Standard and Implementation Defined Restrictions.
58. The consequences of violating limitations on
|
Restrictions that can be checked at compile time result in illegalities if violated. Currently there are no other consequences of violating restrictions.
59. The representation used by the |
The representation is the in-memory representation of the base type of
the type, using the number of bits corresponding to the
type'Size
value, and the natural ordering of the machine.
60. The names and characteristics of the numeric subtypes
declared in the visible part of package |
See items describing the integer and floating-point types supported.
61. The accuracy actually achieved by the elementary functions. See A.5.1(1). |
The elementary functions correspond to the functions available in the C library. Only fast math mode is implemented.
62. The sign of a zero result from some of the operators or
functions in |
The sign of zeroes follows the requirements of the IEEE 754 standard on floating-point.
63. The value of
|
Maximum image width is 6864, see library file s-rannum.ads.
64. The value of
|
Maximum image width is 6864, see library file s-rannum.ads.
65. The algorithms for random number generation. See A.5.2(32). |
The algorithm is the Mersenne Twister, as documented in the source file s-rannum.adb. This version of the algorithm has a period of 2**19937-1.
66. The string representation of a random number generator’s state. See A.5.2(38). |
The value returned by the Image function is the concatenation of the fixed-width decimal representations of the 624 32-bit integers of the state vector.
67. The minimum time interval between calls to the time-dependent Reset procedure that are guaranteed to initiate different random number sequences. See A.5.2(45). |
The minimum period between reset calls to guarantee distinct series of random numbers is one microsecond.
68. The values of the |
Run the compiler with -gnatS to produce a listing of package
Standard
, has the values of all numeric attributes.
69. Any implementation-defined characteristics of the input-output packages. See A.7(14). |
There are no special implementation defined characteristics for these packages.
70. The value of |
All type representations are contiguous, and the Buffer_Size
is
the value of type'Size
rounded up to the next storage unit
boundary.
71. External files for standard input, standard output, and standard error See A.10(5). |
These files are mapped onto the files provided by the C streams libraries. See source file i-cstrea.ads for further details.
72. The accuracy of the value produced by |
If more digits are requested in the output than are represented by the precision of the value, zeroes are output in the corresponding least significant digit positions.
73. The meaning of |
These are mapped onto the argv
and argc
parameters of the
main program in the natural manner.
74. The interpretation of the |
The Form
parameter is not used.
75. The interpretation of the |
The Form
parameter is not used.
76. The interpretation of the |
The Form
parameter is case-insensitive.
Two fields are recognized in the Form
parameter:
preserve=<value>
mode=<value>
<value> starts immediately after the character ’=’ and ends with the character immediately preceding the next comma (’,’) or with the last character of the parameter.
The only possible values for preserve= are:
no_attributes
Do not try to preserve any file attributes. This is the default if no preserve= is found in Form.
all_attributes
Try to preserve all file attributes (timestamps, access rights).
timestamps
Preserve the timestamp of the copied file, but not the other file attributes.
The only possible values for mode= are:
copy
Only do the copy if the destination file does not already exist. If it already exists, Copy_File fails.
overwrite
Copy the file in all cases. Overwrite an already existing destination file.
append
Append the original file to the destination file. If the destination file does not exist, the destination file is a copy of the source file. When mode=append, the field preserve=, if it exists, is not taken into account.
If the Form parameter includes one or both of the fields and the value or values are incorrect, Copy_file fails with Use_Error.
Examples of correct Forms:
Form => "preserve=no_attributes,mode=overwrite" (the default) Form => "mode=append" Form => "mode=copy, preserve=all_attributes"
Examples of incorrect Forms
Form => "preserve=junk" Form => "mode=internal, preserve=timestamps"
77. Implementation-defined convention names. See B.1(11). |
The following convention names are supported
Ada
Ada
Ada_Pass_By_Copy
Allowed for any types except by-reference types such as limited records. Compatible with convention Ada, but causes any parameters with this convention to be passed by copy.
Ada_Pass_By_Reference
Allowed for any types except by-copy types such as scalars. Compatible with convention Ada, but causes any parameters with this convention to be passed by reference.
Assembler
Assembly language
Asm
Synonym for Assembler
Assembly
Synonym for Assembler
C
C
C_Pass_By_Copy
Allowed only for record types, like C, but also notes that record is to be passed by copy rather than reference.
COBOL
COBOL
C_Plus_Plus (or CPP)
C++
Default
Treated the same as C
External
Treated the same as C
Fortran
Fortran
Intrinsic
For support of pragma Import
with convention Intrinsic, see
separate section on Intrinsic Subprograms.
Stdcall
Stdcall (used for Windows implementations only). This convention correspond to the WINAPI (previously called Pascal convention) C/C++ convention under Windows. A routine with this convention cleans the stack before exit. This pragma cannot be applied to a dispatching call.
DLL
Synonym for Stdcall
Win32
Synonym for Stdcall
Stubbed
Stubbed is a special convention used to indicate that the body of the
subprogram will be entirely ignored. Any call to the subprogram
is converted into a raise of the Program_Error
exception. If a
pragma Import
specifies convention stubbed
then no body need
be present at all. This convention is useful during development for the
inclusion of subprograms whose body has not yet been written.
In addition, all otherwise unrecognized convention names are also treated as being synonymous with convention C. In all implementations except for VMS, use of such other names results in a warning. In VMS implementations, these names are accepted silently.
78. The meaning of link names. See B.1(36). |
Link names are the actual names used by the linker.
79. The manner of choosing link names when neither the link name nor the address of an imported or exported entity is specified. See B.1(36). |
The default linker name is that which would be assigned by the relevant external language, interpreting the Ada name as being in all lower case letters.
80. The effect of pragma |
The string passed to Linker_Options
is presented uninterpreted as
an argument to the link command, unless it contains ASCII.NUL characters.
NUL characters if they appear act as argument separators, so for example
pragma Linker_Options ("-labc" & ASCII.NUL & "-ldef");
causes two separate arguments -labc
and -ldef
to be passed to the
linker. The order of linker options is preserved for a given unit. The final
list of options passed to the linker is in reverse order of the elaboration
order. For example, linker options for a body always appear before the options
from the corresponding package spec.
81. The contents of the visible part of package
|
See files with prefix i- in the distributed library.
82. Implementation-defined children of package
|
See files with prefix i- in the distributed library.
83. The types |
Floating
Float
Long_Floating
(Floating) Long_Float
Binary
Integer
Long_Binary
Long_Long_Integer
Decimal_Element
Character
COBOL_Character
Character
For initialization, see the file i-cobol.ads in the distributed library.
84. Support for access to machine instructions. See C.1(1). |
See documentation in file s-maccod.ads in the distributed library.
85. Implementation-defined aspects of access to machine operations. See C.1(9). |
See documentation in file s-maccod.ads in the distributed library.
86. Implementation-defined aspects of interrupts. See C.3(2). |
Interrupts are mapped to signals or conditions as appropriate. See
definition of unit
Ada.Interrupt_Names
in source file a-intnam.ads for details
on the interrupts supported on a particular target.
87. Implementation-defined aspects of pre-elaboration. See C.4(13). |
GNAT does not permit a partition to be restarted without reloading, except under control of the debugger.
88. The semantics of pragma |
Pragma Discard_Names
causes names of enumeration literals to
be suppressed. In the presence of this pragma, the Image attribute
provides the image of the Pos of the literal, and Value accepts
Pos values.
89. The result of the |
The result of this attribute is a string that identifies
the object or component that denotes a given task. If a variable Var
has a task type, the image for this task will have the form Var_XXXXXXXX
,
where the suffix
is the hexadecimal representation of the virtual address of the corresponding
task control block. If the variable is an array of tasks, the image of each
task will have the form of an indexed component indicating the position of a
given task in the array, e.g. Group(5)_XXXXXXX
. If the task is a
component of a record, the image of the task will have the form of a selected
component. These rules are fully recursive, so that the image of a task that
is a subcomponent of a composite object corresponds to the expression that
designates this task.
If a task is created by an allocator, its image depends on the context. If the
allocator is part of an object declaration, the rules described above are used
to construct its image, and this image is not affected by subsequent
assignments. If the allocator appears within an expression, the image
includes only the name of the task type.
If the configuration pragma Discard_Names is present, or if the restriction
No_Implicit_Heap_Allocation is in effect, the image reduces to
the numeric suffix, that is to say the hexadecimal representation of the
virtual address of the control block of the task.
90. The value of |
Protected entries or interrupt handlers can be executed by any
convenient thread, so the value of Current_Task
is undefined.
91. The effect of calling |
The effect of calling Current_Task
from an entry body or
interrupt handler is to return the identification of the task currently
executing the code.
92. Implementation-defined aspects of
|
There are no implementation-defined aspects of Task_Attributes
.
93. Values of all |
The metrics information for GNAT depends on the performance of the underlying operating system. The sources of the run-time for tasking implementation, together with the output from -gnatG can be used to determine the exact sequence of operating systems calls made to implement various tasking constructs. Together with appropriate information on the performance of the underlying operating system, on the exact target in use, this information can be used to determine the required metrics.
94. The declarations of |
See declarations in file system.ads.
95. Implementation-defined execution resources. See D.1(15). |
There are no implementation-defined execution resources.
96. Whether, on a multiprocessor, a task that is waiting for access to a protected object keeps its processor busy. See D.2.1(3). |
On a multi-processor, a task that is waiting for access to a protected object does not keep its processor busy.
97. The affect of implementation defined execution resources on task dispatching. See D.2.1(9). |
Tasks map to threads in the threads package used by GNAT. Where possible and appropriate, these threads correspond to native threads of the underlying operating system.
98. Implementation-defined |
There are no implementation-defined policy-identifiers allowed in this pragma.
99. Implementation-defined aspects of priority inversion. See D.2.2(16). |
Execution of a task cannot be preempted by the implementation processing of delay expirations for lower priority tasks.
100. Implementation-defined task dispatching. See D.2.2(18). |
The policy is the same as that of the underlying threads implementation.
101. Implementation-defined |
The two implementation defined policies permitted in GNAT are
Inheritance_Locking
and Conccurent_Readers_Locking
. On
targets that support the Inheritance_Locking
policy, locking is
implemented by inheritance, i.e. the task owning the lock operates
at a priority equal to the highest priority of any task currently
requesting the lock. On targets that support the
Conccurent_Readers_Locking
policy, locking is implemented with a
read/write lock allowing multiple propected object functions to enter
concurrently.
102. Default ceiling priorities. See D.3(10). |
The ceiling priority of protected objects of the type
System.Interrupt_Priority'Last
as described in the Ada
Reference Manual D.3(10),
103. The ceiling of any protected object used internally by the implementation. See D.3(16). |
The ceiling priority of internal protected objects is
System.Priority'Last
.
104. Implementation-defined queuing policies. See D.4(1). |
There are no implementation-defined queuing policies.
105. On a multiprocessor, any conditions that cause the completion of an aborted construct to be delayed later than what is specified for a single processor. See D.6(3). |
The semantics for abort on a multi-processor is the same as on a single processor, there are no further delays.
106. Any operations that implicitly require heap storage allocation. See D.7(8). |
The only operation that implicitly requires heap storage allocation is task creation.
107. Implementation-defined aspects of pragma
|
There are no such implementation-defined aspects.
108. Implementation-defined aspects of package
|
There are no implementation defined aspects of package Real_Time
.
109. Implementation-defined aspects of
|
Any difference greater than one microsecond will cause the task to be delayed (see D.9(7)).
110. The upper bound on the duration of interrupt blocking caused by the implementation. See D.12(5). |
The upper bound is determined by the underlying operating system. In no cases is it more than 10 milliseconds.
111. The means for creating and executing distributed programs. See E(5). |
The GLADE package provides a utility GNATDIST for creating and executing distributed programs. See the GLADE reference manual for further details.
112. Any events that can result in a partition becoming inaccessible. See E.1(7). |
See the GLADE reference manual for full details on such events.
113. The scheduling policies, treatment of priorities, and management of shared resources between partitions in certain cases. See E.1(11). |
See the GLADE reference manual for full details on these aspects of multi-partition execution.
114. Events that cause the version of a compilation unit to change. See E.3(5). |
Editing the source file of a compilation unit, or the source files of any units on which it is dependent in a significant way cause the version to change. No other actions cause the version number to change. All changes are significant except those which affect only layout, capitalization or comments.
115. Whether the execution of the remote subprogram is immediately aborted as a result of cancellation. See E.4(13). |
See the GLADE reference manual for details on the effect of abort in a distributed application.
116. Implementation-defined aspects of the PCS. See E.5(25). |
See the GLADE reference manual for a full description of all implementation defined aspects of the PCS.
117. Implementation-defined interfaces in the PCS. See E.5(26). |
See the GLADE reference manual for a full description of all implementation defined interfaces.
118. The values of named numbers in the package
|
Max_Scale
+18
Min_Scale
-18
Min_Delta
1.0E-18
Max_Delta
1.0E+18
Max_Decimal_Digits
18
119. The value of |
64
120. The value of |
64
121. The accuracy actually achieved by the complex elementary functions and by other complex arithmetic operations. See G.1(1). |
Standard library functions are used for the complex arithmetic operations. Only fast math mode is currently supported.
122. The sign of a zero result (or a component thereof) from
any operator or function in |
The signs of zero values are as recommended by the relevant implementation advice.
123. The sign of a zero result (or a component thereof) from
any operator or function in
|
The signs of zero values are as recommended by the relevant implementation advice.
124. Whether the strict mode or the relaxed mode is the default. See G.2(2). |
The strict mode is the default. There is no separate relaxed mode. GNAT provides a highly efficient implementation of strict mode.
125. The result interval in certain cases of fixed-to-float conversion. See G.2.1(10). |
For cases where the result interval is implementation dependent, the accuracy is that provided by performing all operations in 64-bit IEEE floating-point format.
126. The result of a floating point arithmetic operation in
overflow situations, when the |
Infinite and NaN values are produced as dictated by the IEEE floating-point standard.
Note that on machines that are not fully compliant with the IEEE floating-point standard, such as Alpha, the -mieee compiler flag must be used for achieving IEEE conforming behavior (although at the cost of a significant performance penalty), so infinite and NaN values are properly generated.
127. The result interval for division (or exponentiation by a negative exponent), when the floating point hardware implements division as multiplication by a reciprocal. See G.2.1(16). |
Not relevant, division is IEEE exact.
128. The definition of close result set, which determines the accuracy of certain fixed point multiplications and divisions. See G.2.3(5). |
Operations in the close result set are performed using IEEE long format floating-point arithmetic. The input operands are converted to floating-point, the operation is done in floating-point, and the result is converted to the target type.
129. Conditions on a |
The result is only defined to be in the perfect result set if the result can be computed by a single scaling operation involving a scale factor representable in 64-bits.
130. The result of a fixed point arithmetic operation in
overflow situations, when the |
Not relevant, Machine_Overflows
is True
for fixed-point
types.
131. The result of an elementary function reference in
overflow situations, when the |
IEEE infinite and Nan values are produced as appropriate.
132. The value of the angle threshold, within which certain elementary functions, complex arithmetic operations, and complex elementary functions yield results conforming to a maximum relative error bound. See G.2.4(10). |
Information on this subject is not yet available.
133. The accuracy of certain elementary functions for parameters beyond the angle threshold. See G.2.4(10). |
Information on this subject is not yet available.
134. The result of a complex arithmetic operation or complex
elementary function reference in overflow situations, when the
|
IEEE infinite and Nan values are produced as appropriate.
135. The accuracy of certain complex arithmetic operations and certain complex elementary functions for parameters (or components thereof) beyond the angle threshold. See G.2.6(8). |
Information on those subjects is not yet available.
136. Information regarding bounded errors and erroneous execution. See H.2(1). |
Information on this subject is not yet available.
137. Implementation-defined aspects of pragma
|
Pragma Inspection_Point
ensures that the variable is live and can
be examined by the debugger at the inspection point.
138. Implementation-defined aspects of pragma
|
There are no implementation-defined aspects of pragma Restrictions
. The
use of pragma Restrictions [No_Exceptions]
has no effect on the
generated code. Checks must suppressed by use of pragma Suppress
.
139. Any restrictions on pragma |
There are no restrictions on pragma Restrictions
.
Next: Representation Clauses and Pragmas, Previous: Implementation Defined Characteristics, Up: Top [Contents][Index]
• Intrinsic Operators: | ||
• Enclosing_Entity: | ||
• Exception_Information: | ||
• Exception_Message: | ||
• Exception_Name: | ||
• File: | ||
• Line: | ||
• Shifts and Rotates: | ||
• Source_Location: |
GNAT allows a user application program to write the declaration:
pragma Import (Intrinsic, name);
providing that the name corresponds to one of the implemented intrinsic subprograms in GNAT, and that the parameter profile of the referenced subprogram meets the requirements. This chapter describes the set of implemented intrinsic subprograms, and the requirements on parameter profiles. Note that no body is supplied; as with other uses of pragma Import, the body is supplied elsewhere (in this case by the compiler itself). Note that any use of this feature is potentially non-portable, since the Ada standard does not require Ada compilers to implement this feature.
Next: Enclosing_Entity, Up: Intrinsic Subprograms [Contents][Index]
All the predefined numeric operators in package Standard
in pragma Import (Intrinsic,..)
declarations. In the binary operator case, the operands must have the same
size. The operand or operands must also be appropriate for
the operator. For example, for addition, the operands must
both be floating-point or both be fixed-point, and the
right operand for "**"
must have a root type of
Standard.Integer'Base
.
You can use an intrinsic operator declaration as in the following example:
type Int1 is new Integer; type Int2 is new Integer; function "+" (X1 : Int1; X2 : Int2) return Int1; function "+" (X1 : Int1; X2 : Int2) return Int2; pragma Import (Intrinsic, "+");
This declaration would permit “mixed mode” arithmetic on items
of the differing types Int1
and Int2
.
It is also possible to specify such operators for private types, if the
full views are appropriate arithmetic types.
Next: Exception_Information, Previous: Intrinsic Operators, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Enclosing_Entity
to obtain the name of
the current subprogram, package, task, entry, or protected subprogram.
Next: Exception_Message, Previous: Enclosing_Entity, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Current_Exception
. The only useful
use of the intrinsic import in this case is the one in this unit,
so an application program should simply call the function
GNAT.Current_Exception.Exception_Information
to obtain
the exception information associated with the current exception.
Next: Exception_Name, Previous: Exception_Information, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Current_Exception
. The only useful
use of the intrinsic import in this case is the one in this unit,
so an application program should simply call the function
GNAT.Current_Exception.Exception_Message
to obtain
the message associated with the current exception.
Next: File, Previous: Exception_Message, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Current_Exception
. The only useful
use of the intrinsic import in this case is the one in this unit,
so an application program should simply call the function
GNAT.Current_Exception.Exception_Name
to obtain
the name of the current exception.
Next: Line, Previous: Exception_Name, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.File
to obtain the name of the current
file.
Next: Shifts and Rotates, Previous: File, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Line
to obtain the number of the current
source line.
Next: Source_Location, Previous: Line, Up: Intrinsic Subprograms [Contents][Index]
In standard Ada, the shift and rotate functions are available only
for the predefined modular types in package Interfaces
. However, in
GNAT it is possible to define these functions for any integer
type (signed or modular), as in this example:
function Shift_Left (Value : T; Amount : Natural) return T;
The function name must be one of
Shift_Left, Shift_Right, Shift_Right_Arithmetic, Rotate_Left, or
Rotate_Right. T must be an integer type. T’Size must be
8, 16, 32 or 64 bits; if T is modular, the modulus
must be 2**8, 2**16, 2**32 or 2**64.
The result type must be the same as the type of Value
.
The shift amount must be Natural.
The formal parameter names can be anything.
Previous: Shifts and Rotates, Up: Intrinsic Subprograms [Contents][Index]
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Source_Location
to obtain the current
source file location.
Next: Standard Library Routines, Previous: Intrinsic Subprograms, Up: Top [Contents][Index]
This section describes the representation clauses accepted by GNAT, and their effect on the representation of corresponding data objects.
GNAT fully implements Annex C (Systems Programming). This means that all the implementation advice sections in chapter 13 are fully implemented. However, these sections only require a minimal level of support for representation clauses. GNAT provides much more extensive capabilities, and this section describes the additional capabilities provided.
Next: Size Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
GNAT requires that all alignment clauses specify a power of 2, and all default alignments are always a power of 2. The default alignment values are as follows:
Storage_Unit
,
and the maximum alignment supported by the target.
(This maximum alignment is given by the GNAT-specific attribute
Standard'Maximum_Alignment
; see Maximum_Alignment.)
For example, for type Long_Float
, the object size is 8 bytes, and the
default alignment will be 8 on any target that supports alignments
this large, but on some targets, the maximum alignment may be smaller
than 8, in which case objects of type Long_Float
will be maximally
aligned.
Pack
is used and all components are packable (see separate section on pragma
Pack
), then the resulting alignment is 1, unless the layout of the
record makes it profitable to increase it.
A special case is when:
In this case, an alignment is chosen to match the size of the record. For example, if we have:
type Small is record A, B : Character; end record; for Small'Size use 16;
then the default alignment of the record type Small
is 2, not 1. This
leads to more efficient code when the record is treated as a unit, and also
allows the type to specified as Atomic
on architectures requiring
strict alignment.
An alignment clause may specify a larger alignment than the default value
up to some maximum value dependent on the target (obtainable by using the
attribute reference Standard'Maximum_Alignment
). It may also specify
a smaller alignment than the default value for enumeration, integer and
fixed point types, as well as for record types, for example
type V is record A : Integer; end record; for V'alignment use 1;
The default alignment for the type V
is 4, as a result of the
Integer field in the record, but it is permissible, as shown, to
override the default alignment of the record with a smaller value.
Note that according to the Ada standard, an alignment clause applies only to the first named subtype. If additional subtypes are declared, then the compiler is allowed to choose any alignment it likes, and there is no way to control this choice. Consider:
type R is range 1 .. 10_000; for R'Alignment use 1; subtype RS is R range 1 .. 1000;
The alignment clause specifies an alignment of 1 for the first named subtype
R
but this does not necessarily apply to RS
. When writing
portable Ada code, you should avoid writing code that explicitly or
implicitly relies on the alignment of such subtypes.
For the GNAT compiler, if an explicit alignment clause is given, this
value is also used for any subsequent subtypes. So for GNAT, in the
above example, you can count on the alignment of RS
being 1. But this
assumption is non-portable, and other compilers may choose different
alignments for the subtype RS
.
Next: Storage_Size Clauses, Previous: Alignment Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
The default size for a type T
is obtainable through the
language-defined attribute T'Size
and also through the
equivalent GNAT-defined attribute T'Value_Size
.
For objects of type T
, GNAT will generally increase the type size
so that the object size (obtainable through the GNAT-defined attribute
T'Object_Size
)
is a multiple of T'Alignment * Storage_Unit
.
For example
type Smallint is range 1 .. 6; type Rec is record Y1 : integer; Y2 : boolean; end record;
In this example, Smallint'Size
= Smallint'Value_Size
= 3,
as specified by the RM rules,
but objects of this type will have a size of 8
(Smallint'Object_Size
= 8),
since objects by default occupy an integral number
of storage units. On some targets, notably older
versions of the Digital Alpha, the size of stand
alone objects of this type may be 32, reflecting
the inability of the hardware to do byte load/stores.
Similarly, the size of type Rec
is 40 bits
(Rec'Size
= Rec'Value_Size
= 40), but
the alignment is 4, so objects of this type will have
their size increased to 64 bits so that it is a multiple
of the alignment (in bits). This decision is
in accordance with the specific Implementation Advice in RM 13.3(43):
A
Size
clause should be supported for an object if the specifiedSize
is at least as large as its subtype’sSize
, and corresponds to a size in storage elements that is a multiple of the object’sAlignment
(if theAlignment
is nonzero).
An explicit size clause may be used to override the default size by increasing it. For example, if we have:
type My_Boolean is new Boolean; for My_Boolean'Size use 32;
then values of this type will always be 32 bits long. In the case of discrete types, the size can be increased up to 64 bits, with the effect that the entire specified field is used to hold the value, sign- or zero-extended as appropriate. If more than 64 bits is specified, then padding space is allocated after the value, and a warning is issued that there are unused bits.
Similarly the size of records and arrays may be increased, and the effect is to add padding bits after the value. This also causes a warning message to be generated.
The largest Size value permitted in GNAT is 2**31-1. Since this is a Size in bits, this corresponds to an object of size 256 megabytes (minus one). This limitation is true on all targets. The reason for this limitation is that it improves the quality of the code in many cases if it is known that a Size value can be accommodated in an object of type Integer.
Next: Size of Variant Record Objects, Previous: Size Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
For tasks, the Storage_Size
clause specifies the amount of space
to be allocated for the task stack. This cannot be extended, and if the
stack is exhausted, then Storage_Error
will be raised (if stack
checking is enabled). Use a Storage_Size
attribute definition clause,
or a Storage_Size
pragma in the task definition to set the
appropriate required size. A useful technique is to include in every
task definition a pragma of the form:
pragma Storage_Size (Default_Stack_Size);
Then Default_Stack_Size
can be defined in a global package, and
modified as required. Any tasks requiring stack sizes different from the
default can have an appropriate alternative reference in the pragma.
You can also use the -d binder switch to modify the default stack size.
For access types, the Storage_Size
clause specifies the maximum
space available for allocation of objects of the type. If this space is
exceeded then Storage_Error
will be raised by an allocation attempt.
In the case where the access type is declared local to a subprogram, the
use of a Storage_Size
clause triggers automatic use of a special
predefined storage pool (System.Pool_Size
) that ensures that all
space for the pool is automatically reclaimed on exit from the scope in
which the type is declared.
A special case recognized by the compiler is the specification of a
Storage_Size
of zero for an access type. This means that no
items can be allocated from the pool, and this is recognized at compile
time, and all the overhead normally associated with maintaining a fixed
size storage pool is eliminated. Consider the following example:
procedure p is type R is array (Natural) of Character; type P is access all R; for P'Storage_Size use 0; -- Above access type intended only for interfacing purposes y : P; procedure g (m : P); pragma Import (C, g); -- … begin -- … y := new R; end;
As indicated in this example, these dummy storage pools are often useful in connection with interfacing where no object will ever be allocated. If you compile the above example, you get the warning:
p.adb:16:09: warning: allocation from empty storage pool p.adb:16:09: warning: Storage_Error will be raised at run time
Of course in practice, there will not be any explicit allocators in the case of such an access declaration.
Next: Biased Representation, Previous: Storage_Size Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
In the case of variant record objects, there is a question whether Size gives information about a particular variant, or the maximum size required for any variant. Consider the following program
with Text_IO; use Text_IO; procedure q is type R1 (A : Boolean := False) is record case A is when True => X : Character; when False => null; end case; end record; V1 : R1 (False); V2 : R1; begin Put_Line (Integer'Image (V1'Size)); Put_Line (Integer'Image (V2'Size)); end q;
Here we are dealing with a variant record, where the True variant requires 16 bits, and the False variant requires 8 bits. In the above example, both V1 and V2 contain the False variant, which is only 8 bits long. However, the result of running the program is:
8 16
The reason for the difference here is that the discriminant value of V1 is fixed, and will always be False. It is not possible to assign a True variant value to V1, therefore 8 bits is sufficient. On the other hand, in the case of V2, the initial discriminant value is False (from the default), but it is possible to assign a True variant value to V2, therefore 16 bits must be allocated for V2 in the general case, even fewer bits may be needed at any particular point during the program execution.
As can be seen from the output of this program, the 'Size
attribute applied to such an object in GNAT gives the actual allocated
size of the variable, which is the largest size of any of the variants.
The Ada Reference Manual is not completely clear on what choice should
be made here, but the GNAT behavior seems most consistent with the
language in the RM.
In some cases, it may be desirable to obtain the size of the current variant, rather than the size of the largest variant. This can be achieved in GNAT by making use of the fact that in the case of a subprogram parameter, GNAT does indeed return the size of the current variant (because a subprogram has no way of knowing how much space is actually allocated for the actual).
Consider the following modified version of the above program:
with Text_IO; use Text_IO; procedure q is type R1 (A : Boolean := False) is record case A is when True => X : Character; when False => null; end case; end record; V2 : R1; function Size (V : R1) return Integer is begin return V'Size; end Size; begin Put_Line (Integer'Image (V2'Size)); Put_Line (Integer'IMage (Size (V2))); V2 := (True, 'x'); Put_Line (Integer'Image (V2'Size)); Put_Line (Integer'IMage (Size (V2))); end q;
The output from this program is
16 8 16 16
Here we see that while the 'Size
attribute always returns
the maximum size, regardless of the current variant value, the
Size
function does indeed return the size of the current
variant value.
Next: Value_Size and Object_Size Clauses, Previous: Size of Variant Record Objects, Up: Representation Clauses and Pragmas [Contents][Index]
In the case of scalars with a range starting at other than zero, it is possible in some cases to specify a size smaller than the default minimum value, and in such cases, GNAT uses an unsigned biased representation, in which zero is used to represent the lower bound, and successive values represent successive values of the type.
For example, suppose we have the declaration:
type Small is range -7 .. -4; for Small'Size use 2;
Although the default size of type Small
is 4, the Size
clause is accepted by GNAT and results in the following representation
scheme:
-7 is represented as 2#00# -6 is represented as 2#01# -5 is represented as 2#10# -4 is represented as 2#11#
Biased representation is only used if the specified Size
clause
cannot be accepted in any other manner. These reduced sizes that force
biased representation can be used for all discrete types except for
enumeration types for which a representation clause is given.
Next: Component_Size Clauses, Previous: Biased Representation, Up: Representation Clauses and Pragmas [Contents][Index]
In Ada 95 and Ada 2005, T'Size
for a type T
is the minimum
number of bits required to hold values of type T
.
Although this interpretation was allowed in Ada 83, it was not required,
and this requirement in practice can cause some significant difficulties.
For example, in most Ada 83 compilers, Natural'Size
was 32.
However, in Ada 95 and Ada 2005,
Natural'Size
is
typically 31. This means that code may change in behavior when moving
from Ada 83 to Ada 95 or Ada 2005. For example, consider:
type Rec is record; A : Natural; B : Natural; end record; for Rec use record at 0 range 0 .. Natural'Size - 1; at 0 range Natural'Size .. 2 * Natural'Size - 1; end record;
In the above code, since the typical size of Natural
objects
is 32 bits and Natural'Size
is 31, the above code can cause
unexpected inefficient packing in Ada 95 and Ada 2005, and in general
there are cases where the fact that the object size can exceed the
size of the type causes surprises.
To help get around this problem GNAT provides two implementation
defined attributes, Value_Size
and Object_Size
. When
applied to a type, these attributes yield the size of the type
(corresponding to the RM defined size attribute), and the size of
objects of the type respectively.
The Object_Size
is used for determining the default size of
objects and components. This size value can be referred to using the
Object_Size
attribute. The phrase “is used” here means that it is
the basis of the determination of the size. The backend is free to
pad this up if necessary for efficiency, e.g. an 8-bit stand-alone
character might be stored in 32 bits on a machine with no efficient
byte access instructions such as the Alpha.
The default rules for the value of Object_Size
for
discrete types are as follows:
Object_Size
for base subtypes reflect the natural hardware
size in bits (run the compiler with -gnatS to find those values
for numeric types). Enumeration types and fixed-point base subtypes have
8, 16, 32 or 64 bits for this size, depending on the range of values
to be stored.
Object_Size
of a subtype is the same as the
Object_Size
of
the type from which it is obtained.
Object_Size
of a derived base type is copied from the parent
base type, and the Object_Size
of a derived first subtype is copied
from the parent first subtype.
The Value_Size
attribute
is the (minimum) number of bits required to store a value
of the type.
This value is used to determine how tightly to pack
records or arrays with components of this type, and also affects
the semantics of unchecked conversion (unchecked conversions where
the Value_Size
values differ generate a warning, and are potentially
target dependent).
The default rules for the value of Value_Size
are as follows:
Value_Size
for a base subtype is the minimum number of bits
required to store all values of the type (including the sign bit
only if negative values are possible).
Value_Size
as the first subtype. This is a
consequence of RM 13.1(14) (“if two subtypes statically match,
then their subtype-specific aspects are the same”.)
Value_Size
corresponding to the minimum
number of bits required to store all values of the subtype. For
dynamic bounds, it is assumed that the value can range down or up
to the corresponding bound of the ancestor
The RM defined attribute Size
corresponds to the
Value_Size
attribute.
The Size
attribute may be defined for a first-named subtype. This sets
the Value_Size
of
the first-named subtype to the given value, and the
Object_Size
of this first-named subtype to the given value padded up
to an appropriate boundary. It is a consequence of the default rules
above that this Object_Size
will apply to all further subtypes. On the
other hand, Value_Size
is affected only for the first subtype, any
dynamic subtypes obtained from it directly, and any statically matching
subtypes. The Value_Size
of any other static subtypes is not affected.
Value_Size
and
Object_Size
may be explicitly set for any subtype using
an attribute definition clause. Note that the use of these attributes
can cause the RM 13.1(14) rule to be violated. If two access types
reference aliased objects whose subtypes have differing Object_Size
values as a result of explicit attribute definition clauses, then it
is erroneous to convert from one access subtype to the other.
At the implementation level, Esize stores the Object_Size and the
RM_Size field stores the Value_Size
(and hence the value of the
Size
attribute,
which, as noted above, is equivalent to Value_Size
).
To get a feel for the difference, consider the following examples (note
that in each case the base is Short_Short_Integer
with a size of 8):
Object_Size Value_Size type x1 is range 0 .. 5; 8 3 type x2 is range 0 .. 5; for x2'size use 12; 16 12 subtype x3 is x2 range 0 .. 3; 16 2 subtype x4 is x2'base range 0 .. 10; 8 4 subtype x5 is x2 range 0 .. dynamic; 16 3* subtype x6 is x2'base range 0 .. dynamic; 8 3*
Note: the entries marked “3*” are not actually specified by the Ada
Reference Manual, but it seems in the spirit of the RM rules to allocate
the minimum number of bits (here 3, given the range for x2
)
known to be large enough to hold the given range of values.
So far, so good, but GNAT has to obey the RM rules, so the question is
under what conditions must the RM Size
be used.
The following is a list
of the occasions on which the RM Size
must be used:
Size
for a type
For record types, the Object_Size
is always a multiple of the
alignment of the type (this is true for all types). In some cases the
Value_Size
can be smaller. Consider:
type R is record X : Integer; Y : Character; end record;
On a typical 32-bit architecture, the X component will be four bytes, and
require four-byte alignment, and the Y component will be one byte. In this
case R'Value_Size
will be 40 (bits) since this is the minimum size
required to store a value of this type, and for example, it is permissible
to have a component of type R in an outer array whose component size is
specified to be 48 bits. However, R'Object_Size
will be 64 (bits),
since it must be rounded up so that this value is a multiple of the
alignment (4 bytes = 32 bits).
For all other types, the Object_Size
and Value_Size are the same (and equivalent to the RM attribute Size
).
Only Size
may be specified for such types.
Next: Bit_Order Clauses, Previous: Value_Size and Object_Size Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
Normally, the value specified in a component size clause must be consistent with the subtype of the array component with regard to size and alignment. In other words, the value specified must be at least equal to the size of this subtype, and must be a multiple of the alignment value.
In addition, component size clauses are allowed which cause the array to be packed, by specifying a smaller value. A first case is for component size values in the range 1 through 63. The value specified must not be smaller than the Size of the subtype. GNAT will accurately honor all packing requests in this range. For example, if we have:
type r is array (1 .. 8) of Natural; for r'Component_Size use 31;
then the resulting array has a length of 31 bytes (248 bits = 8 * 31). Of course access to the components of such an array is considerably less efficient than if the natural component size of 32 is used. A second case is when the subtype of the component is a record type padded because of its default alignment. For example, if we have:
type r is record i : Integer; j : Integer; b : Boolean; end record; type a is array (1 .. 8) of r; for a'Component_Size use 72;
then the resulting array has a length of 72 bytes, instead of 96 bytes if the alignment of the record (4) was obeyed.
Note that there is no point in giving both a component size clause and a pragma Pack for the same array type. if such duplicate clauses are given, the pragma Pack will be ignored.
Next: Effect of Bit_Order on Byte Ordering, Previous: Component_Size Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
For record subtypes, GNAT permits the specification of the Bit_Order
attribute. The specification may either correspond to the default bit
order for the target, in which case the specification has no effect and
places no additional restrictions, or it may be for the non-standard
setting (that is the opposite of the default).
In the case where the non-standard value is specified, the effect is to renumber bits within each byte, but the ordering of bytes is not affected. There are certain restrictions placed on component clauses as follows:
Low_Order_First
being the default, then the following two declarations have exactly
the same effect:
type R1 is record A : Boolean; B : Integer range 1 .. 120; end record; for R1 use record A at 0 range 0 .. 0; B at 0 range 1 .. 7; end record; type R2 is record A : Boolean; B : Integer range 1 .. 120; end record; for R2'Bit_Order use High_Order_First; for R2 use record A at 0 range 7 .. 7; B at 0 range 0 .. 6; end record;
The useful application here is to write the second declaration with the
Bit_Order
attribute definition clause, and know that it will be treated
the same, regardless of whether the target is little-endian or big-endian.
Bit_Order
specification does not affect the ordering of bytes.
In particular, the following attempt at getting an endian-independent integer
does not work:
type R2 is record A : Integer; end record; for R2'Bit_Order use High_Order_First; for R2 use record A at 0 range 0 .. 31; end record;
This declaration will result in a little-endian integer on a
little-endian machine, and a big-endian integer on a big-endian machine.
If byte flipping is required for interoperability between big- and
little-endian machines, this must be explicitly programmed. This capability
is not provided by Bit_Order
.
Since the misconception that Bit_Order automatically deals with all
endian-related incompatibilities is a common one, the specification of
a component field that is an integral number of bytes will always
generate a warning. This warning may be suppressed using pragma
Warnings (Off)
if desired. The following section contains additional
details regarding the issue of byte ordering.
Next: Pragma Pack for Arrays, Previous: Bit_Order Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
In this section we will review the effect of the Bit_Order
attribute
definition clause on byte ordering. Briefly, it has no effect at all, but
a detailed example will be helpful. Before giving this
example, let us review the precise
definition of the effect of defining Bit_Order
. The effect of a
non-standard bit order is described in section 15.5.3 of the Ada
Reference Manual:
2 A bit ordering is a method of interpreting the meaning of the storage place attributes.
To understand the precise definition of storage place attributes in this context, we visit section 13.5.1 of the manual:
13 A record_representation_clause (without the mod_clause) specifies the layout. The storage place attributes (see 13.5.2) are taken from the values of the position, first_bit, and last_bit expressions after normalizing those values so that first_bit is less than Storage_Unit.
The critical point here is that storage places are taken from
the values after normalization, not before. So the Bit_Order
interpretation applies to normalized values. The interpretation
is described in the later part of the 15.5.3 paragraph:
2 A bit ordering is a method of interpreting the meaning of the storage place attributes. High_Order_First (known in the vernacular as “big endian”) means that the first bit of a storage element (bit 0) is the most significant bit (interpreting the sequence of bits that represent a component as an unsigned integer value). Low_Order_First (known in the vernacular as “little endian”) means the opposite: the first bit is the least significant.
Note that the numbering is with respect to the bits of a storage unit. In other words, the specification affects only the numbering of bits within a single storage unit.
We can make the effect clearer by giving an example.
Suppose that we have an external device which presents two bytes, the first byte presented, which is the first (low addressed byte) of the two byte record is called Master, and the second byte is called Slave.
The left most (most significant bit is called Control for each byte, and the remaining 7 bits are called V1, V2, … V7, where V7 is the rightmost (least significant) bit.
On a big-endian machine, we can write the following representation clause
type Data is record Master_Control : Bit; Master_V1 : Bit; Master_V2 : Bit; Master_V3 : Bit; Master_V4 : Bit; Master_V5 : Bit; Master_V6 : Bit; Master_V7 : Bit; Slave_Control : Bit; Slave_V1 : Bit; Slave_V2 : Bit; Slave_V3 : Bit; Slave_V4 : Bit; Slave_V5 : Bit; Slave_V6 : Bit; Slave_V7 : Bit; end record; for Data use record Master_Control at 0 range 0 .. 0; Master_V1 at 0 range 1 .. 1; Master_V2 at 0 range 2 .. 2; Master_V3 at 0 range 3 .. 3; Master_V4 at 0 range 4 .. 4; Master_V5 at 0 range 5 .. 5; Master_V6 at 0 range 6 .. 6; Master_V7 at 0 range 7 .. 7; Slave_Control at 1 range 0 .. 0; Slave_V1 at 1 range 1 .. 1; Slave_V2 at 1 range 2 .. 2; Slave_V3 at 1 range 3 .. 3; Slave_V4 at 1 range 4 .. 4; Slave_V5 at 1 range 5 .. 5; Slave_V6 at 1 range 6 .. 6; Slave_V7 at 1 range 7 .. 7; end record;
Now if we move this to a little endian machine, then the bit ordering within the byte is backwards, so we have to rewrite the record rep clause as:
for Data use record Master_Control at 0 range 7 .. 7; Master_V1 at 0 range 6 .. 6; Master_V2 at 0 range 5 .. 5; Master_V3 at 0 range 4 .. 4; Master_V4 at 0 range 3 .. 3; Master_V5 at 0 range 2 .. 2; Master_V6 at 0 range 1 .. 1; Master_V7 at 0 range 0 .. 0; Slave_Control at 1 range 7 .. 7; Slave_V1 at 1 range 6 .. 6; Slave_V2 at 1 range 5 .. 5; Slave_V3 at 1 range 4 .. 4; Slave_V4 at 1 range 3 .. 3; Slave_V5 at 1 range 2 .. 2; Slave_V6 at 1 range 1 .. 1; Slave_V7 at 1 range 0 .. 0; end record;
It is a nuisance to have to rewrite the clause, especially if
the code has to be maintained on both machines. However,
this is a case that we can handle with the
Bit_Order
attribute if it is implemented.
Note that the implementation is not required on byte addressed
machines, but it is indeed implemented in GNAT.
This means that we can simply use the
first record clause, together with the declaration
for Data'Bit_Order use High_Order_First;
and the effect is what is desired, namely the layout is exactly the same, independent of whether the code is compiled on a big-endian or little-endian machine.
The important point to understand is that byte ordering is not affected.
A Bit_Order
attribute definition never affects which byte a field
ends up in, only where it ends up in that byte.
To make this clear, let us rewrite the record rep clause of the previous
example as:
for Data'Bit_Order use High_Order_First; for Data use record Master_Control at 0 range 0 .. 0; Master_V1 at 0 range 1 .. 1; Master_V2 at 0 range 2 .. 2; Master_V3 at 0 range 3 .. 3; Master_V4 at 0 range 4 .. 4; Master_V5 at 0 range 5 .. 5; Master_V6 at 0 range 6 .. 6; Master_V7 at 0 range 7 .. 7; Slave_Control at 0 range 8 .. 8; Slave_V1 at 0 range 9 .. 9; Slave_V2 at 0 range 10 .. 10; Slave_V3 at 0 range 11 .. 11; Slave_V4 at 0 range 12 .. 12; Slave_V5 at 0 range 13 .. 13; Slave_V6 at 0 range 14 .. 14; Slave_V7 at 0 range 15 .. 15; end record;
This is exactly equivalent to saying (a repeat of the first example):
for Data'Bit_Order use High_Order_First; for Data use record Master_Control at 0 range 0 .. 0; Master_V1 at 0 range 1 .. 1; Master_V2 at 0 range 2 .. 2; Master_V3 at 0 range 3 .. 3; Master_V4 at 0 range 4 .. 4; Master_V5 at 0 range 5 .. 5; Master_V6 at 0 range 6 .. 6; Master_V7 at 0 range 7 .. 7; Slave_Control at 1 range 0 .. 0; Slave_V1 at 1 range 1 .. 1; Slave_V2 at 1 range 2 .. 2; Slave_V3 at 1 range 3 .. 3; Slave_V4 at 1 range 4 .. 4; Slave_V5 at 1 range 5 .. 5; Slave_V6 at 1 range 6 .. 6; Slave_V7 at 1 range 7 .. 7; end record;
Why are they equivalent? Well take a specific field, the Slave_V2
field. The storage place attributes are obtained by normalizing the
values given so that the First_Bit
value is less than 8. After
normalizing the values (0,10,10) we get (1,2,2) which is exactly what
we specified in the other case.
Now one might expect that the Bit_Order
attribute might affect
bit numbering within the entire record component (two bytes in this
case, thus affecting which byte fields end up in), but that is not
the way this feature is defined, it only affects numbering of bits,
not which byte they end up in.
Consequently it never makes sense to specify a starting bit number
greater than 7 (for a byte addressable field) if an attribute
definition for Bit_Order
has been given, and indeed it
may be actively confusing to specify such a value, so the compiler
generates a warning for such usage.
If you do need to control byte ordering then appropriate conditional values must be used. If in our example, the slave byte came first on some machines we might write:
Master_Byte_First constant Boolean := …; Master_Byte : constant Natural := 1 - Boolean'Pos (Master_Byte_First); Slave_Byte : constant Natural := Boolean'Pos (Master_Byte_First); for Data'Bit_Order use High_Order_First; for Data use record Master_Control at Master_Byte range 0 .. 0; Master_V1 at Master_Byte range 1 .. 1; Master_V2 at Master_Byte range 2 .. 2; Master_V3 at Master_Byte range 3 .. 3; Master_V4 at Master_Byte range 4 .. 4; Master_V5 at Master_Byte range 5 .. 5; Master_V6 at Master_Byte range 6 .. 6; Master_V7 at Master_Byte range 7 .. 7; Slave_Control at Slave_Byte range 0 .. 0; Slave_V1 at Slave_Byte range 1 .. 1; Slave_V2 at Slave_Byte range 2 .. 2; Slave_V3 at Slave_Byte range 3 .. 3; Slave_V4 at Slave_Byte range 4 .. 4; Slave_V5 at Slave_Byte range 5 .. 5; Slave_V6 at Slave_Byte range 6 .. 6; Slave_V7 at Slave_Byte range 7 .. 7; end record;
Now to switch between machines, all that is necessary is
to set the boolean constant Master_Byte_First
in
an appropriate manner.
Next: Pragma Pack for Records, Previous: Effect of Bit_Order on Byte Ordering, Up: Representation Clauses and Pragmas [Contents][Index]
Pragma Pack
applied to an array has no effect unless the component type
is packable. For a component type to be packable, it must be one of the
following cases:
For all these cases, if the component subtype size is in the range
1 through 63, then the effect of the pragma Pack
is exactly as though a
component size were specified giving the component subtype size.
For example if we have:
type r is range 0 .. 17; type ar is array (1 .. 8) of r; pragma Pack (ar);
Then the component size of ar
will be set to 5 (i.e. to r'size
,
and the size of the array ar
will be exactly 40 bits.
Note that in some cases this rather fierce approach to packing can produce
unexpected effects. For example, in Ada 95 and Ada 2005,
subtype Natural
typically has a size of 31, meaning that if you
pack an array of Natural
, you get 31-bit
close packing, which saves a few bits, but results in far less efficient
access. Since many other Ada compilers will ignore such a packing request,
GNAT will generate a warning on some uses of pragma Pack
that it guesses
might not be what is intended. You can easily remove this warning by
using an explicit Component_Size
setting instead, which never generates
a warning, since the intention of the programmer is clear in this case.
GNAT treats packed arrays in one of two ways. If the size of the array is known at compile time and is less than 64 bits, then internally the array is represented as a single modular type, of exactly the appropriate number of bits. If the length is greater than 63 bits, or is not known at compile time, then the packed array is represented as an array of bytes, and the length is always a multiple of 8 bits.
Note that to represent a packed array as a modular type, the alignment must be suitable for the modular type involved. For example, on typical machines a 32-bit packed array will be represented by a 32-bit modular integer with an alignment of four bytes. If you explicitly override the default alignment with an alignment clause that is too small, the modular representation cannot be used. For example, consider the following set of declarations:
type R is range 1 .. 3; type S is array (1 .. 31) of R; for S'Component_Size use 2; for S'Size use 62; for S'Alignment use 1;
If the alignment clause were not present, then a 62-bit modular representation would be chosen (typically with an alignment of 4 or 8 bytes depending on the target). But the default alignment is overridden with the explicit alignment clause. This means that the modular representation cannot be used, and instead the array of bytes representation must be used, meaning that the length must be a multiple of 8. Thus the above set of declarations will result in a diagnostic rejecting the size clause and noting that the minimum size allowed is 64.
One special case that is worth noting occurs when the base type of the
component size is 8/16/32 and the subtype is one bit less. Notably this
occurs with subtype Natural
. Consider:
type Arr is array (1 .. 32) of Natural; pragma Pack (Arr);
In all commonly used Ada 83 compilers, this pragma Pack would be ignored,
since typically Natural'Size
is 32 in Ada 83, and in any case most
Ada 83 compilers did not attempt 31 bit packing.
In Ada 95 and Ada 2005, Natural'Size
is required to be 31. Furthermore,
GNAT really does pack 31-bit subtype to 31 bits. This may result in a
substantial unintended performance penalty when porting legacy Ada 83 code.
To help prevent this, GNAT generates a warning in such cases. If you really
want 31 bit packing in a case like this, you can set the component size
explicitly:
type Arr is array (1 .. 32) of Natural; for Arr'Component_Size use 31;
Here 31-bit packing is achieved as required, and no warning is generated, since in this case the programmer intention is clear.
Next: Record Representation Clauses, Previous: Pragma Pack for Arrays, Up: Representation Clauses and Pragmas [Contents][Index]
Pragma Pack
applied to a record will pack the components to reduce
wasted space from alignment gaps and by reducing the amount of space
taken by components. We distinguish between packable components and
non-packable components.
Components of the following types are considered packable:
All packable components occupy the exact number of bits corresponding to
their Size
value, and are packed with no padding bits, i.e. they
can start on an arbitrary bit boundary.
All other types are non-packable, they occupy an integral number of storage units, and are placed at a boundary corresponding to their alignment requirements.
For example, consider the record
type Rb1 is array (1 .. 13) of Boolean; pragma Pack (rb1); type Rb2 is array (1 .. 65) of Boolean; pragma Pack (rb2); type x2 is record l1 : Boolean; l2 : Duration; l3 : Float; l4 : Boolean; l5 : Rb1; l6 : Rb2; end record; pragma Pack (x2);
The representation for the record x2 is as follows:
for x2'Size use 224; for x2 use record l1 at 0 range 0 .. 0; l2 at 0 range 1 .. 64; l3 at 12 range 0 .. 31; l4 at 16 range 0 .. 0; l5 at 16 range 1 .. 13; l6 at 18 range 0 .. 71; end record;
Studying this example, we see that the packable fields l1
and l2
are
of length equal to their sizes, and placed at specific bit boundaries (and
not byte boundaries) to
eliminate padding. But l3
is of a non-packable float type, so
it is on the next appropriate alignment boundary.
The next two fields are fully packable, so l4
and l5
are
minimally packed with no gaps. However, type Rb2
is a packed
array that is longer than 64 bits, so it is itself non-packable. Thus
the l6
field is aligned to the next byte boundary, and takes an
integral number of bytes, i.e. 72 bits.
Next: Enumeration Clauses, Previous: Pragma Pack for Records, Up: Representation Clauses and Pragmas [Contents][Index]
Record representation clauses may be given for all record types, including types obtained by record extension. Component clauses are allowed for any static component. The restrictions on component clauses depend on the type of the component.
For all components of an elementary type, the only restriction on component clauses is that the size must be at least the ’Size value of the type (actually the Value_Size). There are no restrictions due to alignment, and such components may freely cross storage boundaries.
Packed arrays with a size up to and including 64 bits are represented internally using a modular type with the appropriate number of bits, and thus the same lack of restriction applies. For example, if you declare:
type R is array (1 .. 49) of Boolean; pragma Pack (R); for R'Size use 49;
then a component clause for a component of type R may start on any specified bit boundary, and may specify a value of 49 bits or greater.
For packed bit arrays that are longer than 64 bits, there are two cases. If the component size is a power of 2 (1,2,4,8,16,32 bits), including the important case of single bits or boolean values, then there are no limitations on placement of such components, and they may start and end at arbitrary bit boundaries.
If the component size is not a power of 2 (e.g. 3 or 5), then an array of this type longer than 64 bits must always be placed on on a storage unit (byte) boundary and occupy an integral number of storage units (bytes). Any component clause that does not meet this requirement will be rejected.
Any aliased component, or component of an aliased type, must have its normal alignment and size. A component clause that does not meet this requirement will be rejected.
The tag field of a tagged type always occupies an address sized field at the start of the record. No component clause may attempt to overlay this tag. When a tagged type appears as a component, the tag field must have proper alignment
In the case of a record extension T1, of a type T, no component clause applied to the type T1 can specify a storage location that would overlap the first T’Size bytes of the record.
For all other component types, including non-bit-packed arrays, the component can be placed at an arbitrary bit boundary, so for example, the following is permitted:
type R is array (1 .. 10) of Boolean; for R'Size use 80; type Q is record G, H : Boolean; L, M : R; end record; for Q use record G at 0 range 0 .. 0; H at 0 range 1 .. 1; L at 0 range 2 .. 81; R at 0 range 82 .. 161; end record;
Note: the above rules apply to recent releases of GNAT 5. In GNAT 3, there are more severe restrictions on larger components. For non-primitive types, including packed arrays with a size greater than 64 bits, component clauses must respect the alignment requirement of the type, in particular, always starting on a byte boundary, and the length must be a multiple of the storage unit.
Next: Address Clauses, Previous: Record Representation Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
The only restriction on enumeration clauses is that the range of values must be representable. For the signed case, if one or more of the representation values are negative, all values must be in the range:
System.Min_Int .. System.Max_Int
For the unsigned case, where all values are nonnegative, the values must be in the range:
0 .. System.Max_Binary_Modulus;
A confirming representation clause is one in which the values range from 0 in sequence, i.e. a clause that confirms the default representation for an enumeration type. Such a confirming representation is permitted by these rules, and is specially recognized by the compiler so that no extra overhead results from the use of such a clause.
If an array has an index type which is an enumeration type to which an enumeration clause has been applied, then the array is stored in a compact manner. Consider the declarations:
type r is (A, B, C); for r use (A => 1, B => 5, C => 10); type t is array (r) of Character;
The array type t corresponds to a vector with exactly three elements and
has a default size equal to 3*Character'Size
. This ensures efficient
use of space, but means that accesses to elements of the array will incur
the overhead of converting representation values to the corresponding
positional values, (i.e. the value delivered by the Pos
attribute).
Next: Effect of Convention on Representation, Previous: Enumeration Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
The reference manual allows a general restriction on representation clauses, as found in RM 13.1(22):
An implementation need not support representation items containing nonstatic expressions, except that an implementation should support a representation item for a given entity if each nonstatic expression in the representation item is a name that statically denotes a constant declared before the entity.
In practice this is applicable only to address clauses, since this is the only case in which a non-static expression is permitted by the syntax. As the AARM notes in sections 13.1 (22.a-22.h):
22.a Reason: This is to avoid the following sort of thing: 22.b X : Integer := F(…); Y : Address := G(…); for X’Address use Y; 22.c In the above, we have to evaluate the initialization expression for X before we know where to put the result. This seems like an unreasonable implementation burden. 22.d The above code should instead be written like this: 22.e Y : constant Address := G(…); X : Integer := F(…); for X’Address use Y; 22.f This allows the expression “Y” to be safely evaluated before X is created. 22.g The constant could be a formal parameter of mode in. 22.h An implementation can support other nonstatic expressions if it wants to. Expressions of type Address are hardly ever static, but their value might be known at compile time anyway in many cases.
GNAT does indeed permit many additional cases of non-static expressions. In particular, if the type involved is elementary there are no restrictions (since in this case, holding a temporary copy of the initialization value, if one is present, is inexpensive). In addition, if there is no implicit or explicit initialization, then there are no restrictions. GNAT will reject only the case where all three of these conditions hold:
Anchor : Some_Initialized_Type; Overlay : Some_Initialized_Type; for Overlay'Address use Anchor'Address;
However, the prefix of the address clause cannot be an array component, or a component of a discriminated record.
As noted above in section 22.h, address values are typically non-static. In particular the To_Address function, even if applied to a literal value, is a non-static function call. To avoid this minor annoyance, GNAT provides the implementation defined attribute ’To_Address. The following two expressions have identical values:
To_Address (16#1234_0000#) System'To_Address (16#1234_0000#);
except that the second form is considered to be a static expression, and thus when used as an address clause value is always permitted.
Additionally, GNAT treats as static an address clause that is an
unchecked_conversion of a static integer value. This simplifies the porting
of legacy code, and provides a portable equivalent to the GNAT attribute
To_Address
.
Another issue with address clauses is the interaction with alignment requirements. When an address clause is given for an object, the address value must be consistent with the alignment of the object (which is usually the same as the alignment of the type of the object). If an address clause is given that specifies an inappropriately aligned address value, then the program execution is erroneous.
Since this source of erroneous behavior can have unfortunate effects, GNAT
checks (at compile time if possible, generating a warning, or at execution
time with a run-time check) that the alignment is appropriate. If the
run-time check fails, then Program_Error
is raised. This run-time
check is suppressed if range checks are suppressed, or if the special GNAT
check Alignment_Check is suppressed, or if
pragma Restrictions (No_Elaboration_Code)
is in effect.
Finally, GNAT does not permit overlaying of objects of controlled types or composite types containing a controlled component. In most cases, the compiler can detect an attempt at such overlays and will generate a warning at compile time and a Program_Error exception at run time.
An address clause cannot be given for an exported object. More understandably the real restriction is that objects with an address clause cannot be exported. This is because such variables are not defined by the Ada program, so there is no external object to export.
It is permissible to give an address clause and a pragma Import for the same object. In this case, the variable is not really defined by the Ada program, so there is no external symbol to be linked. The link name and the external name are ignored in this case. The reason that we allow this combination is that it provides a useful idiom to avoid unwanted initializations on objects with address clauses.
When an address clause is given for an object that has implicit or explicit initialization, then by default initialization takes place. This means that the effect of the object declaration is to overwrite the memory at the specified address. This is almost always not what the programmer wants, so GNAT will output a warning:
with System; package G is type R is record M : Integer := 0; end record; Ext : R; for Ext'Address use System'To_Address (16#1234_1234#); | >>> warning: implicit initialization of "Ext" may modify overlaid storage >>> warning: use pragma Import for "Ext" to suppress initialization (RM B(24)) end G;
As indicated by the warning message, the solution is to use a (dummy) pragma Import to suppress this initialization. The pragma tell the compiler that the object is declared and initialized elsewhere. The following package compiles without warnings (and the initialization is suppressed):
with System; package G is type R is record M : Integer := 0; end record; Ext : R; for Ext'Address use System'To_Address (16#1234_1234#); pragma Import (Ada, Ext); end G;
A final issue with address clauses involves their use for overlaying variables, as in the following example:
A : Integer; B : Integer; for B'Address use A'Address;
or alternatively, using the form recommended by the RM:
A : Integer; Addr : constant Address := A'Address; B : Integer; for B'Address use Addr;
In both of these cases, A
and B
become aliased to one another via the
address clause. This use of address clauses to overlay
variables, achieving an effect similar to unchecked
conversion was erroneous in Ada 83, but in Ada 95 and Ada 2005
the effect is implementation defined. Furthermore, the
Ada RM specifically recommends that in a situation
like this, B
should be subject to the following
implementation advice (RM 13.3(19)):
19 If the Address of an object is specified, or it is imported or exported, then the implementation should not perform optimizations based on assumptions of no aliases.
GNAT follows this recommendation, and goes further by also applying
this recommendation to the overlaid variable (A
in the above example) in this case. This means that the overlay
works "as expected", in that a modification to one of the variables
will affect the value of the other.
Next: Determining the Representations chosen by GNAT, Previous: Address Clauses, Up: Representation Clauses and Pragmas [Contents][Index]
Normally the specification of a foreign language convention for a type or an object has no effect on the chosen representation. In particular, the representation chosen for data in GNAT generally meets the standard system conventions, and for example records are laid out in a manner that is consistent with C. This means that specifying convention C (for example) has no effect.
There are four exceptions to this general rule:
type Color is (Red, Green, Blue);
8 bits is sufficient to store all values of the type, so by default, objects
of type Color
will be represented using 8 bits. However, normal C
convention is to use 32 bits for all enum values in C, since enum values
are essentially of type int. If pragma Convention C
is specified for an
Ada enumeration type, then the size is modified as necessary (usually to
32 bits) to be consistent with the C convention for enum values.
Note that this treatment applies only to types. If Convention C is given for an enumeration object, where the enumeration type is not Convention C, then Object_Size bits are allocated. For example, for a normal enumeration type, with less than 256 elements, only 8 bits will be allocated for the object. Since this may be a surprise in terms of what C expects, GNAT will issue a warning in this situation. The warning can be suppressed by giving an explicit size clause specifying the desired size.
Fortran has a similar convention for LOGICAL
values (any nonzero
value represents true).
To accommodate the Fortran and C conventions, if a pragma Convention specifies C or Fortran convention for a derived Boolean, as in the following example:
type C_Switch is new Boolean; pragma Convention (C, C_Switch);
then the GNAT generated code will treat any nonzero value as true. For truth values generated by GNAT, the conventional value 1 will be used for True, but when one of these values is read, any nonzero value is treated as True.
Previous: Effect of Convention on Representation, Up: Representation Clauses and Pragmas [Contents][Index]
Although the descriptions in this section are intended to be complete, it is often easier to simply experiment to see what GNAT accepts and what the effect is on the layout of types and objects.
As required by the Ada RM, if a representation clause is not accepted, then
it must be rejected as illegal by the compiler. However, when a
representation clause or pragma is accepted, there can still be questions
of what the compiler actually does. For example, if a partial record
representation clause specifies the location of some components and not
others, then where are the non-specified components placed? Or if pragma
Pack
is used on a record, then exactly where are the resulting
fields placed? The section on pragma Pack
in this chapter can be
used to answer the second question, but it is often easier to just see
what the compiler does.
For this purpose, GNAT provides the option -gnatR. If you compile with this option, then the compiler will output information on the actual representations chosen, in a format similar to source representation clauses. For example, if we compile the package:
package q is type r (x : boolean) is tagged record case x is when True => S : String (1 .. 100); when False => null; end case; end record; type r2 is new r (false) with record y2 : integer; end record; for r2 use record y2 at 16 range 0 .. 31; end record; type x is record y : character; end record; type x1 is array (1 .. 10) of x; for x1'component_size use 11; type ia is access integer; type Rb1 is array (1 .. 13) of Boolean; pragma Pack (rb1); type Rb2 is array (1 .. 65) of Boolean; pragma Pack (rb2); type x2 is record l1 : Boolean; l2 : Duration; l3 : Float; l4 : Boolean; l5 : Rb1; l6 : Rb2; end record; pragma Pack (x2); end q;
using the switch -gnatR we obtain the following output:
Representation information for unit q ------------------------------------- for r'Size use ??; for r'Alignment use 4; for r use record x at 4 range 0 .. 7; _tag at 0 range 0 .. 31; s at 5 range 0 .. 799; end record; for r2'Size use 160; for r2'Alignment use 4; for r2 use record x at 4 range 0 .. 7; _tag at 0 range 0 .. 31; _parent at 0 range 0 .. 63; y2 at 16 range 0 .. 31; end record; for x'Size use 8; for x'Alignment use 1; for x use record y at 0 range 0 .. 7; end record; for x1'Size use 112; for x1'Alignment use 1; for x1'Component_Size use 11; for rb1'Size use 13; for rb1'Alignment use 2; for rb1'Component_Size use 1; for rb2'Size use 72; for rb2'Alignment use 1; for rb2'Component_Size use 1; for x2'Size use 224; for x2'Alignment use 4; for x2 use record l1 at 0 range 0 .. 0; l2 at 0 range 1 .. 64; l3 at 12 range 0 .. 31; l4 at 16 range 0 .. 0; l5 at 16 range 1 .. 13; l6 at 18 range 0 .. 71; end record;
The Size values are actually the Object_Size, i.e. the default size that will be allocated for objects of the type. The ?? size for type r indicates that we have a variant record, and the actual size of objects will depend on the discriminant value.
The Alignment values show the actual alignment chosen by the compiler for each record or array type.
The record representation clause for type r shows where all fields are placed, including the compiler generated tag field (whose location cannot be controlled by the programmer).
The record representation clause for the type extension r2 shows all the fields present, including the parent field, which is a copy of the fields of the parent type of r2, i.e. r1.
The component size and size clauses for types rb1 and rb2 show
the exact effect of pragma Pack
on these arrays, and the record
representation clause for type x2 shows how pragma Pack
affects
this record type.
In some cases, it may be useful to cut and paste the representation clauses generated by the compiler into the original source to fix and guarantee the actual representation to be used.
Next: The Implementation of Standard I/O, Previous: Representation Clauses and Pragmas, Up: Top [Contents][Index]
The Ada Reference Manual contains in Annex A a full description of an extensive set of standard library routines that can be used in any Ada program, and which must be provided by all Ada compilers. They are analogous to the standard C library used by C programs.
GNAT implements all of the facilities described in annex A, and for most purposes the description in the Ada Reference Manual, or appropriate Ada text book, will be sufficient for making use of these facilities.
In the case of the input-output facilities, See The Implementation of Standard I/O, gives details on exactly how GNAT interfaces to the file system. For the remaining packages, the Ada Reference Manual should be sufficient. The following is a list of the packages included, together with a brief description of the functionality that is provided.
For completeness, references are included to other predefined library routines defined in other sections of the Ada Reference Manual (these are cross-indexed from Annex A).
Ada (A.2)
This is a parent package for all the standard library packages. It is usually included implicitly in your program, and itself contains no useful data or routines.
Ada.Calendar (9.6)
Calendar
provides time of day access, and routines for
manipulating times and durations.
Ada.Characters (A.3.1)
This is a dummy parent package that contains no useful entities
Ada.Characters.Handling (A.3.2)
This package provides some basic character handling capabilities, including classification functions for classes of characters (e.g. test for letters, or digits).
Ada.Characters.Latin_1 (A.3.3)
This package includes a complete set of definitions of the characters
that appear in type CHARACTER. It is useful for writing programs that
will run in international environments. For example, if you want an
upper case E with an acute accent in a string, it is often better to use
the definition of UC_E_Acute
in this package. Then your program
will print in an understandable manner even if your environment does not
support these extended characters.
Ada.Command_Line (A.15)
This package provides access to the command line parameters and the name
of the current program (analogous to the use of argc
and argv
in C), and also allows the exit status for the program to be set in a
system-independent manner.
Ada.Decimal (F.2)
This package provides constants describing the range of decimal numbers implemented, and also a decimal divide routine (analogous to the COBOL verb DIVIDE … GIVING … REMAINDER …)
Ada.Direct_IO (A.8.4)
This package provides input-output using a model of a set of records of fixed-length, containing an arbitrary definite Ada type, indexed by an integer record number.
Ada.Dynamic_Priorities (D.5)
This package allows the priorities of a task to be adjusted dynamically as the task is running.
Ada.Exceptions (11.4.1)
This package provides additional information on exceptions, and also contains facilities for treating exceptions as data objects, and raising exceptions with associated messages.
Ada.Finalization (7.6)
This package contains the declarations and subprograms to support the use of controlled types, providing for automatic initialization and finalization (analogous to the constructors and destructors of C++)
Ada.Interrupts (C.3.2)
This package provides facilities for interfacing to interrupts, which includes the set of signals or conditions that can be raised and recognized as interrupts.
Ada.Interrupts.Names (C.3.2)
This package provides the set of interrupt names (actually signal or condition names) that can be handled by GNAT.
Ada.IO_Exceptions (A.13)
This package defines the set of exceptions that can be raised by use of the standard IO packages.
Ada.Numerics
This package contains some standard constants and exceptions used throughout the numerics packages. Note that the constants pi and e are defined here, and it is better to use these definitions than rolling your own.
Ada.Numerics.Complex_Elementary_Functions
Provides the implementation of standard elementary functions (such as
log and trigonometric functions) operating on complex numbers using the
standard Float
and the Complex
and Imaginary
types
created by the package Numerics.Complex_Types
.
Ada.Numerics.Complex_Types
This is a predefined instantiation of
Numerics.Generic_Complex_Types
using Standard.Float
to
build the type Complex
and Imaginary
.
Ada.Numerics.Discrete_Random
This generic package provides a random number generator suitable for generating uniformly distributed values of a specified discrete subtype.
Ada.Numerics.Float_Random
This package provides a random number generator suitable for generating uniformly distributed floating point values in the unit interval.
Ada.Numerics.Generic_Complex_Elementary_Functions
This is a generic version of the package that provides the implementation of standard elementary functions (such as log and trigonometric functions) for an arbitrary complex type.
The following predefined instantiations of this package are provided:
Short_Float
Ada.Numerics.Short_Complex_Elementary_Functions
Float
Ada.Numerics.Complex_Elementary_Functions
Long_Float
Ada.Numerics.Long_Complex_Elementary_Functions
Ada.Numerics.Generic_Complex_Types
This is a generic package that allows the creation of complex types, with associated complex arithmetic operations.
The following predefined instantiations of this package exist
Short_Float
Ada.Numerics.Short_Complex_Complex_Types
Float
Ada.Numerics.Complex_Complex_Types
Long_Float
Ada.Numerics.Long_Complex_Complex_Types
Ada.Numerics.Generic_Elementary_Functions
This is a generic package that provides the implementation of standard elementary functions (such as log an trigonometric functions) for an arbitrary float type.
The following predefined instantiations of this package exist
Short_Float
Ada.Numerics.Short_Elementary_Functions
Float
Ada.Numerics.Elementary_Functions
Long_Float
Ada.Numerics.Long_Elementary_Functions
Ada.Real_Time (D.8)
This package provides facilities similar to those of Calendar
, but
operating with a finer clock suitable for real time control. Note that
annex D requires that there be no backward clock jumps, and GNAT generally
guarantees this behavior, but of course if the external clock on which
the GNAT runtime depends is deliberately reset by some external event,
then such a backward jump may occur.
Ada.Sequential_IO (A.8.1)
This package provides input-output facilities for sequential files, which can contain a sequence of values of a single type, which can be any Ada type, including indefinite (unconstrained) types.
Ada.Storage_IO (A.9)
This package provides a facility for mapping arbitrary Ada types to and from a storage buffer. It is primarily intended for the creation of new IO packages.
Ada.Streams (13.13.1)
This is a generic package that provides the basic support for the
concept of streams as used by the stream attributes (Input
,
Output
, Read
and Write
).
Ada.Streams.Stream_IO (A.12.1)
This package is a specialization of the type Streams
defined in
package Streams
together with a set of operations providing
Stream_IO capability. The Stream_IO model permits both random and
sequential access to a file which can contain an arbitrary set of values
of one or more Ada types.
Ada.Strings (A.4.1)
This package provides some basic constants used by the string handling packages.
Ada.Strings.Bounded (A.4.4)
This package provides facilities for handling variable length strings. The bounded model requires a maximum length. It is thus somewhat more limited than the unbounded model, but avoids the use of dynamic allocation or finalization.
Ada.Strings.Fixed (A.4.3)
This package provides facilities for handling fixed length strings.
Ada.Strings.Maps (A.4.2)
This package provides facilities for handling character mappings and arbitrarily defined subsets of characters. For instance it is useful in defining specialized translation tables.
Ada.Strings.Maps.Constants (A.4.6)
This package provides a standard set of predefined mappings and predefined character sets. For example, the standard upper to lower case conversion table is found in this package. Note that upper to lower case conversion is non-trivial if you want to take the entire set of characters, including extended characters like E with an acute accent, into account. You should use the mappings in this package (rather than adding 32 yourself) to do case mappings.
Ada.Strings.Unbounded (A.4.5)
This package provides facilities for handling variable length strings. The unbounded model allows arbitrary length strings, but requires the use of dynamic allocation and finalization.
Ada.Strings.Wide_Bounded (A.4.7)
Ada.Strings.Wide_Fixed (A.4.7)
Ada.Strings.Wide_Maps (A.4.7)
Ada.Strings.Wide_Maps.Constants (A.4.7)
Ada.Strings.Wide_Unbounded (A.4.7)
These packages provide analogous capabilities to the corresponding
packages without ‘Wide_’ in the name, but operate with the types
Wide_String
and Wide_Character
instead of String
and Character
.
Ada.Strings.Wide_Wide_Bounded (A.4.7)
Ada.Strings.Wide_Wide_Fixed (A.4.7)
Ada.Strings.Wide_Wide_Maps (A.4.7)
Ada.Strings.Wide_Wide_Maps.Constants (A.4.7)
Ada.Strings.Wide_Wide_Unbounded (A.4.7)
These packages provide analogous capabilities to the corresponding
packages without ‘Wide_’ in the name, but operate with the types
Wide_Wide_String
and Wide_Wide_Character
instead
of String
and Character
.
Ada.Synchronous_Task_Control (D.10)
This package provides some standard facilities for controlling task communication in a synchronous manner.
Ada.Tags
This package contains definitions for manipulation of the tags of tagged values.
Ada.Task_Attributes
This package provides the capability of associating arbitrary task-specific data with separate tasks.
Ada.Text_IO
This package provides basic text input-output capabilities for character, string and numeric data. The subpackages of this package are listed next.
Ada.Text_IO.Decimal_IO
Provides input-output facilities for decimal fixed-point types
Ada.Text_IO.Enumeration_IO
Provides input-output facilities for enumeration types.
Ada.Text_IO.Fixed_IO
Provides input-output facilities for ordinary fixed-point types.
Ada.Text_IO.Float_IO
Provides input-output facilities for float types. The following predefined instantiations of this generic package are available:
Short_Float
Short_Float_Text_IO
Float
Float_Text_IO
Long_Float
Long_Float_Text_IO
Ada.Text_IO.Integer_IO
Provides input-output facilities for integer types. The following predefined instantiations of this generic package are available:
Short_Short_Integer
Ada.Short_Short_Integer_Text_IO
Short_Integer
Ada.Short_Integer_Text_IO
Integer
Ada.Integer_Text_IO
Long_Integer
Ada.Long_Integer_Text_IO
Long_Long_Integer
Ada.Long_Long_Integer_Text_IO
Ada.Text_IO.Modular_IO
Provides input-output facilities for modular (unsigned) types
Ada.Text_IO.Complex_IO (G.1.3)
This package provides basic text input-output capabilities for complex data.
Ada.Text_IO.Editing (F.3.3)
This package contains routines for edited output, analogous to the use of pictures in COBOL. The picture formats used by this package are a close copy of the facility in COBOL.
Ada.Text_IO.Text_Streams (A.12.2)
This package provides a facility that allows Text_IO files to be treated as streams, so that the stream attributes can be used for writing arbitrary data, including binary data, to Text_IO files.
Ada.Unchecked_Conversion (13.9)
This generic package allows arbitrary conversion from one type to another of the same size, providing for breaking the type safety in special circumstances.
If the types have the same Size (more accurately the same Value_Size), then the effect is simply to transfer the bits from the source to the target type without any modification. This usage is well defined, and for simple types whose representation is typically the same across all implementations, gives a portable method of performing such conversions.
If the types do not have the same size, then the result is implementation defined, and thus may be non-portable. The following describes how GNAT handles such unchecked conversion cases.
If the types are of different sizes, and are both discrete types, then the effect is of a normal type conversion without any constraint checking. In particular if the result type has a larger size, the result will be zero or sign extended. If the result type has a smaller size, the result will be truncated by ignoring high order bits.
If the types are of different sizes, and are not both discrete types, then the conversion works as though pointers were created to the source and target, and the pointer value is converted. The effect is that bits are copied from successive low order storage units and bits of the source up to the length of the target type.
A warning is issued if the lengths differ, since the effect in this case is implementation dependent, and the above behavior may not match that of some other compiler.
A pointer to one type may be converted to a pointer to another type using unchecked conversion. The only case in which the effect is undefined is when one or both pointers are pointers to unconstrained array types. In this case, the bounds information may get incorrectly transferred, and in particular, GNAT uses double size pointers for such types, and it is meaningless to convert between such pointer types. GNAT will issue a warning if the alignment of the target designated type is more strict than the alignment of the source designated type (since the result may be unaligned in this case).
A pointer other than a pointer to an unconstrained array type may be converted to and from System.Address. Such usage is common in Ada 83 programs, but note that Ada.Address_To_Access_Conversions is the preferred method of performing such conversions in Ada 95 and Ada 2005. Neither unchecked conversion nor Ada.Address_To_Access_Conversions should be used in conjunction with pointers to unconstrained objects, since the bounds information cannot be handled correctly in this case.
Ada.Unchecked_Deallocation (13.11.2)
This generic package allows explicit freeing of storage previously allocated by use of an allocator.
Ada.Wide_Text_IO (A.11)
This package is similar to Ada.Text_IO
, except that the external
file supports wide character representations, and the internal types are
Wide_Character
and Wide_String
instead of Character
and String
. It contains generic subpackages listed next.
Ada.Wide_Text_IO.Decimal_IO
Provides input-output facilities for decimal fixed-point types
Ada.Wide_Text_IO.Enumeration_IO
Provides input-output facilities for enumeration types.
Ada.Wide_Text_IO.Fixed_IO
Provides input-output facilities for ordinary fixed-point types.
Ada.Wide_Text_IO.Float_IO
Provides input-output facilities for float types. The following predefined instantiations of this generic package are available:
Short_Float
Short_Float_Wide_Text_IO
Float
Float_Wide_Text_IO
Long_Float
Long_Float_Wide_Text_IO
Ada.Wide_Text_IO.Integer_IO
Provides input-output facilities for integer types. The following predefined instantiations of this generic package are available:
Short_Short_Integer
Ada.Short_Short_Integer_Wide_Text_IO
Short_Integer
Ada.Short_Integer_Wide_Text_IO
Integer
Ada.Integer_Wide_Text_IO
Long_Integer
Ada.Long_Integer_Wide_Text_IO
Long_Long_Integer
Ada.Long_Long_Integer_Wide_Text_IO
Ada.Wide_Text_IO.Modular_IO
Provides input-output facilities for modular (unsigned) types
Ada.Wide_Text_IO.Complex_IO (G.1.3)
This package is similar to Ada.Text_IO.Complex_IO
, except that the
external file supports wide character representations.
Ada.Wide_Text_IO.Editing (F.3.4)
This package is similar to Ada.Text_IO.Editing
, except that the
types are Wide_Character
and Wide_String
instead of
Character
and String
.
Ada.Wide_Text_IO.Streams (A.12.3)
This package is similar to Ada.Text_IO.Streams
, except that the
types are Wide_Character
and Wide_String
instead of
Character
and String
.
Ada.Wide_Wide_Text_IO (A.11)
This package is similar to Ada.Text_IO
, except that the external
file supports wide character representations, and the internal types are
Wide_Character
and Wide_String
instead of Character
and String
. It contains generic subpackages listed next.
Ada.Wide_Wide_Text_IO.Decimal_IO
Provides input-output facilities for decimal fixed-point types
Ada.Wide_Wide_Text_IO.Enumeration_IO
Provides input-output facilities for enumeration types.
Ada.Wide_Wide_Text_IO.Fixed_IO
Provides input-output facilities for ordinary fixed-point types.
Ada.Wide_Wide_Text_IO.Float_IO
Provides input-output facilities for float types. The following predefined instantiations of this generic package are available:
Short_Float
Short_Float_Wide_Wide_Text_IO
Float
Float_Wide_Wide_Text_IO
Long_Float
Long_Float_Wide_Wide_Text_IO
Ada.Wide_Wide_Text_IO.Integer_IO
Provides input-output facilities for integer types. The following predefined instantiations of this generic package are available:
Short_Short_Integer
Ada.Short_Short_Integer_Wide_Wide_Text_IO
Short_Integer
Ada.Short_Integer_Wide_Wide_Text_IO
Integer
Ada.Integer_Wide_Wide_Text_IO
Long_Integer
Ada.Long_Integer_Wide_Wide_Text_IO
Long_Long_Integer
Ada.Long_Long_Integer_Wide_Wide_Text_IO
Ada.Wide_Wide_Text_IO.Modular_IO
Provides input-output facilities for modular (unsigned) types
Ada.Wide_Wide_Text_IO.Complex_IO (G.1.3)
This package is similar to Ada.Text_IO.Complex_IO
, except that the
external file supports wide character representations.
Ada.Wide_Wide_Text_IO.Editing (F.3.4)
This package is similar to Ada.Text_IO.Editing
, except that the
types are Wide_Character
and Wide_String
instead of
Character
and String
.
Ada.Wide_Wide_Text_IO.Streams (A.12.3)
This package is similar to Ada.Text_IO.Streams
, except that the
types are Wide_Character
and Wide_String
instead of
Character
and String
.
Next: The GNAT Library, Previous: Standard Library Routines, Up: Top [Contents][Index]
GNAT implements all the required input-output facilities described in A.6 through A.14. These sections of the Ada Reference Manual describe the required behavior of these packages from the Ada point of view, and if you are writing a portable Ada program that does not need to know the exact manner in which Ada maps to the outside world when it comes to reading or writing external files, then you do not need to read this chapter. As long as your files are all regular files (not pipes or devices), and as long as you write and read the files only from Ada, the description in the Ada Reference Manual is sufficient.
However, if you want to do input-output to pipes or other devices, such as the keyboard or screen, or if the files you are dealing with are either generated by some other language, or to be read by some other language, then you need to know more about the details of how the GNAT implementation of these input-output facilities behaves.
In this chapter we give a detailed description of exactly how GNAT interfaces to the file system. As always, the sources of the system are available to you for answering questions at an even more detailed level, but for most purposes the information in this chapter will suffice.
Another reason that you may need to know more about how input-output is implemented arises when you have a program written in mixed languages where, for example, files are shared between the C and Ada sections of the same program. GNAT provides some additional facilities, in the form of additional child library packages, that facilitate this sharing, and these additional facilities are also described in this chapter.
• Standard I/O Packages: | ||
• FORM Strings: | ||
• Direct_IO: | ||
• Sequential_IO: | ||
• Text_IO: | ||
• Wide_Text_IO: | ||
• Wide_Wide_Text_IO: | ||
• Stream_IO: | ||
• Text Translation: | ||
• Shared Files: | ||
• Filenames encoding: | ||
• Open Modes: | ||
• Operations on C Streams: | ||
• Interfacing to C Streams: |
Next: FORM Strings, Previous: SPARK, Up: The Implementation of Standard I/O [Contents][Index]
The Standard I/O packages described in Annex A for
are implemented using the C library streams facility; where
fopen
.
fread
/fwrite
.
There is no internal buffering of any kind at the Ada library level. The only buffering is that provided at the system level in the implementation of the library routines that support streams. This facilitates shared use of these streams by mixed language programs. Note though that system level buffering is explicitly enabled at elaboration of the standard I/O packages and that can have an impact on mixed language programs, in particular those using I/O before calling the Ada elaboration routine (e.g. adainit). It is recommended to call the Ada elaboration routine before performing any I/O or when impractical, flush the common I/O streams and in particular Standard_Output before elaborating the Ada code.
Next: Direct_IO, Previous: Standard I/O Packages, Up: The Implementation of Standard I/O [Contents][Index]
The format of a FORM string in GNAT is:
"keyword=value,keyword=value,…,keyword=value"
where letters may be in upper or lower case, and there are no spaces between values. The order of the entries is not important. Currently the following keywords defined.
TEXT_TRANSLATION=[YES|NO] SHARED=[YES|NO] WCEM=[n|h|u|s|e|8|b] ENCODING=[UTF8|8BITS]
The use of these parameters is described later in this section. If an unrecognized keyword appears in a form string, it is silently ignored and not considered invalid.
Next: Sequential_IO, Previous: FORM Strings, Up: The Implementation of Standard I/O [Contents][Index]
Direct_IO can only be instantiated for definite types. This is a
restriction of the Ada language, which means that the records are fixed
length (the length being determined by type'Size
, rounded
up to the next storage unit boundary if necessary).
The records of a Direct_IO file are simply written to the file in index sequence, with the first record starting at offset zero, and subsequent records following. There is no control information of any kind. For example, if 32-bit integers are being written, each record takes 4-bytes, so the record at index K starts at offset (K-1)*4.
There is no limit on the size of Direct_IO files, they are expanded as necessary to accommodate whatever records are written to the file.
Next: Text_IO, Previous: Direct_IO, Up: The Implementation of Standard I/O [Contents][Index]
Sequential_IO may be instantiated with either a definite (constrained) or indefinite (unconstrained) type.
For the definite type case, the elements written to the file are simply the memory images of the data values with no control information of any kind. The resulting file should be read using the same type, no validity checking is performed on input.
For the indefinite type case, the elements written consist of two
parts. First is the size of the data item, written as the memory image
of a Interfaces.C.size_t
value, followed by the memory image of
the data value. The resulting file can only be read using the same
(unconstrained) type. Normal assignment checks are performed on these
read operations, and if these checks fail, Data_Error
is
raised. In particular, in the array case, the lengths must match, and in
the variant record case, if the variable for a particular read operation
is constrained, the discriminants must match.
Note that it is not possible to use Sequential_IO to write variable
length array items, and then read the data back into different length
arrays. For example, the following will raise Data_Error
:
package IO is new Sequential_IO (String); F : IO.File_Type; S : String (1..4); … IO.Create (F) IO.Write (F, "hello!") IO.Reset (F, Mode=>In_File); IO.Read (F, S); Put_Line (S);
On some Ada implementations, this will print hell
, but the program is
clearly incorrect, since there is only one element in the file, and that
element is the string hello!
.
In Ada 95 and Ada 2005, this kind of behavior can be legitimately achieved using Stream_IO, and this is the preferred mechanism. In particular, the above program fragment rewritten to use Stream_IO will work correctly.
Next: Wide_Text_IO, Previous: Sequential_IO, Up: The Implementation of Standard I/O [Contents][Index]
Text_IO files consist of a stream of characters containing the following special control characters:
LF (line feed, 16#0A#) Line Mark FF (form feed, 16#0C#) Page Mark
A canonical Text_IO file is defined as one in which the following conditions are met:
LF
is used only as a line mark, i.e. to mark the end
of the line.
FF
is used only as a page mark, i.e. to mark the
end of a page and consequently can appear only immediately following a
LF
(line mark) character.
LF
(line mark) or LF
-FF
(line mark, page mark). In the former case, the page mark is implicitly
assumed to be present.
A file written using Text_IO will be in canonical form provided that no
explicit LF
or FF
characters are written using Put
or Put_Line
. There will be no FF
character at the end of
the file unless an explicit New_Page
operation was performed
before closing the file.
A canonical Text_IO file that is a regular file (i.e., not a device or a pipe) can be read using any of the routines in Text_IO. The semantics in this case will be exactly as defined in the Ada Reference Manual, and all the routines in Text_IO are fully implemented.
A text file that does not meet the requirements for a canonical Text_IO file has one of the following:
FF
characters not immediately following a
LF
character.
LF
or FF
characters written by
Put
or Put_Line
, which are not logically considered to be
line marks or page marks.
LF
or FF
,
i.e. there is no explicit line mark or page mark at the end of the file.
Text_IO can be used to read such non-standard text files but subprograms
to do with line or page numbers do not have defined meanings. In
particular, a FF
character that does not follow a LF
character may or may not be treated as a page mark from the point of
view of page and line numbering. Every LF
character is considered
to end a line, and there is an implied LF
character at the end of
the file.
Next: Text_IO Reading and Writing Non-Regular Files, Previous: System.Wch_Con (s-wchcon.ads), Up: Text_IO [Contents][Index]
Ada.Text_IO
has a definition of current position for a file that
is being read. No internal buffering occurs in Text_IO, and usually the
physical position in the stream used to implement the file corresponds
to this logical position defined by Text_IO. There are two exceptions:
End_Of_Page
that returns True
, the stream
is positioned past the LF
(line mark) that precedes the page
mark. Text_IO maintains an internal flag so that subsequent read
operations properly handle the logical position which is unchanged by
the End_Of_Page
call.
End_Of_File
that returns True
, if the
Text_IO file was positioned before the line mark at the end of file
before the call, then the logical position is unchanged, but the stream
is physically positioned right at the end of file (past the line mark,
and past a possible page mark following the line mark. Again Text_IO
maintains internal flags so that subsequent read operations properly
handle the logical position.
These discrepancies have no effect on the observable behavior of Text_IO, but if a single Ada stream is shared between a C program and Ada program, or shared (using ‘shared=yes’ in the form string) between two Ada files, then the difference may be observable in some situations.
Next: Get_Immediate, Previous: Text_IO Stream Pointer Positioning, Up: Text_IO [Contents][Index]
A non-regular file is a device (such as a keyboard), or a pipe. Text_IO can be used for reading and writing. Writing is not affected and the sequence of characters output is identical to the normal file case, but for reading, the behavior of Text_IO is modified to avoid undesirable look-ahead as follows:
An input file that is not a regular file is considered to have no page
marks. Any Ascii.FF
characters (the character normally used for a
page mark) appearing in the file are considered to be data
characters. In particular:
Get_Line
and Skip_Line
do not test for a page mark
following a line mark. If a page mark appears, it will be treated as a
data character.
End_Of_Page
always returns False
End_Of_File
will return False
if there is a page mark at
the end of the file.
Output to non-regular files is the same as for regular files. Page marks
may be written to non-regular files using New_Page
, but as noted
above they will not be treated as page marks on input if the output is
piped to another Ada program.
Another important discrepancy when reading non-regular files is that the end
of file indication is not “sticky”. If an end of file is entered, e.g. by
pressing the EOT key,
then end of file
is signaled once (i.e. the test End_Of_File
will yield True
, or a read will
raise End_Error
), but then reading can resume
to read data past that end of
file indication, until another end of file indication is entered.
Next: Treating Text_IO Files as Streams, Previous: Text_IO Reading and Writing Non-Regular Files, Up: Text_IO [Contents][Index]
Get_Immediate returns the next character (including control characters) from the input file. In particular, Get_Immediate will return LF or FF characters used as line marks or page marks. Such operations leave the file positioned past the control character, and it is thus not treated as having its normal function. This means that page, line and column counts after this kind of Get_Immediate call are set as though the mark did not occur. In the case where a Get_Immediate leaves the file positioned between the line mark and page mark (which is not normally possible), it is undefined whether the FF character will be treated as a page mark.
Next: Text_IO Extensions, Previous: Get_Immediate, Up: Text_IO [Contents][Index]
The package Text_IO.Streams
allows a Text_IO file to be treated
as a stream. Data written to a Text_IO file in this stream mode is
binary data. If this binary data contains bytes 16#0A# (LF
) or
16#0C# (FF
), the resulting file may have non-standard
format. Similarly if read operations are used to read from a Text_IO
file treated as a stream, then LF
and FF
characters may be
skipped and the effect is similar to that described above for
Get_Immediate
.
Next: Text_IO Facilities for Unbounded Strings, Previous: Treating Text_IO Files as Streams, Up: Text_IO [Contents][Index]
A package GNAT.IO_Aux in the GNAT library provides some useful extensions
to the standard Text_IO
package:
Next: Wide_Text_IO Stream Pointer Positioning, Previous: Text_IO Extensions, Up: Text_IO [Contents][Index]
The package Ada.Strings.Unbounded.Text_IO
in library files a-suteio.ads/adb
contains some GNAT-specific
subprograms useful for Text_IO operations on unbounded strings:
Put (To_String (U))
except that an extra copy is avoided.
New_Line
.
Similar to the effect of Put_Line (To_String (U))
except
that an extra copy is avoided.
In the above procedures, File
is of type Ada.Text_IO.File_Type
and is optional. If the parameter is omitted, then the standard input or
output file is referenced as appropriate.
The package Ada.Strings.Wide_Unbounded.Wide_Text_IO
in library
files a-swuwti.ads and a-swuwti.adb provides similar extended
Wide_Text_IO
functionality for unbounded wide strings.
The package Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO
in library
files a-szuzti.ads and a-szuzti.adb provides similar extended
Wide_Wide_Text_IO
functionality for unbounded wide wide strings.
Next: Wide_Wide_Text_IO, Previous: Text_IO, Up: The Implementation of Standard I/O [Contents][Index]
Wide_Text_IO
is similar in most respects to Text_IO, except that
both input and output files may contain special sequences that represent
wide character values. The encoding scheme for a given file may be
specified using a FORM parameter:
WCEM=x
as part of the FORM string (WCEM = wide character encoding method), where x is one of the following characters
Hex ESC encoding
Upper half encoding
Shift-JIS encoding
EUC Encoding
UTF-8 encoding
Brackets encoding
The encoding methods match those that can be used in a source program, but there is no requirement that the encoding method used for the source program be the same as the encoding method used for files, and different files may use different encoding methods.
The default encoding method for the standard files, and for opened files for which no WCEM parameter is given in the FORM string matches the wide character encoding specified for the main program (the default being brackets encoding if no coding method was specified with -gnatW).
In this encoding, a wide character is represented by a five character sequence:
ESC a b c d
where a, b, c, d are the four hexadecimal
characters (using upper case letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
16#A345#. This scheme is compatible with use of the full
Wide_Character
set.
The wide character with encoding 16#abcd#, where the upper bit is on (i.e. a is in the range 8-F) is represented as two bytes 16#ab# and 16#cd#. The second byte may never be a format control character, but is not required to be in the upper half. This method can be also used for shift-JIS or EUC where the internal coding matches the external coding.
A wide character is represented by a two character sequence 16#ab# and 16#cd#, with the restrictions described for upper half encoding as described above. The internal character code is the corresponding JIS character according to the standard algorithm for Shift-JIS conversion. Only characters defined in the JIS code set table can be used with this encoding method.
A wide character is represented by a two character sequence 16#ab# and 16#cd#, with both characters being in the upper half. The internal character code is the corresponding JIS character according to the EUC encoding algorithm. Only characters defined in the JIS code set table can be used with this encoding method.
A wide character is represented using UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO 10646-1/Am.2. Depending on the character value, the representation is a one, two, or three byte sequence:
16#0000#-16#007f#: 2#0xxxxxxx# 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx# 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
where the xxx bits correspond to the left-padded bits of the 16-bit character value. Note that all lower half ASCII characters are represented as ASCII bytes and all upper half characters and other wide characters are represented as sequences of upper-half (The full UTF-8 scheme allows for encoding 31-bit characters as 6-byte sequences, but in this implementation, all UTF-8 sequences of four or more bytes length will raise a Constraint_Error, as will all invalid UTF-8 sequences.)
In this encoding, a wide character is represented by the following eight character sequence:
[ " a b c d " ]
where a
, b
, c
, d
are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ["A345"]
is used to represent the wide character with code
16#A345#
.
This scheme is compatible with use of the full Wide_Character set.
On input, brackets coding can also be used for upper half characters,
e.g. ["C1"]
for lower case a. However, on output, brackets notation
is only used for wide characters with a code greater than 16#FF#
.
Note that brackets coding is not normally used in the context of Wide_Text_IO or Wide_Wide_Text_IO, since it is really just designed as a portable way of encoding source files. In the context of Wide_Text_IO or Wide_Wide_Text_IO, it can only be used if the file does not contain any instance of the left bracket character other than to encode wide character values using the brackets encoding method. In practice it is expected that some standard wide character encoding method such as UTF-8 will be used for text input output.
If brackets notation is used, then any occurrence of a left bracket in the input file which is not the start of a valid wide character sequence will cause Constraint_Error to be raised. It is possible to encode a left bracket as ["5B"] and Wide_Text_IO and Wide_Wide_Text_IO input will interpret this as a left bracket.
However, when a left bracket is output, it will be output as a left bracket and not as ["5B"]. We make this decision because for normal use of Wide_Text_IO for outputting messages, it is unpleasant to clobber left brackets. For example, if we write:
Put_Line ("Start of output [first run]");
we really do not want to have the left bracket in this message clobbered so that the output reads:
Start of output ["5B"]first run]
In practice brackets encoding is reasonably useful for normal Put_Line use since we won’t get confused between left brackets and wide character sequences in the output. But for input, or when files are written out and read back in, it really makes better sense to use one of the standard encoding methods such as UTF-8.
For the coding schemes other than UTF-8, Hex, or Brackets encoding, not all wide character values can be represented. An attempt to output a character that cannot be represented using the encoding scheme for the file causes Constraint_Error to be raised. An invalid wide character sequence on input also causes Constraint_Error to be raised.
• Wide_Text_IO Stream Pointer Positioning: | ||
• Wide_Text_IO Reading and Writing Non-Regular Files: |
Next: Wide_Text_IO Reading and Writing Non-Regular Files, Previous: Text_IO Facilities for Unbounded Strings, Up: Wide_Text_IO [Contents][Index]
Ada.Wide_Text_IO
is similar to Ada.Text_IO
in its handling
of stream pointer positioning (see Text_IO). There is one additional
case:
If Ada.Wide_Text_IO.Look_Ahead
reads a character outside the
normal lower ASCII set (i.e. a character in the range:
Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
then although the logical position of the file pointer is unchanged by
the Look_Ahead
call, the stream is physically positioned past the
wide character sequence. Again this is to avoid the need for buffering
or backup, and all Wide_Text_IO
routines check the internal
indication that this situation has occurred so that this is not visible
to a normal program using Wide_Text_IO
. However, this discrepancy
can be observed if the wide text file shares a stream with another file.
Next: Wide_Wide_Text_IO Stream Pointer Positioning, Previous: Wide_Text_IO Stream Pointer Positioning, Up: Wide_Text_IO [Contents][Index]
As in the case of Text_IO, when a non-regular file is read, it is
assumed that the file contains no page marks (any form characters are
treated as data characters), and End_Of_Page
always returns
False
. Similarly, the end of file indication is not sticky, so
it is possible to read beyond an end of file.
Next: Stream_IO, Previous: Wide_Text_IO, Up: The Implementation of Standard I/O [Contents][Index]
Wide_Wide_Text_IO
is similar in most respects to Text_IO, except that
both input and output files may contain special sequences that represent
wide wide character values. The encoding scheme for a given file may be
specified using a FORM parameter:
WCEM=x
as part of the FORM string (WCEM = wide character encoding method), where x is one of the following characters
Hex ESC encoding
Upper half encoding
Shift-JIS encoding
EUC Encoding
UTF-8 encoding
Brackets encoding
The encoding methods match those that can be used in a source program, but there is no requirement that the encoding method used for the source program be the same as the encoding method used for files, and different files may use different encoding methods.
The default encoding method for the standard files, and for opened files for which no WCEM parameter is given in the FORM string matches the wide character encoding specified for the main program (the default being brackets encoding if no coding method was specified with -gnatW).
A wide character is represented using UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO 10646-1/Am.2. Depending on the character value, the representation is a one, two, three, or four byte sequence:
16#000000#-16#00007f#: 2#0xxxxxxx# 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx# 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx# 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
where the xxx bits correspond to the left-padded bits of the 21-bit character value. Note that all lower half ASCII characters are represented as ASCII bytes and all upper half characters and other wide characters are represented as sequences of upper-half characters.
In this encoding, a wide wide character is represented by the following eight character sequence if is in wide character range
[ " a b c d " ]
and by the following ten character sequence if not
[ " a b c d e f " ]
where a
, b
, c
, d
, e
, and f
are the four or six hexadecimal
characters (using uppercase letters) of the wide wide character code. For
example, ["01A345"]
is used to represent the wide wide character
with code 16#01A345#
.
This scheme is compatible with use of the full Wide_Wide_Character set.
On input, brackets coding can also be used for upper half characters,
e.g. ["C1"]
for lower case a. However, on output, brackets notation
is only used for wide characters with a code greater than 16#FF#
.
If is also possible to use the other Wide_Character encoding methods, such as Shift-JIS, but the other schemes cannot support the full range of wide wide characters. An attempt to output a character that cannot be represented using the encoding scheme for the file causes Constraint_Error to be raised. An invalid wide character sequence on input also causes Constraint_Error to be raised.
• Wide_Wide_Text_IO Stream Pointer Positioning: | ||
• Wide_Wide_Text_IO Reading and Writing Non-Regular Files: |
Next: Wide_Wide_Text_IO Reading and Writing Non-Regular Files, Previous: Wide_Text_IO Reading and Writing Non-Regular Files, Up: Wide_Wide_Text_IO [Contents][Index]
Ada.Wide_Wide_Text_IO
is similar to Ada.Text_IO
in its handling
of stream pointer positioning (see Text_IO). There is one additional
case:
If Ada.Wide_Wide_Text_IO.Look_Ahead
reads a character outside the
normal lower ASCII set (i.e. a character in the range:
Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#)
then although the logical position of the file pointer is unchanged by
the Look_Ahead
call, the stream is physically positioned past the
wide character sequence. Again this is to avoid the need for buffering
or backup, and all Wide_Wide_Text_IO
routines check the internal
indication that this situation has occurred so that this is not visible
to a normal program using Wide_Wide_Text_IO
. However, this discrepancy
can be observed if the wide text file shares a stream with another file.
Next: Interfacing to C, Previous: Wide_Wide_Text_IO Stream Pointer Positioning, Up: Wide_Wide_Text_IO [Contents][Index]
As in the case of Text_IO, when a non-regular file is read, it is
assumed that the file contains no page marks (any form characters are
treated as data characters), and End_Of_Page
always returns
False
. Similarly, the end of file indication is not sticky, so
it is possible to read beyond an end of file.
Next: Text Translation, Previous: Wide_Wide_Text_IO, Up: The Implementation of Standard I/O [Contents][Index]
A stream file is a sequence of bytes, where individual elements are
written to the file as described in the Ada Reference Manual. The type
Stream_Element
is simply a byte. There are two ways to read or
write a stream file.
Read
and Write
directly read or write a
sequence of stream elements with no control information.
Next: Shared Files, Previous: Stream_IO, Up: The Implementation of Standard I/O [Contents][Index]
‘Text_Translation=xxx’ may be used as the Form parameter passed to Text_IO.Create and Text_IO.Open: ‘Text_Translation=Yes’ is the default, which means to translate LF to/from CR/LF on Windows systems. ‘Text_Translation=No’ disables this translation; i.e. it uses binary mode. For output files, ‘Text_Translation=No’ may be used to create Unix-style files on Windows. ‘Text_Translation=xxx’ has no effect on Unix systems.
Next: Filenames encoding, Previous: Text Translation, Up: The Implementation of Standard I/O [Contents][Index]
Section A.14 of the Ada Reference Manual allows implementations to provide a wide variety of behavior if an attempt is made to access the same external file with two or more internal files.
To provide a full range of functionality, while at the same time minimizing the problems of portability caused by this implementation dependence, GNAT handles file sharing as follows:
Use_Error
will be
raised. Note that a file that is not explicitly closed by the program
remains open until the program terminates.
When a program that opens multiple files with the same name is ported
from another Ada compiler to GNAT, the effect will be that
Use_Error
is raised.
The documentation of the original compiler and the documentation of the
program should then be examined to determine if file sharing was
expected, and ‘shared=xxx’ parameters added to Open
and Create
calls as required.
When a program is ported from GNAT to some other Ada compiler, no special attention is required unless the ‘shared=xxx’ form parameter is used in the program. In this case, you must examine the documentation of the new compiler to see if it supports the required file sharing semantics, and form strings modified appropriately. Of course it may be the case that the program cannot be ported if the target compiler does not support the required functionality. The best approach in writing portable code is to avoid file sharing (and hence the use of the ‘shared=xxx’ parameter in the form string) completely.
One common use of file sharing in Ada 83 is the use of instantiations of Sequential_IO on the same file with different types, to achieve heterogeneous input-output. Although this approach will work in GNAT if ‘shared=yes’ is specified, it is preferable in Ada to use Stream_IO for this purpose (using the stream attributes)
Next: Open Modes, Previous: Shared Files, Up: The Implementation of Standard I/O [Contents][Index]
An encoding form parameter can be used to specify the filename encoding ‘encoding=xxx’.
In the absence of a ‘encoding=xxx’ form parameter, the encoding is controlled by the ‘GNAT_CODE_PAGE’ environment variable. And if not set ‘utf8’ is assumed.
The current system Windows ANSI code page.
UTF-8 encoding
This encoding form parameter is only supported on the Windows platform. On the other Operating Systems the run-time is supporting UTF-8 natively.
Next: Operations on C Streams, Previous: Filenames encoding, Up: The Implementation of Standard I/O [Contents][Index]
Open
and Create
calls result in a call to fopen
using the mode shown in the following table:
Open
and Create
Call Modes
OPEN CREATE Append_File "r+" "w+" In_File "r" "w+" Out_File (Direct_IO) "r+" "w" Out_File (all other cases) "w" "w" Inout_File "r+" "w+"
If text file translation is required, then either ‘b’ or ‘t’ is added to the mode, depending on the setting of Text. Text file translation refers to the mapping of CR/LF sequences in an external file to LF characters internally. This mapping only occurs in DOS and DOS-like systems, and is not relevant to other systems.
A special case occurs with Stream_IO. As shown in the above table, the
file is initially opened in ‘r’ or ‘w’ mode for the
In_File
and Out_File
cases. If a Set_Mode
operation
subsequently requires switching from reading to writing or vice-versa,
then the file is reopened in ‘r+’ mode to permit the required operation.
Next: Interfacing to C Streams, Previous: Open Modes, Up: The Implementation of Standard I/O [Contents][Index]
The package Interfaces.C_Streams
provides an Ada program with direct
access to the C library functions for operations on C streams:
package Interfaces.C_Streams is -- Note: the reason we do not use the types that are in -- Interfaces.C is that we want to avoid dragging in the -- code in this unit if possible. subtype chars is System.Address; -- Pointer to null-terminated array of characters subtype FILEs is System.Address; -- Corresponds to the C type FILE* subtype voids is System.Address; -- Corresponds to the C type void* subtype int is Integer; subtype long is Long_Integer; -- Note: the above types are subtypes deliberately, and it -- is part of this spec that the above correspondences are -- guaranteed. This means that it is legitimate to, for -- example, use Integer instead of int. We provide these -- synonyms for clarity, but in some cases it may be -- convenient to use the underlying types (for example to -- avoid an unnecessary dependency of a spec on the spec -- of this unit). type size_t is mod 2 ** Standard'Address_Size; NULL_Stream : constant FILEs; -- Value returned (NULL in C) to indicate an -- fdopen/fopen/tmpfile error ---------------------------------- -- Constants Defined in stdio.h -- ---------------------------------- EOF : constant int; -- Used by a number of routines to indicate error or -- end of file IOFBF : constant int; IOLBF : constant int; IONBF : constant int; -- Used to indicate buffering mode for setvbuf call SEEK_CUR : constant int; SEEK_END : constant int; SEEK_SET : constant int; -- Used to indicate origin for fseek call function stdin return FILEs; function stdout return FILEs; function stderr return FILEs; -- Streams associated with standard files -------------------------- -- Standard C functions -- -------------------------- -- The functions selected below are ones that are -- available in UNIX (but not necessarily in ANSI C). -- These are very thin interfaces -- which copy exactly the C headers. For more -- documentation on these functions, see the Microsoft C -- "Run-Time Library Reference" (Microsoft Press, 1990, -- ISBN 1-55615-225-6), which includes useful information -- on system compatibility. procedure clearerr (stream : FILEs); function fclose (stream : FILEs) return int; function fdopen (handle : int; mode : chars) return FILEs; function feof (stream : FILEs) return int; function ferror (stream : FILEs) return int; function fflush (stream : FILEs) return int; function fgetc (stream : FILEs) return int; function fgets (strng : chars; n : int; stream : FILEs) return chars; function fileno (stream : FILEs) return int; function fopen (filename : chars; Mode : chars) return FILEs; -- Note: to maintain target independence, use -- text_translation_required, a boolean variable defined in -- a-sysdep.c to deal with the target dependent text -- translation requirement. If this variable is set, -- then b/t should be appended to the standard mode -- argument to set the text translation mode off or on -- as required. function fputc (C : int; stream : FILEs) return int; function fputs (Strng : chars; Stream : FILEs) return int; function fread (buffer : voids; size : size_t; count : size_t; stream : FILEs) return size_t; function freopen (filename : chars; mode : chars; stream : FILEs) return FILEs; function fseek (stream : FILEs; offset : long; origin : int) return int; function ftell (stream : FILEs) return long; function fwrite (buffer : voids; size : size_t; count : size_t; stream : FILEs) return size_t; function isatty (handle : int) return int; procedure mktemp (template : chars); -- The return value (which is just a pointer to template) -- is discarded procedure rewind (stream : FILEs); function rmtmp return int; function setvbuf (stream : FILEs; buffer : chars; mode : int; size : size_t) return int; function tmpfile return FILEs; function ungetc (c : int; stream : FILEs) return int; function unlink (filename : chars) return int; --------------------- -- Extra functions -- --------------------- -- These functions supply slightly thicker bindings than -- those above. They are derived from functions in the -- C Run-Time Library, but may do a bit more work than -- just directly calling one of the Library functions. function is_regular_file (handle : int) return int; -- Tests if given handle is for a regular file (result 1) -- or for a non-regular file (pipe or device, result 0). --------------------------------- -- Control of Text/Binary Mode -- --------------------------------- -- If text_translation_required is true, then the following -- functions may be used to dynamically switch a file from -- binary to text mode or vice versa. These functions have -- no effect if text_translation_required is false (i.e. in -- normal UNIX mode). Use fileno to get a stream handle. procedure set_binary_mode (handle : int); procedure set_text_mode (handle : int); ---------------------------- -- Full Path Name support -- ---------------------------- procedure full_name (nam : chars; buffer : chars); -- Given a NUL terminated string representing a file -- name, returns in buffer a NUL terminated string -- representing the full path name for the file name. -- On systems where it is relevant the drive is also -- part of the full path name. It is the responsibility -- of the caller to pass an actual parameter for buffer -- that is big enough for any full path name. Use -- max_path_len given below as the size of buffer. max_path_len : integer; -- Maximum length of an allowable full path name on the -- system, including a terminating NUL character. end Interfaces.C_Streams;
Next: Ada.Characters.Latin_9 (a-chlat9.ads), Previous: Operations on C Streams, Up: The Implementation of Standard I/O [Contents][Index]
The packages in this section permit interfacing Ada files to C Stream operations.
with Interfaces.C_Streams; package Ada.Sequential_IO.C_Streams is function C_Stream (F : File_Type) return Interfaces.C_Streams.FILEs; procedure Open (File : in out File_Type; Mode : in File_Mode; C_Stream : in Interfaces.C_Streams.FILEs; Form : in String := ""); end Ada.Sequential_IO.C_Streams; with Interfaces.C_Streams; package Ada.Direct_IO.C_Streams is function C_Stream (F : File_Type) return Interfaces.C_Streams.FILEs; procedure Open (File : in out File_Type; Mode : in File_Mode; C_Stream : in Interfaces.C_Streams.FILEs; Form : in String := ""); end Ada.Direct_IO.C_Streams; with Interfaces.C_Streams; package Ada.Text_IO.C_Streams is function C_Stream (F : File_Type) return Interfaces.C_Streams.FILEs; procedure Open (File : in out File_Type; Mode : in File_Mode; C_Stream : in Interfaces.C_Streams.FILEs; Form : in String := ""); end Ada.Text_IO.C_Streams; with Interfaces.C_Streams; package Ada.Wide_Text_IO.C_Streams is function C_Stream (F : File_Type) return Interfaces.C_Streams.FILEs; procedure Open (File : in out File_Type; Mode : in File_Mode; C_Stream : in Interfaces.C_Streams.FILEs; Form : in String := ""); end Ada.Wide_Text_IO.C_Streams; with Interfaces.C_Streams; package Ada.Wide_Wide_Text_IO.C_Streams is function C_Stream (F : File_Type) return Interfaces.C_Streams.FILEs; procedure Open (File : in out File_Type; Mode : in File_Mode; C_Stream : in Interfaces.C_Streams.FILEs; Form : in String := ""); end Ada.Wide_Wide_Text_IO.C_Streams; with Interfaces.C_Streams; package Ada.Stream_IO.C_Streams is function C_Stream (F : File_Type) return Interfaces.C_Streams.FILEs; procedure Open (File : in out File_Type; Mode : in File_Mode; C_Stream : in Interfaces.C_Streams.FILEs; Form : in String := ""); end Ada.Stream_IO.C_Streams;
In each of these six packages, the C_Stream
function obtains the
FILE
pointer from a currently opened Ada file. It is then
possible to use the Interfaces.C_Streams
package to operate on
this stream, or the stream can be passed to a C program which can
operate on it directly. Of course the program is responsible for
ensuring that only appropriate sequences of operations are executed.
One particular use of relevance to an Ada program is that the
setvbuf
function can be used to control the buffering of the
stream used by an Ada file. In the absence of such a call the standard
default buffering is used.
The Open
procedures in these packages open a file giving an
existing C Stream instead of a file name. Typically this stream is
imported from a C program, allowing an Ada file to operate on an
existing C file.
Next: Interfacing to Other Languages, Previous: The Implementation of Standard I/O, Up: Top [Contents][Index]
The GNAT library contains a number of general and special purpose packages. It represents functionality that the GNAT developers have found useful, and which is made available to GNAT users. The packages described here are fully supported, and upwards compatibility will be maintained in future releases, so you can use these facilities with the confidence that the same functionality will be available in future releases.
The chapter here simply gives a brief summary of the facilities available. The full documentation is found in the spec file for the package. The full sources of these library packages, including both spec and body, are provided with all GNAT releases. For example, to find out the full specifications of the SPITBOL pattern matching capability, including a full tutorial and extensive examples, look in the g-spipat.ads file in the library.
For each entry here, the package name (as it would appear in a with
clause) is given, followed by the name of the corresponding spec file in
parentheses. The packages are children in four hierarchies, Ada
,
Interfaces
, System
, and GNAT
, the latter being a
GNAT-specific hierarchy.
Note that an application program should only use packages in one of these
four hierarchies if the package is defined in the Ada Reference Manual,
or is listed in this section of the GNAT Programmers Reference Manual.
All other units should be considered internal implementation units and
should not be directly with
’ed by application code. The use of
a with
statement that references one of these internal implementation
units makes an application potentially dependent on changes in versions
of GNAT, and will generate a warning message.
Next: Ada.Characters.Wide_Latin_1 (a-cwila1.ads), Previous: Interfacing to C Streams, Up: The GNAT Library [Contents][Index]
Ada.Characters.Latin_9
(a-chlat9.ads)This child of Ada.Characters
provides a set of definitions corresponding to those in the
RM-defined package Ada.Characters.Latin_1
but with the
few modifications required for Latin-9
The provision of such a package
is specifically authorized by the Ada Reference Manual
(RM A.3.3(27)).
Next: Ada.Characters.Wide_Latin_9 (a-cwila9.ads), Previous: Ada.Characters.Latin_9 (a-chlat9.ads), Up: The GNAT Library [Contents][Index]
Ada.Characters.Wide_Latin_1
(a-cwila1.ads)This child of Ada.Characters
provides a set of definitions corresponding to those in the
RM-defined package Ada.Characters.Latin_1
but with the
types of the constants being Wide_Character
instead of Character
. The provision of such a package
is specifically authorized by the Ada Reference Manual
(RM A.3.3(27)).
Next: Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads), Previous: Ada.Characters.Wide_Latin_1 (a-cwila1.ads), Up: The GNAT Library [Contents][Index]
Ada.Characters.Wide_Latin_9
(a-cwila1.ads)This child of Ada.Characters
provides a set of definitions corresponding to those in the
GNAT defined package Ada.Characters.Latin_9
but with the
types of the constants being Wide_Character
instead of Character
. The provision of such a package
is specifically authorized by the Ada Reference Manual
(RM A.3.3(27)).
Next: Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads), Previous: Ada.Characters.Wide_Latin_9 (a-cwila9.ads), Up: The GNAT Library [Contents][Index]
Ada.Characters.Wide_Wide_Latin_1
(a-chzla1.ads)This child of Ada.Characters
provides a set of definitions corresponding to those in the
RM-defined package Ada.Characters.Latin_1
but with the
types of the constants being Wide_Wide_Character
instead of Character
. The provision of such a package
is specifically authorized by the Ada Reference Manual
(RM A.3.3(27)).
Next: Ada.Containers.Formal_Doubly_Linked_Lists (a-cfdlli.ads), Previous: Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads), Up: The GNAT Library [Contents][Index]
Ada.Characters.Wide_Wide_Latin_9
(a-chzla9.ads)This child of Ada.Characters
provides a set of definitions corresponding to those in the
GNAT defined package Ada.Characters.Latin_9
but with the
types of the constants being Wide_Wide_Character
instead of Character
. The provision of such a package
is specifically authorized by the Ada Reference Manual
(RM A.3.3(27)).
Next: Ada.Containers.Formal_Hashed_Maps (a-cfhama.ads), Previous: Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads), Up: The GNAT Library [Contents][Index]
Ada.Containers.Formal_Doubly_Linked_Lists
(a-cfdlli.ads)This child of Ada.Containers
defines a modified version of the Ada 2005
container for doubly linked lists, meant to facilitate formal verification of
code using such containers.
Next: Ada.Containers.Formal_Hashed_Sets (a-cfhase.ads), Previous: Ada.Containers.Formal_Doubly_Linked_Lists (a-cfdlli.ads), Up: The GNAT Library [Contents][Index]
Ada.Containers.Formal_Hashed_Maps
(a-cfhama.ads)This child of Ada.Containers
defines a modified version of the Ada 2005
container for hashed maps, meant to facilitate formal verification of
code using such containers.
Next: Ada.Containers.Formal_Ordered_Maps (a-cforma.ads), Previous: Ada.Containers.Formal_Hashed_Maps (a-cfhama.ads), Up: The GNAT Library [Contents][Index]
Ada.Containers.Formal_Hashed_Sets
(a-cfhase.ads)This child of Ada.Containers
defines a modified version of the Ada 2005
container for hashed sets, meant to facilitate formal verification of
code using such containers.
Next: Ada.Containers.Formal_Ordered_Sets (a-cforse.ads), Previous: Ada.Containers.Formal_Hashed_Sets (a-cfhase.ads), Up: The GNAT Library [Contents][Index]
Ada.Containers.Formal_Ordered_Maps
(a-cforma.ads)This child of Ada.Containers
defines a modified version of the Ada 2005
container for ordered maps, meant to facilitate formal verification of
code using such containers.
Next: Ada.Containers.Formal_Vectors (a-cofove.ads), Previous: Ada.Containers.Formal_Ordered_Maps (a-cforma.ads), Up: The GNAT Library [Contents][Index]
Ada.Containers.Formal_Ordered_Sets
(a-cforse.ads)This child of Ada.Containers
defines a modified version of the Ada 2005
container for ordered sets, meant to facilitate formal verification of
code using such containers.
Next: Ada.Command_Line.Environment (a-colien.ads), Previous: Ada.Containers.Formal_Ordered_Sets (a-cforse.ads), Up: The GNAT Library [Contents][Index]
Ada.Containers.Formal_Vectors
(a-cofove.ads)This child of Ada.Containers
defines a modified version of the Ada 2005
container for vectors, meant to facilitate formal verification of
code using such containers.
Next: Ada.Command_Line.Remove (a-colire.ads), Previous: Ada.Containers.Formal_Vectors (a-cofove.ads), Up: The GNAT Library [Contents][Index]
Ada.Command_Line.Environment
(a-colien.ads)This child of Ada.Command_Line
provides a mechanism for obtaining environment values on systems
where this concept makes sense.
Next: Ada.Command_Line.Response_File (a-clrefi.ads), Previous: Ada.Command_Line.Environment (a-colien.ads), Up: The GNAT Library [Contents][Index]
Ada.Command_Line.Remove
(a-colire.ads)This child of Ada.Command_Line
provides a mechanism for logically removing
arguments from the argument list. Once removed, an argument is not visible
to further calls on the subprograms in Ada.Command_Line
will not
see the removed argument.
Next: Ada.Direct_IO.C_Streams (a-diocst.ads), Previous: Ada.Command_Line.Remove (a-colire.ads), Up: The GNAT Library [Contents][Index]
Ada.Command_Line.Response_File
(a-clrefi.ads)This child of Ada.Command_Line
provides a mechanism facilities for
getting command line arguments from a text file, called a "response file".
Using a response file allow passing a set of arguments to an executable longer
than the maximum allowed by the system on the command line.
Next: Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads), Previous: Ada.Command_Line.Response_File (a-clrefi.ads), Up: The GNAT Library [Contents][Index]
Ada.Direct_IO.C_Streams
(a-diocst.ads)This package provides subprograms that allow interfacing between
C streams and Direct_IO
. The stream identifier can be
extracted from a file opened on the Ada side, and an Ada file
can be constructed from a stream opened on the C side.
Next: Ada.Exceptions.Last_Chance_Handler (a-elchha.ads), Previous: Ada.Direct_IO.C_Streams (a-diocst.ads), Up: The GNAT Library [Contents][Index]
Ada.Exceptions.Is_Null_Occurrence
(a-einuoc.ads)This child subprogram provides a way of testing for the null
exception occurrence (Null_Occurrence
) without raising
an exception.
Next: Ada.Exceptions.Traceback (a-exctra.ads), Previous: Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads), Up: The GNAT Library [Contents][Index]
Ada.Exceptions.Last_Chance_Handler
(a-elchha.ads)This child subprogram is used for handling otherwise unhandled exceptions (hence the name last chance), and perform clean ups before terminating the program. Note that this subprogram never returns.
Next: Ada.Sequential_IO.C_Streams (a-siocst.ads), Previous: Ada.Exceptions.Last_Chance_Handler (a-elchha.ads), Up: The GNAT Library [Contents][Index]
Ada.Exceptions.Traceback
(a-exctra.ads)This child package provides the subprogram (Tracebacks
) to
give a traceback array of addresses based on an exception
occurrence.
Next: Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads), Previous: Ada.Exceptions.Traceback (a-exctra.ads), Up: The GNAT Library [Contents][Index]
Ada.Sequential_IO.C_Streams
(a-siocst.ads)This package provides subprograms that allow interfacing between
C streams and Sequential_IO
. The stream identifier can be
extracted from a file opened on the Ada side, and an Ada file
can be constructed from a stream opened on the C side.
Next: Ada.Strings.Unbounded.Text_IO (a-suteio.ads), Previous: Ada.Sequential_IO.C_Streams (a-siocst.ads), Up: The GNAT Library [Contents][Index]
Ada.Streams.Stream_IO.C_Streams
(a-ssicst.ads)This package provides subprograms that allow interfacing between
C streams and Stream_IO
. The stream identifier can be
extracted from a file opened on the Ada side, and an Ada file
can be constructed from a stream opened on the C side.
Next: Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads), Previous: Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads), Up: The GNAT Library [Contents][Index]
Ada.Strings.Unbounded.Text_IO
(a-suteio.ads)This package provides subprograms for Text_IO for unbounded strings, avoiding the necessity for an intermediate operation with ordinary strings.
Next: Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads), Previous: Ada.Strings.Unbounded.Text_IO (a-suteio.ads), Up: The GNAT Library [Contents][Index]
Ada.Strings.Wide_Unbounded.Wide_Text_IO
(a-swuwti.ads)This package provides subprograms for Text_IO for unbounded wide strings, avoiding the necessity for an intermediate operation with ordinary wide strings.
Next: Ada.Text_IO.C_Streams (a-tiocst.ads), Previous: Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads), Up: The GNAT Library [Contents][Index]
Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO
(a-szuzti.ads)This package provides subprograms for Text_IO for unbounded wide wide strings, avoiding the necessity for an intermediate operation with ordinary wide wide strings.
Next: Ada.Text_IO.Reset_Standard_Files (a-tirsfi.ads), Previous: Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads), Up: The GNAT Library [Contents][Index]
Ada.Text_IO.C_Streams
(a-tiocst.ads)This package provides subprograms that allow interfacing between
C streams and Text_IO
. The stream identifier can be
extracted from a file opened on the Ada side, and an Ada file
can be constructed from a stream opened on the C side.
Next: Ada.Wide_Characters.Unicode (a-wichun.ads), Previous: Ada.Text_IO.C_Streams (a-tiocst.ads), Up: The GNAT Library [Contents][Index]
Ada.Text_IO.Reset_Standard_Files
(a-tirsfi.ads)This procedure is used to reset the status of the standard files used by Ada.Text_IO. This is useful in a situation (such as a restart in an embedded application) where the status of the files may change during execution (for example a standard input file may be redefined to be interactive).
Next: Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads), Previous: Ada.Text_IO.Reset_Standard_Files (a-tirsfi.ads), Up: The GNAT Library [Contents][Index]
Ada.Wide_Characters.Unicode
(a-wichun.ads)This package provides subprograms that allow categorization of Wide_Character values according to Unicode categories.
Next: Ada.Wide_Text_IO.Reset_Standard_Files (a-wrstfi.ads), Previous: Ada.Wide_Characters.Unicode (a-wichun.ads), Up: The GNAT Library [Contents][Index]
Ada.Wide_Text_IO.C_Streams
(a-wtcstr.ads)This package provides subprograms that allow interfacing between
C streams and Wide_Text_IO
. The stream identifier can be
extracted from a file opened on the Ada side, and an Ada file
can be constructed from a stream opened on the C side.
Next: Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads), Previous: Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads), Up: The GNAT Library [Contents][Index]
Ada.Wide_Text_IO.Reset_Standard_Files
(a-wrstfi.ads)This procedure is used to reset the status of the standard files used by Ada.Wide_Text_IO. This is useful in a situation (such as a restart in an embedded application) where the status of the files may change during execution (for example a standard input file may be redefined to be interactive).
Next: Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads), Previous: Ada.Wide_Text_IO.Reset_Standard_Files (a-wrstfi.ads), Up: The GNAT Library [Contents][Index]
Ada.Wide_Wide_Characters.Unicode
(a-zchuni.ads)This package provides subprograms that allow categorization of Wide_Wide_Character values according to Unicode categories.
Next: Ada.Wide_Wide_Text_IO.Reset_Standard_Files (a-zrstfi.ads), Previous: Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads), Up: The GNAT Library [Contents][Index]
Ada.Wide_Wide_Text_IO.C_Streams
(a-ztcstr.ads)This package provides subprograms that allow interfacing between
C streams and Wide_Wide_Text_IO
. The stream identifier can be
extracted from a file opened on the Ada side, and an Ada file
can be constructed from a stream opened on the C side.
Next: GNAT.Altivec (g-altive.ads), Previous: Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads), Up: The GNAT Library [Contents][Index]
Ada.Wide_Wide_Text_IO.Reset_Standard_Files
(a-zrstfi.ads)This procedure is used to reset the status of the standard files used by Ada.Wide_Wide_Text_IO. This is useful in a situation (such as a restart in an embedded application) where the status of the files may change during execution (for example a standard input file may be redefined to be interactive).
Next: GNAT.Altivec.Conversions (g-altcon.ads), Previous: Ada.Wide_Wide_Text_IO.Reset_Standard_Files (a-zrstfi.ads), Up: The GNAT Library [Contents][Index]
GNAT.Altivec
(g-altive.ads)This is the root package of the GNAT AltiVec binding. It provides definitions of constants and types common to all the versions of the binding.
Next: GNAT.Altivec.Vector_Operations (g-alveop.ads), Previous: GNAT.Altivec (g-altive.ads), Up: The GNAT Library [Contents][Index]
GNAT.Altivec.Conversions
(g-altcon.ads)This package provides the Vector/View conversion routines.
Next: GNAT.Altivec.Vector_Types (g-alvety.ads), Previous: GNAT.Altivec.Conversions (g-altcon.ads), Up: The GNAT Library [Contents][Index]
GNAT.Altivec.Vector_Operations
(g-alveop.ads)This package exposes the Ada interface to the AltiVec operations on vector objects. A soft emulation is included by default in the GNAT library. The hard binding is provided as a separate package. This unit is common to both bindings.
Next: GNAT.Altivec.Vector_Views (g-alvevi.ads), Previous: GNAT.Altivec.Vector_Operations (g-alveop.ads), Up: The GNAT Library [Contents][Index]
GNAT.Altivec.Vector_Types
(g-alvety.ads)This package exposes the various vector types part of the Ada binding to AltiVec facilities.
Next: GNAT.Array_Split (g-arrspl.ads), Previous: GNAT.Altivec.Vector_Types (g-alvety.ads), Up: The GNAT Library [Contents][Index]
GNAT.Altivec.Vector_Views
(g-alvevi.ads)This package provides public ’View’ data types from/to which private vector representations can be converted via GNAT.Altivec.Conversions. This allows convenient access to individual vector elements and provides a simple way to initialize vector objects.
Next: GNAT.AWK (g-awk.ads), Previous: GNAT.Altivec.Vector_Views (g-alvevi.ads), Up: The GNAT Library [Contents][Index]
GNAT.Array_Split
(g-arrspl.ads)Useful array-manipulation routines: given a set of separators, split an array wherever the separators appear, and provide direct access to the resulting slices.
Next: GNAT.Bounded_Buffers (g-boubuf.ads), Previous: GNAT.Array_Split (g-arrspl.ads), Up: The GNAT Library [Contents][Index]
GNAT.AWK
(g-awk.ads)Provides AWK-like parsing functions, with an easy interface for parsing one or more files containing formatted data. The file is viewed as a database where each record is a line and a field is a data element in this line.
Next: GNAT.Bounded_Mailboxes (g-boumai.ads), Previous: GNAT.AWK (g-awk.ads), Up: The GNAT Library [Contents][Index]
GNAT.Bounded_Buffers
(g-boubuf.ads)Provides a concurrent generic bounded buffer abstraction. Instances are useful directly or as parts of the implementations of other abstractions, such as mailboxes.
Next: GNAT.Bubble_Sort (g-bubsor.ads), Previous: GNAT.Bounded_Buffers (g-boubuf.ads), Up: The GNAT Library [Contents][Index]
GNAT.Bounded_Mailboxes
(g-boumai.ads)Provides a thread-safe asynchronous intertask mailbox communication facility.
Next: GNAT.Bubble_Sort_A (g-busora.ads), Previous: GNAT.Bounded_Mailboxes (g-boumai.ads), Up: The GNAT Library [Contents][Index]
GNAT.Bubble_Sort
(g-bubsor.ads)Provides a general implementation of bubble sort usable for sorting arbitrary data items. Exchange and comparison procedures are provided by passing access-to-procedure values.
Next: GNAT.Bubble_Sort_G (g-busorg.ads), Previous: GNAT.Bubble_Sort (g-bubsor.ads), Up: The GNAT Library [Contents][Index]
GNAT.Bubble_Sort_A
(g-busora.ads)Provides a general implementation of bubble sort usable for sorting arbitrary
data items. Move and comparison procedures are provided by passing
access-to-procedure values. This is an older version, retained for
compatibility. Usually GNAT.Bubble_Sort
will be preferable.
Next: GNAT.Byte_Order_Mark (g-byorma.ads), Previous: GNAT.Bubble_Sort_A (g-busora.ads), Up: The GNAT Library [Contents][Index]
GNAT.Bubble_Sort_G
(g-busorg.ads)Similar to Bubble_Sort_A
except that the move and sorting procedures
are provided as generic parameters, this improves efficiency, especially
if the procedures can be inlined, at the expense of duplicating code for
multiple instantiations.
Next: GNAT.Byte_Swapping (g-bytswa.ads), Previous: GNAT.Bubble_Sort_G (g-busorg.ads), Up: The GNAT Library [Contents][Index]
GNAT.Byte_Order_Mark
(g-byorma.ads)Provides a routine which given a string, reads the start of the string to see whether it is one of the standard byte order marks (BOM’s) which signal the encoding of the string. The routine includes detection of special XML sequences for various UCS input formats.
Next: GNAT.Calendar (g-calend.ads), Previous: GNAT.Byte_Order_Mark (g-byorma.ads), Up: The GNAT Library [Contents][Index]
GNAT.Byte_Swapping
(g-bytswa.ads)General routines for swapping the bytes in 2-, 4-, and 8-byte quantities. Machine-specific implementations are available in some cases.
Next: GNAT.Calendar.Time_IO (g-catiio.ads), Previous: GNAT.Byte_Swapping (g-bytswa.ads), Up: The GNAT Library [Contents][Index]
GNAT.Calendar
(g-calend.ads)Extends the facilities provided by Ada.Calendar
to include handling
of days of the week, an extended Split
and Time_Of
capability.
Also provides conversion of Ada.Calendar.Time
values to and from the
C timeval
format.
Next: GNAT.CRC32 (g-crc32.ads), Previous: GNAT.Calendar (g-calend.ads), Up: The GNAT Library [Contents][Index]
GNAT.Calendar.Time_IO
(g-catiio.ads)Next: GNAT.Case_Util (g-casuti.ads), Previous: GNAT.Calendar.Time_IO (g-catiio.ads), Up: The GNAT Library [Contents][Index]
GNAT.CRC32
(g-crc32.ads)This package implements the CRC-32 algorithm. For a full description of this algorithm see “Computation of Cyclic Redundancy Checks via Table Look-Up”, Communications of the ACM, Vol. 31 No. 8, pp. 1008-1013, Aug. 1988. Sarwate, D.V.
Next: GNAT.CGI (g-cgi.ads), Previous: GNAT.CRC32 (g-crc32.ads), Up: The GNAT Library [Contents][Index]
GNAT.Case_Util
(g-casuti.ads)A set of simple routines for handling upper and lower casing of strings
without the overhead of the full casing tables
in Ada.Characters.Handling
.
Next: GNAT.CGI.Cookie (g-cgicoo.ads), Previous: GNAT.Case_Util (g-casuti.ads), Up: The GNAT Library [Contents][Index]
GNAT.CGI
(g-cgi.ads)This is a package for interfacing a GNAT program with a Web server via the Common Gateway Interface (CGI). Basically this package parses the CGI parameters, which are a set of key/value pairs sent by the Web server. It builds a table whose index is the key and provides some services to deal with this table.
Next: GNAT.CGI.Debug (g-cgideb.ads), Previous: GNAT.CGI (g-cgi.ads), Up: The GNAT Library [Contents][Index]
GNAT.CGI.Cookie
(g-cgicoo.ads)This is a package to interface a GNAT program with a Web server via the Common Gateway Interface (CGI). It exports services to deal with Web cookies (piece of information kept in the Web client software).
Next: GNAT.Command_Line (g-comlin.ads), Previous: GNAT.CGI.Cookie (g-cgicoo.ads), Up: The GNAT Library [Contents][Index]
GNAT.CGI.Debug
(g-cgideb.ads)This is a package to help debugging CGI (Common Gateway Interface) programs written in Ada.
Next: GNAT.Compiler_Version (g-comver.ads), Previous: GNAT.CGI.Debug (g-cgideb.ads), Up: The GNAT Library [Contents][Index]
GNAT.Command_Line
(g-comlin.ads)Provides a high level interface to Ada.Command_Line
facilities,
including the ability to scan for named switches with optional parameters
and expand file names using wild card notations.
Next: GNAT.Ctrl_C (g-ctrl_c.ads), Previous: GNAT.Command_Line (g-comlin.ads), Up: The GNAT Library [Contents][Index]
GNAT.Compiler_Version
(g-comver.ads)Provides a routine for obtaining the version of the compiler used to compile the program. More accurately this is the version of the binder used to bind the program (this will normally be the same as the version of the compiler if a consistent tool set is used to compile all units of a partition).
Next: GNAT.Current_Exception (g-curexc.ads), Previous: GNAT.Compiler_Version (g-comver.ads), Up: The GNAT Library [Contents][Index]
GNAT.Ctrl_C
(g-ctrl_c.ads)Provides a simple interface to handle Ctrl-C keyboard events.
Next: GNAT.Debug_Pools (g-debpoo.ads), Previous: GNAT.Ctrl_C (g-ctrl_c.ads), Up: The GNAT Library [Contents][Index]
GNAT.Current_Exception
(g-curexc.ads)Provides access to information on the current exception that has been raised without the need for using the Ada 95 / Ada 2005 exception choice parameter specification syntax. This is particularly useful in simulating typical facilities for obtaining information about exceptions provided by Ada 83 compilers.
Next: GNAT.Debug_Utilities (g-debuti.ads), Previous: GNAT.Current_Exception (g-curexc.ads), Up: The GNAT Library [Contents][Index]
GNAT.Debug_Pools
(g-debpoo.ads)Provide a debugging storage pools that helps tracking memory corruption problems. See The GNAT Debug Pool Facility in GNAT User’s Guide.
Next: GNAT.Decode_String (g-decstr.ads), Previous: GNAT.Debug_Pools (g-debpoo.ads), Up: The GNAT Library [Contents][Index]
GNAT.Debug_Utilities
(g-debuti.ads)Provides a few useful utilities for debugging purposes, including conversion to and from string images of address values. Supports both C and Ada formats for hexadecimal literals.
Next: GNAT.Decode_UTF8_String (g-deutst.ads), Previous: GNAT.Debug_Utilities (g-debuti.ads), Up: The GNAT Library [Contents][Index]
GNAT.Decode_String
(g-decstr.ads)A generic package providing routines for decoding wide character and wide wide character strings encoded as sequences of 8-bit characters using a specified encoding method. Includes validation routines, and also routines for stepping to next or previous encoded character in an encoded string. Useful in conjunction with Unicode character coding. Note there is a preinstantiation for UTF-8. See next entry.
Next: GNAT.Directory_Operations (g-dirope.ads), Previous: GNAT.Decode_String (g-decstr.ads), Up: The GNAT Library [Contents][Index]
GNAT.Decode_UTF8_String
(g-deutst.ads)A preinstantiation of GNAT.Decode_Strings for UTF-8 encoding.
Next: GNAT.Directory_Operations.Iteration (g-diopit.ads), Previous: GNAT.Decode_UTF8_String (g-deutst.ads), Up: The GNAT Library [Contents][Index]
GNAT.Directory_Operations
(g-dirope.ads)Provides a set of routines for manipulating directories, including changing the current directory, making new directories, and scanning the files in a directory.
Next: GNAT.Dynamic_HTables (g-dynhta.ads), Previous: GNAT.Directory_Operations (g-dirope.ads), Up: The GNAT Library [Contents][Index]
GNAT.Directory_Operations.Iteration
(g-diopit.ads)A child unit of GNAT.Directory_Operations providing additional operations for iterating through directories.
Next: GNAT.Dynamic_Tables (g-dyntab.ads), Previous: GNAT.Directory_Operations.Iteration (g-diopit.ads), Up: The GNAT Library [Contents][Index]
GNAT.Dynamic_HTables
(g-dynhta.ads)A generic implementation of hash tables that can be used to hash arbitrary data. Provided in two forms, a simple form with built in hash functions, and a more complex form in which the hash function is supplied.
This package provides a facility similar to that of GNAT.HTable
,
except that this package declares a type that can be used to define
dynamic instances of the hash table, while an instantiation of
GNAT.HTable
creates a single instance of the hash table.
Next: GNAT.Encode_String (g-encstr.ads), Previous: GNAT.Dynamic_HTables (g-dynhta.ads), Up: The GNAT Library [Contents][Index]
GNAT.Dynamic_Tables
(g-dyntab.ads)A generic package providing a single dimension array abstraction where the length of the array can be dynamically modified.
This package provides a facility similar to that of GNAT.Table
,
except that this package declares a type that can be used to define
dynamic instances of the table, while an instantiation of
GNAT.Table
creates a single instance of the table type.
Next: GNAT.Encode_UTF8_String (g-enutst.ads), Previous: GNAT.Dynamic_Tables (g-dyntab.ads), Up: The GNAT Library [Contents][Index]
GNAT.Encode_String
(g-encstr.ads)A generic package providing routines for encoding wide character and wide wide character strings as sequences of 8-bit characters using a specified encoding method. Useful in conjunction with Unicode character coding. Note there is a preinstantiation for UTF-8. See next entry.
Next: GNAT.Exception_Actions (g-excact.ads), Previous: GNAT.Encode_String (g-encstr.ads), Up: The GNAT Library [Contents][Index]
GNAT.Encode_UTF8_String
(g-enutst.ads)A preinstantiation of GNAT.Encode_Strings for UTF-8 encoding.
Next: GNAT.Exception_Traces (g-exctra.ads), Previous: GNAT.Encode_UTF8_String (g-enutst.ads), Up: The GNAT Library [Contents][Index]
GNAT.Exception_Actions
(g-excact.ads)Provides callbacks when an exception is raised. Callbacks can be registered for specific exceptions, or when any exception is raised. This can be used for instance to force a core dump to ease debugging.
Next: GNAT.Exceptions (g-except.ads), Previous: GNAT.Exception_Actions (g-excact.ads), Up: The GNAT Library [Contents][Index]
GNAT.Exception_Traces
(g-exctra.ads)Provides an interface allowing to control automatic output upon exception occurrences.
Next: GNAT.Expect (g-expect.ads), Previous: GNAT.Exception_Traces (g-exctra.ads), Up: The GNAT Library [Contents][Index]
GNAT.Exceptions
(g-expect.ads)Normally it is not possible to raise an exception with
a message from a subprogram in a pure package, since the
necessary types and subprograms are in Ada.Exceptions
which is not a pure unit. GNAT.Exceptions
provides a
facility for getting around this limitation for a few
predefined exceptions, and for example allow raising
Constraint_Error
with a message from a pure subprogram.
Next: GNAT.Expect.TTY (g-exptty.ads), Previous: GNAT.Exceptions (g-except.ads), Up: The GNAT Library [Contents][Index]
GNAT.Expect
(g-expect.ads)Provides a set of subprograms similar to what is available
with the standard Tcl Expect tool.
It allows you to easily spawn and communicate with an external process.
You can send commands or inputs to the process, and compare the output
with some expected regular expression. Currently GNAT.Expect
is implemented on all native GNAT ports except for OpenVMS.
It is not implemented for cross ports, and in particular is not
implemented for VxWorks or LynxOS.
Next: GNAT.Float_Control (g-flocon.ads), Previous: GNAT.Expect (g-expect.ads), Up: The GNAT Library [Contents][Index]
GNAT.Expect.TTY
(g-exptty.ads)As GNAT.Expect but using pseudo-terminal.
Currently GNAT.Expect.TTY
is implemented on all native GNAT
ports except for OpenVMS. It is not implemented for cross ports, and
in particular is not implemented for VxWorks or LynxOS.
Next: GNAT.Heap_Sort (g-heasor.ads), Previous: GNAT.Expect.TTY (g-exptty.ads), Up: The GNAT Library [Contents][Index]
GNAT.Float_Control
(g-flocon.ads)Provides an interface for resetting the floating-point processor into the mode required for correct semantic operation in Ada. Some third party library calls may cause this mode to be modified, and the Reset procedure in this package can be used to reestablish the required mode.
Next: GNAT.Heap_Sort_A (g-hesora.ads), Previous: GNAT.Float_Control (g-flocon.ads), Up: The GNAT Library [Contents][Index]
GNAT.Heap_Sort
(g-heasor.ads)Provides a general implementation of heap sort usable for sorting arbitrary data items. Exchange and comparison procedures are provided by passing access-to-procedure values. The algorithm used is a modified heap sort that performs approximately N*log(N) comparisons in the worst case.
Next: GNAT.Heap_Sort_G (g-hesorg.ads), Previous: GNAT.Heap_Sort (g-heasor.ads), Up: The GNAT Library [Contents][Index]
GNAT.Heap_Sort_A
(g-hesora.ads)Provides a general implementation of heap sort usable for sorting arbitrary
data items. Move and comparison procedures are provided by passing
access-to-procedure values. The algorithm used is a modified heap sort
that performs approximately N*log(N) comparisons in the worst case.
This differs from GNAT.Heap_Sort
in having a less convenient
interface, but may be slightly more efficient.
Next: GNAT.HTable (g-htable.ads), Previous: GNAT.Heap_Sort_A (g-hesora.ads), Up: The GNAT Library [Contents][Index]
GNAT.Heap_Sort_G
(g-hesorg.ads)Similar to Heap_Sort_A
except that the move and sorting procedures
are provided as generic parameters, this improves efficiency, especially
if the procedures can be inlined, at the expense of duplicating code for
multiple instantiations.
Next: GNAT.IO (g-io.ads), Previous: GNAT.Heap_Sort_G (g-hesorg.ads), Up: The GNAT Library [Contents][Index]
GNAT.HTable
(g-htable.ads)A generic implementation of hash tables that can be used to hash arbitrary data. Provides two approaches, one a simple static approach, and the other allowing arbitrary dynamic hash tables.
Next: GNAT.IO_Aux (g-io_aux.ads), Previous: GNAT.HTable (g-htable.ads), Up: The GNAT Library [Contents][Index]
GNAT.IO
(g-io.ads)A simple preelaborable input-output package that provides a subset of simple Text_IO functions for reading characters and strings from Standard_Input, and writing characters, strings and integers to either Standard_Output or Standard_Error.
Next: GNAT.Lock_Files (g-locfil.ads), Previous: GNAT.IO (g-io.ads), Up: The GNAT Library [Contents][Index]
GNAT.IO_Aux
(g-io_aux.ads)Provides some auxiliary functions for use with Text_IO, including a test for whether a file exists, and functions for reading a line of text.
Next: GNAT.MBBS_Discrete_Random (g-mbdira.ads), Previous: GNAT.IO_Aux (g-io_aux.ads), Up: The GNAT Library [Contents][Index]
GNAT.Lock_Files
(g-locfil.ads)Provides a general interface for using files as locks. Can be used for providing program level synchronization.
Next: GNAT.MBBS_Float_Random (g-mbflra.ads), Previous: GNAT.Lock_Files (g-locfil.ads), Up: The GNAT Library [Contents][Index]
GNAT.MBBS_Discrete_Random
(g-mbdira.ads)The original implementation of Ada.Numerics.Discrete_Random
. Uses
a modified version of the Blum-Blum-Shub generator.
Next: GNAT.MD5 (g-md5.ads), Previous: GNAT.MBBS_Discrete_Random (g-mbdira.ads), Up: The GNAT Library [Contents][Index]
GNAT.MBBS_Float_Random
(g-mbflra.ads)The original implementation of Ada.Numerics.Float_Random
. Uses
a modified version of the Blum-Blum-Shub generator.
Next: GNAT.Memory_Dump (g-memdum.ads), Previous: GNAT.MBBS_Float_Random (g-mbflra.ads), Up: The GNAT Library [Contents][Index]
GNAT.MD5
(g-md5.ads)Implements the MD5 Message-Digest Algorithm as described in RFC 1321.
Next: GNAT.Most_Recent_Exception (g-moreex.ads), Previous: GNAT.MD5 (g-md5.ads), Up: The GNAT Library [Contents][Index]
GNAT.Memory_Dump
(g-memdum.ads)Provides a convenient routine for dumping raw memory to either the standard output or standard error files. Uses GNAT.IO for actual output.
Next: GNAT.OS_Lib (g-os_lib.ads), Previous: GNAT.Memory_Dump (g-memdum.ads), Up: The GNAT Library [Contents][Index]
GNAT.Most_Recent_Exception
(g-moreex.ads)Provides access to the most recently raised exception. Can be used for various logging purposes, including duplicating functionality of some Ada 83 implementation dependent extensions.
Next: GNAT.Perfect_Hash_Generators (g-pehage.ads), Previous: GNAT.Most_Recent_Exception (g-moreex.ads), Up: The GNAT Library [Contents][Index]
GNAT.OS_Lib
(g-os_lib.ads)Provides a range of target independent operating system interface functions, including time/date management, file operations, subprocess management, including a portable spawn procedure, and access to environment variables and error return codes.
Next: GNAT.Random_Numbers (g-rannum.ads), Previous: GNAT.OS_Lib (g-os_lib.ads), Up: The GNAT Library [Contents][Index]
GNAT.Perfect_Hash_Generators
(g-pehage.ads)Provides a generator of static minimal perfect hash functions. No collisions occur and each item can be retrieved from the table in one probe (perfect property). The hash table size corresponds to the exact size of the key set and no larger (minimal property). The key set has to be know in advance (static property). The hash functions are also order preserving. If w2 is inserted after w1 in the generator, their hashcode are in the same order. These hashing functions are very convenient for use with realtime applications.
Next: GNAT.Regexp (g-regexp.ads), Previous: GNAT.Perfect_Hash_Generators (g-pehage.ads), Up: The GNAT Library [Contents][Index]
GNAT.Random_Numbers
(g-rannum.ads)Provides random number capabilities which extend those available in the standard Ada library and are more convenient to use.
Next: GNAT.Registry (g-regist.ads), Previous: GNAT.Random_Numbers (g-rannum.ads), Up: The GNAT Library [Contents][Index]
GNAT.Regexp
(g-regexp.ads)A simple implementation of regular expressions, using a subset of regular expression syntax copied from familiar Unix style utilities. This is the simples of the three pattern matching packages provided, and is particularly suitable for “file globbing” applications.
Next: GNAT.Regpat (g-regpat.ads), Previous: GNAT.Regexp (g-regexp.ads), Up: The GNAT Library [Contents][Index]
GNAT.Registry
(g-regist.ads)This is a high level binding to the Windows registry. It is possible to do simple things like reading a key value, creating a new key. For full registry API, but at a lower level of abstraction, refer to the Win32.Winreg package provided with the Win32Ada binding
Next: GNAT.Secondary_Stack_Info (g-sestin.ads), Previous: GNAT.Registry (g-regist.ads), Up: The GNAT Library [Contents][Index]
GNAT.Regpat
(g-regpat.ads)A complete implementation of Unix-style regular expression matching, copied from the original V7 style regular expression library written in C by Henry Spencer (and binary compatible with this C library).
Next: GNAT.Semaphores (g-semaph.ads), Previous: GNAT.Regpat (g-regpat.ads), Up: The GNAT Library [Contents][Index]
GNAT.Secondary_Stack_Info
(g-sestin.ads)Provide the capability to query the high water mark of the current task’s secondary stack.
Next: GNAT.Serial_Communications (g-sercom.ads), Previous: GNAT.Secondary_Stack_Info (g-sestin.ads), Up: The GNAT Library [Contents][Index]
GNAT.Semaphores
(g-semaph.ads)Provides classic counting and binary semaphores using protected types.
Next: GNAT.SHA1 (g-sha1.ads), Previous: GNAT.Semaphores (g-semaph.ads), Up: The GNAT Library [Contents][Index]
GNAT.Serial_Communications
(g-sercom.ads)Provides a simple interface to send and receive data over a serial port. This is only supported on GNU/Linux and Windows.
Next: GNAT.SHA224 (g-sha224.ads), Previous: GNAT.Serial_Communications (g-sercom.ads), Up: The GNAT Library [Contents][Index]
GNAT.SHA1
(g-sha1.ads)Implements the SHA-1 Secure Hash Algorithm as described in FIPS PUB 180-3 and RFC 3174.
Next: GNAT.SHA256 (g-sha256.ads), Previous: GNAT.SHA1 (g-sha1.ads), Up: The GNAT Library [Contents][Index]
GNAT.SHA224
(g-sha224.ads)Implements the SHA-224 Secure Hash Algorithm as described in FIPS PUB 180-3.
Next: GNAT.SHA384 (g-sha384.ads), Previous: GNAT.SHA224 (g-sha224.ads), Up: The GNAT Library [Contents][Index]
GNAT.SHA256
(g-sha256.ads)Implements the SHA-256 Secure Hash Algorithm as described in FIPS PUB 180-3.
Next: GNAT.SHA512 (g-sha512.ads), Previous: GNAT.SHA256 (g-sha256.ads), Up: The GNAT Library [Contents][Index]
GNAT.SHA384
(g-sha384.ads)Implements the SHA-384 Secure Hash Algorithm as described in FIPS PUB 180-3.
Next: GNAT.Signals (g-signal.ads), Previous: GNAT.SHA384 (g-sha384.ads), Up: The GNAT Library [Contents][Index]
GNAT.SHA512
(g-sha512.ads)Implements the SHA-512 Secure Hash Algorithm as described in FIPS PUB 180-3.
Next: GNAT.Sockets (g-socket.ads), Previous: GNAT.SHA512 (g-sha512.ads), Up: The GNAT Library [Contents][Index]
GNAT.Signals
(g-signal.ads)Provides the ability to manipulate the blocked status of signals on supported targets.
Next: GNAT.Source_Info (g-souinf.ads), Previous: GNAT.Signals (g-signal.ads), Up: The GNAT Library [Contents][Index]
GNAT.Sockets
(g-socket.ads)A high level and portable interface to develop sockets based applications.
This package is based on the sockets thin binding found in
GNAT.Sockets.Thin
. Currently GNAT.Sockets
is implemented
on all native GNAT ports except for OpenVMS. It is not implemented
for the LynxOS cross port.
Next: GNAT.Spelling_Checker (g-speche.ads), Previous: GNAT.Sockets (g-socket.ads), Up: The GNAT Library [Contents][Index]
GNAT.Source_Info
(g-souinf.ads)Provides subprograms that give access to source code information known at compile time, such as the current file name and line number.
Next: GNAT.Spelling_Checker_Generic (g-spchge.ads), Previous: GNAT.Source_Info (g-souinf.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spelling_Checker
(g-speche.ads)Provides a function for determining whether one string is a plausible near misspelling of another string.
Next: GNAT.Spitbol.Patterns (g-spipat.ads), Previous: GNAT.Spelling_Checker (g-speche.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spelling_Checker_Generic
(g-spchge.ads)Provides a generic function that can be instantiated with a string type for determining whether one string is a plausible near misspelling of another string.
Next: GNAT.Spitbol (g-spitbo.ads), Previous: GNAT.Spelling_Checker_Generic (g-spchge.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spitbol.Patterns
(g-spipat.ads)A complete implementation of SNOBOL4 style pattern matching. This is the most elaborate of the pattern matching packages provided. It fully duplicates the SNOBOL4 dynamic pattern construction and matching capabilities, using the efficient algorithm developed by Robert Dewar for the SPITBOL system.
Next: GNAT.Spitbol.Table_Boolean (g-sptabo.ads), Previous: GNAT.Spitbol.Patterns (g-spipat.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spitbol
(g-spitbo.ads)The top level package of the collection of SPITBOL-style functionality, this package provides basic SNOBOL4 string manipulation functions, such as Pad, Reverse, Trim, Substr capability, as well as a generic table function useful for constructing arbitrary mappings from strings in the style of the SNOBOL4 TABLE function.
Next: GNAT.Spitbol.Table_Integer (g-sptain.ads), Previous: GNAT.Spitbol (g-spitbo.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spitbol.Table_Boolean
(g-sptabo.ads)A library level of instantiation of GNAT.Spitbol.Patterns.Table
for type Standard.Boolean
, giving an implementation of sets of
string values.
Next: GNAT.Spitbol.Table_VString (g-sptavs.ads), Previous: GNAT.Spitbol.Table_Boolean (g-sptabo.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spitbol.Table_Integer
(g-sptain.ads)A library level of instantiation of GNAT.Spitbol.Patterns.Table
for type Standard.Integer
, giving an implementation of maps
from string to integer values.
Next: GNAT.SSE (g-sse.ads), Previous: GNAT.Spitbol.Table_Integer (g-sptain.ads), Up: The GNAT Library [Contents][Index]
GNAT.Spitbol.Table_VString
(g-sptavs.ads)A library level of instantiation of GNAT.Spitbol.Patterns.Table
for
a variable length string type, giving an implementation of general
maps from strings to strings.
Next: GNAT.SSE.Vector_Types (g-ssvety.ads), Previous: GNAT.Spitbol.Table_VString (g-sptavs.ads), Up: The GNAT Library [Contents][Index]
GNAT.SSE
(g-sse.ads)Root of a set of units aimed at offering Ada bindings to a subset of the Intel(r) Streaming SIMD Extensions with GNAT on the x86 family of targets. It exposes vector component types together with a general introduction to the binding contents and use.
Next: GNAT.Strings (g-string.ads), Previous: GNAT.SSE (g-sse.ads), Up: The GNAT Library [Contents][Index]
GNAT.SSE.Vector_Types
(g-ssvety.ads)SSE vector types for use with SSE related intrinsics.
Next: GNAT.String_Split (g-strspl.ads), Previous: GNAT.SSE.Vector_Types (g-ssvety.ads), Up: The GNAT Library [Contents][Index]
GNAT.Strings
(g-string.ads)Common String access types and related subprograms. Basically it defines a string access and an array of string access types.
Next: GNAT.Table (g-table.ads), Previous: GNAT.Strings (g-string.ads), Up: The GNAT Library [Contents][Index]
GNAT.String_Split
(g-strspl.ads)Useful string manipulation routines: given a set of separators, split
a string wherever the separators appear, and provide direct access
to the resulting slices. This package is instantiated from
GNAT.Array_Split
.
Next: GNAT.Task_Lock (g-tasloc.ads), Previous: GNAT.String_Split (g-strspl.ads), Up: The GNAT Library [Contents][Index]
GNAT.Table
(g-table.ads)A generic package providing a single dimension array abstraction where the length of the array can be dynamically modified.
This package provides a facility similar to that of GNAT.Dynamic_Tables
,
except that this package declares a single instance of the table type,
while an instantiation of GNAT.Dynamic_Tables
creates a type that can be
used to define dynamic instances of the table.
Next: GNAT.Time_Stamp (g-timsta.ads), Previous: GNAT.Table (g-table.ads), Up: The GNAT Library [Contents][Index]
GNAT.Task_Lock
(g-tasloc.ads)A very simple facility for locking and unlocking sections of code using a single global task lock. Appropriate for use in situations where contention between tasks is very rarely expected.
Next: GNAT.Threads (g-thread.ads), Previous: GNAT.Task_Lock (g-tasloc.ads), Up: The GNAT Library [Contents][Index]
GNAT.Time_Stamp
(g-timsta.ads)Provides a simple function that returns a string YYYY-MM-DD HH:MM:SS.SS that represents the current date and time in ISO 8601 format. This is a very simple routine with minimal code and there are no dependencies on any other unit.
Next: GNAT.Traceback (g-traceb.ads), Previous: GNAT.Time_Stamp (g-timsta.ads), Up: The GNAT Library [Contents][Index]
GNAT.Threads
(g-thread.ads)Provides facilities for dealing with foreign threads which need to be known by the GNAT run-time system. Consult the documentation of this package for further details if your program has threads that are created by a non-Ada environment which then accesses Ada code.
Next: GNAT.Traceback.Symbolic (g-trasym.ads), Previous: GNAT.Threads (g-thread.ads), Up: The GNAT Library [Contents][Index]
GNAT.Traceback
(g-traceb.ads)Provides a facility for obtaining non-symbolic traceback information, useful in various debugging situations.
Next: GNAT.UTF_32 (g-utf_32.ads), Previous: GNAT.Traceback (g-traceb.ads), Up: The GNAT Library [Contents][Index]
GNAT.Traceback.Symbolic
(g-trasym.ads)Next: GNAT.UTF_32_Spelling_Checker (g-u3spch.ads), Previous: GNAT.Traceback.Symbolic (g-trasym.ads), Up: The GNAT Library [Contents][Index]
GNAT.UTF_32
(g-table.ads)This is a package intended to be used in conjunction with the
Wide_Character
type in Ada 95 and the
Wide_Wide_Character
type in Ada 2005 (available
in GNAT
in Ada 2005 mode). This package contains
Unicode categorization routines, as well as lexical
categorization routines corresponding to the Ada 2005
lexical rules for identifiers and strings, and also a
lower case to upper case fold routine corresponding to
the Ada 2005 rules for identifier equivalence.
Next: GNAT.Wide_Spelling_Checker (g-wispch.ads), Previous: GNAT.UTF_32 (g-utf_32.ads), Up: The GNAT Library [Contents][Index]
GNAT.Wide_Spelling_Checker
(g-u3spch.ads)Provides a function for determining whether one wide wide string is a plausible near misspelling of another wide wide string, where the strings are represented using the UTF_32_String type defined in System.Wch_Cnv.
Next: GNAT.Wide_String_Split (g-wistsp.ads), Previous: GNAT.UTF_32_Spelling_Checker (g-u3spch.ads), Up: The GNAT Library [Contents][Index]
GNAT.Wide_Spelling_Checker
(g-wispch.ads)Provides a function for determining whether one wide string is a plausible near misspelling of another wide string.
Next: GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads), Previous: GNAT.Wide_Spelling_Checker (g-wispch.ads), Up: The GNAT Library [Contents][Index]
GNAT.Wide_String_Split
(g-wistsp.ads)Useful wide string manipulation routines: given a set of separators, split
a wide string wherever the separators appear, and provide direct access
to the resulting slices. This package is instantiated from
GNAT.Array_Split
.
Next: GNAT.Wide_Wide_String_Split (g-zistsp.ads), Previous: GNAT.Wide_String_Split (g-wistsp.ads), Up: The GNAT Library [Contents][Index]
GNAT.Wide_Wide_Spelling_Checker
(g-zspche.ads)Provides a function for determining whether one wide wide string is a plausible near misspelling of another wide wide string.
Next: Interfaces.C.Extensions (i-cexten.ads), Previous: GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads), Up: The GNAT Library [Contents][Index]
GNAT.Wide_Wide_String_Split
(g-zistsp.ads)Useful wide wide string manipulation routines: given a set of separators, split
a wide wide string wherever the separators appear, and provide direct access
to the resulting slices. This package is instantiated from
GNAT.Array_Split
.
Next: Interfaces.C.Streams (i-cstrea.ads), Previous: GNAT.Wide_Wide_String_Split (g-zistsp.ads), Up: The GNAT Library [Contents][Index]
Interfaces.C.Extensions
(i-cexten.ads)This package contains additional C-related definitions, intended for use with either manually or automatically generated bindings to C libraries.
Next: Interfaces.CPP (i-cpp.ads), Previous: Interfaces.C.Extensions (i-cexten.ads), Up: The GNAT Library [Contents][Index]
Interfaces.C.Streams
(i-cstrea.ads)This package is a binding for the most commonly used operations on C streams.
Next: Interfaces.Packed_Decimal (i-pacdec.ads), Previous: Interfaces.C.Streams (i-cstrea.ads), Up: The GNAT Library [Contents][Index]
Interfaces.CPP
(i-cpp.ads)This package provides facilities for use in interfacing to C++. It is primarily intended to be used in connection with automated tools for the generation of C++ interfaces.
Next: Interfaces.VxWorks (i-vxwork.ads), Previous: Interfaces.CPP (i-cpp.ads), Up: The GNAT Library [Contents][Index]
Interfaces.Packed_Decimal
(i-pacdec.ads)This package provides a set of routines for conversions to and from a packed decimal format compatible with that used on IBM mainframes.
Next: Interfaces.VxWorks.IO (i-vxwoio.ads), Previous: Interfaces.Packed_Decimal (i-pacdec.ads), Up: The GNAT Library [Contents][Index]
Interfaces.VxWorks
(i-vxwork.ads)This package provides a limited binding to the VxWorks API. In particular, it interfaces with the VxWorks hardware interrupt facilities.
Next: System.Address_Image (s-addima.ads), Previous: Interfaces.VxWorks (i-vxwork.ads), Up: The GNAT Library [Contents][Index]
Interfaces.VxWorks.IO
(i-vxwoio.ads)This package provides a binding to the ioctl (IO/Control) function of VxWorks, defining a set of option values and function codes. A particular use of this package is to enable the use of Get_Immediate under VxWorks.
Next: System.Assertions (s-assert.ads), Previous: Interfaces.VxWorks.IO (i-vxwoio.ads), Up: The GNAT Library [Contents][Index]
System.Address_Image
(s-addima.ads)This function provides a useful debugging function that gives an (implementation dependent) string which identifies an address.
Next: System.Memory (s-memory.ads), Previous: System.Address_Image (s-addima.ads), Up: The GNAT Library [Contents][Index]
System.Assertions
(s-assert.ads)This package provides the declaration of the exception raised by an run-time assertion failure, as well as the routine that is used internally to raise this assertion.
Next: System.Partition_Interface (s-parint.ads), Previous: System.Assertions (s-assert.ads), Up: The GNAT Library [Contents][Index]
System.Memory
(s-memory.ads)This package provides the interface to the low level routines used
by the generated code for allocation and freeing storage for the
default storage pool (analogous to the C routines malloc and free.
It also provides a reallocation interface analogous to the C routine
realloc. The body of this unit may be modified to provide alternative
allocation mechanisms for the default pool, and in addition, direct
calls to this unit may be made for low level allocation uses (for
example see the body of GNAT.Tables
).
Next: System.Pool_Global (s-pooglo.ads), Previous: System.Memory (s-memory.ads), Up: The GNAT Library [Contents][Index]
System.Partition_Interface
(s-parint.ads)This package provides facilities for partition interfacing. It
is used primarily in a distribution context when using Annex E
with GLADE
.
Next: System.Pool_Local (s-pooloc.ads), Previous: System.Partition_Interface (s-parint.ads), Up: The GNAT Library [Contents][Index]
System.Pool_Global
(s-pooglo.ads)This package provides a storage pool that is equivalent to the default storage pool used for access types for which no pool is specifically declared. It uses malloc/free to allocate/free and does not attempt to do any automatic reclamation.
Next: System.Restrictions (s-restri.ads), Previous: System.Pool_Global (s-pooglo.ads), Up: The GNAT Library [Contents][Index]
System.Pool_Local
(s-pooloc.ads)This package provides a storage pool that is intended for use with locally defined access types. It uses malloc/free for allocate/free, and maintains a list of allocated blocks, so that all storage allocated for the pool can be freed automatically when the pool is finalized.
Next: System.Rident (s-rident.ads), Previous: System.Pool_Local (s-pooloc.ads), Up: The GNAT Library [Contents][Index]
System.Restrictions
(s-restri.ads)This package provides facilities for accessing at run time the status of restrictions specified at compile time for the partition. Information is available both with regard to actual restrictions specified, and with regard to compiler determined information on which restrictions are violated by one or more packages in the partition.
Next: System.Strings.Stream_Ops (s-ststop.ads), Previous: System.Restrictions (s-restri.ads), Up: The GNAT Library [Contents][Index]
System.Rident
(s-rident.ads)This package provides definitions of the restrictions
identifiers supported by GNAT, and also the format of
the restrictions provided in package System.Restrictions.
It is not normally necessary to with
this generic package
since the necessary instantiation is included in
package System.Restrictions.
Next: System.Task_Info (s-tasinf.ads), Previous: System.Rident (s-rident.ads), Up: The GNAT Library [Contents][Index]
System.Strings.Stream_Ops
(s-ststop.ads)This package provides a set of stream subprograms for standard string types. It is intended primarily to support implicit use of such subprograms when stream attributes are applied to string types, but the subprograms in this package can be used directly by application programs.
Next: System.Wch_Cnv (s-wchcnv.ads), Previous: System.Strings.Stream_Ops (s-ststop.ads), Up: The GNAT Library [Contents][Index]
System.Task_Info
(s-tasinf.ads)This package provides target dependent functionality that is used
to support the Task_Info
pragma
Next: System.Wch_Con (s-wchcon.ads), Previous: System.Task_Info (s-tasinf.ads), Up: The GNAT Library [Contents][Index]
System.Wch_Cnv
(s-wchcnv.ads)This package provides routines for converting between
wide and wide wide characters and a representation as a value of type
Standard.String
, using a specified wide character
encoding method. It uses definitions in
package System.Wch_Con
.
Next: Text_IO Stream Pointer Positioning, Previous: System.Wch_Cnv (s-wchcnv.ads), Up: The GNAT Library [Contents][Index]
System.Wch_Con
(s-wchcon.ads)This package provides definitions and descriptions of
the various methods used for encoding wide characters
in ordinary strings. These definitions are used by
the package System.Wch_Cnv
.
Next: Specialized Needs Annexes, Previous: The GNAT Library, Up: Top [Contents][Index]
The facilities in annex B of the Ada Reference Manual are fully implemented in GNAT, and in addition, a full interface to C++ is provided.
• Interfacing to C: | ||
• Interfacing to C++: | ||
• Interfacing to COBOL: | ||
• Interfacing to Fortran: | ||
• Interfacing to non-GNAT Ada code: |
Next: Interfacing to C++, Previous: Wide_Wide_Text_IO Reading and Writing Non-Regular Files, Up: Interfacing to Other Languages [Contents][Index]
Interfacing to C with GNAT can use one of two approaches:
Interfaces.C
may be used.
Pragma Convention C
may be applied to Ada types, but mostly has no
effect, since this is the default. The following table shows the
correspondence between Ada scalar types and the corresponding C types.
Integer
int
Short_Integer
short
Short_Short_Integer
signed char
Long_Integer
long
Long_Long_Integer
long long
Short_Float
float
Float
float
Long_Float
double
Long_Long_Float
This is the longest floating-point type supported by the hardware.
Additionally, there are the following general correspondences between Ada and C types:
Convention C
is specified, which causes them to have int
length. Without pragma Convention C
, Ada enumeration types map to
8, 16, or 32 bits (i.e. C types signed char
, short
,
int
, respectively) depending on the number of values passed.
This is the only case in which pragma Convention C
affects the
representation of an Ada type.
type'Size
value in Ada.
Next: Interfacing to COBOL, Previous: Interfacing to C, Up: Interfacing to Other Languages [Contents][Index]
The interface to C++ makes use of the following pragmas, which are primarily intended to be constructed automatically using a binding generator tool, although it is possible to construct them by hand.
Using these pragmas it is possible to achieve complete inter-operability between Ada tagged types and C++ class definitions. See Implementation Defined Pragmas, for more details.
pragma CPP_Class ([Entity =>] LOCAL_NAME)
The argument denotes an entity in the current declarative region that is declared as a tagged or untagged record type. It indicates that the type corresponds to an externally declared C++ class type, and is to be laid out the same way that C++ would lay out the type.
Note: Pragma CPP_Class
is currently obsolete. It is supported
for backward compatibility but its functionality is available
using pragma Import
with Convention
= CPP
.
pragma CPP_Constructor ([Entity =>] LOCAL_NAME)
This pragma identifies an imported function (imported in the usual way
with pragma Import
) as corresponding to a C++ constructor.
A few restrictions are placed on the use of the Access
attribute
in conjunction with subprograms subject to convention CPP
: the
attribute may be used neither on primitive operations of a tagged
record type with convention CPP
, imported or not, nor on
subprograms imported with pragma CPP_Constructor
.
In addition, C++ exceptions are propagated and can be handled in an
others
choice of an exception handler. The corresponding Ada
occurrence has no message, and the simple name of the exception identity
contains ‘Foreign_Exception’. Finalization and awaiting dependent
tasks works properly when such foreign exceptions are propagated.
Next: Interfacing to Fortran, Previous: Interfacing to C++, Up: Interfacing to Other Languages [Contents][Index]
Interfacing to COBOL is achieved as described in section B.4 of the Ada Reference Manual.
Next: Interfacing to non-GNAT Ada code, Previous: Interfacing to COBOL, Up: Interfacing to Other Languages [Contents][Index]
Interfacing to Fortran is achieved as described in section B.5 of the
Ada Reference Manual. The pragma Convention Fortran
, applied to a
multi-dimensional array causes the array to be stored in column-major
order as required for convenient interface to Fortran.
Next: Machine Code Insertions, Previous: Interfacing to Fortran, Up: Interfacing to Other Languages [Contents][Index]
It is possible to specify the convention Ada
in a pragma
Import
or pragma Export
. However this refers to
the calling conventions used by GNAT, which may or may not be
similar enough to those used by some other Ada 83 / Ada 95 / Ada 2005
compiler to allow interoperation.
If arguments types are kept simple, and if the foreign compiler generally follows system calling conventions, then it may be possible to integrate files compiled by other Ada compilers, provided that the elaboration issues are adequately addressed (for example by eliminating the need for any load time elaboration).
In particular, GNAT running on VMS is designed to be highly compatible with the DEC Ada 83 compiler, so this is one case in which it is possible to import foreign units of this type, provided that the data items passed are restricted to simple scalar values or simple record types without variants, or simple array types with fixed bounds.
Next: Implementation of Specific Ada Features, Previous: Interfacing to Other Languages, Up: Top [Contents][Index]
Ada 95 and Ada 2005 define a number of Specialized Needs Annexes, which are not required in all implementations. However, as described in this chapter, GNAT implements all of these annexes:
The Systems Programming Annex is fully implemented.
The Real-Time Systems Annex is fully implemented.
Stub generation is fully implemented in the GNAT compiler. In addition, a complete compatible PCS is available as part of the GLADE system, a separate product. When the two products are used in conjunction, this annex is fully implemented.
The Information Systems annex is fully implemented.
The Numerics Annex is fully implemented.
The Safety and Security Annex (termed the High-Integrity Systems Annex in Ada 2005) is fully implemented.
Next: Implementation of Ada 2012 Features, Previous: Specialized Needs Annexes, Up: Top [Contents][Index]
This chapter describes the GNAT implementation of several Ada language facilities.
Next: GNAT Implementation of Tasking, Previous: Interfacing to non-GNAT Ada code, Up: Implementation of Specific Ada Features [Contents][Index]
Package Machine_Code
provides machine code support as described
in the Ada Reference Manual in two separate forms:
The two features are similar, and both are closely related to the mechanism provided by the asm instruction in the GNU C compiler. Full understanding and use of the facilities in this package requires understanding the asm instruction, see Assembler Instructions with C Expression Operands in Using the GNU Compiler Collection (GCC).
Calls to the function Asm
and the procedure Asm
have identical
semantic restrictions and effects as described below. Both are provided so
that the procedure call can be used as a statement, and the function call
can be used to form a code_statement.
The first example given in the GCC documentation is the C asm
instruction:
asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
The equivalent can be written for GNAT as:
Asm ("fsinx %1 %0", My_Float'Asm_Output ("=f", result), My_Float'Asm_Input ("f", angle));
The first argument to Asm
is the assembler template, and is
identical to what is used in GNU C. This string must be a static
expression. The second argument is the output operand list. It is
either a single Asm_Output
attribute reference, or a list of such
references enclosed in parentheses (technically an array aggregate of
such references).
The Asm_Output
attribute denotes a function that takes two
parameters. The first is a string, the second is the name of a variable
of the type designated by the attribute prefix. The first (string)
argument is required to be a static expression and designates the
constraint for the parameter (e.g. what kind of register is
required). The second argument is the variable to be updated with the
result. The possible values for constraint are the same as those used in
the RTL, and are dependent on the configuration file used to build the
GCC back end. If there are no output operands, then this argument may
either be omitted, or explicitly given as No_Output_Operands
.
The second argument of my_float'Asm_Output
functions as
though it were an out
parameter, which is a little curious, but
all names have the form of expressions, so there is no syntactic
irregularity, even though normally functions would not be permitted
out
parameters. The third argument is the list of input
operands. It is either a single Asm_Input
attribute reference, or
a list of such references enclosed in parentheses (technically an array
aggregate of such references).
The Asm_Input
attribute denotes a function that takes two
parameters. The first is a string, the second is an expression of the
type designated by the prefix. The first (string) argument is required
to be a static expression, and is the constraint for the parameter,
(e.g. what kind of register is required). The second argument is the
value to be used as the input argument. The possible values for the
constant are the same as those used in the RTL, and are dependent on
the configuration file used to built the GCC back end.
If there are no input operands, this argument may either be omitted, or
explicitly given as No_Input_Operands
. The fourth argument, not
present in the above example, is a list of register names, called the
clobber argument. This argument, if given, must be a static string
expression, and is a space or comma separated list of names of registers
that must be considered destroyed as a result of the Asm
call. If
this argument is the null string (the default value), then the code
generator assumes that no additional registers are destroyed.
The fifth argument, not present in the above example, called the
volatile argument, is by default False
. It can be set to
the literal value True
to indicate to the code generator that all
optimizations with respect to the instruction specified should be
suppressed, and that in particular, for an instruction that has outputs,
the instruction will still be generated, even if none of the outputs are
used. See Assembler Instructions with C Expression Operands in Using the GNU Compiler Collection (GCC), for the full description.
Generally it is strongly advisable to use Volatile for any ASM statement
that is missing either input or output operands, or when two or more ASM
statements appear in sequence, to avoid unwanted optimizations. A warning
is generated if this advice is not followed.
The Asm
subprograms may be used in two ways. First the procedure
forms can be used anywhere a procedure call would be valid, and
correspond to what the RM calls “intrinsic” routines. Such calls can
be used to intersperse machine instructions with other Ada statements.
Second, the function forms, which return a dummy value of the limited
private type Asm_Insn
, can be used in code statements, and indeed
this is the only context where such calls are allowed. Code statements
appear as aggregates of the form:
Asm_Insn'(Asm (…)); Asm_Insn'(Asm_Volatile (…));
In accordance with RM rules, such code statements are allowed only within subprograms whose entire body consists of such statements. It is not permissible to intermix such statements with other Ada statements.
Typically the form using intrinsic procedure calls is more convenient
and more flexible. The code statement form is provided to meet the RM
suggestion that such a facility should be made available. The following
is the exact syntax of the call to Asm
. As usual, if named notation
is used, the arguments may be given in arbitrary order, following the
normal rules for use of positional and named arguments)
ASM_CALL ::= Asm ( [Template =>] static_string_EXPRESSION [,[Outputs =>] OUTPUT_OPERAND_LIST ] [,[Inputs =>] INPUT_OPERAND_LIST ] [,[Clobber =>] static_string_EXPRESSION ] [,[Volatile =>] static_boolean_EXPRESSION] ) OUTPUT_OPERAND_LIST ::= [PREFIX.]No_Output_Operands | OUTPUT_OPERAND_ATTRIBUTE | (OUTPUT_OPERAND_ATTRIBUTE {,OUTPUT_OPERAND_ATTRIBUTE}) OUTPUT_OPERAND_ATTRIBUTE ::= SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME) INPUT_OPERAND_LIST ::= [PREFIX.]No_Input_Operands | INPUT_OPERAND_ATTRIBUTE | (INPUT_OPERAND_ATTRIBUTE {,INPUT_OPERAND_ATTRIBUTE}) INPUT_OPERAND_ATTRIBUTE ::= SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
The identifiers No_Input_Operands
and No_Output_Operands
are declared in the package Machine_Code
and must be referenced
according to normal visibility rules. In particular if there is no
use
clause for this package, then appropriate package name
qualification is required.
Next: GNAT Implementation of Shared Passive Packages, Previous: Machine Code Insertions, Up: Implementation of Specific Ada Features [Contents][Index]
This chapter outlines the basic GNAT approach to tasking (in particular, a multi-layered library for portability) and discusses issues related to compliance with the Real-Time Systems Annex.
• Mapping Ada Tasks onto the Underlying Kernel Threads: | ||
• Ensuring Compliance with the Real-Time Annex: |
Next: Ensuring Compliance with the Real-Time Annex, Up: GNAT Implementation of Tasking [Contents][Index]
GNAT’s run-time support comprises two layers:
In GNAT, Ada’s tasking services rely on a platform and OS independent layer known as GNARL. This code is responsible for implementing the correct semantics of Ada’s task creation, rendezvous, protected operations etc.
GNARL decomposes Ada’s tasking semantics into simpler lower level operations such as create a thread, set the priority of a thread, yield, create a lock, lock/unlock, etc. The spec for these low-level operations constitutes GNULLI, the GNULL Interface. This interface is directly inspired from the POSIX real-time API.
If the underlying executive or OS implements the POSIX standard faithfully, the GNULL Interface maps as is to the services offered by the underlying kernel. Otherwise, some target dependent glue code maps the services offered by the underlying kernel to the semantics expected by GNARL.
Whatever the underlying OS (VxWorks, UNIX, Windows, etc.) the key point is that each Ada task is mapped on a thread in the underlying kernel. For example, in the case of VxWorks, one Ada task = one VxWorks task.
In addition Ada task priorities map onto the underlying thread priorities. Mapping Ada tasks onto the underlying kernel threads has several advantages:
Some threads libraries offer a mechanism to fork a new process, with the child process duplicating the threads from the parent. GNAT does not support this functionality when the parent contains more than one task.
Previous: Mapping Ada Tasks onto the Underlying Kernel Threads, Up: GNAT Implementation of Tasking [Contents][Index]
Although mapping Ada tasks onto the underlying threads has significant advantages, it does create some complications when it comes to respecting the scheduling semantics specified in the real-time annex (Annex D).
For instance the Annex D requirement for the FIFO_Within_Priorities
scheduling policy states:
When the active priority of a ready task that is not running changes, or the setting of its base priority takes effect, the task is removed from the ready queue for its old active priority and is added at the tail of the ready queue for its new active priority, except in the case where the active priority is lowered due to the loss of inherited priority, in which case the task is added at the head of the ready queue for its new active priority.
While most kernels do put tasks at the end of the priority queue when a task changes its priority, (which respects the main FIFO_Within_Priorities requirement), almost none keep a thread at the beginning of its priority queue when its priority drops from the loss of inherited priority.
As a result most vendors have provided incomplete Annex D implementations.
The GNAT run-time, has a nice cooperative solution to this problem which ensures that accurate FIFO_Within_Priorities semantics are respected.
The principle is as follows. When an Ada task T is about to start running, it checks whether some other Ada task R with the same priority as T has been suspended due to the loss of priority inheritance. If this is the case, T yields and is placed at the end of its priority queue. When R arrives at the front of the queue it executes.
Note that this simple scheme preserves the relative order of the tasks that were ready to execute in the priority queue where R has been placed at the end.
Next: Code Generation for Array Aggregates, Previous: GNAT Implementation of Tasking, Up: Implementation of Specific Ada Features [Contents][Index]
GNAT fully implements the pragma Shared_Passive
for
the purpose of designating shared passive packages.
This allows the use of passive partitions in the
context described in the Ada Reference Manual; i.e., for communication
between separate partitions of a distributed application using the
features in Annex E.
However, the implementation approach used by GNAT provides for more extensive usage as follows:
This allows separate programs to access the data in passive partitions, using protected objects for synchronization where needed. The only requirement is that the two programs have a common shared file system. It is even possible for programs running on different machines with different architectures (e.g. different endianness) to communicate via the data in a passive partition.
The data in a passive package can persist from one run of a program to another, so that a later program sees the final values stored by a previous run of the same program.
The implementation approach used is to store the data in files. A separate stream file is created for each object in the package, and an access to an object causes the corresponding file to be read or written.
The environment variable SHARED_MEMORY_DIRECTORY
should be
set to the directory to be used for these files.
The files in this directory
have names that correspond to their fully qualified names. For
example, if we have the package
package X is pragma Shared_Passive (X); Y : Integer; Z : Float; end X;
and the environment variable is set to /stemp/
, then the files created
will have the names:
/stemp/x.y /stemp/x.z
These files are created when a value is initially written to the object, and the files are retained until manually deleted. This provides the persistence semantics. If no file exists, it means that no partition has assigned a value to the variable; in this case the initial value declared in the package will be used. This model ensures that there are no issues in synchronizing the elaboration process, since elaboration of passive packages elaborates the initial values, but does not create the files.
The files are written using normal Stream_IO
access.
If you want to be able
to communicate between programs or partitions running on different
architectures, then you should use the XDR versions of the stream attribute
routines, since these are architecture independent.
If active synchronization is required for access to the variables in the shared passive package, then as described in the Ada Reference Manual, the package may contain protected objects used for this purpose. In this case a lock file (whose name is ___lock (three underscores) is created in the shared memory directory. This is used to provide the required locking semantics for proper protected object synchronization.
As of January 2003, GNAT supports shared passive packages on all platforms except for OpenVMS.
Next: The Size of Discriminated Records with Default Discriminants, Previous: GNAT Implementation of Shared Passive Packages, Up: Implementation of Specific Ada Features [Contents][Index]
Aggregates have a rich syntax and allow the user to specify the values of complex data structures by means of a single construct. As a result, the code generated for aggregates can be quite complex and involve loops, case statements and multiple assignments. In the simplest cases, however, the compiler will recognize aggregates whose components and constraints are fully static, and in those cases the compiler will generate little or no executable code. The following is an outline of the code that GNAT generates for various aggregate constructs. For further details, you will find it useful to examine the output produced by the -gnatG flag to see the expanded source that is input to the code generator. You may also want to examine the assembly code generated at various levels of optimization.
The code generated for aggregates depends on the context, the component values, and the type. In the context of an object declaration the code generated is generally simpler than in the case of an assignment. As a general rule, static component values and static subtypes also lead to simpler code.
Next: Constant aggregates with unconstrained nominal types, Up: Code Generation for Array Aggregates [Contents][Index]
For the declarations:
type One_Dim is array (1..10) of integer; ar0 : constant One_Dim := (1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
GNAT generates no executable code: the constant ar0 is placed in static memory. The same is true for constant aggregates with named associations:
Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1 => 1, 5 .. 10 => 0); Cr3 : constant One_Dim := (others => 7777);
The same is true for multidimensional constant arrays such as:
type two_dim is array (1..3, 1..3) of integer; Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
The same is true for arrays of one-dimensional arrays: the following are static:
type ar1b is array (1..3) of boolean; type ar_ar is array (1..3) of ar1b; None : constant ar1b := (others => false); -- fully static None2 : constant ar_ar := (1..3 => None); -- fully static
However, for multidimensional aggregates with named associations, GNAT will generate assignments and loops, even if all associations are static. The following two declarations generate a loop for the first dimension, and individual component assignments for the second dimension:
Zero1: constant two_dim := (1..3 => (1..3 => 0)); Zero2: constant two_dim := (others => (others => 0));
Next: Aggregates with static bounds, Previous: Static constant aggregates with static bounds, Up: Code Generation for Array Aggregates [Contents][Index]
In such cases the aggregate itself establishes the subtype, so that
associations with others
cannot be used. GNAT determines the
bounds for the actual subtype of the aggregate, and allocates the
aggregate statically as well. No code is generated for the following:
type One_Unc is array (natural range <>) of integer; Cr_Unc : constant One_Unc := (12,24,36);
Next: Aggregates with non-static bounds, Previous: Constant aggregates with unconstrained nominal types, Up: Code Generation for Array Aggregates [Contents][Index]
In all previous examples the aggregate was the initial (and immutable) value of a constant. If the aggregate initializes a variable, then code is generated for it as a combination of individual assignments and loops over the target object. The declarations
Cr_Var1 : One_Dim := (2, 5, 7, 11, 0, 0, 0, 0, 0, 0); Cr_Var2 : One_Dim := (others > -1);
generate the equivalent of
Cr_Var1 (1) := 2; Cr_Var1 (2) := 3; Cr_Var1 (3) := 5; Cr_Var1 (4) := 11; for I in Cr_Var2'range loop Cr_Var2 (I) := -1; end loop;
Next: Aggregates in assignment statements, Previous: Aggregates with static bounds, Up: Code Generation for Array Aggregates [Contents][Index]
If the bounds of the aggregate are not statically compatible with the bounds of the nominal subtype of the target, then constraint checks have to be generated on the bounds. For a multidimensional array, constraint checks may have to be applied to sub-arrays individually, if they do not have statically compatible subtypes.
Previous: Aggregates with non-static bounds, Up: Code Generation for Array Aggregates [Contents][Index]
In general, aggregate assignment requires the construction of a temporary, and a copy from the temporary to the target of the assignment. This is because it is not always possible to convert the assignment into a series of individual component assignments. For example, consider the simple case:
A := (A(2), A(1));
This cannot be converted into:
A(1) := A(2); A(2) := A(1);
So the aggregate has to be built first in a separate location, and then copied into the target. GNAT recognizes simple cases where this intermediate step is not required, and the assignments can be performed in place, directly into the target. The following sufficient criteria are applied:
If any of these conditions are violated, the aggregate will be built in a temporary (created either by the front-end or the code generator) and then that temporary will be copied onto the target.
Next: Strict Conformance to the Ada Reference Manual, Previous: Code Generation for Array Aggregates, Up: Implementation of Specific Ada Features [Contents][Index]
If a discriminated type T
has discriminants with default values, it is
possible to declare an object of this type without providing an explicit
constraint:
type Size is range 1..100; type Rec (D : Size := 15) is record Name : String (1..D); end T; Word : Rec;
Such an object is said to be unconstrained. The discriminant of the object can be modified by a full assignment to the object, as long as it preserves the relation between the value of the discriminant, and the value of the components that depend on it:
Word := (3, "yes"); Word := (5, "maybe"); Word := (5, "no"); -- raises Constraint_Error
In order to support this behavior efficiently, an unconstrained object is
given the maximum size that any value of the type requires. In the case
above, Word
has storage for the discriminant and for
a String
of length 100.
It is important to note that unconstrained objects do not require dynamic
allocation. It would be an improper implementation to place on the heap those
components whose size depends on discriminants. (This improper implementation
was used by some Ada83 compilers, where the Name
component above
would have
been stored as a pointer to a dynamic string). Following the principle that
dynamic storage management should never be introduced implicitly,
an Ada compiler should reserve the full size for an unconstrained declared
object, and place it on the stack.
This maximum size approach has been a source of surprise to some users, who expect the default values of the discriminants to determine the size reserved for an unconstrained object: “If the default is 15, why should the object occupy a larger size?” The answer, of course, is that the discriminant may be later modified, and its full range of values must be taken into account. This is why the declaration:
type Rec (D : Positive := 15) is record Name : String (1..D); end record; Too_Large : Rec;
is flagged by the compiler with a warning:
an attempt to create Too_Large
will raise Storage_Error
,
because the required size includes Positive'Last
bytes. As the first example indicates, the proper approach is to declare an
index type of “reasonable” range so that unconstrained objects are not too
large.
One final wrinkle: if the object is declared to be aliased
, or if it is
created in the heap by means of an allocator, then it is not
unconstrained:
it is constrained by the default values of the discriminants, and those values
cannot be modified by full assignment. This is because in the presence of
aliasing all views of the object (which may be manipulated by different tasks,
say) must be consistent, so it is imperative that the object, once created,
remain invariant.
Previous: The Size of Discriminated Records with Default Discriminants, Up: Implementation of Specific Ada Features [Contents][Index]
The dynamic semantics defined by the Ada Reference Manual impose a set of run-time checks to be generated. By default, the GNAT compiler will insert many run-time checks into the compiled code, including most of those required by the Ada Reference Manual. However, there are three checks that are not enabled in the default mode for efficiency reasons: arithmetic overflow checking for integer operations (including division by zero), checks for access before elaboration on subprogram calls, and stack overflow checking (most operating systems do not perform this check by default).
Strict conformance to the Ada Reference Manual can be achieved by adding three compiler options for overflow checking for integer operations (-gnato), dynamic checks for access-before-elaboration on subprogram calls and generic instantiations (-gnatE), and stack overflow checking (-fstack-check).
Note that the result of a floating point arithmetic operation in overflow and
invalid situations, when the Machine_Overflows
attribute of the result
type is False
, is to generate IEEE NaN and infinite values. This is the
case for machines compliant with the IEEE floating-point standard, but on
machines that are not fully compliant with this standard, such as Alpha, the
-mieee compiler flag must be used for achieving IEEE confirming
behavior (although at the cost of a significant performance penalty), so
infinite and NaN values are properly generated.
Next: Obsolescent Features, Previous: Implementation of Specific Ada Features, Up: Top [Contents][Index]
This chapter contains a complete list of Ada 2012 features that have been
implemented as of GNAT version 6.4. Generally, these features are only
available if the -gnat12 (Ada 2012 features enabled) flag is set
or if the configuration pragma Ada_2012
is used.
However, new pragmas, attributes, and restrictions are
unconditionally available, since the Ada 95 standard allows the addition of
new pragmas, attributes, and restrictions (there are exceptions, which are
documented in the individual descriptions), and also certain packages
were made available in earlier versions of Ada.
An ISO date (YYYY-MM-DD) appears in parentheses on the description line. This date shows the implementation date of the feature. Any wavefront subsequent to this date will contain the indicated feature, as will any subsequent releases. A date of 0000-00-00 means that GNAT has always implemented the feature, or implemented it as soon as it appeared as a binding interpretation.
Each feature corresponds to an Ada Issue (“AI”) approved by the Ada standardization group (ISO/IEC JTC1/SC22/WG9) for inclusion in Ada 2012. The features are ordered based on the relevant sections of the Ada Reference Manual (“RM”). When a given AI relates to multiple points in the RM, the earliest is used.
A complete description of the AIs may be found in www.ada-auth.org/ai05-summary.html.
Both universally and existentially quantified expressions are implemented. They use the new syntax for iterators proposed in AI05-139-2, as well as the standard Ada loop syntax.
RM References: 1.01.04 (12) 2.09 (2/2) 4.04 (7) 4.05.09 (0)
Wide characters in the unicode category other_format are now allowed in source programs between tokens, but not within a token such as an identifier.
RM References: 2.01 (4/2) 2.02 (7)
Wide characters in the unicode category other_format are not permitted within an identifier, since this can be a security problem. The error message for this case has been improved to be more specific, but GNAT has never allowed such characters to appear in identifiers.
RM References: 2.03 (3.1/2) 2.03 (4/2) 2.03 (5/2) 2.03 (5.1/2) 2.03 (5.2/2) 2.03 (5.3/2) 2.09 (2/2)
This AI is an earlier version of AI-163. It simplifies the rules for legal placement of pragmas. In the case of lists that allow pragmas, if the list may have no elements, then the list may consist solely of pragmas.
RM References: 2.08 (7)
A statement sequence may be composed entirely of pragmas. It is no longer
necessary to add a dummy null
statement to make the sequence legal.
RM References: 2.08 (7) 2.08 (16)
This is an editorial change only, described as non-testable in the AI.
RM References: 3.01 (7)
Aspect specifications have been fully implemented except for pre and post- conditions, and type invariants, which have their own separate AI’s. All forms of declarations listed in the AI are supported. The following is a list of the aspects supported (with GNAT implementation aspects marked)
Ada_2005 | – GNAT |
Ada_2012 | – GNAT |
Address | |
Alignment | |
Atomic | |
Atomic_Components | |
Bit_Order | |
Component_Size | |
Contract_Case | – GNAT |
Discard_Names | |
External_Tag | |
Favor_Top_Level | – GNAT |
Inline | |
Inline_Always | – GNAT |
Invariant | – GNAT |
Machine_Radix | |
No_Return | |
Object_Size | – GNAT |
Pack | |
Persistent_BSS | – GNAT |
Post | |
Pre | |
Predicate | |
Preelaborable_Initialization | |
Pure_Function | – GNAT |
Remote_Access_Type | – GNAT |
Shared | – GNAT |
Size | |
Storage_Pool | |
Storage_Size | |
Stream_Size | |
Suppress | |
Suppress_Debug_Info | – GNAT |
Test_Case | – GNAT |
Type_Invariant | |
Unchecked_Union | |
Universal_Aliasing | – GNAT |
Unmodified | – GNAT |
Unreferenced | – GNAT |
Unreferenced_Objects | – GNAT |
Unsuppress | |
Value_Size | – GNAT |
Volatile | |
Volatile_Components | |
Warnings | – GNAT |
Note that for aspects with an expression, e.g. Size
, the expression is
treated like a default expression (visibility is analyzed at the point of
occurrence of the aspect, but evaluation of the expression occurs at the
freeze point of the entity involved.
RM References: 3.02.01 (3) 3.02.02 (2) 3.03.01 (2/2) 3.08 (6) 3.09.03 (1.1/2) 6.01 (2/2) 6.07 (2/2) 9.05.02 (2/2) 7.01 (3) 7.03 (2) 7.03 (3) 9.01 (2/2) 9.01 (3/2) 9.04 (2/2) 9.04 (3/2) 9.05.02 (2/2) 11.01 (2) 12.01 (3) 12.03 (2/2) 12.04 (2/2) 12.05 (2) 12.06 (2.1/2) 12.06 (2.2/2) 12.07 (2) 13.01 (0.1/2) 13.03 (5/1) 13.03.01 (0)
If an equality operator ("=") is declared for a type, then the implicitly declared inequality operator ("/=") is a primitive operation of the type. This is the only reasonable interpretation, and is the one always implemented by GNAT, but the RM was not entirely clear in making this point.
RM References: 3.02.03 (6) 6.06 (6)
In Ada 2012, a qualified expression is considered to be syntactically a name,
meaning that constructs such as A'(F(X)).B
are now legal. This is
useful in disambiguating some cases of overloading.
RM References: 3.03 (11) 3.03 (21) 4.01 (2) 4.04 (7) 4.07 (3) 5.04 (7)
This is an RM editorial change only. The section that lists objects that are constant failed to include the current instance of a protected object within a protected function. This has always been treated as a constant in GNAT.
RM References: 3.03 (21)
The wording in the RM implied that if you have a general access to a
constrained object, it could be used to modify the discriminants. This was
obviously not intended. Constraint_Error
should be raised, and GNAT
has always done so in this situation.
RM References: 3.03 (23) 3.10.02 (26/2) 4.01 (9) 6.04.01 (17) 8.05.01 (5/2)
This is an editorial change only, to make more widespread use of the Ada 2012 “immutably limited”.
RM References: 3.03 (23.4/3)
In general it is illegal for a type derived from a formal limited type to be nonlimited. This AI makes an exception to this rule: derivation is legal if it appears in the private part of the generic, and the formal type is not tagged. If the type is tagged, the legality check must be applied to the private part of the package.
RM References: 3.04 (5.1/2) 6.02 (7)
From Ada 2005 on, soft hyphen is considered a non-graphic character, which
means that it has a special name (SOFT_HYPHEN
) in conjunction with the
Image
and Value
attributes for the character types. Strictly
speaking this is an inconsistency with Ada 95, but in practice the use of
these attributes is so obscure that it will not cause problems.
RM References: 3.05.02 (2/2) A.01 (35/2) A.03.03 (21)
Character'Value
(0000-00-00)
This AI allows Character'Value
to accept the string '?'
where
?
is any character including non-graphic control characters. GNAT has
always accepted such strings. It also allows strings such as
HEX_00000041
to be accepted, but GNAT does not take advantage of this
permission and raises Constraint_Error
, as is certainly still
permitted.
RM References: 3.05 (56/2)
Ada 2012 relaxes the restriction that forbids discriminants of tagged types to have default expressions by allowing them when the type is limited. It is often useful to define a default value for a discriminant even though it can’t be changed by assignment.
RM References: 3.07 (9.1/2) 3.07.02 (3)
It is illegal to assign an anonymous access constant to an anonymous access variable. The RM did not have a clear rule to prevent this, but GNAT has always generated an error for this usage.
RM References: 3.07 (16) 3.07.01 (9) 6.04.01 (6) 8.06 (27/2)
This AI extends the syntax of membership tests to simplify complex conditions that can be expressed as membership in a subset of values of any type. It introduces syntax for a list of expressions that may be used in loop contexts as well.
RM References: 3.08.01 (5) 4.04 (3) 4.05.02 (3) 4.05.02 (5) 4.05.02 (27)
The function Ada.Tags.Type_Is_Abstract
returns True
if invoked
with the tag of an abstract type, and False
otherwise.
RM References: 3.09 (7.4/2) 3.09 (12.4/2)
This is an editorial change only. The RM defines calls with controlling results, but uses the term “function with controlling result” without an explicit definition.
RM References: 3.09.02 (2/2)
This AI clarifies dispatching rules, and simply confirms that dispatching executes the operation of the parent type when there is no explicitly or implicitly declared operation for the descendant type. This has always been the case in all versions of GNAT.
RM References: 3.09.02 (20/2) 3.09.02 (20.1/2) 3.09.02 (20.2/2)
The RM as written implied that in some cases it was possible to create an object of an abstract type, by having an abstract extension inherit a non- abstract constructor from its parent type. This mistake has been corrected in GNAT and in the RM, and this construct is now illegal.
RM References: 3.09.03 (4/2)
A return_subtype_indication cannot denote an abstract subtype. GNAT has never permitted such usage.
RM References: 3.09.03 (8/3)
This AI resolves a conflict between two rules involving inherited abstract operations and predefined operators. If a derived numeric type inherits an abstract operator, it overrides the predefined one. This interpretation was always the one implemented in GNAT.
RM References: 3.09.03 (4/3)
This AI covers a number of issues regarding returning abstract types. In particular generic functions cannot have abstract result types or access result types designated an abstract type. There are some other cases which are detailed in the AI. Note that this binding interpretation has not been retrofitted to operate before Ada 2012 mode, since it caused a significant number of regressions.
RM References: 3.09.03 (8) 3.09.03 (10) 6.05 (8/2)
This is an editorial change only, there are no testable consequences short of checking for the absence of generated code for an interface declaration.
RM References: 3.09.04 (18/2)
The wording in the Ada 2005 RM concerning characteristics of incomplete views was incorrect and implied that some programs intended to be legal were now illegal. GNAT had never considered such programs illegal, so it has always implemented the intent of this AI.
RM References: 3.10.01 (2.4/2) 3.10.01 (2.6/2)
Incomplete types are made more useful by allowing them to be completed by private types and private extensions.
RM References: 3.10.01 (2.5/2) 3.10.01 (2.6/2) 3.10.01 (3) 3.10.01 (4/2)
An unintentional omission in the RM implied some inconsistent restrictions on the use of anonymous access to subprogram values. These restrictions were not intentional, and have never been enforced by GNAT.
RM References: 3.10.01 (6) 3.10.01 (9.2/2)
A choice list in a record aggregate can include several components of (distinct) anonymous access types as long as they have matching designated subtypes.
RM References: 4.03.01 (16)
This AI addresses a wording problem in the RM that appears to permit some complex cases of aggregates with non-static discriminants. GNAT has always implemented the intended semantics.
RM References: 4.03.01 (17)
Conditional expressions are permitted. The form of such an expression is:
(if expr then expr {elsif expr then expr} [else expr])
The parentheses can be omitted in contexts where parentheses are present
anyway, such as subprogram arguments and pragma arguments. If the else
clause is omitted, else True is assumed;
thus (if A then B)
is a way to conveniently represent
(A implies B) in standard logic.
RM References: 4.03.03 (15) 4.04 (1) 4.04 (7) 4.05.07 (0) 4.07 (2) 4.07 (3) 4.09 (12) 4.09 (33) 5.03 (3) 5.03 (4) 7.05 (2.1/2)
This AI confirms that an association of the form Indx => <>
in an
array aggregate must raise Constraint_Error
if Indx
is out of range. The RM specified a range check on other associations, but
not when the value of the association was defaulted. GNAT has always inserted
a constraint check on the index value.
RM References: 4.03.03 (29)
Equality of untagged record composes, so that the predefined equality for a
composite type that includes a component of some untagged record type
R
uses the equality operation of R
(which may be user-defined
or predefined). This makes the behavior of untagged records identical to that
of tagged types in this respect.
This change is an incompatibility with previous versions of Ada, but it corrects a non-uniformity that was often a source of confusion. Analysis of a large number of industrial programs indicates that in those rare cases where a composite type had an untagged record component with a user-defined equality, either there was no use of the composite equality, or else the code expected the same composability as for tagged types, and thus had a bug that would be fixed by this change.
RM References: 4.05.02 (9.7/2) 4.05.02 (14) 4.05.02 (15) 4.05.02 (24) 8.05.04 (8)
This AI clarifies the equivalence rule given for the dynamic semantics of exponentiation: the value of the operation can be obtained by repeated multiplication, but the operation can be implemented otherwise (for example using the familiar divide-by-two-and-square algorithm, even if this is less accurate), and does not imply repeated reads of a volatile base.
RM References: 4.05.06 (11)
Case expressions are permitted. This allows use of constructs such as:
X := (case Y is when 1 => 2, when 2 => 3, when others => 31)
RM References: 4.05.07 (0) 4.05.08 (0) 4.09 (12) 4.09 (33)
The assignment Ptr := new not null Some_Ptr;
will raise
Constraint_Error
because the default value of the allocated object is
null. This useless construct is illegal in Ada 2012.
RM References: 4.08 (2)
Allocation and Deallocation from an empty storage pool (i.e. allocation or deallocation of a pointer for which a static storage size clause of zero has been given) is now illegal and is detected as such. GNAT previously gave a warning but not an error.
RM References: 4.08 (5.3/2) 13.11.02 (4) 13.11.02 (17)
It is not necessary to have a statement following a label, so a label can appear at the end of a statement sequence without the need for putting a null statement afterwards, but it is not allowable to have only labels and no real statements in a statement sequence.
RM References: 5.01 (2)
The new syntax for iterating over arrays and containers is now implemented.
Iteration over containers is for now limited to read-only iterators. Only
default iterators are supported, with the syntax: for Elem of C
.
RM References: 5.05
For full conformance, the profiles of anonymous-access-to-subprogram parameters must match. GNAT has always enforced this rule.
RM References: 6.03.01 (18)
This AI confirms that access_to_constant indication must match for mode conformance. This was implemented in GNAT when the qualifier was originally introduced in Ada 2005.
RM References: 6.03.01 (16/2)
For full conformance, in the case of access parameters, the null exclusion
must match (either both or neither must have not null
).
RM References: 6.03.02 (18)
This AI clarifies the rules for named associations in subprogram calls and generic instantiations. The rules have been in place since Ada 83.
RM References: 6.04.01 (2) 12.03 (9)
Null exclusion checks are not made for out
parameters when
evaluating the actual parameters. GNAT has never generated these checks.
RM References: 6.04.01 (13)
The return object declared in an extended_return_statement may be declared constant. This was always intended, and GNAT has always allowed it.
RM References: 6.05 (2.1/2) 3.03 (10/2) 3.03 (21) 6.05 (5/2) 6.05 (5.7/2)
If a function returns a class-wide type, the object of an extended return statement can be declared with a specific type that is covered by the class- wide type. This has been implemented in GNAT since the introduction of extended returns. Note AI-0103 complements this AI by imposing matching rules for constrained return types.
RM References: 6.05 (5.2/2) 6.05 (5.3/2) 6.05 (5.6/2) 6.05 (5.8/2) 6.05 (8/2)
If the return subtype of a function is an elementary type or a constrained type, the subtype indication in an extended return statement must match statically this return subtype.
RM References: 6.05 (5.2/2)
The RM had some incorrect wording implying wrong treatment of abnormal completion in an extended return. GNAT has always implemented the intended correct semantics as described by this AI.
RM References: 6.05 (22/2)
The implementation permissions for raising Constraint_Error
early on a function call when it was clear an exception would be raised were over-permissive and allowed mishandling of discriminants in some cases. GNAT did
not take advantage of these incorrect permissions in any case.
RM References: 6.05 (24/2)
In Ada 2012, the declaration of a primitive operation of a type extension or private extension can also override an inherited primitive that is not visible at the point of this declaration.
RM References: 7.03.01 (6) 8.03 (23) 8.03.01 (5/2) 8.03.01 (6/2)
A full constant may have a null exclusion even if its associated deferred constant does not. GNAT has always allowed this.
RM References: 7.04 (6/2) 7.04 (7.1/2)
This AI clarifies the role of incomplete views and plugs an omission in the RM. GNAT always correctly restricted the use of incomplete views and types.
RM References: 7.05 (3/2) 7.05 (6/2)
The actual for a formal nonlimited derived type cannot be limited. In particular, a formal derived type that extends a limited interface but which is not explicitly limited cannot be instantiated with a limited type.
RM References: 7.05 (5/2) 12.05.01 (5.1/2)
This AI clarifies that “needs finalization” is part of dynamic semantics, and therefore depends on the run-time characteristics of an object (i.e. its tag) and not on its nominal type. As the AI indicates: “we do not expect this to affect any implementation”.
RM References: 7.06.01 (6) 7.06.01 (7) 7.06.01 (8) 7.06.01 (9/2)
This is an editorial change only. The intended behavior is already checked by an existing ACATS test, which GNAT has always executed correctly.
RM References: 7.06.01 (17.1/1)
Record representation clauses concerning Unchecked_Union types cannot mention the discriminant of the type. The type of a component declared in the variant part of an Unchecked_Union cannot be controlled, have controlled components, nor have protected or task parts. If an Unchecked_Union type is declared within the body of a generic unit or its descendants, then the type of a component declared in the variant part cannot be a formal private type or a formal private extension declared within the same generic unit.
RM References: 7.06 (9.4/2) B.03.03 (9/2) B.03.03 (10/2)
This AI corrects a simple omission in the RM. Return objects have always been visible within an extended return statement.
RM References: 8.03 (17)
This AI fixes a wording gap in the RM. An operation of a synchronized interface can be implemented by a protected or task entry, but the abstract operation is not being overridden in the usual sense, and it must be stated separately that this implementation is legal. This has always been the case in GNAT.
RM References: 9.01 (9.2/2) 9.04 (11.1/2)
Requeue is permitted to a protected, synchronized or task interface primitive
providing it is known that the overriding operation is an entry. Otherwise
the requeue statement has the same effect as a procedure call. Use of pragma
Implemented
provides a way to impose a static requirement on the
overriding operation by adhering to one of the implementation kinds: entry,
protected procedure or any of the above.
RM References: 9.05 (9) 9.05.04 (2) 9.05.04 (3) 9.05.04 (5) 9.05.04 (6) 9.05.04 (7) 9.05.04 (12)
If an Atomic object has a pragma Pack
or a Component_Size
attribute, then individual components may not be addressable by independent
tasks. However, if the representation clause has no effect (is confirming),
then independence is not compromised. Furthermore, in GNAT, specification of
other appropriately addressable component sizes (e.g. 16 for 8-bit
characters) also preserves independence. GNAT now gives very clear warnings
both for the declaration of such a type, and for any assignment to its components.
RM References: 9.10 (1/3) C.06 (22/2) C.06 (23/2)
This AI introduces the new pragmas Independent
and
Independent_Components
,
which control guaranteeing independence of access to objects and components.
The AI also requires independence not unaffected by confirming rep clauses.
RM References: 9.10 (1) 13.01 (15/1) 13.02 (9) 13.03 (13) C.06 (2) C.06 (4) C.06 (6) C.06 (9) C.06 (13) C.06 (14)
This AI clarifies that task signalling for reading 'Terminated
only
occurs if the result is True. GNAT semantics has always been consistent with
this notion of task signalling.
RM References: 9.10 (6.1/1)
This AI confirms that an incomplete type from a limited view does not have discriminants. This has always been the case in GNAT.
RM References: 10.01.01 (12.3/2)
This AI clarifies the description of limited views: a limited view of a package includes only one view of a type that has an incomplete declaration and a full declaration (there is no possible ambiguity in a client package). This AI also fixes an omission: a nested package in the private part has no limited view. GNAT always implemented this correctly.
RM References: 10.01.01 (12.2/2) 10.01.01 (12.3/2)
This AI clarifies that a declaration does not include a context clause, and confirms that it is illegal to have a context in which both a limited and a nonlimited view of a package are accessible. Such double visibility was always rejected by GNAT.
RM References: 10.01.02 (12/2) 10.01.02 (21/2) 10.01.02 (22/2)
This AI clarifies the visibility of private children of generic units within instantiations of a parent. GNAT has always handled this correctly.
RM References: 10.01.02 (12/2)
This AI confirms that a limited with clause in a child unit cannot name an ancestor of the unit. This has always been checked in GNAT.
RM References: 10.01.02 (20/2)
This AI fills a gap in the description of library unit pragmas. The pragma clearly must apply to a library unit, even if it does not carry the name of the enclosing unit. GNAT has always enforced the required check.
RM References: 10.01.05 (7)
The RM makes certain limited with clauses illegal because of categorization considerations, when the corresponding normal with would be legal. This is not intended, and GNAT has always implemented the recommended behavior.
RM References: 10.02.01 (11/1) 10.02.01 (17/2)
This AI remedies some inconsistencies in the legality rules for Pure units. Derived access types are legal in a pure unit (on the assumption that the rule for a zero storage pool size has been enforced on the ancestor type). The rules are enforced in generic instances and in subunits. GNAT has always implemented the recommended behavior.
RM References: 10.02.01 (15.1/2) 10.02.01 (15.4/2) 10.02.01 (15.5/2) 10.02.01 (17/2)
This AI refines the rules for the cases with limited parameters which do not allow the implementations to omit “redundant”. GNAT now properly conforms to the requirements of this binding interpretation.
RM References: 10.02.01 (18/2)
This AI covers various omissions in the RM regarding the raising of exceptions. GNAT has always implemented the intended semantics.
RM References: 11.04.01 (10.1/2) 11 (2)
This AI plugs a gap in the RM which appeared to allow some obviously intended illegal instantiations. GNAT has never allowed these instantiations.
RM References: 12.07 (16)
This AI concerns giving names to various representation aspects, but the
practical effect is simply to make the use of duplicate
Atomic
[_Components
],
Volatile
[_Components
] and
Independent
[_Components
] pragmas illegal, and GNAT
now performs this required check.
RM References: 13.01 (8)
The RM appeared to allow representation pragmas on generic formal parameters, but this was not intended, and GNAT has never permitted this usage.
RM References: 13.01 (9.1/1)
It is now illegal to give an inappropriate component size or a pragma
Pack
that attempts to change the component size in the case of atomic
or aliased components. Previously GNAT ignored such an attempt with a
warning.
RM References: 13.02 (6.1/2) 13.02 (7) C.06 (10) C.06 (11) C.06 (21)
The RM permitted the use of dynamic expressions (such as ptr.all)
for stream attributes, but these were never useful and are now illegal. GNAT
has always regarded such expressions as illegal.
RM References: 13.03 (4) 13.03 (6) 13.13.02 (38/2)
The prefix of 'Address
cannot statically denote a subprogram with
convention Intrinsic
. The use of the Address
attribute raises
Program_Error
if the prefix denotes a subprogram with convention
Intrinsic
.
RM References: 13.03 (11/1)
This AI requires that the alignment of a class-wide object be no greater than the alignment of any type in the class. GNAT has always followed this recommendation.
RM References: 13.03 (29) 13.11 (16)
Type invariants may be specified for private types using the aspect notation.
Aspect Type_Invariant
may be specified for any private type,
Type_Invariant'Class
can
only be specified for tagged types, and is inherited by any descendent of the
tagged types. The invariant is a boolean expression that is tested for being
true in the following situations: conversions to the private type, object
declarations for the private type that are default initialized, and
[in] out
parameters and returned result on return from any primitive operation for
the type that is visible to a client.
GNAT defines the synonyms Invariant
for Type_Invariant
and
Invariant'Class
for Type_Invariant'Class
.
RM References: 13.03.03 (00)
In Ada 2012, compilers are required to support unchecked conversion where the target alignment is a multiple of the source alignment. GNAT always supported this case (and indeed all cases of differing alignments, doing copies where required if the alignment was reduced).
RM References: 13.09 (7)
The handling of invalid values is now designated to be implementation defined. This is a documentation change only, requiring Annex M in the GNAT Reference Manual to document this handling. In GNAT, checks for invalid values are made only when necessary to avoid erroneous behavior. Operations like assignments which cannot cause erroneous behavior ignore the possibility of invalid values and do not do a check. The date given above applies only to the documentation change, this behavior has always been implemented by GNAT.
RM References: 13.09.01 (10)
This AI introduces a new attribute Max_Alignment_For_Allocation
,
analogous to Max_Size_In_Storage_Elements
, but for alignment instead
of size.
RM References: 13.11 (16) 13.11 (21) 13.11.01 (0) 13.11.01 (1) 13.11.01 (2) 13.11.01 (3)
The new Ada 2012 notion of parameterized expressions is implemented. The form is:
function specification is (expression)
This is exactly equivalent to the corresponding function body that returns the expression, but it can appear in a package spec. Note that the expression must be parenthesized.
RM References: 13.11.01 (3/2)
Neither of these two pragmas may appear within a generic template, because the generic might be instantiated at other than the library level.
RM References: 13.11.02 (16) C.03.01 (7/2) C.03.01 (8/2)
A new restriction No_Default_Stream_Attributes
prevents the use of any
of the default stream attributes for elementary types. If this restriction is
in force, then it is necessary to provide explicit subprograms for any
stream attributes used.
RM References: 13.12.01 (4/2) 13.13.02 (40/2) 13.13.02 (52/2)
The Stream_Size
attribute returns the default number of bits in the
stream representation of the given type.
This value is not affected by the presence
of stream subprogram attributes for the type. GNAT has always implemented
this interpretation.
RM References: 13.13.02 (1.2/2)
This AI is an editorial change only. It removes the need for a tag check that can never fail.
RM References: 13.13.02 (34/2)
The RM as written appeared to limit the possibilities of declaring read attribute procedures for private scalar types. This limitation was not intended, and has never been enforced by GNAT.
RM References: 13.13.02 (50/2) 13.13.02 (51/2)
This AI clarifies the fact that all remote access types support external streaming. This fixes an obvious oversight in the definition of the language, and GNAT always implemented the intended correct rules.
RM References: 13.13.02 (52/2)
The RM suggests that primitive subprograms of a specific tagged type are frozen when the tagged type is frozen. This would be an incompatible change and is not intended. GNAT has never attempted this kind of freezing and its behavior is consistent with the recommendation of this AI.
RM References: 13.14 (2) 13.14 (3/1) 13.14 (8.1/1) 13.14 (10) 13.14 (14) 13.14 (15.1/2)
So-called “Taft-amendment types” (i.e., types that are completed in package bodies) are not frozen by the occurrence of bodies in the enclosing declarative part. GNAT always implemented this properly.
RM References: 13.14 (3/1)
This AI extends the definition of remote access types to include access to limited, synchronized, protected or task class-wide interface types. GNAT already implemented this extension.
RM References: A (4) E.02.02 (9/1) E.02.02 (9.2/1) E.02.02 (14/2) E.02.02 (18)
The code points 170 (FEMININE ORDINAL INDICATOR
),
181 (MICRO SIGN
), and
186 (MASCULINE ORDINAL INDICATOR
) are technically considered
lower case letters by Unicode.
However, they are not allowed in identifiers, and they
return False
to Ada.Characters.Handling.Is_Letter/Is_Lower
.
This behavior is consistent with that defined in Ada 95.
RM References: A.03.02 (59) A.04.06 (7)
Two new packages Ada.Wide_[Wide_]Characters.Handling
provide
classification functions for Wide_Character
and
Wide_Wide_Character
, as well as providing
case folding routines for Wide_[Wide_]Character
and
Wide_[Wide_]String
.
RM References: A.03.05 (0) A.03.06 (0)
A new version of Find_Token
is added to all relevant string packages,
with an extra parameter From
. Instead of starting at the first
character of the string, the search for a matching Token starts at the
character indexed by the value of From
.
These procedures are available in all versions of Ada
but if used in versions earlier than Ada 2012 they will generate a warning
that an Ada 2012 subprogram is being used.
RM References: A.04.03 (16) A.04.03 (67) A.04.03 (68/1) A.04.04 (51) A.04.05 (46)
The wording in the Ada 2005 RM implied an incompatible handling of the
Index
functions, resulting in raising an exception instead of
returning zero in some situations.
This was not intended and has been corrected.
GNAT always returned zero, and is thus consistent with this AI.
RM References: A.04.03 (56.2/2) A.04.03 (58.5/2)
The packages Ada.Strings.UTF_Encoding
, together with its child
packages, Conversions
, Strings
, Wide_Strings
,
and Wide_Wide_Strings
have been
implemented. These packages (whose documentation can be found in the spec
files a-stuten.ads, a-suenco.ads, a-suenst.ads,
a-suewst.ads, a-suezst.ads) allow encoding and decoding of
String
, Wide_String
, and Wide_Wide_String
values using UTF coding schemes (including UTF-8, UTF-16LE, UTF-16BE, and
UTF-16), as well as conversions between the different UTF encodings. With
the exception of Wide_Wide_Strings
, these packages are available in
Ada 95 and Ada 2005 mode as well as Ada 2012 mode.
The Wide_Wide_Strings package
is available in Ada 2005 mode as well as Ada 2012 mode (but not in Ada 95
mode since it uses Wide_Wide_Character
).
RM References: A.04.11
These are minor errors in the description on three points. The intent on all these points has always been clear, and GNAT has always implemented the correct intended semantics.
RM References: A.10.05 (37) A.10.07 (8/1) A.10.07 (10) A.10.07 (12) A.10.08 (10) A.10.08 (24)
This AI places restrictions on allowed instantiations of generic containers. These restrictions are not checked by the compiler, so there is nothing to change in the implementation. This affects only the RM documentation.
RM References: A.18 (4/2) A.18.02 (231/2) A.18.03 (145/2) A.18.06 (56/2) A.18.08 (66/2) A.18.09 (79/2) A.18.26 (5/2) A.18.26 (9/2)
This package provides an interface for identifying the current locale.
RM References: A.19 A.19.01 A.19.02 A.19.03 A.19.05 A.19.06 A.19.07 A.19.08 A.19.09 A.19.10 A.19.11 A.19.12 A.19.13
The compiler is not required to support exporting an Ada subprogram with
convention C if there are parameters or a return type of an unconstrained
array type (such as String
). GNAT allows such declarations but
generates warnings. It is possible, but complicated, to write the
corresponding C code and certainly such code would be specific to GNAT and
non-portable.
RM References: B.01 (17) B.03 (62) B.03 (71.1/2)
It is clearly the intention that No_Task_Hierarchy
is intended to
forbid tasks declared locally within subprograms, or functions returning task
objects, and that is the implementation that GNAT has always provided.
However the language in the RM was not sufficiently clear on this point.
Thus this is a documentation change in the RM only.
RM References: D.07 (3/3)
The restriction No_Relative_Delays
forbids any calls to the subprogram
Ada.Real_Time.Timing_Events.Set_Handler
.
RM References: D.07 (5) D.07 (10/2) D.07 (10.4/2) D.07 (10.7/2)
This AI introduces a new pragma Default_Storage_Pool
, which can be
used to control storage pools globally.
In particular, you can force every access
type that is used for allocation (new) to have an explicit storage pool,
or you can declare a pool globally to be used for all access types that lack
an explicit one.
RM References: D.07 (8)
This AI introduces a new restriction No_Allocators_After_Elaboration
,
which says that no dynamic allocation will occur once elaboration is
completed.
In general this requires a run-time check, which is not required, and which
GNAT does not attempt. But the static cases of allocators in a task body or
in the body of the main program are detected and flagged at compile or bind
time.
RM References: D.07 (19.1/2) H.04 (23.3/2)
A new package System.Multiprocessors
is added, together with the
definition of pragma CPU
for controlling task affinity. A new no
dependence restriction, on System.Multiprocessors.Dispatching_Domains
,
is added to the Ravenscar profile.
RM References: D.13.01 (4/2) D.16
This is a documentation only issue regarding wording of metric requirements, that does not affect the implementation of the compiler.
RM References: D.15 (24/2)
Remote types packages are now allowed to depend on preelaborated packages. This was formerly considered illegal.
RM References: E.02.02 (6)
Restriction No_Anonymous_Allocators
prevents the use of allocators
where the type of the returned value is an anonymous access type.
RM References: H.04 (8/1)
Next: GNU Free Documentation License, Previous: Implementation of Ada 2012 Features, Up: Top [Contents][Index]
This chapter describes features that are provided by GNAT, but are considered obsolescent since there are preferred ways of achieving the same effect. These features are provided solely for historical compatibility purposes.
• pragma No_Run_Time: | ||
• pragma Ravenscar: | ||
• pragma Restricted_Run_Time: |
Next: pragma Ravenscar, Up: Obsolescent Features [Contents][Index]
The pragma No_Run_Time
is used to achieve an affect similar
to the use of the "Zero Foot Print" configurable run time, but without
requiring a specially configured run time. The result of using this
pragma, which must be used for all units in a partition, is to restrict
the use of any language features requiring run-time support code. The
preferred usage is to use an appropriately configured run-time that
includes just those features that are to be made accessible.
Next: pragma Restricted_Run_Time, Previous: pragma No_Run_Time, Up: Obsolescent Features [Contents][Index]
The pragma Ravenscar
has exactly the same effect as pragma
Profile (Ravenscar)
. The latter usage is preferred since it
is part of the new Ada 2005 standard.
Previous: pragma Ravenscar, Up: Obsolescent Features [Contents][Index]
The pragma Restricted_Run_Time
has exactly the same effect as
pragma Profile (Restricted)
. The latter usage is
preferred since the Ada 2005 pragma Profile
is intended for
this kind of implementation dependent addition.
Next: Index, Previous: Obsolescent Features, Up: Top [Contents][Index]
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Ada.Characters.Handling
Get_Immediate
Export
Interfaces
Interrupts
Discard_Names
Ada.Characters.Latin_9
(a-chlat9.ads)Ada.Characters.Wide_Latin_1
(a-cwila1.ads)Ada.Characters.Wide_Latin_9
(a-cwila1.ads)Ada.Characters.Wide_Wide_Latin_1
(a-chzla1.ads)Ada.Characters.Wide_Wide_Latin_9
(a-chzla9.ads)Ada.Containers.Formal_Doubly_Linked_Lists
(a-cfdlli.ads)Ada.Containers.Formal_Hashed_Maps
(a-cfhama.ads)Ada.Containers.Formal_Hashed_Sets
(a-cfhase.ads)Ada.Containers.Formal_Ordered_Maps
(a-cforma.ads)Ada.Containers.Formal_Ordered_Sets
(a-cforse.ads)Ada.Containers.Formal_Vectors
(a-cofove.ads)Ada.Command_Line.Environment
(a-colien.ads)Ada.Command_Line.Remove
(a-colire.ads)Ada.Command_Line.Response_File
(a-clrefi.ads)Ada.Direct_IO.C_Streams
(a-diocst.ads)Ada.Exceptions.Is_Null_Occurrence
(a-einuoc.ads)Ada.Exceptions.Last_Chance_Handler
(a-elchha.ads)Ada.Exceptions.Traceback
(a-exctra.ads)Ada.Sequential_IO.C_Streams
(a-siocst.ads)Ada.Streams.Stream_IO.C_Streams
(a-ssicst.ads)Ada.Strings.Unbounded.Text_IO
(a-suteio.ads)Ada.Strings.Wide_Unbounded.Wide_Text_IO
(a-swuwti.ads)Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO
(a-szuzti.ads)Ada.Text_IO.C_Streams
(a-tiocst.ads)Ada.Text_IO.Reset_Standard_Files
(a-tirsfi.ads)Ada.Wide_Characters.Unicode
(a-wichun.ads)Ada.Wide_Text_IO.C_Streams
(a-wtcstr.ads)Ada.Wide_Text_IO.Reset_Standard_Files
(a-wrstfi.ads)Ada.Wide_Wide_Characters.Unicode
(a-zchuni.ads)Ada.Wide_Wide_Text_IO.C_Streams
(a-ztcstr.ads)Ada.Wide_Wide_Text_IO.Reset_Standard_Files
(a-zrstfi.ads)GNAT.Altivec
(g-altive.ads)GNAT.Altivec.Conversions
(g-altcon.ads)GNAT.Altivec.Vector_Operations
(g-alveop.ads)GNAT.Altivec.Vector_Types
(g-alvety.ads)GNAT.Altivec.Vector_Views
(g-alvevi.ads)GNAT.Array_Split
(g-arrspl.ads)GNAT.AWK
(g-awk.ads)GNAT.Bounded_Buffers
(g-boubuf.ads)GNAT.Bounded_Mailboxes
(g-boumai.ads)GNAT.Bubble_Sort
(g-bubsor.ads)GNAT.Bubble_Sort_A
(g-busora.ads)GNAT.Bubble_Sort_G
(g-busorg.ads)GNAT.Byte_Order_Mark
(g-byorma.ads)GNAT.Byte_Swapping
(g-bytswa.ads)GNAT.Calendar
(g-calend.ads)GNAT.Calendar.Time_IO
(g-catiio.ads)GNAT.CRC32
(g-crc32.ads)GNAT.Case_Util
(g-casuti.ads)GNAT.CGI
(g-cgi.ads)GNAT.CGI.Cookie
(g-cgicoo.ads)GNAT.CGI.Debug
(g-cgideb.ads)GNAT.Command_Line
(g-comlin.ads)GNAT.Compiler_Version
(g-comver.ads)GNAT.Ctrl_C
(g-ctrl_c.ads)GNAT.Current_Exception
(g-curexc.ads)GNAT.Debug_Pools
(g-debpoo.ads)GNAT.Debug_Utilities
(g-debuti.ads)GNAT.Decode_String
(g-decstr.ads)GNAT.Decode_UTF8_String
(g-deutst.ads)GNAT.Directory_Operations
(g-dirope.ads)GNAT.Directory_Operations.Iteration
(g-diopit.ads)GNAT.Dynamic_HTables
(g-dynhta.ads)GNAT.Dynamic_Tables
(g-dyntab.ads)GNAT.Encode_String
(g-encstr.ads)GNAT.Encode_UTF8_String
(g-enutst.ads)GNAT.Exception_Actions
(g-excact.ads)GNAT.Exception_Traces
(g-exctra.ads)GNAT.Exceptions
(g-expect.ads)GNAT.Expect
(g-expect.ads)GNAT.Expect.TTY
(g-exptty.ads)GNAT.Float_Control
(g-flocon.ads)GNAT.Heap_Sort
(g-heasor.ads)GNAT.Heap_Sort_A
(g-hesora.ads)GNAT.Heap_Sort_G
(g-hesorg.ads)GNAT.HTable
(g-htable.ads)GNAT.IO
(g-io.ads)GNAT.IO_Aux
(g-io_aux.ads)GNAT.Lock_Files
(g-locfil.ads)GNAT.MBBS_Discrete_Random
(g-mbdira.ads)GNAT.MBBS_Float_Random
(g-mbflra.ads)GNAT.MD5
(g-md5.ads)GNAT.Memory_Dump
(g-memdum.ads)GNAT.Most_Recent_Exception
(g-moreex.ads)GNAT.OS_Lib
(g-os_lib.ads)GNAT.Perfect_Hash_Generators
(g-pehage.ads)GNAT.Random_Numbers
(g-rannum.ads)GNAT.Regexp
(g-regexp.ads)GNAT.Registry
(g-regist.ads)GNAT.Regpat
(g-regpat.ads)GNAT.Secondary_Stack_Info
(g-sestin.ads)GNAT.Semaphores
(g-semaph.ads)GNAT.Serial_Communications
(g-sercom.ads)GNAT.SHA1
(g-sha1.ads)GNAT.SHA224
(g-sha224.ads)GNAT.SHA256
(g-sha256.ads)GNAT.SHA384
(g-sha384.ads)GNAT.SHA512
(g-sha512.ads)GNAT.Signals
(g-signal.ads)GNAT.Sockets
(g-socket.ads)GNAT.Source_Info
(g-souinf.ads)GNAT.Spelling_Checker
(g-speche.ads)GNAT.Spelling_Checker_Generic
(g-spchge.ads)GNAT.Spitbol.Patterns
(g-spipat.ads)GNAT.Spitbol
(g-spitbo.ads)GNAT.Spitbol.Table_Boolean
(g-sptabo.ads)GNAT.Spitbol.Table_Integer
(g-sptain.ads)GNAT.Spitbol.Table_VString
(g-sptavs.ads)GNAT.SSE
(g-sse.ads)GNAT.SSE.Vector_Types
(g-ssvety.ads)GNAT.Strings
(g-string.ads)GNAT.String_Split
(g-strspl.ads)GNAT.Table
(g-table.ads)GNAT.Task_Lock
(g-tasloc.ads)GNAT.Time_Stamp
(g-timsta.ads)GNAT.Threads
(g-thread.ads)GNAT.Traceback
(g-traceb.ads)GNAT.Traceback.Symbolic
(g-trasym.ads)GNAT.UTF_32
(g-table.ads)GNAT.Wide_Spelling_Checker
(g-u3spch.ads)GNAT.Wide_Spelling_Checker
(g-wispch.ads)GNAT.Wide_String_Split
(g-wistsp.ads)GNAT.Wide_Wide_Spelling_Checker
(g-zspche.ads)GNAT.Wide_Wide_String_Split
(g-zistsp.ads)Interfaces.C.Extensions
(i-cexten.ads)Interfaces.C.Streams
(i-cstrea.ads)Interfaces.CPP
(i-cpp.ads)Interfaces.Packed_Decimal
(i-pacdec.ads)Interfaces.VxWorks
(i-vxwork.ads)Interfaces.VxWorks.IO
(i-vxwoio.ads)System.Address_Image
(s-addima.ads)System.Assertions
(s-assert.ads)System.Memory
(s-memory.ads)System.Partition_Interface
(s-parint.ads)System.Pool_Global
(s-pooglo.ads)System.Pool_Local
(s-pooloc.ads)System.Restrictions
(s-restri.ads)System.Rident
(s-rident.ads)System.Strings.Stream_Ops
(s-ststop.ads)System.Task_Info
(s-tasinf.ads)System.Wch_Cnv
(s-wchcnv.ads)System.Wch_Con
(s-wchcon.ads)