home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
OS/2 Shareware BBS: 10 Tools
/
10-Tools.zip
/
adav313.zip
/
gnat-3_13p-docs.zip
/
gnat_rm.INF
(
.txt
)
< prev
next >
Wrap
OS/2 Help File
|
2001-09-16
|
227KB
|
8,120 lines
ΓòÉΓòÉΓòÉ 1. -Preface- ΓòÉΓòÉΓòÉ
ΓòÉΓòÉΓòÉ 2. GNAT Reference Manual ΓòÉΓòÉΓòÉ
GNAT Reference Manual
GNAT, The GNU Ada 95 Compiler
Version 3.13p Date: 2000/05/16 04:55:48
Ada Core Technologies, Inc.
(C) Copyright 1995-2000, Ada Core Technologies - All Rights Reserved
This document may be copied, in whole or in part, in any form or by any means,
as is or with alterations, provided that (1) alterations are clearly marked as
alterations and (2) this copyright notice is included unmodified in any copy.
Silicon Graphics and IRIS are registered trademarks and IRIX is a trademark of
Silicon Graphics, Inc.
IBM PC is a trademark of International Business Machines Corporation.
UNIX is a registered trademark of AT&T Bell Laboratories. DIGITAL
VADS is a registered trademark of Rational Software Inc.
The following are trademarks of Digital Equipment Corporation: DEC, DEC Ada,
DECthreads, Digital, OpenVMS, and VAX.
About This Guide About This Guide
Implementation Defined PragmasImplementation Defined Pragmas
Implementation Defined AttributesImplementation Defined Attributes
Implementation Advice Implementation Advice
Implementation Defined CharacteristicsImplementation Defined Characteristics
Representation Clauses and PragmasRepresentation Clauses and Pragmas
Standard Library Routines Standard Library Routines
The Implementation of Standard I/OThe Implementation of Standard I/O
The GNAT Library The GNAT Library
Interfacing to Other LanguagesInterfacing to Other Languages
Machine Code Insertions Machine Code Insertions
GNAT Implementation of TaskingGNAT Implementation of Tasking
Code generation for array aggregatesCode generation for array aggregates
Specialized Needs Annexes Specialized Needs Annexes
Compatibility Guide Compatibility Guide
Index --- The Detailed Node Listing --- About This
Guide
What This Reference Manual ContainsWhat This Reference Manual Contains
Related Information Related Information The Implementation of
Standard I/O
Standard I/O Packages Standard I/O Packages
FORM Strings FORM Strings
Direct_IO Direct_IO
Sequential_IO Sequential_IO
Text_IO Text_IO
Wide_Text_IO Wide_Text_IO
Stream_IO Stream_IO
Shared Files Shared Files
Open Modes Open Modes
Operations on C Streams Operations on C Streams
Interfacing to C Streams Interfacing to C Streams The GNAT Library
GNAT.Bubble_Sort_A (g-busora.ads)GNAT.Bubble_Sort_A (g-busora.ads)
GNAT.Bubble_Sort_G (g-busorg.ads)GNAT.Bubble_Sort_G (g-busorg.ads)
GNAT.Calendar (g-calend.ads) GNAT.Calendar (g-calend.ads)
GNAT.Case_Util (g-casuti) GNAT.Case_Util (g-casuti)
GNAT.Calendar.Time_IO (g-catiio.ads)GNAT.Calendar.Time_IO (g-catiio.ads)
GNAT.Command_Line (g-comlin.ads)GNAT.Command_Line (g-comlin.ads)
GNAT.Current_Exception (g-curexc.ads)GNAT.Current_Exception (g-curexc.ads)
GNAT.Debug_Pools (g-debpoo.ads)GNAT.Debug_Pools (g-debpoo.ads)
GNAT.Debug_Utilities (g-debuti.ads)GNAT.Debug_Utilities (g-debuti.ads)
GNAT.Directory_Operations (g-dirope.ads)GNAT.Directory_Operations
(g-dirope.ads)
GNAT.Float_Control (g-flocon.ads)GNAT.Float_Control (g-flocon.ads)
GNAT.Heap_Sort_A (g-hesora.ads)GNAT.Heap_Sort_A (g-hesora.ads)
GNAT.Heap_Sort_G (g-hesorg.ads)GNAT.Heap_Sort_G (g-hesorg.ads)
GNAT.HTable (g-htable.ads) GNAT.HTable (g-htable.ads)
GNAT.IO (g-io.ads) GNAT.IO (g-io.ads)
GNAT.IO_Aux (g-io_aux.ads) GNAT.IO_Aux (g-io_aux.ads)
GNAT.Lock_Files (g-locfil.ads)GNAT.Lock_Files (g-locfil.ads)
GNAT.OS_Lib (g-os_lib.ads) GNAT.OS_Lib (g-os_lib.ads)
GNAT.Regexp (g-regexp.ads) GNAT.Regexp (g-regexp.ads)
GNAT.Regpat (g-regpat.ads) GNAT.Regpat (g-regpat.ads)
GNAT.Spell_Checker (g-speche.ads)GNAT.Spell_Checker (g-speche.ads)
GNAT.Spitbol.Patterns (g-spipat.ads)GNAT.Spitbol.Patterns (g-spipat.ads)
GNAT.Spitbol (g-spitbo.ads) GNAT.Spitbol (g-spitbo.ads)
GNAT.SPITBOL.Table_Boolean (g-sptabo.ads)GNAT.SPITBOL.Table_Boolean
(g-sptabo.ads)
GNAT.SPITBOL.Table_Integer (g-sptain.ads)GNAT.SPITBOL.Table_Integer
(g-sptain.ads)
GNAT.SPITBOL.Table_VString (g-sptavs.ads)GNAT.SPITBOL.Table_VString
(g-sptavs.ads)
GNAT.Table (g-table.ads) GNAT.Table (g-table.ads)
GNAT.Task_Lock (g-tasloc.ads) GNAT.Task_Lock (g-tasloc.ads)
GNAT.Threads (g-thread.ads) GNAT.Threads (g-thread.ads)
GNAT.Traceback (g-traceb.ads) GNAT.Traceback (g-traceb.ads)
GNAT.Traceback.Symbolic (g-trasym.ads)GNAT.Traceback.Symbolic (g-trasym.ads)
Text_IO
Text_IO Stream Pointer PositioningText_IO Stream Pointer Positioning
Text_IO Reading and Writing Non-Regular FilesText_IO Reading and Writing
Non-Regular Files
Get_Immediate Get_Immediate
Treating Text_IO Files as StreamsTreating Text_IO Files as Streams
Text_IO Extensions Text_IO Extensions
Text_IO Facilities for Unbounded StringsText_IO Facilities for Unbounded
Strings Wide_Text_IO
Wide_Text_IO Stream Pointer PositioningWide_Text_IO Stream Pointer Positioning
Wide_Text_IO Reading and Writing Non-Regular FilesWide_Text_IO Reading and
Writing Non-Regular Files Interfacing to Other
Languages
Interfacing to C Interfacing to C
Interfacing to C++ Interfacing to C++
Interfacing to COBOL Interfacing to COBOL
Interfacing to Fortran Interfacing to Fortran
Interfacing to non-GNAT Ada codeInterfacing to non-GNAT Ada code GNAT
Implementation of Tasking
Mapping Ada Tasks onto the Underlying Kernel ThreadsMapping Ada Tasks onto the
Underlying Kernel Threads
Ensuring Compliance with the Real-Time AnnexEnsuring Compliance with the
Real-Time Annex
ΓòÉΓòÉΓòÉ 3. About This Guide ΓòÉΓòÉΓòÉ
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 standard.
Ada 95 is designed to be highly portable,and guarantees that, for most
programs, Ada 95 compilers behave in exactly the same manner on different
machines. However, since Ada 95 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 ContainsWhat This Reference Manual Contains
Conventions Conventions
Related Information Related Information
ΓòÉΓòÉΓòÉ 3.1. What This Reference Manual Contains ΓòÉΓòÉΓòÉ
This reference manual contains the following chapters:
Implementation Defined Pragmas lists GNAT implementation-dependent
pragmas, which can be used to extend and enhance the functionality of the
compiler.
Implementation Defined Attributes lists GNAT implementation-dependent
attributes which can be used to extend and enhance the functionality of
the compiler.
Implementation Advice provides information on generally desirable
behavior which are not requirements that all compilers must follow since
it cannot be provided on all systems, or which may be undesirable on some
systems.
Implementation Defined Characteristics provides a guide to minimizing
implementation dependent features.
Representation Clauses and Pragmas describes in detail the way that GNAT
represents data, and in particular the exact set of representation
clauses and pragmas that is accepted.
Standard Library Routines provides a listing of packages and a brief
description of the functionality that is provided by Ada's extensive set
of standard library routines as implemented by GNAT.
The Implementation of Standard I/O details how the GNAT implementation of
the input-output facilities.
Interfacing to Other Languages describes how programs written in Ada
using GNAT can be interfaced to other programming languages.
Specialized Needs Annexes describes the GNAT implementation of all of the
special needs annexes.
Compatibility Guide includes sections on compatibility of GNAT with other
Ada 83 and Ada 95 compilation systems, to assist in porting code from
other environments.
This reference manual assumes that you are familiar with Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, Jan 1995.
ΓòÉΓòÉΓòÉ 3.2. Conventions ΓòÉΓòÉΓòÉ
Following are examples of the typographical and graphic conventions used in
this guide:
Functions, utility program names, standard names, and classes.
'Option flags'
'File Names', 'button names', and 'field names'.
Variables.
Emphasis.
[optional information or parameters]
Examples are described by text
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.
ΓòÉΓòÉΓòÉ 3.3. Related Information ΓòÉΓòÉΓòÉ
See the following documents for further information on GNAT
GNAT User's Guide, which provides information on how to use the GNAT
compiler system.
Ada 95 Reference Manual, which contains all reference material for the
Ada 95 programming language.
Ada 95 Annotated Reference Manual, which is an annotated version of the
standard reference manual cited above. The annotations describe detailed
aspects of the design decision, and in particular contain useful sections
on Ada 83 compatibility.
DEC Ada, Technical Overview and Comparison on DIGITAL Platforms, which
contains specific information on compatibility between GNAT and DEC Ada
83 systems.
DEC Ada, Language Reference Manual, part number AA-PYZAB-TK which
describes in detail the pragmas and attributes provided by the DEC Ada 83
compiler system.
ΓòÉΓòÉΓòÉ 4. Implementation Defined Pragmas ΓòÉΓòÉΓòÉ
Ada 95 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 95 Reference Manual.
In addition, Ada 95 allows implementations to define additional pragmas whose
meaning is defined by the implementation. GNAT provides a number of these
implementation-dependent 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 may 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.
pragma Abort_Defer
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).
pragma Ada_83
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 new Ada 95 keywords 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 legacy
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.
pragma Ada_95
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.
pragma Annotate
Syntax:
pragma Annotate (IDENTIFIER {, ARG});
ARG ::= NAME | EXPRESSION
This pragma is used to annotate programs. identifier identifies the type of
annotation. GNAT verifies this is an identifier, but does not otherwise
analyze it. The arg argument can be either a string literal or an expression.
String literals are assumed to be of type Standard.String. Names of entities
are simply analyzed as entity names. All other expressions 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. This pragma is intended for use by external
tools, including ASIS.
pragma Assert
Syntax:
pragma Assert (
boolean_EXPRESSION
[, static_string_EXPRESSION])
The effect of this pragma depends on whether the corresponding command line
switch is set to activate assertions. If assertions are inactive, the pragma
has no effect. If assertions are enabled, then the semantics of the pragma is
exactly equivalent to:
if not boolean_EXPRESSION then
System.Assertions.Raise_Assert_Failure
(string_EXPRESSION);
end if;
The effect of the call is to raise System.Assertions.Assert_Failure. The
string argument, if given, is the message associated with the exception
occurrence. 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:
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 J > 3 then
pragma (Assert (K > 3, "Bad value for K"));
null;
end if;
If the boolean expression has side effects, 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. You should generally avoid side effects in the
expression arguments of this pragma. 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.
pragma Ast_Entry
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.
pragma C_Pass_By_Copy
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:
1. The size of the record type does not exceed
static_integer_expression.
2. The record type has Convention C.
3. The formal parameter has this record type, and the subprogram
has a foreign (non-Ada) convention.
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.
pragma Comment
Syntax:
pragma Comment (static_string_EXPRESSION);
Synonymous for pragma Ident.
pragma Common_Object
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.
pragma Complex_Representation
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.
pragma Component_Alignment
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.
pragma CPP_Class
Syntax:
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.
If (and only if) the type is tagged, at least one component in the
record must be of type Interfaces.CPP.Vtable_Ptr, corresponding to
the C++ Vtable (or Vtables in the case of multiple inheritance)
used for dispatching.
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).
Pragma CPP_Class is intended primarily for automatic generation
using an automatic binding generator tool. Ada Core Technologies
does not currently supply such a tool; See Interfacing to C++ for
more details.
pragma CPP_Constructor
Syntax:
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. The
argument is a name that must have been previously mentioned in a
pragma Import with Convention CPP, and must be of one of the
following forms:
1. function Fname return T'Class
2. function Fname (┬╖┬╖┬╖) return T'Class
where T is a tagged type to which the pragma CPP_Class applies.
The first form is the default constructor, used when an object of
type T is created on the Ada side with no explicit constructor.
Other constructors (including the copy constructor, which is
simply a special case of the second form in which the one and only
argument is of type T), can only appear in two contexts:
1. On the right side of an initialization of an object of type
T.
2. In an extension aggregate for an object of a type derived
from T.
Although the constructor is described as a function that returns a
value on the Ada side, it is typically a procedure with an extra
implicit argument (the object being initialized) at the
implementation level. GNAT issues the appropriate call, whatever
it is, to get the object properly initialized.
In the case of derived objects, you may use one of two possible
forms for declaring and creating an object:
1. New_Object : Derived_T
2. New_Object : Derived_T := (constructor-function-call with
┬╖┬╖┬╖)
In the first case the default constructor is called and extension
fields if any are initialized according to the default
initialization expressions in the Ada declaration. In the second
case, the given constructor is called and the extension aggregate
indicates the explicit values of the extension fields.
If no constructors are imported, it is impossible to create any
objects on the Ada side. If no default constructor is imported,
only the initialization forms using an explicit call to a
constructor are permitted.
Pragma CPP_Constructor is intended primarily for automatic
generation using an automatic binding generator tool. Ada Core
Technologies does not currently supply such a tool; See
Interfacing to C++ for more details.
pragma CPP_Destructor ([Entity =>] LOCAL_NAME);
This pragma identifies an imported procedure (imported in the usual
way with pragma Import) as corresponding to a C++ destructor.
LOCAL_NAME must be previously mentioned in a pragma Import with
Convention CPP, and be of the following form:
procedure Fname (obj : in out T'Class);
where T is a tagged type to which pragma CPP_Class applies. This
procedure will be called automatically on scope exit if any
objects of T are created on the Ada side.
Pragma CPP_Destructor is intended primarily for automatic
generation using an automatic binding generator tool. Ada Core
Technologies does not currently supply such a tool; See
Interfacing to C++ for more details.
pragma CPP_Virtual
Syntax:
pragma CPP_Virtual
[Entity =>] ENTITY,
[, [Vtable_Ptr =>] vtable_ENTITY,]
[, [Position =>] static_integer_EXPRESSION])
This pragma serves the same function as pragma Import in that case
of a virtual function imported from C++. The Entity argument must
be a primitive subprogram of a tagged type to which pragma
CPP_Class applies. The Vtable_Ptr argument specifies the
Vtable_Ptr component which contains the entry for this virtual
function. The Position argument is the sequential number counting
virtual functions for this Vtable starting at 1.
The Vtable_Ptr and Position arguments may be omitted if there is
one Vtable_Ptr present (single inheritance case) and all virtual
functions are imported. In that case the compiler can deduce both
these values.
No External_Name or Link_Name arguments are required for a virtual
function, since it is always accessed indirectly via the
appropriate Vtable entry.
Pragma CPP_Virtual is intended primarily for automatic generation
using an automatic binding generator tool. Ada Core Technologies
does not currently supply such a tool; See Interfacing to C++ for
more details.
pragma CPP_Vtable
Syntax:
pragma CPP_Vtable (
[Entity =>] ENTITY,
[Vtable_Ptr =>] vtable_ENTITY,
[Entry_Count =>] static_integer_EXPRESSION);
Given a record to which the pragma CPP_Class applies, this pragma
can be specified for each component of type
CPP.Interfaces.Vtable_Ptr. Entity is the tagged type, Vtable_Ptr
is the record field of type Vtable_Ptr, and Entry_Count is the
number of virtual functions on the C++ side. Not all of these
functions need to be imported on the Ada side.
You may omit the CPP_Vtable pragma if there is only one Vtable_Ptr
component in the record and all virtual functions are imported on
the Ada side (the default value for the entry count in this case
is simply the total number of virtual functions).
Pragma CPP_Vtable is intended primarily for automatic generation
using an automatic binding generator tool. Ada Core Technologies
does not currently supply such a tool; See Interfacing to C++ for
more details.
pragma Debug
Syntax:
pragma Debug (PROCEDURE_CALL_STATEMENT);
If assertions are not enabled on the command line, this pragma has
no effect. If asserts are enabled, the semantics of the pragma is
exactly equivalent to the procedure call. Pragmas are permitted in
sequences of declarations, so you can use pragma Debug to
intersperse calls to debug procedures in the middle of
declarations.
pragma Eliminate
Syntax:
pragma Eliminate (
[Unit_Name =>] IDENTIFIER |
SELECTED_COMPONENT);
pragma Eliminate (
[Unit_Name =>] IDENTIFIER |
SELECTED_COMPONENT
[Entity =>] IDENTIFIER |
SELECTED_COMPONENT |
STRING_LITERAL]
[,[Parameter_Types =>] PARAMETER_TYPES]
[,[Result_Type =>] result_SUBTYPE_NAME]]);
PARAMETER_TYPES ::= (SUBTYPE_NAME {, SUBTYPE_NAME})
SUBTYPE_NAME ::= STRING_LITERAL
This pragma indicates that the given entity is unused in a
program. The entity may be either a subprogram or a variable.
If the entity to be eliminated is a library level subprogram, then
the first form of pragma Eliminate is used with only a single
argument. In this form, the Unit_Name argument specifies the name
of the library level unit to be eliminated.
In all other cases, both Unit_Name and Entity arguments are
required. item is an entity of a library package, then the first
argument specifies the unit name, and the second argument
specifies the particular entity. If the second argument is in
string form, it must correspond to the internal manner in which
GNAT stores entity names (see compilation unit Namet in the
compiler sources for details). The third and fourth parameters are
optionally used to distinguish between overloaded subprograms, in
a manner similar to that used for the extended Import and Export
pragmas, except that the subtype names are always given as string
literals, again corresponding to the internal manner in which GNAT
stores entity names.
The effect of the pragma is to allow the compiler to optionally
eliminate the code or data associated with the named entity. If
the declaration of the entity would have resulted in side effects,
these side effects may or may not occur in the resulting program.
Any reference to an eliminated entity may cause a compile time
error, link time error, or incorrect results at runtime.
The intention of pragma Eliminate is to allow a program to be
compiled in a system independent manner, with unused entities
eliminated, without the requirement of modifying the source text.
Normally the required set of Eliminate pragmas is constructed
automatically using the gnatelim tool.
Note that the reason this pragma takes string literals where names
might be expected is that a pragma Eliminate can appear in a
context where the relevant names are not visible.
pragma Export_Exception
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.
pragma Export_Function ┬╖┬╖┬╖
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
| SUBTYPE_MARK {, SUBTYPE_MARK}
MECHANISM ::=
MECHANISM_NAME
| (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION})
MECHANISM_ASSOCIATION ::=
[formal_parameter_NAME =>] MECHANISM_NAME
MECHANISM_NAME ::=
Value
| Reference
| Descriptor [([Class =>] CLASS_NAME)]
CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
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 foriegn 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.
Passing by descriptor is supported only on the OpenVMS ports of
GNAT.
pragma Export_Object ┬╖┬╖┬╖
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.
pragma Export_Procedure ┬╖┬╖┬╖
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
| SUBTYPE_MARK {, SUBTYPE_MARK}
MECHANISM ::=
MECHANISM_NAME
| (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION})
MECHANISM_ASSOCIATION ::=
[formal_parameter_NAME =>] MECHANISM_NAME
MECHANISM_NAME ::=
Value
| Reference
| Descriptor [([Class =>] CLASS_NAME)]
CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
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 foriegn
convention.
pragma Export_Valued_Procedure
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
| SUBTYPE_MARK {, SUBTYPE_MARK}
MECHANISM ::=
MECHANISM_NAME
| (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION})
MECHANISM_ASSOCIATION ::=
[formal_parameter_NAME =>] MECHANISM_NAME
MECHANISM_NAME ::=
Value
| Reference
| Descriptor [([Class =>] CLASS_NAME)]
CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
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 foriegn convention.
pragma Extend_System
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 95 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.
pragma External_Name_Casing
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
Implicit external names are derived from identifiers.
The most common case arises when a standard Ada 95
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
Explicit external names are given as string literals.
The most common case arises when a standard Ada 95
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.
pragma Finalize_Storage_Only
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.
pragma Float_Representation
Syntax:
pragma Float_Representation (FLOAT_REP);
FLOAT_REP ::= VAX_Float | IEEE_Float
This pragma is implemented only in the OpenVMS implementation of
GNAT. It allows control over the internal representation chosen
for the predefined floating point types declared in the packages
Standard and System. For further details on this pragma, see the
DEC Ada Language Reference Manual, section 3.5.7a. Note that to
use this pragma, the standard runtime libraries must be
recompiled. See the description of the GNAT LIBRARY command in the
OpenVMS version of the GNAT Users Guide for details on the use of
this command.
pragma Ident
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. The maximum permitted length of the string
literal is 31 characters. This pragma is allowed only in the
outermost declarative part or declarative items of a compilation
unit. On OpenVMS systems, the effect of the pragma is identical to
the effect of the DEC Ada 83 pragma of the same name.
pragma Import_Exception
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.
pragma Import_Function ┬╖┬╖┬╖
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
| SUBTYPE_MARK {, SUBTYPE_MARK}
MECHANISM ::=
MECHANISM_NAME
| (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION})
MECHANISM_ASSOCIATION ::=
[formal_parameter_NAME =>] MECHANISM_NAME
MECHANISM_NAME ::=
Value
| Reference
| 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_Name 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.
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 to OpenVMS ports of
GNAT
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.
pragma Import_Object
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.
pragma Import_Procedure
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
| SUBTYPE_MARK {, SUBTYPE_MARK}
MECHANISM ::=
MECHANISM_NAME
| (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION})
MECHANISM_ASSOCIATION ::=
[formal_parameter_NAME =>] MECHANISM_NAME
MECHANISM_NAME ::=
Value
| Reference
| 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.
pragma Import_Valued_Procedure ┬╖┬╖┬╖
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
| SUBTYPE_MARK {, SUBTYPE_MARK}
MECHANISM ::=
MECHANISM_NAME
| (MECHANISM_ASSOCIATION {, MECHANISM_ASSOCIATION})
MECHANISM_ASSOCIATION ::=
[formal_parameter_NAME =>] MECHANISM_NAME
MECHANISM_NAME ::=
Value
| Reference
| 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.
pragma Inline_Always
Syntax:
pragma Inline_Always (NAME [, NAME]);
Similar to pragma Inline except that inlining is not subject to
the use of option -gnatn for inter-unit inlining.
pragma Inline_Generic
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.
pragma Interface
Syntax:
pragma Interface (
[Convention =>] convention_identifier,
[Entity =>] local_name
[, [External_Name =>] static_string_expression],
[, [Link_Name =>] static_string_expression]);
This pragma is identifical in syntax and semantics to the standard
Ada 95 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.
pragma Interface_Name
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.
pragma Linker_Alias
Syntax:
pragma Linker_Alias (
[Entity =>] LOCAL_NAME
[Alias =>] static_string_EXPRESSION);
This pragma establishes a linker alias for the given named entity.
For further details on the exact effect, consult the GCC manual.
pragma Linker_Section
Syntax:
pragma Linker_Section (
[Entity =>] LOCAL_NAME
[Section =>] static_string_EXPRESSION);
This pragma specifies the name of the linker section for the given
entity. For further details on the exact effect, consult the GCC
manual.
pragma No_Run_Time
Syntax:
pragma No_Run_Time;
This is a configuration pragma that makes sure the user code does
not use nor need anything from the GNAT run time. This is mostly
useful in context where code certification is required. Please
consult the GNORT product documentation for additional
information.
pragma Normalize_Scalars
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. This will be out of
range of the subtype only if the subtype range
excludes this value.
Standard.Wide_Character
Objects whose root type is Standard.Wide_Character are
initialized to Wide_Character'Last. This will be out
of range of the subtype only if the subtype range
excludes this value.
Integer types
Objects of an integer type are initialized to
base_type'First, where base_type is the base type of
the object type. This will be out of range of the
subtype only if the subtype range excludes this value.
For example, if you declare the subtype:
subtype Ityp is integer range 1 ┬╖┬╖ 10;
then objects of type x will be initialized to
Integer'First, a negative number that is certainly
outside the range of subtype Ityp.
Real types
Objects of all real types (fixed and floating) are
initialized to base_type'First, where base_Type is the
base type of the object type. This will be out of
range of the subtype only if the subtype range
excludes this value.
Modular types
Objects of a modular type are initialized to typ'Last.
This will be out of range of the subtype only if the
subtype excludes this value.
Enumeration types
Objects of an enumeration type are initialized to all
one-bits, i.e. to the value 2 ** typ'Size - 1. This
will be out of range of the enumeration subtype in all
cases except where the subtype contains exactly 2**8,
2**16, or 2**32.
pragma Long_Float
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 ┬╖┬╖ 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. See the description of the
GNAT LIBRARY command in the OpenVMS version of the GNAT Users
Guide for details on the use of this command.
pragma Machine_Attribute ┬╖┬╖┬╖
Syntax:
pragma Machine_Attribute (
[Attribute_Name =>] string_EXPRESSION,
[Entity =>] LOCAL_NAME);
Machine dependent attributes can be specified for types and/or
declarations. Currently only subprogram entities are supported.
This pragma is semantically equivalent to __attribute__((
string_expression)) in GNU C, where string_expression> is
recognized by the GNU C macros VALID_MACHINE_TYPE_ATTRIBUTE and
VALID_MACHINE_DECL_ATTRIBUTE which are defined in the
configuration header file 'tm.h' for each machine. See the GCC
manual for further information.
pragma Main_Storage
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.
pragma No_Return
Syntax:
pragma No_Return (procedure_LOCAL_NAME);
procedure_local_NAME 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, and also may not contain any implicit return
statements from falling off the end of a statement sequence. 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.
pragma Passive
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 no 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).
pragma Polling
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/adb.
A standard alternative unit (called 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 the GNAT User's Guide for details.
pragma Propagate_Exceptions
Syntax:
pragma Propagate_Exceptions (subprogram_LOCAL_NAME);
This pragma indicates that the given entity, which is the name of
an imported foreign-langauge subprogram may receive an Ada
exception, and that the exception should be propagated. It is
relevant only if zero cost exception handling is in use, and is
thus never needed if the alternative longjmp/setjmp implementation
of exceptions is used (although it is harmless to use it in such
cases).
The implementation of fast exceptions always properly propagates
exceptions through Ada code, as described in the Ada Reference
Manual. However, this manual is silent about the propagation of
exceptions through foreign code. For example, consider the
situation where P1 calls P2, and P2 calls P3, where P1 and P3 are
in Ada, but P2 is in C. P3 raises an Ada exception. The question
is whether or not it will be propagated through P2 and can be
handled in P1.
For the longjmp/setjmp implementation of exceptions, the answer is
always yes. For some targets on which zero cost exception handling
is implemented, the answer is also always yes. However, there are
some targets, notably in the current version all x86 architecture
targets, in which the answer is that such propagation does not
happen automatically. If such propagation is required on these
targets, it is mandatory to use Propagate_Exceptions to name all
foreign language routines through which Ada exceptions may be
propagated.
pragma Psect_Object
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.
Pure_Function
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). If 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: All functions in a Pure package are automatically pure, and
there is no need to use pragma Pure_Function in this case.
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.
pragma Ravenscar
Syntax:
pragma Ravenscar
A configuration pragma that establishes the following set of
restrictions:
No_Abort_Statements
[RM D.7] There are no abort_statements, and there are
no calls to Task_Identification.Abort_Task.
No_Select_Statements
There are no select_statements.
No_Task_Hierarchy
[RM D.7] All (non-environment) tasks depend directly
on the environment task of the partition.
No_Task_Allocators
[RM D.7] There are no allocators for task types or
types containing task subcomponents.
No_Dynamic_Priorities
[RM D.7] There are no semantic dependencies on the
package Dynamic_Priorities.
No_Terminate_Alternatives
[RM D.7] There are no selective_accepts with
terminate_alternatives
No_Dynamic_Interrupts
There are no semantic dependencies on Ada.Interrupts.
No_Protected_Type_Allocators
There are no allocators for protected types or types
containing protected subcomponents.
No_Local_Protected_Objects
Protected objects and access types that designate such
objects shall be declared only at library level.
No_Requeue
Requeue statements are not allowed.
No_Calendar
There are no semantic dependencies on the package
Ada.Calendar.
No_Relative_Delay
There are no delay_relative_statements.
No_Task_Attributes
There are no semantic dependencies on the
Ada.Task_Attributes package and there are no
references to the attributes Callable and Terminated
[RM 9.9].
Static_Storage_Size
The expression for pragma Storage_Size is static.
Boolean_Entry_Barriers
Entry barrier condition expressions shall be boolean
objects which are declared in the protected type which
contains the entry.
Max_Asynchronous_Select_Nesting = 0
[RM D.7] Specifies the maximum dynamic nesting level
of asynchronous_selects. A value of zero prevents the
use of any asynchronous_select.
Max_Task_Entries = 0
[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. A
value of zero indicates that no rendezvous are
possible. For the Ravenscar pragma, the value of
Max_Task_Entries is always 0 (zero).
Max_Protected_Entries = 1
[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. For the Ravenscar pragma the value of
Max_Protected_Entries is always 1.
Max_Select_Alternatives = 0
[RM D.7] Specifies the maximum number of alternatives
in a selective_accept. For the Ravenscar pragma the
value if always 0.
No_Task_Termination
Tasks which terminate are erroneous.
No_Entry_Queue
No task can be queued on a protected entry. Note that
this restrictions is checked at run time. The
violation of this restriction generates a
Program_Error exception.
This set of restrictions corresponds to the definition of the
"Ravenscar Profile" for limited tasking, devised and published by
the International Workshop On Real Time Ada", 1997.
The above set is a superset of the restrictions provided by pragma
Restricted_Run_Time, it includes six additional restrictions
(Boolean_Entry_Barriers, No_Select_Statements, No_Calendar,
Static_Storage_Size, No_Relative_Delay and No_Task_Termination).
This means that pragma Ravenscar, like the pragma
Restricted_Run_Time, automatically causes the use of a simplified,
more efficient version of the tasking run-time system.
pragma Restricted_Run_Time
Syntax:
pragma Restricted_Run_Time
A configuration pragma that establishes the following set of
restrictions:
1. No_Abort_Statements
2. No_Asynchronous_Control
3. No_Entry_Queue
4. No_Task_Hierarchy
5. No_Task_Allocators
6. No_Dynamic_Priorities
7. No_Terminate_Alternatives
8. No_Dynamic_Interrupts
9. No_Protected_Type_Allocators
10.No_Local_Protected_Objects
11.No_Requeue
12.No_Task_Attributes
13.Max_Asynchronous_Select_Nesting = 0
14.Max_Task_Entries = 0
15.Max_Protected_Entries = 1
16.Max_Select_Alternatives = 0
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.
pragma Share_Generic
Syntax:
pragma Share_Generic (NAME {, NAME});
This pragma is recognized for compatibility with other Ada
compilers but is ignored by GNAT. GNAT does not provide the
capability for sharing of generic code. All generic instantiations
result in making an inlined copy of the template with appropriate
substitutions.
pragma Source_File_Name
Syntax:
pragma Source_File_Name (
[Unit_Name =>] unit_NAME,
[FNAME_DESIG =>] STRING_LITERAL);
FNAME_DESIG => Body_File_Name | Spec_File_Name
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.
Another form of this pragma allows separate names to be specified
for a body (other than a subunit) and a subunit:
pragma Source_File_Name (
[Unit_Name =>] unit_NAME,
Body_File_Name => STRING_LITERAL,
Subunit_File_Name => STRING_LITERAL);
This form permits a given compilation environment to contain both
a subunit and, for example, a package body of the same name. The
Ada Reference Manual permits environments to contain both files,
although only one of them may be included in a single partition.
pragma Source_Reference
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.
pragma Stream_Convert
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 95 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 used for Standard.String, and this same
representation is expected when a value of this type is read from
the stream.
pragma Style_Checks
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 on the gcc or
gnatmake line. 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 checks (its use is equivalent to
the use of the gnaty switch with no options. See GNAT User's Guide
for details.
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; -- incrrect, wrong case
pragma Style_Checks (Off, Arg);
Rf2 : Integer := ARG; -- OK, no error
pragma Subtitle
Syntax:
pragma Subtitle ([Subtitle =>] STRING_LITERAL);
This pragma is recognized for compatibility with other Ada
compilers but is ignored by GNAT.
pragma Suppress_All
Syntax:
pragma Suppress_All;
This pragma can only appear immediately following a compilation
unit. The effect is to apply Suppress (All_Checks) to the unit
which it follows. This pragma is implemented for compatibility
with DEC Ada 83 usage. The use of pragma Suppress (All_Checks) as
a normal configuration pragma is the preferred usage in GNAT.
pragma Suppress_Initialization
Syntax:
pragma Suppress_Initialization ([Entity =>] type_Name);
This pragma suppresses any implicit or explicit initialization
associated with the given type name for all variables of this
type.
pragma Task_Info
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 aspect 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 specification of package System.Task_Info in the runtime
library.
pragma Task_Storage
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.
pragma Time_Slice
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.
pragma Title
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.
pragma Unchecked_Union
Syntax:
pragma Unchecked_Union (first_subtype_LOCAL_NAME)
This pragma is used to declare that the specified type should be
represented in a manner equivalent to a C union type, and is
intended only for use in interfacing with C code that uses union
types. In Ada terms, the named type must obey the following rules:
1. It is a non-tagged non-limited record type.
2. It has a single discrete discriminant with a default value.
3. The component list consists of a single variant part.
4. Each variant has a component list with a single component.
5. No nested variants are allowed.
6. No component has an explicit default value.
7. No component has a non-static constraint.
In addition, given a type that meets the above requirements, the
following restrictions apply to its use throughout the program:
1. The discriminant name can be mentioned only in an aggregate.
2. No subtypes may be created of this type.
3. The type may not be constrained by giving a discriminant
value.
4. The type cannot be passed as the actual for a generic formal
with a discriminant.
Equality and inequality operations on unchecked_unions are not
available, since there is no discriminant to compare and the
compiler does not even know how many bits to compare. It is
implementation dependent whether this is detected at compile time
as an illegality or whether it is undetected and considered to be
an erroneous construct. In GNAT, a direct comparison is illegal,
but GNAT does not attempt to catch the composite case (where two
composites are compared that contain an unchecked union
component), so such comparisons are simply considered erroneous.
The layout of the resulting type corresponds exactly to a C union,
where each branch of the union corresponds to a single variant in
the Ada record. The semantics of the Ada program is not changed in
any way by the pragma, i.e. provided the above restrictions are
followed, and no erroneous incorrect references to fields or
erroneous comparisons occur, the semantics is exactly as described
by the Ada reference manual. Pragma Suppress (Discriminant_Check)
applies implicitly to the type and the default convention is C
pragma Unimplemented_Unit
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.
pragma Unreserve_All_Interrupts
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 an 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 specification 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.
pragma Unsuppress
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.
pragma Use_VADS_Size
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 programs. This is
intended to aid in the handling of legacy code which depends on
the interpretation of Size as implemented in the VADS compiler.
See description of the VADS_Size attribute for further details.
pragma Volatile
Syntax:
pragma Volatile (local_NAME)
This pragma is defined by the Ada 95 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 implementation of pragma Volatile is upwards
compatible with the implementation in Dec Ada 83.
pragma Warnings
Syntax:
pragma Warnings (On | Off [, LOCAL_NAME]);
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 is 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).
pragma Weak_External
Syntax:
pragma Weak_External ([Entity =>] LOCAL_NAME);
This pragma specifies that the given entity should be marked as a
weak external (one that does not have to be resolved) for the
linker. For further details, consult the GCC manual.
ΓòÉΓòÉΓòÉ 5. Implementation Defined Attributes ΓòÉΓòÉΓòÉ
Ada 95 defines (throughout the Ada 95 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 95 Reference Manual.
In addition, Ada 95 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
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).
Address_Size
Standard'Address_Size (Standard is the only allowed prefix) is a
static constant giving the number of bits in an Address. It is used
primarily for constructing the definition of Memory_Size in package
Standard, but may be freely used in user programs.
Asm_Input
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
Asm_Output
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
AST_Entry
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.
Bit
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.
Bit_Position
R.C'Bit, 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.
Code_Address
The 'Address attribute may be applied to subprograms in Ada 95, but
the intended effect from the Ada 95 reference manual 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.
Default_Bit_Order
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.
Elaborated
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.
Elab_Body
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.
Elab_Spec
This attribute can only be applied to a program unit name. It
returns the entity for the corresponding elaboration procedure for
elaborating the specification 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.
Emax
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.
Enum_Rep
For every enumeration subtype S, S'Enum_Rep denotes a function with
the following specification:
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.
Epsilon
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.
Fixed_Value
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 equivalent to first converting the argument to the integer
type used to represent S, and then doing an unchecked conversion to the
fixed-point type. This attribute is primarily intended for use in
implementation of the input-output functions for fixed-point values.
Has_Discriminants
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.
Img
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 = " & type'Image (X));
where type is the subtype of the object X.
Integer_Value
For every integer type S, S'Integer_Value denotes a function with
the following specification:
function S'Integer_Value (Arg : Universal_Fixed)
return S;
The value returned is the integer value V, such that
Arg = V * type'Small
The effect is thus equivalent to first doing an unchecked convert from the
fixed-point type to its corresponding implementation type, and then converting
the result to the target integer type. This attribute is primarily intended
for use in implementation of the standard input-output functions for
fixed-point values.
Large
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.
Machine_Size
This attribute is identical to the Object_Size attribute. It is
provided for compatibility with the DEC Ada 83 attribute of this
name.
Mantissa
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.
Max_Interrupt_Priority
Standard'Max_Interrupt_Priority (Standard is the only permissible
prefix), provides the value System.Max_Interrupt_Priority and is
intended primarily for constructing this definition in package
System.
Max_Priority
Standard'Max_Priority (Standard is the only permissible prefix)
provides the value System.Max_Priority and is intended primarily for
constructing this definition in package System.
Maximum_Alignment
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. This
is useful when an external object is imported and its alignment
requirements are unknown.
Mechanism_Code
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:
1
by copy (value)
2
by reference
3
by descriptor (default descriptor class)
4
by descriptor (UBS: unaligned bit string)
5
by descriptor (UBSB: aligned bit string with arbitrary
bounds)
6
by descriptor (UBA: unaligned bit array)
7
by descriptor (S: string, also scalar access type
parameter)
8
by descriptor (SB: string with arbitrary bounds)
9
by descriptor (A: contiguous array)
10
by descriptor ( NCA: non-contiguous array)
Values from 3-10 are only relevant to Digital OpenVMS
implementations.
Null_Parameter
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.
Object_Size
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).
The type'Object_Size attribute has been added to GNAT to allow the
default object size of a type to be easily determined. For
example, Natural'Object_Size is 32, and Rec'Object_Size (for the
record type in the above example) will be 64. Note also that,
unlike the situation with the Size attribute as defined in the Ada
RM, the Object_Size attribute can be specified individually for
different subtypes. For example:
type R is new Integer;
subtype R1 is R range 1 ┬╖┬╖ 10;
subtype R2 is R range 1 ┬╖┬╖ 10;
for R2'Object_Size use 8;
In this example, R'Object_Size and R1'Object_Size are both 32
since the default object size for a subtype is the same as the
object size for the the parent subtype. This means that objects of
type R or R1 will by default be 32 bits (four bytes). But objects
of type R2 will be only 8 bits (one byte), since R2'Object_Size
has been set to 8.
Passed_By_Reference
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.
Range_Length
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.
Safe_Emax
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.
Safe_Large
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.
Safe_Large
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.
Small
The Small attribute is defined in Ada 95 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.
Storage_Unit
Standard'Storage_Unit (Standard is the only permissible prefix)
provides the value System.Storage_Unit and is intended primarily for
constructing this definition in package System.
Tick
Standard'Tick (Standard is the only permissible prefix) provides the
value of System.Tick and is intended primarily for constructing this
definition in package System.
To_Address
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).
Type_Class
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.
UET_Address
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,a-except.adb' for
details on how this attribute is used in the implementation.
Universal_Literal_String
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). This is used
internally for the construction of values of the floating-point
attributes from the file 'ttypef.ads', but may also be used by user
programs.
Unrestricted_Access
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 95
accessibility rules restrict this usage).
VADS_Size
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.
Value_Size
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.
Word_Size
Standard'Word_Size (Standard is the only permissible prefix)
provides the value System.Word_Size and is intended primarily for
constructing this definition in package System.
ΓòÉΓòÉΓòÉ 6. Implementation Advice ΓòÉΓòÉΓòÉ
The main text of the Ada 95 Reference Manual describes the required behavior
of all Ada 95 compilers, and the GNAT compiler conforms to these requirements.
In addition, there are sections throughout the Ada 95 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 95 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.
1.1.3(20): Error Detection
If an implementation detects the use of an unsupported Specialized
Needs Annex feature at run time, it should raise Program_Error if
feasible. Not relevant. All specialized needs annex features are
either supported, or diagnosed at compile time.
1.1.3(31): Child Units
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.
1.1.5(12): Bounded Errors
If an implementation detects a bounded error or erroneous execution,
it should raise Program_Error. Followed in all cases in which the
implementation detects a bounded error or erroneous execution. Not
all such situations are detected at runtime.
2.8(16): Pragmas
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
CPP_Destructor
Affects semantics
CPP_Virtual
Affects semantics
CPP_Vtable
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.
2.8(17-19): 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 Import;
A pragma used to configure the environment by adding, removing, or
replacing library_items. See response to paragraph 16 of this same
section.
3.5.2(5): Alternative Character Sets
If an implementation supports a mode with alternative
interpretations for Character and Wide_Character, the set of graphic
characters of Character should nevertheless remain a proper subset
of the set of graphic characters of Wide_Character. Any character
set ``localizations'' should be reflected in the results of the
subprograms defined in the language-defined package
Characters.Handling (see A.3) available in such a mode. In a mode
with an alternative interpretation of Character, the implementation
should also support a corresponding change in what is a legal
identifier_letter. 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.
3.5.4(28): Integer Types
An implementation should support Long_Integer in addition to Integer
if the target machine supports 32-bit (or longer) arithmetic. No
other named integer subtypes are recommended for package Standard.
Instead, appropriate named integer subtypes should be provided in
the library package Interfaces (see B.2). 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.
3.5.4(29): Integer Types
An implementation for a two's complement machine should support
modular types with a binary modulus up to System.Max_Int*2+2. An
implementation should support a non-binary modules up to
Integer'Last. Followed.
3.5.5(8): Enumeration Values
For the evaluation of a call on S'Pos for an enumeration subtype, if
the value of the operand does not correspond to the internal code
for any enumeration literal of its type (perhaps due to an
un-initialized variable), then the implementation should raise
Program_Error. This is particularly important for enumeration types
with noncontiguous internal codes specified by an
enumeration_representation_clause. Followed.
3.5.7(17): Float Types
An implementation should support Long_Float in addition to Float if
the target machine supports 11 or more digits of precision. No other
named floating point subtypes are recommended for package Standard.
Instead, appropriate named floating point subtypes should be
provided in the library package Interfaces (see B.2). 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.
3.6.2(11): Multidimensional Arrays
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
Convention (Fortran, ┬╖┬╖┬╖) applies to a multidimensional array type,
then column-major order should be used instead (see B.5,
``Interfacing with Fortran''). Followed.
9.6(30-31): Duration'Small
Whenever possible in an implementation, the value of Duration'Small
should be no greater than 100 microseconds. Followed.
(Duration'Small = 10**(-9)).
The time base for delay_relative_statements should be monotonic; it
need not be the same time base as used for Calendar.Clock. Followed.
10.2.1(12): Consistent Representation
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.
11.4.1(19): Exception Information
Exception_Message by default and Exception_Information should
produce information useful for debugging. Exception_Message should
be short, about one line. Exception_Information can be long.
Exception_Message should not include the Exception_Name.
Exception_Information should include both the Exception_Name and the
Exception_Message. 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.
11.5(28): Suppression of Checks
The implementation should minimize the code executed for checks that
have been suppressed. Followed.
13.1 (21-24): Representation Clauses
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. GNAT does
not support non-static expressions in representation clauses unless
they are constants declared before the entity. For example:
X : typ;
for X'Address use To_address (16#2000#);
will be rejected, since the To_Address expression is non-static.
Instead write:
X_Address : constant Address : =
To_Address ((16#2000#);
X : typ;
for X'Address use X_Address;
An implementation need not support a specification for the Size
for a given composite subtype, nor the size or storage place for
an object (including a component) of a given composite subtype,
unless the constraints on the subtype and its composite
subcomponents (if any) are all static constraints. 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.
13.2(6-8): Packed Types
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 Pack is:
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 record_representation_clause that applies to the
type; the implementation may, but need not, reorder components or
cross aligned word boundaries to improve the packing. A component
whose Size is greater than the word size may be allocated an
integral number of words. Followed. Tight packing of arrays is
supported for all component sizes up to 32-bits, which is the word
size on typical implementations of GNAT.
An implementation should support Address clauses for imported
subprograms. Followed.
13.3(14-19): Address Clauses
For an array X, X'Address should point at the first component of the
array, and not at the array bounds. Followed.
The recommended level of support for the Address attribute is:
X'Address should produce a useful result if X is an object that is
aliased or of a by-reference type, or is an entity whose Address has
been specified. 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 Address clauses for imported
subprograms. Followed.
Objects (including subcomponents) that are aliased or of a
by-reference type should be allocated on storage element boundaries.
Followed.
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. Followed.
13.3(29-35): Alignment Clauses
The recommended level of support for the Alignment attribute for
subtypes is:
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 Alignments for
combinations of Sizes and Alignments that cannot be easily loaded
and stored by available machine instructions. Followed.
An implementation need not support specified Alignments that are
greater than the maximum Alignment the implementation ever returns
by default. Followed.
The recommended level of support for the Alignment attribute for
objects is:
Same as above, for subtypes, but in addition: Followed.
For stand-alone library-level objects of statically constrained
subtypes, the implementation should support all Alignments supported
by the target linker. For example, page alignment is likely to be
supported for such objects, but not for subtypes. Followed.
13.3(42-43): Size Clauses
The recommended level of support for the Size attribute of objects
is:
A Size clause should be supported for an object if the specified
Size is at least as large as its subtype's Size, and corresponds to
a size in storage elements that is a multiple of the object's
Alignment (if the Alignment is nonzero). Followed.
13.3(50-56): Size Clauses
If the Size of a subtype is specified, and allows for efficient
independent addressability (see 9.10) on the target architecture,
then the Size of the following objects of the subtype should equal
the Size of the subtype:
Aliased objects (including components). Followed.
Size clause on a composite subtype should not affect the internal
layout of components. Followed.
The recommended level of support for the Size attribute of subtypes
is:
The Size (if not specified) of a static discrete or fixed point
subtype should be the number of bits needed to represent each value
belonging to the subtype using an unbiased representation, leaving
space for a sign bit only if the subtype contains negative values.
If such a subtype is a first subtype, then an implementation should
support a specified Size for it that reflects this representation.
Followed.
For a subtype implemented with levels of indirection, the Size
should include the size of the pointers, but not the size of what
they point at. Followed.
13.3(71-73): Component Size Clauses
The recommended level of support for the Component_Size attribute
is:
An implementation need not support specified Component_Sizes that
are less than the Size of the component subtype. Followed.
An implementation should support specified Component_Sizes that are
factors and multiples of the word size. For such Component_Sizes,
the array should contain no gaps between components. For other
Component_Sizes (if supported), the array should contain no gaps
between components when packing is also specified; the
implementation should forbid this combination in cases where it
cannot support a no-gaps representation. Followed.
13.4(9-10): Enumeration Representation Clauses
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 System.Min_Int.System.Max_Int. Followed.
13.5.1(17-22): Record Representation Clauses
The recommended level of support for
record_representation_clauses is:
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 Size
of the component subtype, and it starts and ends on a boundary that
obeys the Alignment of the component subtype. Followed.
If the default bit ordering applies to the declaration of a given
type, then for a component whose subtype's Size is less than the
word size, any storage place that does not cross an aligned word
boundary should be supported. 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 component_clause for a
component of an extension part if the storage place is not after the
storage places of all components of the parent type, whether or not
those storage places had been specified. Followed. The above advice
on record representation clauses is followed, and all mentioned
features are implemented.
13.5.2(5): Storage Place Attributes
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.
13.5.3(7-8): Bit Ordering
The recommended level of support for the non-default bit ordering
is:
If Word_Size = Storage_Unit, then the implementation should support
the non-default bit ordering in addition to the default bit
ordering. Followed. Word size does not equal storage size in this
implementation. Thus non-default bit ordering is not supported.
13.7(37): Address as Private
Address should be of a private type. Followed.
13.7.1(16): Address Operations
Operations in System and its children should reflect the target
environment semantics as closely as is reasonable. For example, on
most machines, it makes sense for address arithmetic to ``wrap
around.'' Operations that do not make sense should raise
Program_Error. Followed. Address arithmetic is modular arithmetic
that wraps around. No operation raises Program_Error, since all
operations make sense.
13.9(14-17): Unchecked Conversion
The Size of an array object should not include its bounds; hence,
the bounds should not be part of the converted data. 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.
13.11(23-25): Implicit Heap Usage
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:
1. At initial elaboration time, to allocate dynamically sized
global objects.
2. To allocate space for a task when a task is created.
3. To extend the secondary stack dynamically when needed. The
secondary stack is used for returning variable length
results.
A default (implementation-provided) storage pool for an access-to-
constant type should not have overhead to support de-allocation 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.
13.11.2(17): Unchecked De-allocation
For a standard storage pool, Free should actually reclaim the
storage. Followed.
13.13.2(17): Stream Oriented Attributes
If a stream element is the same size as a storage element, then the
normal in-memory representation should be used by Read and Write for
scalar objects. Otherwise, Read and Write should use the smallest
number of stream elements needed to represent all values in the base
range of the scalar type. Followed.
A.1(52): Implementation Advice
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.
A.3.2(49): Ada.Characters.Handling
If an implementation provides a localized definition of Character or
Wide_Character, then the effects of the subprograms in
Characters.Handling should reflect the localizations. See also
3.5.2. Followed. GNAT provides no such localized definitions.
A.4.4(106): Bounded-Length String Handling
Bounded string objects should not be implemented by implicit
pointers and dynamic allocation. Followed. No implicit pointers or
dynamic allocation are used.
A.5.2(46-47): Random Number Generation
Any storage associated with an object of type Generator should be
reclaimed on exit from the scope of the object. Followed.
If the generator period is sufficiently long in relation to the
number of distinct initiator values, then each possible value of
Initiator passed to Reset should initiate a sequence of random
numbers that does not, in a practical sense, overlap the sequence
initiated by any other value. If this is not possible, then the
mapping between initiator values and generator states should be a
rapidly varying function of the initiator value. Followed. The
generator period is sufficiently long for the first condition here
to hold true.
A.10.7(23): Get_Immediate
The Get_Immediate procedures should be implemented with unbuffered
input. For a device such as a keyboard, input should be available if
a key has already been typed, whereas for a disk file, input should
always be available except at end of file. For a file associated
with a keyboard-like device, any line-editing features of the
underlying operating system should be disabled during the execution
of Get_Immediate. Followed.
B.1(39-41): Pragma Export
If an implementation supports pragma Export to a given language,
then it should also allow the main subprogram to be written in that
language. It should support some mechanism for invoking the
elaboration of the Ada library units included in the system, and for
invoking the finalization of the environment task. On typical
systems, the recommended mechanism is to provide two subprograms
whose link names are adainit and adafinal. adainit should contain
the elaboration code for library units. adafinal should contain the
finalization code. These subprograms should have no effect the
second and subsequent time they are called. Followed.
Automatic elaboration of pre-elaborated packages should be provided
when pragma Export is supported. 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 Intrinsic, an
implementation should support Import and Export pragmas for objects
of L-compatible types and for subprograms, and pragma Convention for
L-eligible types and for subprograms, presuming the other language
has corresponding features. Pragma Convention need not be supported
for scalar types. Followed.
B.2(12-13): Package 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 Interfaces. Followed. An additional package not defined
in the Ada 95 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.
B.3(63-71): Interfacing with C
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 in scalar parameter is passed as a scalar argument to a C
function. Followed.
An Ada in parameter of an access-to-object type with designated type
T is passed as a t* argument to a C function, where t is the C type
corresponding to the Ada type T. Followed.
An Ada access T parameter, or an Ada out or in out parameter of an
elementary type T, is passed as a t* argument to a C function, where
t is the C type corresponding to the Ada type T. In the case of an
elementary out or in out parameter, a pointer to a temporary copy is
used to preserve by-copy semantics. Followed.
An Ada parameter of a record type T, of any mode, is passed as a t*
argument to a C function, where t is the C structure corresponding
to the Ada type T. 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 t* argument to a C function, where t is the C
type corresponding to the Ada type T. 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.
B.4(95-98): Interfacing with COBOL
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.
B.5(22-26): Interfacing with Fortran
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.
C.1(3-5): Access to Machine Operations
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 Assembler. 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.
C.1(10-16): Access to Machine Operations
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.
C.3(28): Interrupt Support
If the Ceiling_Locking policy is not in effect, the implementation
should provide means for the application to specify which interrupts
are to be blocked during protected actions, if the underlying system
allows for a finer-grain control of interrupt blocking. Followed.
The underlying system does not allow for finer-grain control of
interrupt blocking.
C.3.1(20-21): Protected Procedure Handlers
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.
C.3.2(25): Package 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
Parameterless_Handler should be specified in a child package of
Interrupts, with the same operations as in the predefined package
Interrupts. Followed.
C.4(14): Pre-elaboration Requirements
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.
C.5(8): Pragma 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.
C.7.2(30): The Package Task_Attributes
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.
D.3(17): Locking Policies
The implementation should use names that end with '_Locking' for
locking policies defined by the implementation. Followed. No such
implementation-defined locking policies exist.
D.4(16): Entry Queuing Policies
Names that end with '_Queuing' should be used for all
implementation-defined queuing policies. Followed. No such
implementation-defined queueing policies exist.
D.6(9-10): Preemptive Abort
Even though the abort_statement is included in the list of
potentially blocking operations (see 9.5.1), it is recommended that
this statement be implemented in a way that never requires the task
executing the abort_statement to block. 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.
D.7(21): Tasking Restrictions
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
Ravenscar and pragma Restricted_Run_Time for more details.
D.8(47-49): Monotonic Time
When appropriate, implementations should provide configuration
mechanisms to change the value of Tick. Such configuration
mechanisms are not appropriate to this implementation and are thus
not supported.
It is recommended that Calendar.Clock and Real_Time.Clock be
implemented as transformations of the same time base. Followed.
It is recommended that the best time base which exists in the
underlying system be available to the application through Clock.
Best may mean highest accuracy or largest range. Followed.
E.5(28-29): Partition Communication Subsystem
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. For information on GLADE, contact Ada Core
Technologies.
The Write operation on a stream of type Params_Stream_Type should
raise Storage_Error if it runs out of space trying to write the Item
into the stream. Followed by GLADE, a separately supplied PCS that
can be used with GNAT. For information on GLADE, contact Ada Core
Technologies.
F(7): COBOL Support
If COBOL (respectively, C) is widely supported in the target
environment, implementations supporting the Information Systems
Annex should provide the child package Interfaces.COBOL
(respectively, Interfaces.C) specified in Annex B and should support
a convention_identifier of COBOL (respectively, C) in the
interfacing pragmas (see Annex B), thus allowing Ada programs to
interface with programs written in that language. Followed.
F.1(2): Decimal Radix Support
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.
G: Numerics
If Fortran (respectively, C) is widely supported in the target
environment, implementations supporting the Numerics Annex should
provide the child package Interfaces.Fortran (respectively,
Interfaces.C) specified in Annex B and should support a
convention_identifier of Fortran (respectively, C) in the
interfacing pragmas (see Annex B), thus allowing Ada programs to
interface with programs written in that language. Followed.
G.1.1(56-58): Complex Types
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 Signed_Zeros attribute of the component type is True (and which
therefore conform to IEC 559:1989 in regard to the handling of the
sign of zero in predefined arithmetic operations), the latter
technique will not generate the required result when the imaginary
component of the complex operand is a negatively signed zero.
(Explicit addition of the negative zero to the zero obtained during
promotion yields a positive zero.) Analogous advice applies in the
case of addition of a complex operand and a pure-imaginary operand,
and in the case of subtraction of a complex operand and a real or
pure-imaginary operand. Not followed.
Implementations in which Real'Signed_Zeros is True should attempt to
provide a rational treatment of the signs of zero results and result
components. As one example, the result of the Argument function
should have the sign of the imaginary component of the parameter X
when the point represented by that parameter lies on the positive
real axis; as another, the sign of the imaginary component of the
Compose_From_Polar function should be the same as (respectively, the
opposite of) that of the Argument parameter when that parameter has
a value of zero and the Modulus parameter has a nonnegative
(respectively, negative) value. Followed.
G.1.2(49): Complex Elementary Functions
Implementations in which Complex_Types.Real'Signed_Zeros is True
should attempt to provide a rational treatment of the signs of zero
results and result components. For example, many of the complex
elementary functions have components that are odd functions of one
of the parameter components; in these cases, the result component
should have the sign of the parameter component at the origin. Other
complex elementary functions have zero components whose sign is
opposite that of a parameter component at the origin, or is always
positive or always negative. Followed.
G.2.4(19): Accuracy Requirements
The versions of the forward trigonometric functions without a Cycle
parameter should not be implemented by calling the corresponding
version with a Cycle parameter of 2.0*Numerics.Pi, since this will
not provide the required accuracy in some portions of the domain.
For the same reason, the version of Log without a Base parameter
should not be implemented by calling the corresponding version with
a Base parameter of Numerics.e. Followed.
G.2.6(15): Complex Arithmetic Accuracy
The version of the Compose_From_Polar function without a Cycle
parameter should not be implemented by calling the corresponding
version with a Cycle parameter of 2.0*Numerics.Pi, since this will
not provide the required accuracy in some portions of the domain.
Followed.
ΓòÉΓòÉΓòÉ 7. Implementation Defined Characteristics ΓòÉΓòÉΓòÉ
In addition to the implementation dependent pragmas and attributes, and the
implementation advice, there are a number of other features of Ada 95 that are
potentially implementation dependent. These are mentioned throughout the Ada
95 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 95 Reference Manual.
2. Whether or not each recommendation given in Implementation Advice is
followed. See 1.1.2(37).
See Implementation Advice.
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 code_statements cause external interactions. See 1.1.3(10).
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 an the maximum length of a lexical
element is also 255 characters.
10. Implementation defined pragmas. See 2.8(14).
See Implementation Defined Pragmas.
11. Effect of pragma Optimize. See 2.8(27).
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 S'Image when some of
the graphic characters of S'Wide_Image are not defined in Character. See
3.5(37).
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 Standard. See 3.5.4(25).
Short_Short_Integer
8 bit signed
Short_Integer
(Short) 16 bit signed
Integer
32 bit signed
Long_Integer
32 bit signed
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 Standard. See 3.5.7(16).
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.
20. The result of Tags.Expanded_Name for types declared within an unnamed
block_statement. See 3.9(10).
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 Calendar.Time. See 9.6(23).
The time base used is that provided by the C library function gettimeofday.
25. The time zone used for package Calendar operations. See 9.6(24).
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 delay_until_statements of select_statements. See 9.6(29).
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
Component_Size is specified for the object. See 9.10(1).
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).
See separate section on binding and linking programs.
32. The implementation-defined means, if any, of specifying which compilation
units are needed by a given compilation unit. See 10.2(2).
See separate section on compilation unit.
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 library_items. See 10.2(18).
The first constraint on ordering is that it meets the requirements of chapter
10 of the Ada 95 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.
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. See 11.4.1(10).
Exception message returns the null string unless a specific message has been
passed by the program.
40. The result of Exceptions.Exception_Name for types declared within an
unnamed block_statement. See 11.4.1(12).
Blocks have implementation defined names of the form Bnnn where nnn is an
integer.
41. The information returned by Exception_Information. See 11.4.1(13).
Exception_Information contains the expanded name of the exception in upper
case, and no other information.
42. Implementation-defined check names. See 11.5(27).
No implementation-defined check names are supported.
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 indefinite subtypes. See 13.3(48).
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 = Storage_Unit, the default bit ordering. See 13.5.3(5).
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 System and its
language-defined children. See 13.7(2).
See the definition of these packages in files 'system.ads' and 's-stoele.ads'.
51. The contents of the visible part of package System.Machine_Code, and the
meaning of code_statements. See 13.8(7).
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 and 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.
53. The manner of choosing a storage pool for an access type when
Storage_Pool is not specified for the type. See 13.11(17).
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_Sizeis 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. See 13.11(18).
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 Restrictions. See 13.12(7).
All RM defined Restriction identifiers are implemented. The following
additional restriction identifiers are provided. There are two separate lists
of implementation dependent restriction identifiers. The first set requires
consistency throughout a partition (in other words, if the restriction
identifier is used for any unit in the partition, then all units in the
partition must obey the restriction.
Boolean_Entry_Barriers
This restriction ensures at compile time that barriers in entry
declarations for protected types are restricted to references to
simple boolean variables defined in the private part of the
protected type. No other form of entry barriers is permitted. This
is one of the restrictions of the Ravenscar profile for limited
tasking (see also pragma Ravenscar).
Max_Entry_Queue_Depth => Expr
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. This restriction is not checked at compile time. A program
execution is erroneous if an attempt is made to queue more than the
specified number of tasks on such an entry.
No_Calendar
This restriction ensures at compile time that there is no implicit
or explicit dependence on the package Ada.Calendar.
No_Dynamic_Interrupts
This restriction ensures at compile time that there is no attempt to
dynamically associate interrupts. Only static association is
allowed.
No_Enumeration_Maps
This restriction ensures at compile time that no operations
requiring enumeration maps are used (that is Image and Value
attributes applied to enumeration types).
No_Entry_Calls_In_Elaboration_Code
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.
No_Exception_Handlers
This restriction ensures at compile time that there are no explicit
exception handlers.
No_Implicit_Conditionals
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. The details and use of this
restriction are described in more detail in the GNORT Reference
Manual.
No_Implicit_Conditionals
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. The details and use of this
restriction are described in more detail in the GNORT Reference
Manual.
No_Local_Protected_Objects
This restriction ensures at compile time that protected objects are
only declared at the library level.
No_Protected_Type_Allocators
This restriction ensures at compile time that there are no allocator
expressions that attempt to allocate protected objects.
No_Select_Statements
This restriction ensures at compile time no select statements of any
kind are permitted, that is the keyword select may not appear. This
is one of the restrictions of the Ravenscar profile for limited
tasking (see also pragma Ravenscar).
No_Standard_Storage_Pools
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.
No_Streams
This restriction ensures at compile time that there are no implicit
or explicit dependencies on the package Ada.Streams.
No_Task_Attributes
This restriction ensures at compile time that there are no implicit
or explicit dependencies on the package Ada.Task_Attributes.
No_Task_Termination
This restriction ensures at compile time that no terminate
alternatives appear in any task body.
No_Wide_Characters
This restriction ensures at compile time that no uses of the types
Wide_Character or Wide_String appear, and that no wide character
literals appear in the program (that is literals representing
characters not in type Character.
Static_Priorities
This restriction ensures at compile time that all priority
expressions are static, and that there are no dependencies on the
package Ada.Dynamic_Priorities.
Static_Storage_Size
This restriction ensures at compile time that any expression
appearing in a Storage_Size pragma or attribute definition clause is
static.
The second set of implementation dependent attributes does not require
partition-wide consistency. The restriction may be enforced for a single unit
without any effect on any of the other units in the partition.
No_Elaboration_Code
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 by others.
No_Entry_Queue
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.
No_Implementation_Attributes
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 95 Reference Manual.
No_Implementation_Pragmas
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 95 Reference Manual.
No_Implementation_Restrictions
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 95 Reference Manual.
58. The consequences of violating limitations on Restrictions pragmas. See
13.12(9).
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 Read and Write attributes of elementary
types in terms of stream elements. See 13.13.2(9).
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 Standard. See A.1(3).
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
Numerics.Generic_Elementary_Functions, when Float_Type'Signed_Zeros is True.
See A.5.1(46).
The sign of zeroes follows the requirements of the IEEE 754 standard on
floating-point.
63. The value of Numerics.Float_Random.Max_Image_Width. See A.5.2(27).
Maximum image width is 649, see library file 'a-numran.ads'.
64. The value of Numerics.Discrete_Random.Max_Image_Width. See A.5.2(27).
Maximum image width is 80, see library file 'a-nudira.ads'.
65. The algorithms for random number generation. See A.5.2(32).
The algorithm is documented in the source files 'a-numran.ads' and
'a-numran.adb'.
66. The string representation of a random number generator's state. See
A.5.2(38).
See the documentation contained in the file 'a-numran.adb'.
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 Model_Mantissa, Model_Emin, Model_Epsilon, Model,
Safe_First, and Safe_Last attributes, if the Numerics Annex is not supported.
See A.5.3(72).
See the source file 'ttypef.ads' for 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 Buffer_Size in Storage_IO. See A.9(10).
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 Put. See A.10.9(36).
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 Argument_Count, Argument, and Command_Name. See A.15(1).
These are mapped onto the argv and argc parameters of the main program in the
natural manner.
74. Implementation-defined convention names. See B.1(11).
The following convention names are supported
Ada
Ada
Asm
Assembly language
Assembler
Assembly language
C
C
C_Pass_By_Copy
Treated like C, except for record types
COBOL
COBOL
CPP
C++
Default
Treated the same as C
DLL
DLL (used for Windows implementations only) is handled like the
Stdcall convention. This convention is used to access variables and
functions (with Stdcall convention) in a DLL.
External
Treated the same as C
Fortran
Fortran
Intrinsic
Intrinsic
Stdcall
Stdcall (used for Windows implementations only). This convention
correspond to the WINAPI (previously called Pascal convention) C/C++
convention under Windows. A function with this convention clean the
stack before exit.
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.
75. The meaning of link names. See B.1(36).
Link names are the actual names used by the linker.
76. 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.
77. The effect of pragma Linker_Options. See B.1(37).
The string passed to Linker_Options is presented uninterpreted as an argument
to the link command.
78. The contents of the visible part of package Interfaces and its
language-defined descendants. See B.2(1).
See files with prefix 'i-' in the distributed library.
79. Implementation-defined children of package Interfaces. The contents of
the visible part of package Interfaces. See B.2(11).
See files with prefix 'i-' in the distributed library.
80. The types Floating, Long_Floating, Binary, Long_Binary, Decimal_ Element,
and COBOL_Character; and the initialization of the variables Ada_To_COBOL and
COBOL_To_Ada, in Interfaces.COBOL. See B.4(50).
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.
81. Support for access to machine instructions. See C.1(1).
See documentation in file 's-maccod.ads' in the distributed library.
82. Implementation-defined aspects of access to machine operations. See
C.1(9).
See documentation in file 's-maccod.ads' in the distributed library.
83. 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.
84. 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.
85. The semantics of pragma Discard_Names. See C.5(7).
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.
86. The result of the Task_Identification.Image attribute. See C.7.1(7).
The result of this attribute is an 8-digit hexadecimal string representing the
virtual address of the task control block.
87. The value of Current_Task when in a protected entry or interrupt handler.
See C.7.1(17).
Protected entries or interrupt handlers can be executed by any convenient
thread, so the value of Current_Task is undefined.
88. The effect of calling Current_Task from an entry body or interrupt
handler. See C.7.1(19).
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.
89. Implementation-defined aspects of Task_Attributes. See C.7.2(19).
There are no implementation-defined aspects of Task_Attributes.
90. Values of all Metrics. See D(2).
The metrics information for GNAT depends on the performance of the unerlying
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.
91. The declarations of Any_Priority and Priority. See D.1(11).
See declarations in file 'system.ads'.
92. Implementation-defined execution resources. See D.1(15).
There are no implementation-defined execution resources.
93. 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.
94. 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.
95. Implementation-defined policy_identifiers allowed in a pragma
Task_Dispatching_Policy. See D.2.2(3).
There are no implementation-defined policy-identifiers allowed in this pragma.
96. 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.
97. Implementation defined task dispatching. See D.2.2(18).
The policy is the same as that of the underlying threads implementation.
98. Implementation-defined policy_identifiers allowed in a pragma
Locking_Policy. See D.3(4).
There are no implementation defined policy identifiers allowed in this pragma.
99. 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 95 Reference Manual
D.3(10),
100. 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.
101. Implementation-defined queuing policies. See D.4(1).
There are no implementation-defined queueing policies.
102. 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.
103. Any operations that implicitly require heap storage allocation. See
D.7(8).
The only operation that implicitly requires heap storage allocation is task
creation.
104. Implementation-defined aspects of pragma Restrictions. See D.7(20).
There are no such implementation-defined aspects.
105. Implementation-defined aspects of package Real_Time. See D.8(17).
There are no implementation defined aspects of package Real_Time.
106. Implementation-defined aspects of delay_statements. See D.9(8).
Any difference greater than one microsecond will cause the task to be delayed
(see D.9(7)).
107. 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.
108. 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.
109. 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.
110. 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.
111. 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.
112. 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.
113. 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.
114. Implementation-defined interfaces in the PCS. See E.5(26).
See the GLADE reference manual for a full description of all implementation
defined interfaces.
115. The values of named numbers in the package Decimal. See F.2(7).
Max_Scale
+18
Min_Scale
-18
Min_Delta
1.0E-18
Max_Delta
1.0E+18
Max_Decimal_Digits
18
116. The value of Max_Picture_Length in the package Text_IO.Editing. See
F.3.3(16).
64
117. The value of Max_Picture_Length in the package Wide_Text_IO.Editing. See
F.3.4(5).
64
118. 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.
119. The sign of a zero result (or a component thereof) from any operator or
function in Numerics.Generic_Complex_Types, when Real'Signed_Zeros is True.
See G.1.1(53).
The signs of zero values are as recommended by the relevant implementation
advice.
120. The sign of a zero result (or a component thereof) from any operator or
function in Numerics.Generic_Complex_Elementary_Functions, when
Real'Signed_Zeros is True. See G.1.2(45).
The signs of zero values are as recommended by the relevant implementation
advice.
121. 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.
122. 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.
123. The result of a floating point arithmetic operation in overflow
situations, when the Machine_Overflows attribute of the result type is False.
See G.2.1(13).
Infinite and Nan values are produced as dictated by the IEEE floating-point
standard.
124. 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.
125. 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.
126. Conditions on a universal_real operand of a fixed point multiplication
or division for which the result shall be in the perfect result set. See
G.2.3(22).
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.
127. The result of a fixed point arithmetic operation in overflow situations,
when the Machine_Overflows attribute of the result type is False. See
G.2.3(27).
Not relevant, Machine_Overflows is True for fixed-point types.
128. The result of an elementary function reference in overflow situations,
when the Machine_Overflows attribute of the result type is False. See
G.2.4(4).
IEEE infinite and Nan values are produced as appropriate.
129. 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.
130. 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.
131. The result of a complex arithmetic operation or complex elementary
function reference in overflow situations, when the Machine_Overflows
attribute of the corresponding real type is False. See G.2.6(5).
IEEE infinite and Nan values are produced as appropriate.
132. 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.
133. Information regarding bounded errors and erroneous execution. See
H.2(1).
Information on this subject is not yet available.
134. Implementation-defined aspects of pragma Inspection_Point. See H.3.2(8).
Pragma Inspection_Point ensures that the variable is live and can be examined
by the debugger at the inspection point.
135. Implementation-defined aspects of pragma Restrictions. See H.4(25).
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.
136. Any restrictions on pragma Restrictions. See H.4(27).
There are no restrictions on pragma Restrictions.
ΓòÉΓòÉΓòÉ 8. Representation Clauses and Pragmas ΓòÉΓòÉΓòÉ
Alignment Clauses Alignment Clauses
Size Clauses Size Clauses
Biased Representation Biased Representation
Value_Size and Object_Size ClausesValue_Size and Object_Size Clauses
Component_Size Clauses Component_Size Clauses
Bit_Order Clauses Bit_Order Clauses
Pragma Pack for Arrays Pragma Pack for Arrays
Pragma Pack for Records Pragma Pack for Records
Record Representation Clauses Record Representation Clauses
Enumeration Clauses Enumeration Clauses
Address Clauses Address Clauses
Effect of Convention on RepresentationEffect of Convention on Representation
Determining the Representations chosen by GNATDetermining the Representations
chosen by GNAT
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 mininal level of support for representation
clauses. GNAT provides much more extensive capabilities, and this section
describes the additional capabilities provided.
ΓòÉΓòÉΓòÉ 8.1. Alignment Clauses ΓòÉΓòÉΓòÉ
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:
Primitive Types
For primitive types, the alignment is the maximum of the actual size of
objects of the type, and the maximum alignment supported by the target.
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.
Arrays
For arrays, the alignment is equal to the alignment of the component type
for the normal case where no packing or component size is given. If the
array is packed, and the packing is effective (see separate section on
packed arrays), then the alignment will be one for long packed arrays, or
arrays whose length is not known at compile time. For short packed
arrays, which are handled internally as modular types, the alignment will
be as described for primitive types, e.g. a packed array of length 31
bits will have an object size of four bytes, and an alignment of 4.
Records
For the normal non-packed case, the alignment of a record is equal to the
maximum alignment of any of its components. For tagged records, this
includes the implicit access type used for the tag. If a pragma Pack is
used and all fields are packable (see separate section on pragma Pack),
then the resulting alignment is 1.
An alignment clause may always specify a larger alignment than the default
value, up to some maximum value dependent on the target (obtainable by using
the attribute reference System'Maximum_Alignment). The only case in which it
is permissible to specify a smaller alignment than the default value is in the
case of a record for which a record representation clause is given. In this
case, packable fields for which a component clause is given still result in a
default alignment corresponding to the original type, but this may be
overridden, since these components in fact only require an alignment of one
byte. For example, given
type v is record
a : integer;
end record;
for v use record
a at 0 range 0 ┬╖┬╖ 31;
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 since this field is placed with a component clause, it is
permissible, as shown, to override the default alignment of the record to a
smaller value.
ΓòÉΓòÉΓòÉ 8.2. Size Clauses ΓòÉΓòÉΓòÉ
The default size of types is as specified in the reference manual. For
objects, GNAT will generally increase the type size so that the object size is
a multiple of storage units, and also a multiple of the alignment. For example
type Smallint is range 1 ┬╖┬╖ 6;
type Rec is record
y1 : integer;
y2 : boolean;
end record;
In this example, Smallint has a size of 3, as specified by the RM rules, but
objects of this type will have a size of 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, 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. The reason for this decision, which is in
accordance with the specific note in RM 13.3(43):
A Size clause should be supported for an object if the specified
Size is at least as large as its subtype's Size, and corresponds
to a size in storage elements that is a multiple of the object's
Alignment (if the Alignment 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 objects 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.
ΓòÉΓòÉΓòÉ 8.3. Biased Representation ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 8.4. Value_Size and Object_Size Clauses ΓòÉΓòÉΓòÉ
In Ada 95, the Size of a discrete type is the minimum number of bits required
to hold values of the type. 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, Natural'Size is typically 31. This means that code
may change in behavior when moving from Ada 83 to Ada 95. For example,
consider:
type Rec is record;
A : Natural;
B : Natural;
end record;
for Rec use record
for A use at 0 range 0 ┬╖┬╖ Natural'Size - 1;
for B use 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 in general there are surprising cases where the fact that the
object size can exceed the size of the type causes suprises.
To help get around this problem GNAT provides two implementation dependent
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 fixed-point and discrete
types are as follows:
The Object_Size for base subtypes reflect the natural hardware size in
bits (run the utility gnatpsta 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.
The Object_Size of a subtype is the same as the Object_Size of the type
from which it is obtained.
The 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 number of bits required to store a value of
the type. This size can be referred to using the Value_Size attribute. 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:
The 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).
If a subtype statically matches the first subtype of a given type, then
it has by default the same 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".)
All other subtypes have a 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; 12 12
subtype x3 is x2 range 0 ┬╖┬╖ 3; 12 2
subtype x4 is x2'base range 0 ┬╖┬╖ 10; 8 4
subtype x5 is x2 range 0 ┬╖┬╖ dynamic; 12 (7)
subtype x6 is x2'base range 0 ┬╖┬╖ dynamic; 8 (7)
Note: the entries marked (7) are not actually specified by the Ada 95 RM, but
it seems in the spirit of the RM rules to allocate the minimum number of bits
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:
Component size for packed arrays or records
Value of the attribute Size for a type
Warning about sizes not matching for unchecked conversion
For types other than discrete and fixed-point 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.
ΓòÉΓòÉΓòÉ 8.5. Component_Size Clauses ΓòÉΓòÉΓòÉ
Normally, the value specified in a component 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. The cases in which this is allowed are
for component size values in the range 1-63. 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'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.
ΓòÉΓòÉΓòÉ 8.6. Bit_Order Clauses ΓòÉΓòÉΓòÉ
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 bit, but the ordering of bytes is not affected.
There are certain restrictions placed on component clauses as follows:
Components fitting within a single storage unit.
These are unrestricted, and the effect is merely to renumber bits. For
example if we are on a little-endian machine with 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 : Boolean;
end record;
for R2'Bit_Order use High_Order_First;
for R1 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.
Components occuping an integral number of bytes
These are components that exactly fit in two or more bytes. Such
component declarations are allowed, but have no effect, since it is
important to realize that the Bit_Order specification does not affect the
ordering of bytes. In particular, the following attempt at getting an
endian-indepedent integer does not work:
type R2 is record
A : Integer;
end record;
for R2'Bit_Order use High_Order_First;
for R1 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.
Components that are positioned across byte boundaries
but do not occupy an integral number of bytes. Given that bytes are not
reordered, such fields would occupny a non-contiguous sequence of bits in
memory, requiring non-trivial code to reassemble. They are for this
reason not permitted, and any component clause specifying such a layout
will be flagged as illegal by GNAT.
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 Suppress if desired.
ΓòÉΓòÉΓòÉ 8.7. Pragma Pack for Arrays ΓòÉΓòÉΓòÉ
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:
Any scalar type
Any fixed-point type
Any type whose size is specified with a size clause
Any packed array type with a static size
For all these cases, if the component subtype size is in the range 1- 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, type 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.
ΓòÉΓòÉΓòÉ 8.8. Pragma Pack for Records ΓòÉΓòÉΓòÉ
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 package components and non-packable
components. Components of the following types are considered packable:
All scalar types are packable.
All fixed-point types are represented internally as integers, and are
packable.
Small packed arrays, whose size does not exceed 64 bits, and where the
size is statically known at compile time, are represented internally as
modular integers, and so they are also 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.
ΓòÉΓòÉΓòÉ 8.9. Record Representation Clauses ΓòÉΓòÉΓòÉ
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 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.
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.
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.
ΓòÉΓòÉΓòÉ 8.10. Enumeration Clauses ΓòÉΓòÉΓòÉ
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 non negative, 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).
ΓòÉΓòÉΓòÉ 8.11. Address Clauses ΓòÉΓòÉΓòÉ
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:
The type of the item is non-elementary (e.g. a record or array).
There is explicit or implicit initialization required for the object.
The address value is non-static.
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.
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 so 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 addres 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;
ΓòÉΓòÉΓòÉ 8.12. Effect of Convention on Representation ΓòÉΓòÉΓòÉ
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 three exceptions to this general rule:
Convention Fortran and array subtypes
If pragma Convention Fortran is specified for an array subtype, then in
accordance with the implementation advice in section 3.6.2(11) of the Ada
Reference Manual, the array will be stored in a Fortran-compatible
column-major manner, instead of the normal default row-major order.
Convention C and enumeration types
GNAT normally stores enumeration types in 8, 16, or 32 bits as required
to accomodate all values of the type. For example, for the enumeration
type declared by:
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.
Convention C/Fortran and Boolean types
In C, the usual convention for boolean values, that is values used for
conditions, is that zero represents false, and non-zero values represent
true. In Ada, the normal convention is that two specific values,
typically 0/1, are used to represent false/true respectively.
Fortran has a similar convention for LOGICAL values (any non-zero value
represents true).
To accomodate 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 non-zero 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 non-zero value is treated as True.
ΓòÉΓòÉΓòÉ 8.13. Determining the Representations chosen by GNAT ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 9. Standard Library Routines ΓòÉΓòÉΓòÉ
The Ada 95 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 95 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 95 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 95 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 package provides a random number generator suitable for
generating random integer values from a specified range.
Ada.Numerics.Float_Random
This package provides a random number generator suitable for
generating uniformly distributed floating point values.
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 an
trigonometric functions) for an arbitrary complex type.
The following predefined instantiations of this package exist
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.
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 package 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.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.
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.
ΓòÉΓòÉΓòÉ 10. The Implementation of Standard I/O ΓòÉΓòÉΓòÉ
GNAT implements all the required input-output facilities described in A.6
through A.14. These sections of the Ada 95 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 95 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 Standard I/O Packages
FORM Strings FORM Strings
Direct_IO Direct_IO
Sequential_IO Sequential_IO
Text_IO Text_IO
Wide_Text_IO Wide_Text_IO
Stream_IO Stream_IO
Shared Files Shared Files
Open Modes Open Modes
Operations on C Streams Operations on C Streams
Interfacing to C Streams Interfacing to C Streams
ΓòÉΓòÉΓòÉ 10.1. Standard I/O Packages ΓòÉΓòÉΓòÉ
The Standard I/O packages described in Annex A for
Ada.Text_IO
Ada.Text_IO.Complex_IO
Ada.Text_IO.Text_Streams,
Ada.Wide_Text_IO
Ada.Wide_Text_IO.Complex_IO,
Ada.Wide_Text_IO.Text_Streams
Ada.Stream_IO
Ada.Sequential_IO
Ada.Direct_IO
are implemented using the C library streams facility; where
All files are opened using fopen.
All input/output operations use 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 C
library routines that support streams. This facilitates shared use of these
streams by mixed language programs.
ΓòÉΓòÉΓòÉ 10.2. FORM Strings ΓòÉΓòÉΓòÉ
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 there are two
keywords defined.
SHARED=[YES|NO]
WCEM=[n|h|u|s\e]
The use of these parameters is described later in this section.
ΓòÉΓòÉΓòÉ 10.3. Direct_IO ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 10.4. Sequential_IO ΓòÉΓòÉΓòÉ
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, 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.
ΓòÉΓòÉΓòÉ 10.5. Text_IO ΓòÉΓòÉΓòÉ
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:
The character LF is used only as a line mark, i.e. to mark the end of the
line.
The character 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.
The file ends with either 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 95 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:
The file contains FF characters not immediately following a LF character.
The file contains LF or FF characters written by Put or Put_Line, which
are not logically considered to be line marks or page marks.
The file ends in a character other than 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.
Text_IO Stream Pointer PositioningText_IO Stream Pointer Positioning
Text_IO Reading and Writing Non-Regular FilesText_IO Reading and Writing
Non-Regular Files
Get_Immediate Get_Immediate
Treating Text_IO Files as StreamsTreating Text_IO Files as Streams
Text_IO Extensions Text_IO Extensions
Text_IO Facilities for Unbounded StringsText_IO Facilities for Unbounded
Strings
ΓòÉΓòÉΓòÉ 10.5.1. Stream Pointer Positioning ΓòÉΓòÉΓòÉ
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:
After a call to 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.
After a call to 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.
ΓòÉΓòÉΓòÉ 10.5.2. Reading and Writing Non-Regular Files ΓòÉΓòÉΓòÉ
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.
This avoids the need to wait for an extra character to be typed or
entered from the pipe to complete one of these operations.
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 signalled 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.
ΓòÉΓòÉΓòÉ 10.5.3. Get_Immediate ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 10.5.4. Treating Text_IO Files as Streams ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 10.5.5. Text_IO Extensions ΓòÉΓòÉΓòÉ
A package GNAT.IO_Aux in the GNAT library provides some useful extensions to
the standard Text_IO package:
function File_Exists (Name : String) return Boolean;
Determines if a file of the given name exists and can be successfully
opened (without actually performing the open operation).
function Get_Line return String;
Reads a string from the standard input file. The value returned is
exactly the length of the line that was read.
function Get_Line (File : Ada.Text_IO.File_Type) return String;
Similar, except that the parameter File specifies the file from which the
string is to be read.
ΓòÉΓòÉΓòÉ 10.5.6. Text_IO Facilities for Unbounded Strings ΓòÉΓòÉΓòÉ
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:
function Get_Line (File : File_Type) return Unbounded_String;
Reads a line from the specified file and returns the result as an
unbounded string.
procedure Put (File : File_Type; U : Unbounded_String);
Writes the value of the given unbounded string to the specified file
Similar to the effect of Put (To_String (U)) except that an extra copy is
avoided.
procedure Put_Line (File : File_Type; U : Unbounded_String);
Writes the value of the given unbounded string to the specified file,
followed by a 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/adb provides similar extended Wide_Text_IO functionality for
unbounded wide strings.
ΓòÉΓòÉΓòÉ 10.6. Wide_Text_IO ΓòÉΓòÉΓòÉ
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
'h'
Hex ESC encoding
'u'
Upper half encoding
's'
Shift-JIS encoding
'e'
EUC Encoding
'8'
UTF-8 encoding
'b'
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).
Hex Coding
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.
Upper Half Coding
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.
Shift JIS 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.
EUC Coding
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.
UTF-8 Coding
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 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 illegal UTF-8 sequences.)
Brackets Coding
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#.
For the coding schemes other than Hex and 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 PositioningWide_Text_IO Stream Pointer Positioning
Wide_Text_IO Reading and Writing Non-Regular FilesWide_Text_IO Reading and
Writing Non-Regular Files
ΓòÉΓòÉΓòÉ 10.6.1. Stream Pointer Positioning ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 10.6.2. Reading and Writing Non-Regular Files ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 10.7. Stream_IO ΓòÉΓòÉΓòÉ
A stream file is a sequence of bytes, where individual elements are written to
the file as described in the Ada 95 reference manual. The type Stream_Element
is simply a byte. There are two ways to read or write a stream file.
The operations Read and Write directly read or write a sequence of stream
elements with no control information.
The stream attributes applied to a stream file transfer data in the
manner described for stream attributes.
ΓòÉΓòÉΓòÉ 10.8. Shared Files ΓòÉΓòÉΓòÉ
Section A.14 of the Ada 95 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:
In the absence of a 'shared=xxx' form parameter, an attempt to open two
or more files with the same full name is considered an error and is not
supported. The exception Use_Error will be raised. Note that a file that
is not explicitly closed by the program remains open until the program
terminates.
If the form parameter 'shared=no' appears in the form string, the file
can be opened or created with its own separate stream identifier,
regardless of whether other files sharing the same external file are
opened. The exact effect depends on how the C stream routines handle
multiple accesses to the same external files using separate streams.
If the form parameter 'shared=yes' appears in the form string for each of
two or more files opened using the same full name, the same stream is
shared between these files, and the semantics are as described in Ada 95
Reference Manual, Section A.14.
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 heterogenous
input-output. Although this approach will work in GNAT if 'shared=yes' is
specified, it is preferable in Ada 95 to use Stream_IO for this purpose (using
the stream attributes)
ΓòÉΓòÉΓòÉ 10.9. Open Modes ΓòÉΓòÉΓòÉ
Open and Create calls result in a call to fopen using the mode shown in Table
6.1
Table 6-1 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.
ΓòÉΓòÉΓòÉ 10.10. Operations on C Streams ΓòÉΓòÉΓòÉ
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 DOS, OS/2, UNIX and Xenix (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;
ΓòÉΓòÉΓòÉ 10.11. Interfacing to C Streams ΓòÉΓòÉΓòÉ
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.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 five 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.
ΓòÉΓòÉΓòÉ 11. The GNAT Library ΓòÉΓòÉΓòÉ
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.
GNAT.Bubble_Sort_A (g-busora.ads)GNAT.Bubble_Sort_A (g-busora.ads)
GNAT.Bubble_Sort_G (g-busorg.ads)GNAT.Bubble_Sort_G (g-busorg.ads)
GNAT.Calendar (g-calend.ads) GNAT.Calendar (g-calend.ads)
GNAT.Case_Util (g-casuti) GNAT.Case_Util (g-casuti)
GNAT.Calendar.Time_IO (g-catiio.ads)GNAT.Calendar.Time_IO (g-catiio.ads)
GNAT.Command_Line (g-comlin.ads)GNAT.Command_Line (g-comlin.ads)
GNAT.Current_Exception (g-curexc.ads)GNAT.Current_Exception (g-curexc.ads)
GNAT.Debug_Pools (g-debpoo.ads)GNAT.Debug_Pools (g-debpoo.ads)
GNAT.Debug_Utilities (g-debuti.ads)GNAT.Debug_Utilities (g-debuti.ads)
GNAT.Directory_Operations (g-dirope.ads)GNAT.Directory_Operations
(g-dirope.ads)
GNAT.Float_Control (g-flocon.ads)GNAT.Float_Control (g-flocon.ads)
GNAT.Heap_Sort_A (g-hesora.ads)GNAT.Heap_Sort_A (g-hesora.ads)
GNAT.Heap_Sort_G (g-hesorg.ads)GNAT.Heap_Sort_G (g-hesorg.ads)
GNAT.HTable (g-htable.ads) GNAT.HTable (g-htable.ads)
GNAT.IO (g-io.ads) GNAT.IO (g-io.ads)
GNAT.IO_Aux (g-io_aux.ads) GNAT.IO_Aux (g-io_aux.ads)
GNAT.Lock_Files (g-locfil.ads)GNAT.Lock_Files (g-locfil.ads)
GNAT.OS_Lib (g-os_lib.ads) GNAT.OS_Lib (g-os_lib.ads)
GNAT.Regexp (g-regexp.ads) GNAT.Regexp (g-regexp.ads)
GNAT.Regpat (g-regpat.ads) GNAT.Regpat (g-regpat.ads)
GNAT.Spell_Checker (g-speche.ads)GNAT.Spell_Checker (g-speche.ads)
GNAT.Spitbol.Patterns (g-spipat.ads)GNAT.Spitbol.Patterns (g-spipat.ads)
GNAT.Spitbol (g-spitbo.ads) GNAT.Spitbol (g-spitbo.ads)
GNAT.SPITBOL.Table_Boolean (g-sptabo.ads)GNAT.SPITBOL.Table_Boolean
(g-sptabo.ads)
GNAT.SPITBOL.Table_Integer (g-sptain.ads)GNAT.SPITBOL.Table_Integer
(g-sptain.ads)
GNAT.SPITBOL.Table_VString (g-sptavs.ads)GNAT.SPITBOL.Table_VString
(g-sptavs.ads)
GNAT.Table (g-table.ads) GNAT.Table (g-table.ads)
GNAT.Task_Lock (g-tasloc.ads) GNAT.Task_Lock (g-tasloc.ads)
GNAT.Threads (g-thread.ads) GNAT.Threads (g-thread.ads)
GNAT.Traceback (g-traceb.ads) GNAT.Traceback (g-traceb.ads)
GNAT.Traceback.Symbolic (g-trasym.ads)GNAT.Traceback.Symbolic (g-trasym.ads)
ΓòÉΓòÉΓòÉ 11.1. GNAT.Bubble_Sort_A (g-busora.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.2. GNAT.Bubble_Sort_G (g-busorg.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.3. GNAT.Calendar (g-calend.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.4. GNAT.Case_Util (g-casuti) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.5. GNAT.Calendar.Time_IO (g-catiio.ads) ΓòÉΓòÉΓòÉ
Provides an extended capability for formatted output of time values with full
user control over the format. Modeled on the GNU Date specification.
ΓòÉΓòÉΓòÉ 11.6. GNAT.Command_Line (g-comlin.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.7. GNAT.Current_Exception (g-curexc.ads) ΓòÉΓòÉΓòÉ
Provides access to information on the current exception that has been raised
without the need for using the Ada-95 exception choice parameter specification
syntax. This is particularly useful in mimicing typical facilities for
obtaining information about exceptions provided by Ada 83 compilers.
ΓòÉΓòÉΓòÉ 11.8. GNAT.Debug_Pools (g-debpoo.ads) ΓòÉΓòÉΓòÉ
Provide a debugging storage pools that helps tracking memory corruption
problems. See section "Finding memory problems with GNAT Debug Pool" in the
GNAT User's guide.
ΓòÉΓòÉΓòÉ 11.9. GNAT.Debug_Utilities (g-debuti.ads) ΓòÉΓòÉΓòÉ
Provides a few useful utilities for debugging purposes, including conversion
to and from string images of address values.
ΓòÉΓòÉΓòÉ 11.10. GNAT.Directory_Operations (g-dirope.ads) ΓòÉΓòÉΓòÉ
Provides a set of routines for manipulating directories, including changing
the current directory, making new directories, and scanning the files in a
directory.
ΓòÉΓòÉΓòÉ 11.11. GNAT.Float_Control (g-flocon.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.12. GNAT.Heap_Sort_A (g-hesora.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.13. GNAT.Heap_Sort_G (g-hesorg.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.14. GNAT.HTable (g-htable.ads) ΓòÉΓòÉΓòÉ
A generic implementation of hash tables that can be used to hash arbitrary
data. Provides two approaches, one a simple static aproach, and the other
allowing arbitrary dynamic hash tables.
ΓòÉΓòÉΓòÉ 11.15. GNAT.IO (g-io.ads) ΓòÉΓòÉΓòÉ
A simple preealborable input-output package that provides a subset of simple
Text_IO functions for reading and writing strings and characters.
ΓòÉΓòÉΓòÉ 11.16. GNAT.IO_Aux (g-io_aux.ads) ΓòÉΓòÉΓòÉ
Provides some auxliiary functions for use with Text_IO, including a test for
whether a file exists, and functions for reading a line of text.
ΓòÉΓòÉΓòÉ 11.17. GNAT.Lock_Files (g-locfil.ads) ΓòÉΓòÉΓòÉ
Provides a general interface for using files as locks. Can be used for
providing program level synchronization.
ΓòÉΓòÉΓòÉ 11.18. GNAT.OS_Lib (g-os_lib.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.19. GNAT.Regexp (g-regexp.ads) ΓòÉΓòÉΓòÉ
A simple implementation of regular expressions, using a subset of regular
expression syntax copied from famoiliar Unix style utilities. This is the
simples of the three pattern matching packages provided, and is particularly
suitable for "file globbing" applications.
ΓòÉΓòÉΓòÉ 11.20. GNAT.Regpat (g-regpat.ads) ΓòÉΓòÉΓòÉ
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).
ΓòÉΓòÉΓòÉ 11.21. GNAT.Spell_Checker (g-speche.ads) ΓòÉΓòÉΓòÉ
Provides a function for determining whether one string is a plausible near
misspelling of another string.
ΓòÉΓòÉΓòÉ 11.22. GNAT.Spitbol.Patterns (g-spipat.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.23. GNAT.Spitbol (g-spitbo.ads) ΓòÉΓòÉΓòÉ
The top level package of the collection of SPITBOL-style funcionality, this
package provides basic SNOBOL4 string manipulation functions, such as Pad,
Reverse, Trim, Substr capability, as well as a generic table function useful
for contructing arbitrary mappings from strings in the style of the SNOBOL4
TABLE function.
ΓòÉΓòÉΓòÉ 11.24. GNAT.SPITBOL.Table_Boolean (g-sptabo.ads) ΓòÉΓòÉΓòÉ
A library level of instantiation of GNAT.Spitbol.Patterns.Table for type
Standard.Boolean, giving an implementation of sets of string values.
ΓòÉΓòÉΓòÉ 11.25. GNAT.SPITBOL.Table_Integer (g-sptain.ads) ΓòÉΓòÉΓòÉ
A library level of instantiation of GNAT.Spitbol.Patterns.Table for type
Standard.Integer, giving an implementation of maps from string to integer
values.
ΓòÉΓòÉΓòÉ 11.26. GNAT.SPITBOL.Table_VString (g-sptavs.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.27. GNAT.Table (g-table.ads) ΓòÉΓòÉΓòÉ
A generic package providing a single dimension array abstraction where the
length of the array can be dynamically modified.
ΓòÉΓòÉΓòÉ 11.28. GNAT.Task_Lock (g-tasloc.ads) ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 11.29. GNAT.Threads (g-thread.ads) ΓòÉΓòÉΓòÉ
Provides facilities for creating and destroying threads with explicit calls.
These threads are known to the GNAT run-time system. These subprograms are
exported C-convention procedures intended to be called from foreign code. By
using these primitives rather than directly calling operating systems
routines, compatibility with the Ada tasking runt-time is provided.
ΓòÉΓòÉΓòÉ 11.30. GNAT.Traceback (g-traceb.ads) ΓòÉΓòÉΓòÉ
Provides a facility for obtaining non-symbolic traceback information, useful
in various debugging situations.
ΓòÉΓòÉΓòÉ 11.31. GNAT.Traceback.Symbolic (g-trasym.ads) ΓòÉΓòÉΓòÉ
Provides symbolic traceback information that includes the subprogram name and
line number information
ΓòÉΓòÉΓòÉ 12. Interfacing to Other Languages ΓòÉΓòÉΓòÉ
The facilities in annex B of the Ada 95 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 C++ Interfacing to C++
Interfacing to COBOL Interfacing to COBOL
Interfacing to Fortran Interfacing to Fortran
Interfacing to non-GNAT Ada codeInterfacing to non-GNAT Ada code
ΓòÉΓòÉΓòÉ 12.1. Interfacing to C ΓòÉΓòÉΓòÉ
Interfacing to C with GNAT can use one of two approaches:
1. The types in the package Interfaces.C may be used.
2. Standard Ada types may be used directly. This may be less portable to
other compilers, but will work on all GNAT compilers, which guarantee
correspondence between the C and Ada types.
Pragma Convention C maybe 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.
Ada enumeration types map to C enumeration types directly if pragma
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.
Ada access types map to C pointers, except for the case of pointers to
unconstrained types in Ada, which have no direct C equivalent.
Ada arrays map directly to C arrays.
Ada records map directly to C structures.
Packed Ada records map to C structures where all members are bit fields
of the length corresponding to the type'Size value in Ada.
ΓòÉΓòÉΓòÉ 12.2. Interfacing to C++ ΓòÉΓòÉΓòÉ
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. Ada Core Technologies does
not currently supply a suitable binding generator tool.
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.
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.
pragma CPP_Vtable ┬╖┬╖┬╖
One CPP_Vtable pragma can be present for each component of type
CPP.Interfaces.Vtable_Ptr in a record to which pragma CPP_Class
applies.
ΓòÉΓòÉΓòÉ 12.3. Interfacing to COBOL ΓòÉΓòÉΓòÉ
Interfacing to COBOL is achieved as described in section B.4 of the Ada 95
reference manual.
ΓòÉΓòÉΓòÉ 12.4. Interfacing to Fortran ΓòÉΓòÉΓòÉ
Interfacing to Fortran is achieved as described in section B.5 of the
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.
ΓòÉΓòÉΓòÉ 12.5. Interfacing to non-GNAT Ada code ΓòÉΓòÉΓòÉ
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 or Ada 95
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.
ΓòÉΓòÉΓòÉ 13. Machine Code Insertions ΓòÉΓòÉΓòÉ
Package Machine_Code provides machine code support as described in the Ada 95
Reference Manual in two separate forms:
Machine code statements, consisting of qualified expressions that fit the
requirements of RM section 13.8.
An intrinsic callable procedure, providing an alternative mechanism of
including machine instructions in a subprogram.
The two features are similar, and both 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 as described in Using and Porting GNU CC by Richard Stallman.
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 GNU CC 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 CC. 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 the full description in the GCC manual for
further details.
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 (of course 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 ::=
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 ::=
No_Input_Operands
| INPUT_OPERAND_ATTRIBUTE
| (INPUT_OPERAND_ATTRIBUTE {,INPUT_OPERAND_ATTRIBUTE})
INPUT_OPERAND_ATTRIBUTE ::=
SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
ΓòÉΓòÉΓòÉ 14. GNAT Implementation of Tasking ΓòÉΓòÉΓòÉ
Mapping Ada Tasks onto the Underlying Kernel ThreadsMapping Ada Tasks onto the
Underlying Kernel Threads
Ensuring Compliance with the Real-Time AnnexEnsuring Compliance with the
Real-Time Annex
ΓòÉΓòÉΓòÉ 14.1. Mapping Ada Tasks onto the Underlying Kernel Threads ΓòÉΓòÉΓòÉ
GNAT run-time system comprises two layers:
GNARL (GNAT Run-time Layer)
GNULL (GNAT Low-level Library)
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, rendez-vous, 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, OS/2, Windows NT, 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
1 Ada task = 1 VxWorks task
In addition Ada task priorities map onto the underlying thread priorities.
Mapping Ada tasks onto the underlying kernel threads has several advantages:
1. The underlying scheduler is used to schedule the Ada tasks. This makes
Ada tasks as efficient as kernel threads from a scheduling standpoint.
2. Interaction with code written in C containing threads is eased since at
the lowest level Ada tasks and C threads map onto the same underlying
kernel concept.
3. When an Ada task is blocked during I/O the remaining Ada tasks are able
to proceed.
4. On multi-processor systems Ada Tasks can execute in parallel.
ΓòÉΓòÉΓòÉ 14.2. Ensuring Compliance with the Real-Time Annex ΓòÉΓòÉΓòÉ
The reader will be quick to notice that while 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 Annex D requires that for the FIFO_Within_Priorities scheduling
policy we have:
9 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.
ΓòÉΓòÉΓòÉ 15. Code generation for array aggregates ΓòÉΓòÉΓòÉ
Static constant aggregates with static boundsStatic constant aggregates with
static bounds
Constant aggregates with an unconstrained nominal typesConstant aggregates
with an unconstrained nominal types
Aggregates with static bounds Aggregates with static bounds
Aggregates with non-static boundsAggregates with non-static bounds
Aggregates in assignments statementsAggregates in assignments statements
Aggregate 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, the user 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. The user will 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.
ΓòÉΓòÉΓòÉ 15.1. Static constant aggregates with static bounds ΓòÉΓòÉΓòÉ
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);
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));
ΓòÉΓòÉΓòÉ 15.2. Constant aggregates with an unconstrained nominal types ΓòÉΓòÉΓòÉ
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);
ΓòÉΓòÉΓòÉ 15.3. Aggregates with static bounds ΓòÉΓòÉΓòÉ
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);
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;
ΓòÉΓòÉΓòÉ 15.4. Aggregates with non-static bounds ΓòÉΓòÉΓòÉ
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.
ΓòÉΓòÉΓòÉ 15.5. Aggregates in assignments statements ΓòÉΓòÉΓòÉ
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:
1. The bounds of the aggregate are static, and the associations are static.
2. The components of the aggregate are static constants, names of
simple variables that are not renamings, or expressions not involving
indexed components whose operands obey these rules.
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.
ΓòÉΓòÉΓòÉ 16. Specialized Needs Annexes ΓòÉΓòÉΓòÉ
Ada 95 defines a number of specialized needs annexes, which are not required
in all implementations. However, as described in this chapter, GNAT implements
all of these special needs annexes:
Systems Programming (Annex C)
The systems programming annex is fully implemented.
Real-Time Systems (Annex D)
The real-time systems annex is fully implemented.
Distributed Systems (Annex E)
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 available from Ada Core
Technologies. When the two products are used in conjunction, this
annex is fully implemented.
Information Systems (Annex F)
The information systems annex is fully implemented.
Numerics (Annex G)
The numerics annex is fully implemented.
Safety and Security (Annex H)
The safety and security annex is fully implemented.
ΓòÉΓòÉΓòÉ 17. Compatibility Guide ΓòÉΓòÉΓòÉ
This chapter contains sections that describe compatibility issues between GNAT
and other Ada 83 and Ada 95 compilation systems, to aid in porting
applications developed in other Ada environments.
Compatibility with Ada 83 Compatibility with Ada 83
Compatibility with DEC Ada 83 Compatibility with DEC Ada 83
Compatibility with Other Ada 95 SystemsCompatibility with Other Ada 95 Systems
Representation Clauses Representation Clauses
ΓòÉΓòÉΓòÉ 17.1. Compatibility with Ada 83 ΓòÉΓòÉΓòÉ
Ada 95 is designed to be highly upwards compatible with Ada 83. In particular,
the design intention is that the difficulties associated with moving from Ada
83 to Ada 95 should be no greater than those that occur when moving from one
Ada 83 system to another.
However, there are a number of points at which there are minor
incompatibilities. The Ada 95 Annotated Reference Manual contains full details
of these issues, and should be consulted for a complete treatment. In practice
the following are the most likely issues to be encountered.
Character range
The range of Standard.Character is now the full 256 characters of
Latin-1, whereas in most Ada 83 implementations it was restricted to
128 characters. This may show up as compile time or runtime errors.
The desirable fix is to adapt the program to accommodate the full
character set, but in some cases it may be convenient to define a
subtype or derived type of Character that covers only the restricted
range.
New reserved words
The identifiers abstract, aliased, protected, requeue, tagged, and
until are reserved in Ada 95. Existing Ada 83 code using any of
these identifiers must be edited to use some alternative name.
Freezing rules
The rules in Ada 95 are slightly different with regard to the point
at which entities are frozen, and representation pragmas and clauses
are not permitted past the freeze point. This shows up most
typically in the form of an error message complaining that a
representation item appears too late, and the appropriate corrective
action is to move the item nearer to the declaration of the entity
to which it refers.
A particular case is that representation pragmas (including the
extended DEC Ada 83 compatibility pragmas such as Export_Procedure),
cannot be applied to a subprogram body. If necessary, a separate
subprogram declaration must be introduced to which the pragma can be
applied.
Optional bodies for library packages
In Ada 83, a package that did not require a package body was
nevertheless allowed to have one. This lead to certain surprises in
compiling large systems (situations in which the body could be
unexpectedly ignored). In Ada 95, if a package does not require a
body then it is not permitted to have a body. To fix this problem,
simply remove a redundant body if it is empty, or, if it is
non-empty, introduce a dummy declaration into the spec that makes
the body required. One approach is to add a private part to the
package declaration (if necessary), and define a parameterless
procedure called Requires_Body, which must then be given a dummy
procedure body in the package body, which then becomes required.
Numeric_Error is now the same as Constraint_Error
In Ada 95, the exception Numeric_Error is a renaming of
Constraint_Error. This means that it is illegal to have separate
exception handlers for the two exceptions. The fix is simply to
remove the handler for the Numeric_Error case (since even in Ada 83,
a compiler was free to raise Constraint_Error in place of
Numeric_Error in all cases).
Indefinite subtypes in generics
In Ada 83, it was permissible to pass an indefinite type (e.g.
String) as the actual for a generic formal private type, but then
the instantiation would be illegal if there were any instances of
declarations of variables of this type in the generic body. In Ada
95, to avoid this clear violation of the contract model, the generic
declaration clearly indicates whether or not such instantiations are
permitted. If a generic formal parameter has explicit unknown
discriminants, indicated by using (<>) after the type name, then it
can be instantiated with indefinite types, but no variables can be
declared of this type. Any attempt to declare a variable will result
in an illegality at the time the generic is declared. If the (<>)
notation is not used, then it is illegal to instantiate the generic
with an indefinite type. This will show up as a compile time error,
and the fix is usually simply to add the (<>) to the generic
declaration.
All implementations of GNAT provide a switch that causes GNAT to operate in
Ada 83 mode. In this mode, some but not all compatibility problems of the type
described above are handled automatically. For example, the new Ada 95
protected keywords are not recognized in this mode. However, in practice, it
is usually advisable to make the necessary modifications to the program to
remove the need for using this switch.
ΓòÉΓòÉΓòÉ 17.2. Compatibility with Other Ada 95 Systems ΓòÉΓòÉΓòÉ
Providing that programs avoid the use of implementation dependent and
implementation defined features of Ada 95, as documented in the Ada 95
reference manual, there should be a high degree of portability between GNAT
and other Ada 95 systems. The following are specific items which have proved
troublesome in moving GNAT programs to other Ada 95 compilers, but do not
affect porting code to GNAT.
Ada 83 Pragmas and Attributes
Ada 95 compilers are allowed, but not required, to implement the
missing Ada 83 pragmas and attributes that are no longer defined in
Ada 95. GNAT implements all such pragmas and attributes, eliminating
this as a compatibility concern, but some other Ada 95 compilers
reject these pragmas and attributes.
Special-needs Annexes
GNAT implements the full set of special needs annexes. At the
current time, it is the only Ada 95 compiler to do so. This means
that programs making use of these features may not be portable to
other Ada 95 compilation systems.
Representation Clauses
Some other Ada 95 compilers implement only the minimal set of
representation clauses required by the Ada 95 reference manual. GNAT
goes far beyond this minimal set, as described in the next section.
ΓòÉΓòÉΓòÉ 17.3. Representation Clauses ΓòÉΓòÉΓòÉ
The Ada 83 reference manual was quite vague in describing both the minimal
required implementation of representation clauses, and also their precise
effects. The Ada 95 reference manual is much more explicit, but the minimal
set of capabilities required in Ada 95 is quite limited.
GNAT implements the full required set of capabilities described in the Ada 95
reference manual, but also goes much beyond this, and in particular an effort
has been made to be compatible with existing Ada 83 usage to the greatest
extent possible.
A few cases exist in which Ada 83 compiler behavior is incompatible with
requirements in the Ada 95 reference manual. These are instances of
intentional or accidental dependence on specific implementation dependent
characteristics of these Ada 83 compilers. The following is a list of the
cases most likely to arise in existing legacy Ada 83 code.
Implicit Packing
Some Ada 83 compilers allowed a Size specification to cause implicit
packing of an array or record. This is specifically disallowed by
implementation advice in the Ada 83 reference manual (for good
reason, this usage can cause expensive implicit conversions to occur
in the code). The problem will show up as an error message rejecting
the size clause. The fix is simply to provide the explicit pragma
Pack.
Meaning of Size Attribute
The Size attribute in Ada 95 for discrete types is defined as being
the minimal number of bits required to hold values of the type. For
example, on a 32-bit machine, the size of Natural will typically be
31 and not 32 (since no sign bit is required). Some Ada 83 compilers
gave 31, and some 32 in this situation. This problem will usually
show up as a compile time error, but not always. It is a good idea
to check all uses of the 'Size attribute when porting Ada 83 code.
The GNAT specific attribute Object_Size can provide a useful way of
duplicating the behavior of some Ada 83 compiler systems.
Size of Access Types
A common assumption in Ada 83 code is that an access type is in fact
a pointer, and that therefore it will be the same size as a
System.Address value. This assumption is true for GNAT in most cases
with one exception. For the case of a pointer to an unconstrained
array type (where the bounds may vary from one value of the access
type to another), the default is to use a "fat pointer", which is
represented as two separate pointers, one to the bounds, and one to
the array. This representation has a number of advantages, including
improved efficiency. However, it may cause some difficulties in
porting existing Ada 83 code which makes the assumption that, for
example, pointers fit in 32 bits on a machine with 32-bit
addressing.
To get around this problem, GNAT also permits the use of "thin
pointers" for access types in this case (where the designated type
is an unconstrained array type). These thin pointers are indeed the
same size as a System.Address value. To specify a thin pointer, use
a size clause for the type, for example:
type X is access all String;
for X'Size use System.Address'Size;
which will cause the type X to be represented using a single pointer. When
using this representation, the bounds are right behind the array. This
representation is slightly less efficient, and does not allow quite such
flexibility in the use of foreign pointers or in using the Unrestricted_Access
attribute to create pointers to non-aliased objects. But for any standard
portable use of the access type it will work in a functionally correct manner
and allow porting of existing code. Note that another way of forcing a thin
pointer representation is to use a component size clause for the element size
in an array, or a record representation clause for an access field in a
record.
ΓòÉΓòÉΓòÉ 17.4. Compatibility with DEC Ada 83 ΓòÉΓòÉΓòÉ
The VMS version of GNAT fully implements all the pragmas and attributes
provided by DEC Ada 83, as well as providing the standard DEC Ada 83
libraries, including Starlet. In addition, data layouts and parameter passing
conventions are highly compatible. This means that porting existing DEC Ada 83
code to GNAT in VMS systems should be easier than most other porting efforts.
The following are some of the most significant differences between GNAT and
DEC Ada 83.
Default floating-point representation
In GNAT, the default floating-point format is IEEE, whereas in DEC
Ada 83, it is VMS format. GNAT does implement the necessary pragmas
(Long_Float, Float_Representation) for changing this default.
System
The package System in GNAT exactly corresponds to the definition in
the Ada 95 reference manual, which means that it excludes many of
the DEC Ada 83 extensions. However, a separate package Aux_DEC is
provided that contains the additional definitions, and a special
pragma, Extend_System allows this package to be treated
transparently as an extension of package System.
To_Address
The definitions provided by Aux_DEC are exactly compatible with
those in the DEC Ada 83 version of System, with one exception. DEC
Ada provides the following declarations:
TO_ADDRESS(INTEGER)
TO_ADDRESS(UNSIGNED_LONGWORD)
TO_ADDRESS(universal_integer)
The version of TO_ADDRESS taking a universal integer argument is in fact an
extension to Ada 83 not strictly compatible with the reference manual. In
GNAT, we are constrained to be exactly compatible with the standard, and this
means we cannot provide this capability. In DEC Ada 83, the point of this
definition is to deal with a call like:
TO_ADDRESS (16#12777#);
Normally, according to the Ada 83 standard, one would expect this to be
ambiguous, since it matches both the INTEGER and UNSIGNED_LONGWORD forms of
TO_ADDRESS. However, in DEC Ada 83, there is no ambiguity, since the
definition using universal_integer takes precedence.
In GNAT, since the version with universal_integer cannot be supplied, it is
not possible to be 100% compatible. Since there are many programs using
numeric constants for the argument to TO_ADDRESS, the decision in GNAT was to
change the name of the function in the UNSIGNED_LONGWORD case, so the
declarations provided in the GNAT version of AUX_Dec are:
function To_Address (X : Integer) return Address;
pragma Pure_Function (To_Address);
function To_Address_Long (X : Unsigned_Longword)
return Address;
pragma Pure_Function (To_Address_Long);
This means that programs using TO_ADDRESS for UNSIGNED_LONGWORD must change
the name to TO_ADDRESS_LONG.
Task_Id values
The Task_Id values assigned will be different in the two systems,
and GNAT does not provide a specified value for the Task_Id of the
environment task, which in GNAT is treated like any other declared
task.
For full details on these and other less significant compatibility issues, see
appendix E of the Digital publication entitled "DEC Ada, Technical Overview
and Comparison on DIGITAL Platforms".
For GNAT running on other than VMS systems, all the DEC Ada 83 pragmas and
attributes are recognized, although only a subset of them can sensibly be
implemented. The description of pragmas in this reference manual indicates
whether or not they are applicable to non-VMS systems.
ΓòÉΓòÉΓòÉ 18. Index ΓòÉΓòÉΓòÉ
-gnatR switch Determining the
Representations chosen by
GNAT
Access, unrestricted Implementation Defined
Attributes
Accuracy requirements Implementation Advice
Accuracy, complex arithmetic Implementation Advice
Ada 83 attributes Implementation Defined
Attributes
Implementation Defined
Attributes
Implementation Defined
Attributes
Implementation Defined
Attributes
Implementation Defined
Attributes
Implementation Defined
Attributes
Implementation Defined
Attributes
Implementation Defined
Attributes
Ada 95 ISO/ANSI Standard What This Reference Manual
Contains
Address Clause Address Clauses
Address clauses Implementation Advice
Address of subprogram code Implementation Defined
Attributes
Address, as private type Implementation Advice
Address, operations of Implementation Advice
Alignment Clause Alignment Clauses
Alignment clauses Implementation Advice
Alignment, default Alignment Clauses
Alignment, maximum Implementation Defined
Attributes
Alignments of components Implementation Defined
Pragmas
Alternative Character Sets Implementation Advice
Argument passing mechanisms Implementation Defined
Pragmas
Arrays, extendable GNAT.Table (g-table.ads)
Arrays, multidimensional Implementation Advice
Biased representation Biased Representation
Big endian Implementation Defined
Attributes
Bit ordering Implementation Advice
Bit_Order Clause Bit_Order Clauses
Bounded errors Implementation Advice
Bounded-length strings Implementation Advice
C, interfacing with Implementation Advice
Calendar GNAT.Calendar (g-calend.ads)
GNAT.Calendar.Time_IO
(g-catiio.ads)
Casing of External names Implementation Defined
Pragmas
Casing utilities GNAT.Case_Util (g-casuti)
Character Sets Implementation Advice
Checks, suppression of Implementation Advice
Child Units Implementation Advice
COBOL support Implementation Advice
COBOL, interfacing with Implementation Advice
Command line GNAT.Command_Line
(g-comlin.ads)
Complex arithmetic accuracy Implementation Advice
Complex elementary functions Implementation Advice
Complex types Implementation Advice
Component Clause Record Representation
Clauses
Component_Size Clause Component_Size Clauses
Component_Size clauses Implementation Advice
Convention, effect on representation Effect of Convention on
Representation
Conventions, typographical Conventions
Current exception GNAT.Current_Exception
(g-curexc.ads)
Debugging GNAT.Debug_Pools
(g-debpoo.ads)
GNAT.Debug_Utilities
(g-debuti.ads)
Dec Ada 83 Implementation Defined
Pragmas
Dec Ada 83 casing compatibility Implementation Defined
Pragmas
Decimal radix support Implementation Advice
Deferring aborts Implementation Defined
Pragmas
Directory operations GNAT.Directory_Operations
(g-dirope.ads)
Discriminants, testing for Implementation Defined
Attributes
Elimination of unused subprograms Implementation Defined
Pragmas
Entry queuing policies Implementation Advice
Enumeration representation clauses Implementation Advice
Enumeration values Implementation Advice
Error detection Implementation Advice
Exception information Implementation Advice
Exception retrieval GNAT.Current_Exception
(g-curexc.ads)
External Names, casing Implementation Defined
Pragmas
File locking GNAT.Lock_Files
(g-locfil.ads)
Float types Implementation Advice
Floating-Point Processor GNAT.Float_Control
(g-flocon.ads)
Foreign threads GNAT.Threads (g-thread.ads)
Fortran, interfacing with Implementation Advice
Get_Immediate Get_Immediate
GNAT.Bubble_Sort_A (g-busora.ads) GNAT.Bubble_Sort_A
(g-busora.ads)
GNAT.Bubble_Sort_G (g-busorg.ads) GNAT.Bubble_Sort_G
(g-busorg.ads)
GNAT.Calendar (g-calend.ads) GNAT.Calendar (g-calend.ads)
GNAT.Calendar.Time_IO (g-catiio.ads) GNAT.Calendar.Time_IO
(g-catiio.ads)
GNAT.Case_Util (g-casuti) GNAT.Case_Util (g-casuti)
GNAT.Command_Line (g-comlin.ads) GNAT.Command_Line
(g-comlin.ads)
GNAT.Current_Exception (g-curexc.ads) GNAT.Current_Exception
(g-curexc.ads)
GNAT.Debug_Pools (g-debpoo.ads) GNAT.Debug_Pools
(g-debpoo.ads)
GNAT.Debug_Utilities (g-debuti.ads) GNAT.Debug_Utilities
(g-debuti.ads)
GNAT.Directory_Operations (g-dirope.ads) GNAT.Directory_Operations
(g-dirope.ads)
GNAT.Float_Control (g-flocon.ads) GNAT.Float_Control
(g-flocon.ads)
GNAT.Heap_Sort_A (g-hesora.ads) GNAT.Heap_Sort_A
(g-hesora.ads)
GNAT.Heap_Sort_G (g-hesorg.ads) GNAT.Heap_Sort_G
(g-hesorg.ads)
GNAT.HTable (g-htable.ads) GNAT.HTable (g-htable.ads)
GNAT.IO (g-io.ads) GNAT.IO (g-io.ads)
GNAT.IO_Aux (g-io_aux.ads) GNAT.IO_Aux (g-io_aux.ads)
GNAT.Lock_Files (g-locfil.ads) GNAT.Lock_Files
(g-locfil.ads)
GNAT.OS_Lib (g-os_lib.ads) GNAT.OS_Lib (g-os_lib.ads)
GNAT.Regexp (g-regexp.ads) GNAT.Regexp (g-regexp.ads)
GNAT.Regpat (g-regpat.ads) GNAT.Regpat (g-regpat.ads)
GNAT.Spell_Checker (g-speche.ads) GNAT.Spell_Checker
(g-speche.ads)
GNAT.Spitbol (g-spitbo.ads) GNAT.Spitbol (g-spitbo.ads)
GNAT.Spitbol.Patterns (g-spipat.ads) GNAT.Spitbol.Patterns
(g-spipat.ads)
GNAT.SPITBOL.Table_Boolean (g-sptabo.ads) GNAT.SPITBOL.Table_Boolean
(g-sptabo.ads)
GNAT.SPITBOL.Table_Integer (g-sptain.ads) GNAT.SPITBOL.Table_Integer
(g-sptain.ads)
GNAT.SPITBOL.Table_VString (g-sptavs.ads) GNAT.SPITBOL.Table_VString
(g-sptavs.ads)
GNAT.Table (g-table.ads) GNAT.Table (g-table.ads)
GNAT.Task_Lock (g-tasloc.ads) GNAT.Task_Lock
(g-tasloc.ads)
GNAT.Threads (g-thread.ads) GNAT.Threads (g-thread.ads)
GNAT.Traceback (g-traceb.ads) GNAT.Traceback
(g-traceb.ads)
GNAT.Traceback.Symbolic (g-trasym.ads) GNAT.Traceback.Symbolic
(g-trasym.ads)
Hash tables GNAT.HTable (g-htable.ads)
Heap usage, implicit Implementation Advice
Implementation-dependent features About This Guide
Initialization, suppression of Implementation Defined
Pragmas
Input/Output facilities GNAT.IO (g-io.ads)
GNAT.IO_Aux (g-io_aux.ads)
Integer maps GNAT.SPITBOL.Table_Integer
(g-sptain.ads)
Integer types Implementation Advice
Interfacing to C++ Implementation Defined
Pragmas
Interfacing with C++ Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Interrupt priority, maximum Implementation Defined
Attributes
Interrupt support Implementation Advice
Little endian Implementation Defined
Attributes
Locking GNAT.Task_Lock
(g-tasloc.ads)
Locking Policies Implementation Advice
Locking using files GNAT.Lock_Files
(g-locfil.ads)
Machine operations Implementation Advice
Maps GNAT.SPITBOL.Table_Integer
(g-sptain.ads)
GNAT.SPITBOL.Table_VString
(g-sptavs.ads)
Multidimensional arrays Implementation Advice
Named numbers, representation of Implementation Defined
Attributes
Numerics Implementation Advice
OpenVMS Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Pragmas
Implementation Defined
Attributes
Implementation Defined
Attributes
Operating System interface GNAT.OS_Lib (g-os_lib.ads)
Operations, on Address Implementation Advice
Package Interfaces Implementation Advice
Package Interrupts Implementation Advice
Package Task_Attributes Implementation Advice
Packed types Implementation Advice
Parameters, passing mechanism Implementation Defined
Attributes
Parameters, when passed by reference Implementation Defined
Attributes
Partition communication subsystem Implementation Advice
Passing by copy Implementation Defined
Pragmas
Passing by descriptor Implementation Defined
Pragmas
Implementation Defined
Pragmas
Patterm matching GNAT.Spitbol.Patterns
(g-spipat.ads)
Pattern matching GNAT.Regexp (g-regexp.ads)
GNAT.Regpat (g-regpat.ads)
PCS Implementation Advice
Portability About This Guide
Pragma Pack (for arrays) Pragma Pack for Arrays
Pragma Pack (for records) Pragma Pack for Records
Pragma, representation Representation Clauses and
Pragmas
Pragmas Implementation Advice
Pre-elaboration requirements Implementation Advice
Preemptive abort Implementation Advice
Priority, maximum Implementation Defined
Attributes
Protected procedure handlers Implementation Advice
Random number generation Implementation Advice
Record Representation Clause Record Representation
Clauses
Record representation clauses Implementation Advice
Regular expressions GNAT.Regexp (g-regexp.ads)
GNAT.Regpat (g-regpat.ads)
Representation Clause Representation Clauses and
Pragmas
Representation clauses Implementation Advice
Representation Clauses and
Pragmas
Representation clauses, enumeration Implementation Advice
Representation clauses, records Implementation Advice
Representation of enums Implementation Defined
Attributes
Representation Pragma Representation Clauses and
Pragmas
Representation, determination of Determining the
Representations chosen by
GNAT
Return values, passing mechanism Implementation Defined
Attributes
Sets of strings GNAT.SPITBOL.Table_Boolean
(g-sptabo.ads)
Simple I/O GNAT.IO (g-io.ads)
Size Clause Size Clauses
Size clauses Implementation Advice
Size for biased representation Biased Representation
Size of Address Implementation Defined
Attributes
Size, of objects Value_Size and Object_Size
Clauses
Size, setting for not-first subtype Implementation Defined
Attributes
Size, used for objects Implementation Defined
Attributes
Size, VADS compatibility Implementation Defined
Pragmas
Implementation Defined
Attributes
Sorting GNAT.Bubble_Sort_A
(g-busora.ads)
GNAT.Bubble_Sort_G
(g-busorg.ads)
GNAT.Heap_Sort_A
(g-hesora.ads)
GNAT.Heap_Sort_G
(g-hesorg.ads)
Spawn capability GNAT.OS_Lib (g-os_lib.ads)
Spell checking GNAT.Spell_Checker
(g-speche.ads)
SPITBOL interface GNAT.Spitbol (g-spitbo.ads)
SPITBOL pattern matching GNAT.Spitbol.Patterns
(g-spipat.ads)
SPITBOL Tables GNAT.SPITBOL.Table_Boolean
(g-sptabo.ads)
GNAT.SPITBOL.Table_Integer
(g-sptain.ads)
GNAT.SPITBOL.Table_VString
(g-sptavs.ads)
Storage place attributes Implementation Advice
Stream files Treating Text_IO Files as
Streams
Stream oriented attributes Implementation Advice
String maps GNAT.SPITBOL.Table_VString
(g-sptavs.ads)
Subprogram address Implementation Defined
Attributes
Suppressing initialization Implementation Defined
Pragmas
Suppression of checks Implementation Advice
system, extending Implementation Defined
Pragmas
Table implementation GNAT.Table (g-table.ads)
Task locking GNAT.Task_Lock
(g-tasloc.ads)
Task synchronization GNAT.Task_Lock
(g-tasloc.ads)
Tasking restrictions Implementation Advice
Text_IO GNAT.IO_Aux (g-io_aux.ads)
Text_IO extensions Text_IO Extensions
Text_IO for unbounded strings Text_IO Facilities for
Unbounded Strings
Threads, foreign GNAT.Threads (g-thread.ads)
Time GNAT.Calendar.Time_IO
(g-catiio.ads)
Time, monotonic Implementation Advice
Trace back facilities GNAT.Traceback
(g-traceb.ads)
GNAT.Traceback.Symbolic
(g-trasym.ads)
Typographical conventions Conventions
Unbounded_String, Text_IO operations Text_IO Facilities for
Unbounded Strings
Unchecked conversion Implementation Advice
Unchecked deallocation Implementation Advice
Unions in C Implementation Defined
Pragmas
Zero address, passing Implementation Defined
Attributes
Zero Cost Exceptions Implementation Defined
Pragmas
(.txt)
(.txt)