Annex B
(normative)
Interface to Other Languages
1 This Annex describes features for writing mixed-language programs. General
interface support is presented first; then specific support for C, COBOL, and
Fortran is defined, in terms of language interface packages for each of these
languages.
B.1 Interfacing Pragmas
1 A pragma Import is used to import an entity defined in a foreign language
into an Ada program, thus allowing a foreign-language subprogram to be called
from Ada, or a foreign-language variable to be accessed from Ada. In contrast,
a pragma Export is used to export an Ada entity to a foreign language, thus
allowing an Ada subprogram to be called from a foreign language, or an Ada
object to be accessed from a foreign language. The pragmas Import and Export
are intended primarily for objects and subprograms, although implementations
are allowed to support other entities.
2 A pragma Convention is used to specify that an Ada entity should use the
conventions of another language. It is intended primarily for types and "
callback" subprograms. For example, "pragma Convention(Fortran, Matrix);"
implies that Matrix should be represented according to the conventions of the
supported Fortran implementation, namely column-major order.
3 A pragma Linker_Options is used to specify the system linker parameters
needed when a given compilation unit is included in a partition.
Syntax
4 An interfacing pragma is a representation pragma that is one of the
pragmas Import, Export, or Convention. Their forms, together with that
of the related pragma Linker_Options, are as follows:
5 pragma Import(
[Convention =>] convention_identifier, [Entity =>] local_name
[, [External_Name =>] string_expression] [, [Link_Name =>]
string_expression]);
6 pragma Export(
[Convention =>] convention_identifier, [Entity =>] local_name
[, [External_Name =>] string_expression] [, [Link_Name =>]
string_expression]);
7 pragma Convention([Convention =>] convention_identifier,[Entity =>]
local_name);
8 pragma Linker_Options(string_expression);
9 A pragma Linker_Options is allowed only at the place of a
declarative_item.
9.1/1 For pragmas Import and Export, the argument for Link_Name shall not be
given without the pragma_argument_identifier unless the argument for
External_Name is given.
Name Resolution Rules
10 The expected type for a string_expression in an interfacing pragma or in
pragma Linker_Options is String.
Legality Rules
11 The convention_identifier of an interfacing pragma shall be the name of a
convention. The convention names are implementation defined, except for
certain language-defined ones, such as Ada and Intrinsic, as explained in
6.3.1, "Conformance Rules". Additional convention names generally represent
the calling conventions of foreign languages, language implementations, or
specific run-time models. The convention of a callable entity is its calling
convention.
12 If L is a convention_identifier for a language, then a type T is said to
be compatible with convention L, (alternatively, is said to be an L-compatible
type) if any of the following conditions are met:
13 * T is declared in a language interface package corresponding to L and
is defined to be L-compatible (see B.3, B.3.1, B.3.2, B.4, B.5),
14 * Convention L has been specified for T in a pragma Convention, and T is
eligible for convention L; that is:
15 * T is an array type with either an unconstrained or
statically-constrained first subtype, and its component type is
L-compatible,
16 * T is a record type that has no discriminants and that only has
components with statically-constrained subtypes, and each
component type is L-compatible,
17 * T is an access-to-object type, and its designated type is
L-compatible,
18 * T is an access-to-subprogram type, and its designated profile's
parameter and result types are all L-compatible.
19 * T is derived from an L-compatible type,
20 * The implementation permits T as an L-compatible type.
21 If pragma Convention applies to a type, then the type shall either be
compatible with or eligible for the convention specified in the pragma.
22 A pragma Import shall be the completion of a declaration. Notwithstanding
any rule to the contrary, a pragma Import may serve as the completion of any
kind of (explicit) declaration if supported by an implementation for that kind
of declaration. If a completion is a pragma Import, then it shall appear in
the same declarative_part, package_specification, task_definition or
protected_definition as the declaration. For a library unit, it shall appear
in the same compilation, before any subsequent compilation_units other than
pragmas. If the local_name denotes more than one entity, then the pragma
Import is the completion of all of them.
23 An entity specified as the Entity argument to a pragma Import (or
pragma Export) is said to be imported (respectively, exported).
24 The declaration of an imported object shall not include an explicit
initialization expression. Default initializations are not performed.
25 The type of an imported or exported object shall be compatible with the
convention specified in the corresponding pragma.
26 For an imported or exported subprogram, the result and parameter types
shall each be compatible with the convention specified in the corresponding
pragma.
27 The external name and link name string_expressions of a pragma Import or
Export, and the string_expression of a pragma Linker_Options, shall be static.
Static Semantics
28 Import, Export, and Convention pragmas are representation pragmas that
specify the convention aspect of representation. In addition, Import and
Export pragmas specify the imported and exported aspects of representation,
respectively.
29 An interfacing pragma is a program unit pragma when applied to a program
unit (see 10.1.5).
30 An interfacing pragma defines the convention of the entity denoted by the
local_name. The convention represents the calling convention or representation
convention of the entity. For an access-to-subprogram type, it represents the
calling convention of designated subprograms. In addition:
31 * A pragma Import specifies that the entity is defined externally (that
is, outside the Ada program).
32 * A pragma Export specifies that the entity is used externally.
33 * A pragma Import or Export optionally specifies an entity's external
name, link name, or both.
34 An external name is a string value for the name used by a foreign language
program either for an entity that an Ada program imports, or for referring to
an entity that an Ada program exports.
35 A link name is a string value for the name of an exported or imported
entity, based on the conventions of the foreign language's compiler in
interfacing with the system's linker tool.
36 The meaning of link names is implementation defined. If neither a link
name nor the Address attribute of an imported or exported entity is specified,
then a link name is chosen in an implementation-defined manner, based on the
external name if one is specified.
37 Pragma Linker_Options has the effect of passing its string argument as a
parameter to the system linker (if one exists), if the immediately enclosing
compilation unit is included in the partition being linked. The interpretation
of the string argument, and the way in which the string arguments from
multiple Linker_Options pragmas are combined, is implementation defined.
Dynamic Semantics
38 Notwithstanding what this International Standard says elsewhere, the
elaboration of a declaration denoted by the local_name of a pragma Import does
not create the entity. Such an elaboration has no other effect than to allow
the defining name to denote the external entity.
Erroneous Execution
38.1/2 It is the programmer's responsibility to ensure that the use of
interfacing pragmas does not violate Ada semantics; otherwise, program
execution is erroneous.
Implementation Advice
39 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.
40 Automatic elaboration of preelaborated packages should be provided when
pragma Export is supported.
41 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.
NOTES
42 1 Implementations may place restrictions on interfacing pragmas; for
example, requiring each exported entity to be declared at the library
level.
43 2 A pragma Import specifies the conventions for accessing external
entities. It is possible that the actual entity is written in assembly
language, but reflects the conventions of a particular language. For
example, pragma Import(Ada, ...) can be used to interface to an
assembly language routine that obeys the Ada compiler's calling
conventions.
44 3 To obtain "call-back" to an Ada subprogram from a foreign language
environment, pragma Convention should be specified both for the
access-to-subprogram type and the specific subprogram(s) to which
'Access is applied.
45 4 It is illegal to specify more than one of Import, Export, or
Convention for a given entity.
46 5 The local_name in an interfacing pragma can denote more than one
entity in the case of overloading. Such a pragma applies to all of the
denoted entities.
47 6 See also 13.8, "Machine Code Insertions".
48 7 If both External_Name and Link_Name are specified for an Import or
Export pragma, then the External_Name is ignored.
49/2 This paragraph was deleted.
Examples
50 Example of interfacing pragmas:
51 package Fortran_Library is
function Sqrt (X : Float) return Float;
function Exp (X : Float) return Float;
private
pragma Import(Fortran, Sqrt);
pragma Import(Fortran, Exp);
end Fortran_Library;
B.2 The Package Interfaces
1 Package Interfaces is the parent of several library packages that declare
types and other entities useful for interfacing to foreign languages. It also
contains some implementation-defined types that are useful across more than
one language (in particular for interfacing to assembly language).
Static Semantics
2 The library package Interfaces has the following skeletal declaration:
3
package Interfaces is
pragma Pure(Interfaces);
4 type Integer_n is range -2**(n-1) .. 2**(n-1) - 1; --2's complement
5 type Unsigned_n is mod 2**n;
6 function Shift_Left (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Shift_Right (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Shift_Right_Arithmetic (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Rotate_Left (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Rotate_Right (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
...
end Interfaces;
Implementation Requirements
7 An implementation shall provide the following declarations in the visible
part of package Interfaces:
8 * Signed and modular integer types of n bits, if supported by the target
architecture, for each n that is at least the size of a storage
element and that is a factor of the word size. The names of these
types are of the form Integer_n for the signed types, and Unsigned_n
for the modular types;
9 * For each such modular type in Interfaces, shifting and rotating
subprograms as specified in the declaration of Interfaces above. These
subprograms are Intrinsic. They operate on a bit-by-bit basis, using
the binary representation of the value of the operands to yield a
binary representation for the result. The Amount parameter gives the
number of bits by which to shift or rotate. For shifting, zero bits
are shifted in, except in the case of Shift_Right_Arithmetic, where
one bits are shifted in if Value is at least half the modulus.
10 * Floating point types corresponding to each floating point format fully
supported by the hardware.
10.1/2 Support for interfacing to any foreign language is optional. However,
an implementation shall not provide any attribute, library unit, or pragma
having the same name as an attribute, library unit, or pragma (respectively)
specified in the following clauses of this Annex unless the provided construct
is either as specified in those clauses or is more limited in capability than
that required by those clauses. A program that attempts to use an unsupported
capability of this Annex shall either be identified by the implementation
before run time or shall raise an exception at run time.
Implementation Permissions
11 An implementation may provide implementation-defined library units that
are children of Interfaces, and may add declarations to the visible part of
Interfaces in addition to the ones defined above.
11.1/2 A child package of package Interfaces with the name of a convention may
be provided independently of whether the convention is supported by the pragma
Convention and vice versa. Such a child 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.
Implementation Advice
12/2 This paragraph was deleted.
13 An implementation supporting an interface to C, COBOL, or Fortran should
provide the corresponding package or packages described in the following
clauses.
B.3 Interfacing with C and C++
1/2 The facilities relevant to interfacing with the C language and the
corresponding subset of the C++ language are the package Interfaces.C and its
children; support for the Import, Export, and Convention pragmas with
convention_identifier C; and support for the Convention pragma with
convention_identifier C_Pass_By_Copy.
2/2 The package Interfaces.C contains the basic types, constants and
subprograms that allow an Ada program to pass scalars and strings to C and C++
functions. When this clause mentions a C entity, the reference also applies to
the corresponding entity in C++.
Static Semantics
3 The library package Interfaces.C has the following declaration:
4 package Interfaces.C is
pragma Pure(C);
5 -- Declarations based on C's <limits.h>
6 CHAR_BIT : constant := implementation-defined; -- typically 8
SCHAR_MIN : constant := implementation-defined; -- typically -128
SCHAR_MAX : constant := implementation-defined; -- typically 127
UCHAR_MAX : constant := implementation-defined; -- typically 255
7 -- Signed and Unsigned Integers
type int is range implementation-defined;
type short is range implementation-defined;
type long is range implementation-defined;
8 type signed_char is range SCHAR_MIN .. SCHAR_MAX;
for signed_char'Size use CHAR_BIT;
9 type unsigned is mod implementation-defined;
type unsigned_short is mod implementation-defined;
type unsigned_long is mod implementation-defined;
10 type unsigned_char is mod (UCHAR_MAX+1);
for unsigned_char'Size use CHAR_BIT;
11 subtype plain_char is implementation-defined;
12 type ptrdiff_t is range implementation-defined;
13 type size_t is mod implementation-defined;
14 -- Floating Point
15 type C_float is digits implementation-defined;
16 type double is digits implementation-defined;
17 type long_double is digits implementation-defined;
18 -- Characters and Strings
19 type char is <implementation-defined character type>;
20/1 nul : constant char := implementation-defined;
21 function To_C (Item : in Character) return char;
22 function To_Ada (Item : in char) return Character;
23 type char_array is array (size_t range <>) of aliased char;
pragma Pack(char_array);
for char_array'Component_Size use CHAR_BIT;
24 function Is_Nul_Terminated (Item : in char_array) return Boolean;
25 function To_C (Item : in String;
Append_Nul : in Boolean := True)
return char_array;
26 function To_Ada (Item : in char_array;
Trim_Nul : in Boolean := True)
return String;
27 procedure To_C (Item : in String;
Target : out char_array;
Count : out size_t;
Append_Nul : in Boolean := True);
28 procedure To_Ada (Item : in char_array;
Target : out String;
Count : out Natural;
Trim_Nul : in Boolean := True);
29 -- Wide Character and Wide String
30/1 type wchar_t is <implementation-defined character type>;
31/1 wide_nul : constant wchar_t := implementation-defined;
32 function To_C (Item : in Wide_Character) return wchar_t;
function To_Ada (Item : in wchar_t ) return Wide_Character;
33 type wchar_array is array (size_t range <>) of aliased wchar_t;
34 pragma Pack(wchar_array);
35 function Is_Nul_Terminated (Item : in wchar_array) return Boolean;
36 function To_C (Item : in Wide_String;
Append_Nul : in Boolean := True)
return wchar_array;
37 function To_Ada (Item : in wchar_array;
Trim_Nul : in Boolean := True)
return Wide_String;
38 procedure To_C (Item : in Wide_String;
Target : out wchar_array;
Count : out size_t;
Append_Nul : in Boolean := True);
39 procedure To_Ada (Item : in wchar_array;
Target : out Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
39.1/2 -- ISO/IEC 10646:2003 compatible types defined by ISO/IEC TR 19769:2004.
39.2/2 type char16_t is <implementation-defined character type>;
39.3/2 char16_nul : constant char16_t := implementation-defined;
39.4/2 function To_C (Item : in Wide_Character) return char16_t;
function To_Ada (Item : in char16_t) return Wide_Character;
39.5/2 type char16_array is array (size_t range <>) of aliased char16_t;
39.6/2 pragma Pack(char16_array);
39.7/2 function Is_Nul_Terminated (Item : in char16_array) return Boolean;
function To_C (Item : in Wide_String;
Append_Nul : in Boolean := True)
return char16_array;
39.8/2 function To_Ada (Item : in char16_array;
Trim_Nul : in Boolean := True)
return Wide_String;
39.9/2 procedure To_C (Item : in Wide_String;
Target : out char16_array;
Count : out size_t;
Append_Nul : in Boolean := True);
39.10/2 procedure To_Ada (Item : in char16_array;
Target : out Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
39.11/2 type char32_t is <implementation-defined character type>;
39.12/2 char32_nul : constant char32_t := implementation-defined;
39.13/2 function To_C (Item : in Wide_Wide_Character) return char32_t;
function To_Ada (Item : in char32_t) return Wide_Wide_Character;
39.14/2 type char32_array is array (size_t range <>) of aliased char32_t;
39.15/2 pragma Pack(char32_array);
39.16/2 function Is_Nul_Terminated (Item : in char32_array) return Boolean;
function To_C (Item : in Wide_Wide_String;
Append_Nul : in Boolean := True)
return char32_array;
39.17/2 function To_Ada (Item : in char32_array;
Trim_Nul : in Boolean := True)
return Wide_Wide_String;
39.18/2 procedure To_C (Item : in Wide_Wide_String;
Target : out char32_array;
Count : out size_t;
Append_Nul : in Boolean := True);
39.19/2 procedure To_Ada (Item : in char32_array;
Target : out Wide_Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
40 Terminator_Error : exception;
41 end Interfaces.C;
42 Each of the types declared in Interfaces.C is C-compatible.
43/2 The types int, short, long, unsigned, ptrdiff_t, size_t, double, char,
wchar_t, char16_t, and char32_t correspond respectively to the C types having
the same names. The types signed_char, unsigned_short, unsigned_long, unsigned_-
char, C_float, and long_double correspond respectively to the C types signed
char, unsigned short, unsigned long, unsigned char, float, and long double.
44 The type of the subtype plain_char is either signed_char or unsigned_char,
depending on the C implementation.
45 function To_C (Item : in Character) return char;
function To_Ada (Item : in char ) return Character;
46 The functions To_C and To_Ada map between the Ada type Character
and the C type char.
47 function Is_Nul_Terminated (Item : in char_array) return Boolean;
48 The result of Is_Nul_Terminated is True if Item contains nul, and
is False otherwise.
49 function To_C (Item : in String; Append_Nul : in Boolean := True)
return char_array;
function To_Ada (Item : in char_array; Trim_Nul : in Boolean := True)
return String;
50/2 The result of To_C is a char_array value of length Item'Length (if
Append_Nul is False) or Item'Length+1 (if Append_Nul is True). The
lower bound is 0. For each component Item(I), the corresponding
component in the result is To_C applied to Item(I). The value nul
is appended if Append_Nul is True. If Append_Nul is False and
Item'Length is 0, then To_C propagates Constraint_Error.
51 The result of To_Ada is a String whose length is Item'Length (if
Trim_Nul is False) or the length of the slice of Item preceding
the first nul (if Trim_Nul is True). The lower bound of the result
is 1. If Trim_Nul is False, then for each component Item(I) the
corresponding component in the result is To_Ada applied to
Item(I). If Trim_Nul is True, then for each component Item(I)
before the first nul the corresponding component in the result is
To_Ada applied to Item(I). The function propagates
Terminator_Error if Trim_Nul is True and Item does not contain nul.
52 procedure To_C (Item : in String;
Target : out char_array;
Count : out size_t;
Append_Nul : in Boolean := True);
procedure To_Ada (Item : in char_array;
Target : out String;
Count : out Natural;
Trim_Nul : in Boolean := True);
53 For procedure To_C, each element of Item is converted (via the
To_C function) to a char, which is assigned to the corresponding
element of Target. If Append_Nul is True, nul is then assigned to
the next element of Target. In either case, Count is set to the
number of Target elements assigned. If Target is not long enough,
Constraint_Error is propagated.
54 For procedure To_Ada, each element of Item (if Trim_Nul is False)
or each element of Item preceding the first nul (if Trim_Nul is
True) is converted (via the To_Ada function) to a Character, which
is assigned to the corresponding element of Target. Count is set
to the number of Target elements assigned. If Target is not long
enough, Constraint_Error is propagated. If Trim_Nul is True and
Item does not contain nul, then Terminator_Error is propagated.
55 function Is_Nul_Terminated (Item : in wchar_array) return Boolean;
56 The result of Is_Nul_Terminated is True if Item contains wide_nul,
and is False otherwise.
57 function To_C (Item : in Wide_Character) return wchar_t;
function To_Ada (Item : in wchar_t ) return Wide_Character;
58 To_C and To_Ada provide the mappings between the Ada and C wide
character types.
59 function To_C (Item : in Wide_String;
Append_Nul : in Boolean := True)
return wchar_array;
function To_Ada (Item : in wchar_array;
Trim_Nul : in Boolean := True)
return Wide_String;
procedure To_C (Item : in Wide_String;
Target : out wchar_array;
Count : out size_t;
Append_Nul : in Boolean := True);
procedure To_Ada (Item : in wchar_array;
Target : out Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
60 The To_C and To_Ada subprograms that convert between Wide_String
and wchar_array have analogous effects to the To_C and To_Ada
subprograms that convert between String and char_array, except
that wide_nul is used instead of nul.
60.1/2 function Is_Nul_Terminated (Item : in char16_array) return Boolean;
60.2/2 The result of Is_Nul_Terminated is True if Item contains
char16_nul, and is False otherwise.
60.3/2 function To_C (Item : in Wide_Character) return char16_t;
function To_Ada (Item : in char16_t ) return Wide_Character;
60.4/2 To_C and To_Ada provide mappings between the Ada and C 16-bit
character types.
60.5/2 function To_C (Item : in Wide_String;
Append_Nul : in Boolean := True)
return char16_array;
function To_Ada (Item : in char16_array;
Trim_Nul : in Boolean := True)
return Wide_String;
procedure To_C (Item : in Wide_String;
Target : out char16_array;
Count : out size_t;
Append_Nul : in Boolean := True);
procedure To_Ada (Item : in char16_array;
Target : out Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
60.6/2 The To_C and To_Ada subprograms that convert between Wide_String
and char16_array have analogous effects to the To_C and To_Ada
subprograms that convert between String and char_array, except
that char16_nul is used instead of nul.
60.7/2 function Is_Nul_Terminated (Item : in char32_array) return Boolean;
60.8/2 The result of Is_Nul_Terminated is True if Item contains
char16_nul, and is False otherwise.
60.9/2 function To_C (Item : in Wide_Wide_Character) return char32_t;
function To_Ada (Item : in char32_t ) return Wide_Wide_Character;
60.10/2 To_C and To_Ada provide mappings between the Ada and C 32-bit
character types.
60.11/2 function To_C (Item : in Wide_Wide_String;
Append_Nul : in Boolean := True)
return char32_array;
function To_Ada (Item : in char32_array;
Trim_Nul : in Boolean := True)
return Wide_Wide_String;
procedure To_C (Item : in Wide_Wide_String;
Target : out char32_array;
Count : out size_t;
Append_Nul : in Boolean := True);
procedure To_Ada (Item : in char32_array;
Target : out Wide_Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
60.12/2 The To_C and To_Ada subprograms that convert between
Wide_Wide_String and char32_array have analogous effects to the
To_C and To_Ada subprograms that convert between String and
char_array, except that char32_nul is used instead of nul.
60.13/1 A Convention pragma with convention_identifier C_Pass_By_Copy shall
only be applied to a type.
60.14/2 The eligibility rules in B.1 do not apply to convention
C_Pass_By_Copy. Instead, a type T is eligible for convention C_Pass_By_Copy if
T is an unchecked union type or if T is a record type that has no
discriminants and that only has components with statically constrained
subtypes, and each component is C-compatible.
60.15/1 If a type is C_Pass_By_Copy-compatible then it is also C-compatible.
Implementation Requirements
61/1 An implementation shall support pragma Convention with a C
convention_identifier for a C-eligible type (see B.1). An implementation shall support
pragma Convention with a C_Pass_By_Copy convention_identifier for a
C_Pass_By_Copy-eligible type.
Implementation Permissions
62 An implementation may provide additional declarations in the C interface
packages.
Implementation Advice
62.1/2 The constants nul, wide_nul, char16_nul, and char32_nul should have a
representation of zero.
63 An implementation should support the following interface correspondences
between Ada and C.
64 * An Ada procedure corresponds to a void-returning C function.
65 * An Ada function corresponds to a non-void C function.
66 * An Ada in scalar parameter is passed as a scalar argument to a C
function.
67 * 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.
68 * 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.
68.1/2 * An Ada parameter of a (record) type T of convention C_Pass_By_Copy,
of mode in, is passed as a t argument to a C function, where t is the
C struct corresponding to the Ada type T.
69/2 * An Ada parameter of a record type T, of any mode, other than an in
parameter of a type of convention C_Pass_By_Copy, is passed as a t*
argument to a C function, where t is the C struct corresponding to the
Ada type T.
70 * 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.
71 * 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.
71.1/2 An Ada parameter of a private type is passed as specified for the full
view of the type.
NOTES
72 8 Values of type char_array are not implicitly terminated with nul.
If a char_array is to be passed as a parameter to an imported C
function requiring nul termination, it is the programmer's
responsibility to obtain this effect.
73 9 To obtain the effect of C's sizeof(item_type), where Item_Type is
the corresponding Ada type, evaluate the expression:
size_t(Item_Type'Size/CHAR_BIT).
74/2 This paragraph was deleted.
75 10 A C function that takes a variable number of arguments can
correspond to several Ada subprograms, taking various specific numbers
and types of parameters.
Examples
76 Example of using the Interfaces.C package:
77 --Calling the C Library Function strcpy
with Interfaces.C;
procedure Test is
package C renames Interfaces.C;
use type C.char_array;
-- Call <string.h>strcpy:
-- C definition of strcpy: char *strcpy(char *s1, const char *s2);
-- This function copies the string pointed to by s2 (including the terminating null character)
-- into the array pointed to by s1. If copying takes place between objects that overlap,
-- the behavior is undefined. The strcpy function returns the value of s1.
78 -- Note: since the C function's return value is of no interest, the Ada interface is a procedure
procedure Strcpy (Target : out C.char_array;
Source : in C.char_array);
79 pragma Import(C, Strcpy, "strcpy");
80 Chars1 : C.char_array(1..20);
Chars2 : C.char_array(1..20);
81 begin
Chars2(1..6) := "qwert" & C.nul;
82 Strcpy(Chars1, Chars2);
83 -- Now Chars1(1..6) = "qwert" & C.Nul
84 end Test;
B.3.1 The Package Interfaces.C.Strings
1 The package Interfaces.C.Strings declares types and subprograms allowing
an Ada program to allocate, reference, update, and free C-style strings. In
particular, the private type chars_ptr corresponds to a common use of "char
*" in C programs, and an object of this type can be passed to a subprogram to
which pragma Import(C,...) has been applied, and for which "char *" is the
type of the argument of the C function.
Static Semantics
2 The library package Interfaces.C.Strings has the following declaration:
3 package Interfaces.C.Strings is
pragma Preelaborate(Strings);
4 type char_array_access is access all char_array;
5/2 type chars_ptr is private;
pragma Preelaborable_Initialization(chars_ptr);
6/2 type chars_ptr_array
is array (size_t range <>) of aliased chars_ptr;
7 Null_Ptr : constant chars_ptr;
8 function To_Chars_Ptr (Item : in char_array_access;
Nul_Check : in Boolean := False)
return chars_ptr;
9 function New_Char_Array (Chars : in char_array) return chars_ptr;
10 function New_String (Str : in String) return chars_ptr;
11 procedure Free (Item : in out chars_ptr);
12 Dereference_Error : exception;
13 function Value (Item : in chars_ptr) return char_array;
14 function Value (Item : in chars_ptr; Length : in size_t)
return char_array;
15 function Value (Item : in chars_ptr) return String;
16 function Value (Item : in chars_ptr; Length : in size_t)
return String;
17 function Strlen (Item : in chars_ptr) return size_t;
18 procedure Update (Item : in chars_ptr;
Offset : in size_t;
Chars : in char_array;
Check : in Boolean := True);
19 procedure Update (Item : in chars_ptr;
Offset : in size_t;
Str : in String;
Check : in Boolean := True);
20 Update_Error : exception;
21 private
... -- not specified by the language
end Interfaces.C.Strings;
22 The type chars_ptr is C-compatible and corresponds to the use of C's "
char *" for a pointer to the first char in a char array terminated by nul.
When an object of type chars_ptr is declared, its value is by default set to
Null_Ptr, unless the object is imported (see B.1).
23 function To_Chars_Ptr (Item : in char_array_access;
Nul_Check : in Boolean := False)
return chars_ptr;
24/1 If Item is null, then To_Chars_Ptr returns Null_Ptr. If Item is
not null, Nul_Check is True, and Item.all does not contain nul,
then the function propagates Terminator_Error; otherwise
To_Chars_Ptr performs a pointer conversion with no allocation of
memory.
25 function New_Char_Array (Chars : in char_array) return chars_ptr;
26 This function returns a pointer to an allocated object initialized
to Chars(Chars'First .. Index) & nul, where
27 * Index = Chars'Last if Chars does not contain nul, or
28 * Index is the smallest size_t value I such that Chars(I+1) =
nul.
28.1 Storage_Error is propagated if the allocation fails.
29 function New_String (Str : in String) return chars_ptr;
30 This function is equivalent to New_Char_Array(To_C(Str)).
31 procedure Free (Item : in out chars_ptr);
32 If Item is Null_Ptr, then Free has no effect. Otherwise, Free
releases the storage occupied by Value(Item), and resets Item to
Null_Ptr.
33 function Value (Item : in chars_ptr) return char_array;
34 If Item = Null_Ptr then Value propagates Dereference_Error.
Otherwise Value returns the prefix of the array of chars pointed
to by Item, up to and including the first nul. The lower bound of
the result is 0. If Item does not point to a nul-terminated
string, then execution of Value is erroneous.
35 function Value (Item : in chars_ptr; Length : in size_t)
return char_array;
36/1 If Item = Null_Ptr then Value propagates Dereference_Error.
Otherwise Value returns the shorter of two arrays, either the
first Length chars pointed to by Item, or Value(Item). The lower
bound of the result is 0. If Length is 0, then Value propagates
Constraint_Error.
37 function Value (Item : in chars_ptr) return String;
38 Equivalent to To_Ada(Value(Item), Trim_Nul=>True).
39 function Value (Item : in chars_ptr; Length : in size_t)
return String;
40/1 Equivalent to To_Ada(Value(Item, Length) & nul, Trim_Nul=>True).
41 function Strlen (Item : in chars_ptr) return size_t;
42 Returns Val'Length-1 where Val = Value(Item); propagates
Dereference_Error if Item = Null_Ptr.
43 procedure Update (Item : in chars_ptr;
Offset : in size_t;
Chars : in char_array;
Check : Boolean := True);
44/1 If Item = Null_Ptr, then Update propagates Dereference_Error.
Otherwise, this procedure updates the value pointed to by Item,
starting at position Offset, using Chars as the data to be copied
into the array. Overwriting the nul terminator, and skipping with
the Offset past the nul terminator, are both prevented if Check is
True, as follows:
45 * Let N = Strlen(Item). If Check is True, then:
46 * If Offset+Chars'Length>N, propagate Update_Error.
47 * Otherwise, overwrite the data in the array pointed to by
Item, starting at the char at position Offset, with the
data in Chars.
48 * If Check is False, then processing is as above, but with no
check that Offset+Chars'Length>N.
49 procedure Update (Item : in chars_ptr;
Offset : in size_t;
Str : in String;
Check : in Boolean := True);
50/2 Equivalent to Update(Item, Offset, To_C(Str, Append_Nul => False),
Check).
Erroneous Execution
51 Execution of any of the following is erroneous if the Item parameter is
not null_ptr and Item does not point to a nul-terminated array of chars.
52 * a Value function not taking a Length parameter,
53 * the Free procedure,
54 * the Strlen function.
55 Execution of Free(X) is also erroneous if the chars_ptr X was not returned
by New_Char_Array or New_String.
56 Reading or updating a freed char_array is erroneous.
57 Execution of Update is erroneous if Check is False and a call with Check
equal to True would have propagated Update_Error.
NOTES
58 11 New_Char_Array and New_String might be implemented either through
the allocation function from the C environment ("malloc") or through
Ada dynamic memory allocation ("new"). The key points are
59 * the returned value (a chars_ptr) is represented as a C "char *" so
that it may be passed to C functions;
60 * the allocated object should be freed by the programmer via a call
of Free, not by a called C function.
B.3.2 The Generic Package Interfaces.C.Pointers
1 The generic package Interfaces.C.Pointers allows the Ada programmer to
perform C-style operations on pointers. It includes an access type Pointer,
Value functions that dereference a Pointer and deliver the designated array,
several pointer arithmetic operations, and "copy" procedures that copy the
contents of a source pointer into the array designated by a destination
pointer. As in C, it treats an object Ptr of type Pointer as a pointer to the
first element of an array, so that for example, adding 1 to Ptr yields a
pointer to the second element of the array.
2 The generic allows two styles of usage: one in which the array is
terminated by a special terminator element; and another in which the
programmer needs to keep track of the length.
Static Semantics
3 The generic library package Interfaces.C.Pointers has the following
declaration:
4 generic
type Index is (<>);
type Element is private;
type Element_Array is array (Index range <>) of aliased Element;
Default_Terminator : Element;
package Interfaces.C.Pointers is
pragma Preelaborate(Pointers);
5 type Pointer is access all Element;
6 function Value(Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return Element_Array;
7 function Value(Ref : in Pointer;
Length : in ptrdiff_t)
return Element_Array;
8 Pointer_Error : exception;
9 -- C-style Pointer arithmetic
10 function "+" (Left : in Pointer; Right : in ptrdiff_t) return Pointer;
function "+" (Left : in ptrdiff_t; Right : in Pointer) return Pointer;
function "-" (Left : in Pointer; Right : in ptrdiff_t) return Pointer;
function "-" (Left : in Pointer; Right : in Pointer) return ptrdiff_t;
11 procedure Increment (Ref : in out Pointer);
procedure Decrement (Ref : in out Pointer);
12 pragma Convention (Intrinsic, "+");
pragma Convention (Intrinsic, "-");
pragma Convention (Intrinsic, Increment);
pragma Convention (Intrinsic, Decrement);
13 function Virtual_Length (Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return ptrdiff_t;
14 procedure Copy_Terminated_Array
(Source : in Pointer;
Target : in Pointer;
Limit : in ptrdiff_t := ptrdiff_t'Last;
Terminator : in Element := Default_Terminator);
15 procedure Copy_Array (Source : in Pointer;
Target : in Pointer;
Length : in ptrdiff_t);
16 end Interfaces.C.Pointers;
17 The type Pointer is C-compatible and corresponds to one use of C's "
Element *". An object of type Pointer is interpreted as a pointer to the
initial Element in an Element_Array. Two styles are supported:
18 * Explicit termination of an array value with Default_Terminator (a
special terminator value);
19 * Programmer-managed length, with Default_Terminator treated simply as a
data element.
20 function Value(Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return Element_Array;
21 This function returns an Element_Array whose value is the array
pointed to by Ref, up to and including the first Terminator; the
lower bound of the array is Index'First.
Interfaces.C.Strings.Dereference_Error is propagated if Ref is
null.
22 function Value(Ref : in Pointer;
Length : in ptrdiff_t)
return Element_Array;
23 This function returns an Element_Array comprising the first Length
elements pointed to by Ref. The exception
Interfaces.C.Strings.Dereference_Error is propagated if Ref is
null.
24 The "+" and "-" functions perform arithmetic on Pointer values, based on
the Size of the array elements. In each of these functions, Pointer_Error is
propagated if a Pointer parameter is null.
25 procedure Increment (Ref : in out Pointer);
26 Equivalent to Ref := Ref+1.
27 procedure Decrement (Ref : in out Pointer);
28 Equivalent to Ref := Ref-1.
29 function Virtual_Length (Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return ptrdiff_t;
30 Returns the number of Elements, up to the one just before the
first Terminator, in Value(Ref, Terminator).
31 procedure Copy_Terminated_Array
(Source : in Pointer;
Target : in Pointer;
Limit : in ptrdiff_t := ptrdiff_t'Last;
Terminator : in Element := Default_Terminator);
32 This procedure copies Value(Source, Terminator) into the array
pointed to by Target; it stops either after Terminator has been
copied, or the number of elements copied is Limit, whichever
occurs first. Dereference_Error is propagated if either Source or
Target is null.
33 procedure Copy_Array (Source : in Pointer;
Target : in Pointer;
Length : in ptrdiff_t);
34 This procedure copies the first Length elements from the array
pointed to by Source, into the array pointed to by Target.
Dereference_Error is propagated if either Source or Target is
null.
Erroneous Execution
35 It is erroneous to dereference a Pointer that does not designate an
aliased Element.
36 Execution of Value(Ref, Terminator) is erroneous if Ref does not designate
an aliased Element in an Element_Array terminated by Terminator.
37 Execution of Value(Ref, Length) is erroneous if Ref does not designate an
aliased Element in an Element_Array containing at least Length Elements
between the designated Element and the end of the array, inclusive.
38 Execution of Virtual_Length(Ref, Terminator) is erroneous if Ref does not
designate an aliased Element in an Element_Array terminated by Terminator.
39 Execution of Copy_Terminated_Array(Source, Target, Limit, Terminator) is
erroneous in either of the following situations:
40 * Execution of both Value(Source, Terminator) and Value(Source, Limit)
are erroneous, or
41 * Copying writes past the end of the array containing the Element
designated by Target.
42 Execution of Copy_Array(Source, Target, Length) is erroneous if either
Value(Source, Length) is erroneous, or copying writes past the end of the
array containing the Element designated by Target.
NOTES
43 12 To compose a Pointer from an Element_Array, use 'Access on the
first element. For example (assuming appropriate instantiations):
44 Some_Array : Element_Array(0..5) ;
Some_Pointer : Pointer := Some_Array(0)'Access;
Examples
45 Example of Interfaces.C.Pointers:
46 with Interfaces.C.Pointers;
with Interfaces.C.Strings;
procedure Test_Pointers is
package C renames Interfaces.C;
package Char_Ptrs is
new C.Pointers (Index => C.size_t,
Element => C.char,
Element_Array => C.char_array,
Default_Terminator => C.nul);
47 use type Char_Ptrs.Pointer;
subtype Char_Star is Char_Ptrs.Pointer;
48 procedure Strcpy (Target_Ptr, Source_Ptr : Char_Star) is
Target_Temp_Ptr : Char_Star := Target_Ptr;
Source_Temp_Ptr : Char_Star := Source_Ptr;
Element : C.char;
begin
if Target_Temp_Ptr = null or Source_Temp_Ptr = null then
raise C.Strings.Dereference_Error;
end if;
49/1 loop
Element := Source_Temp_Ptr.all;
Target_Temp_Ptr.all := Element;
exit when C."="(Element, C.nul);
Char_Ptrs.Increment(Target_Temp_Ptr);
Char_Ptrs.Increment(Source_Temp_Ptr);
end loop;
end Strcpy;
begin
...
end Test_Pointers;
B.3.3 Pragma Unchecked_Union
1/2 A pragma Unchecked_Union specifies an interface correspondence between a
given discriminated type and some C union. The pragma specifies that the
associated type shall be given a representation that leaves no space for its
discriminant(s).
Syntax
2/2 The form of a pragma Unchecked_Union is as follows:
3/2 pragma Unchecked_Union (first_subtype_local_name);
Legality Rules
4/2 Unchecked_Union is a representation pragma, specifying the unchecked union
aspect of representation.
5/2 The first_subtype_local_name of a pragma Unchecked_Union shall denote an
unconstrained discriminated record subtype having a variant_part.
6/2 A type to which a pragma Unchecked_Union applies is called an unchecked
union type. A subtype of an unchecked union type is defined to be an unchecked
union subtype. An object of an unchecked union type is defined to be an
unchecked union object.
7/2 All component subtypes of an unchecked union type shall be C-compatible.
8/2 If a component subtype of an unchecked union type is subject to a
per-object constraint, then the component subtype shall be an unchecked union
subtype.
9/2 Any name that denotes a discriminant of an object of an unchecked union
type shall occur within the declarative region of the type.
10/2 A component declared in a variant_part of an unchecked union type shall
not have a controlled, protected, or task part.
11/2 The completion of an incomplete or private type declaration having a
known_discriminant_part shall not be an unchecked union type.
12/2 An unchecked union subtype shall only be passed as a generic actual
parameter if the corresponding formal type has no known discriminants or is an
unchecked union type.
Static Semantics
13/2 An unchecked union type is eligible for convention C.
14/2 All objects of an unchecked union type have the same size.
15/2 Discriminants of objects of an unchecked union type are of size zero.
16/2 Any check which would require reading a discriminant of an unchecked
union object is suppressed (see 11.5). These checks include:
17/2 * The check performed when addressing a variant component (i.e., a
component that was declared in a variant part) of an unchecked union
object that the object has this component (see 4.1.3).
18/2 * Any checks associated with a type or subtype conversion of a value of
an unchecked union type (see 4.6). This includes, for example, the
check associated with the implicit subtype conversion of an assignment
statement.
19/2 * The subtype membership check associated with the evaluation of a
qualified expression (see 4.7) or an uninitialized allocator (see
4.8).
Dynamic Semantics
20/2 A view of an unchecked union object (including a type conversion or
function call) has inferable discriminants if it has a constrained nominal
subtype, unless the object is a component of an enclosing unchecked union
object that is subject to a per-object constraint and the enclosing object
lacks inferable discriminants.
21/2 An expression of an unchecked union type has inferable discriminants if
it is either a name of an object with inferable discriminants or a qualified
expression whose subtype_mark denotes a constrained subtype.
22/2 Program_Error is raised in the following cases:
23/2 * Evaluation of the predefined equality operator for an unchecked union
type if either of the operands lacks inferable discriminants.
24/2 * Evaluation of the predefined equality operator for a type which has a
subcomponent of an unchecked union type whose nominal subtype is
unconstrained.
25/2 * Evaluation of a membership test if the subtype_mark denotes a
constrained unchecked union subtype and the expression lacks inferable
discriminants.
26/2 * Conversion from a derived unchecked union type to an unconstrained
non-unchecked-union type if the operand of the conversion lacks
inferable discriminants.
27/2 * Execution of the default implementation of the Write or Read
attribute of an unchecked union type.
28/2 * Execution of the default implementation of the Output or Input
attribute of an unchecked union type if the type lacks default
discriminant values.
Implementation Permissions
29/2 An implementation may require that pragma Controlled be specified for the
type of an access subcomponent of an unchecked union type.
NOTES
30/2 13 The use of an unchecked union to obtain the effect of an unchecked
conversion results in erroneous execution (see 11.5). Execution of the
following example is erroneous even if Float'Size = Integer'Size:
31/2 type T (Flag : Boolean := False) is
record
case Flag is
when False =>
F1 : Float := 0.0;
when True =>
F2 : Integer := 0;
end case;
end record;
pragma Unchecked_Union (T);
32/2 X : T;
Y : Integer := X.F2; -- erroneous
B.4 Interfacing with COBOL
1 The facilities relevant to interfacing with the COBOL language are the
package Interfaces.COBOL and support for the Import, Export and Convention
pragmas with convention_identifier COBOL.
2 The COBOL interface package supplies several sets of facilities:
3 * A set of types corresponding to the native COBOL types of the
supported COBOL implementation (so-called "internal COBOL
representations"), allowing Ada data to be passed as parameters to
COBOL programs
4 * A set of types and constants reflecting external data representations
such as might be found in files or databases, allowing COBOL-generated
data to be read by an Ada program, and Ada-generated data to be read
by COBOL programs
5 * A generic package for converting between an Ada decimal type value and
either an internal or external COBOL representation
Static Semantics
6 The library package Interfaces.COBOL has the following declaration:
7 package Interfaces.COBOL is
pragma Preelaborate(COBOL);
8 -- Types and operations for internal data representations
9 type Floating is digits implementation-defined;
type Long_Floating is digits implementation-defined;
10 type Binary is range implementation-defined;
type Long_Binary is range implementation-defined;
11 Max_Digits_Binary : constant := implementation-defined;
Max_Digits_Long_Binary : constant := implementation-defined;
12 type Decimal_Element is mod implementation-defined;
type Packed_Decimal
is array (Positive range <>) of Decimal_Element;
pragma Pack(Packed_Decimal);
13 type COBOL_Character is implementation-defined character type;
14 Ada_To_COBOL
: array (Character) of COBOL_Character := implementation-defined;
15 COBOL_To_Ada
: array (COBOL_Character) of Character := implementation-defined;
16 type Alphanumeric is array (Positive range <>) of COBOL_Character;
pragma Pack(Alphanumeric);
17 function To_COBOL (Item : in String) return Alphanumeric;
function To_Ada (Item : in Alphanumeric) return String;
18 procedure To_COBOL (Item : in String;
Target : out Alphanumeric;
Last : out Natural);
19 procedure To_Ada (Item : in Alphanumeric;
Target : out String;
Last : out Natural);
20 type Numeric is array (Positive range <>) of COBOL_Character;
pragma Pack(Numeric);
21 -- Formats for COBOL data representations
22 type Display_Format is private;
23 Unsigned : constant Display_Format;
Leading_Separate : constant Display_Format;
Trailing_Separate : constant Display_Format;
Leading_Nonseparate : constant Display_Format;
Trailing_Nonseparate : constant Display_Format;
24 type Binary_Format is private;
25 High_Order_First : constant Binary_Format;
Low_Order_First : constant Binary_Format;
Native_Binary : constant Binary_Format;
26 type Packed_Format is private;
27 Packed_Unsigned : constant Packed_Format;
Packed_Signed : constant Packed_Format;
28 -- Types for external representation of COBOL binary data
29 type Byte is mod 2**COBOL_Character'Size;
type Byte_Array is array (Positive range <>) of Byte;
pragma Pack (Byte_Array);
30 Conversion_Error : exception;
31 generic
type Num is delta <> digits <>;
package Decimal_Conversions is
32 -- Display Formats: data values are represented as Numeric
33 function Valid (Item : in Numeric;
Format : in Display_Format) return Boolean;
34 function Length (Format : in Display_Format) return Natural;
35 function To_Decimal (Item : in Numeric;
Format : in Display_Format) return Num;
36 function To_Display (Item : in Num;
Format : in Display_Format) return Numeric;
37 -- Packed Formats: data values are represented as Packed_Decimal
38 function Valid (Item : in Packed_Decimal;
Format : in Packed_Format) return Boolean;
39 function Length (Format : in Packed_Format) return Natural;
40 function To_Decimal (Item : in Packed_Decimal;
Format : in Packed_Format) return Num;
41 function To_Packed (Item : in Num;
Format : in Packed_Format) return Packed_Decimal;
42 -- Binary Formats: external data values are represented as Byte_Array
43 function Valid (Item : in Byte_Array;
Format : in Binary_Format) return Boolean;
44 function Length (Format : in Binary_Format) return Natural;
function To_Decimal (Item : in Byte_Array;
Format : in Binary_Format) return Num;
45 function To_Binary (Item : in Num;
Format : in Binary_Format) return Byte_Array;
46 -- Internal Binary formats: data values are of type Binary or Long_Binary
47 function To_Decimal (Item : in Binary) return Num;
function To_Decimal (Item : in Long_Binary) return Num;
48 function To_Binary (Item : in Num) return Binary;
function To_Long_Binary (Item : in Num) return Long_Binary;
49 end Decimal_Conversions;
50 private
... -- not specified by the language
end Interfaces.COBOL;
51 Each of the types in Interfaces.COBOL is COBOL-compatible.
52 The types Floating and Long_Floating correspond to the native types in
COBOL for data items with computational usage implemented by floating point.
The types Binary and Long_Binary correspond to the native types in COBOL for
data items with binary usage, or with computational usage implemented by
binary.
53 Max_Digits_Binary is the largest number of decimal digits in a numeric
value that is represented as Binary. Max_Digits_Long_Binary is the largest
number of decimal digits in a numeric value that is represented as Long_Binary.
54 The type Packed_Decimal corresponds to COBOL's packed-decimal usage.
55 The type COBOL_Character defines the run-time character set used in the
COBOL implementation. Ada_To_COBOL and COBOL_To_Ada are the mappings between
the Ada and COBOL run-time character sets.
56 Type Alphanumeric corresponds to COBOL's alphanumeric data category.
57 Each of the functions To_COBOL and To_Ada converts its parameter based on
the mappings Ada_To_COBOL and COBOL_To_Ada, respectively. The length of the
result for each is the length of the parameter, and the lower bound of the
result is 1. Each component of the result is obtained by applying the relevant
mapping to the corresponding component of the parameter.
58 Each of the procedures To_COBOL and To_Ada copies converted elements from
Item to Target, using the appropriate mapping (Ada_To_COBOL or COBOL_To_Ada,
respectively). The index in Target of the last element assigned is returned in
Last (0 if Item is a null array). If Item'Length exceeds Target'Length,
Constraint_Error is propagated.
59 Type Numeric corresponds to COBOL's numeric data category with display
usage.
60 The types Display_Format, Binary_Format, and Packed_Format are used in
conversions between Ada decimal type values and COBOL internal or external
data representations. The value of the constant Native_Binary is either
High_Order_First or Low_Order_First, depending on the implementation.
61 function Valid (Item : in Numeric;
Format : in Display_Format) return Boolean;
62 The function Valid checks that the Item parameter has a value
consistent with the value of Format. If the value of Format is
other than Unsigned, Leading_Separate, and Trailing_Separate, the
effect is implementation defined. If Format does have one of these
values, the following rules apply:
63/1 * Format=Unsigned: if Item comprises one or more decimal digit
characters then Valid returns True, else it returns False.
64/1 * Format=Leading_Separate: if Item comprises a single occurrence
of the plus or minus sign character, and then one or more
decimal digit characters, then Valid returns True, else it
returns False.
65/1 * Format=Trailing_Separate: if Item comprises one or more
decimal digit characters and finally a plus or minus sign
character, then Valid returns True, else it returns False.
66 function Length (Format : in Display_Format) return Natural;
67 The Length function returns the minimal length of a Numeric value
sufficient to hold any value of type Num when represented as
Format.
68 function To_Decimal (Item : in Numeric;
Format : in Display_Format) return Num;
69 Produces a value of type Num corresponding to Item as represented
by Format. The number of digits after the assumed radix point in
Item is Num'Scale. Conversion_Error is propagated if the value
represented by Item is outside the range of Num.
70 function To_Display (Item : in Num;
Format : in Display_Format) return Numeric;
71/1 This function returns the Numeric value for Item, represented in
accordance with Format. The length of the returned value is
Length(Format), and the lower bound is 1. Conversion_Error is
propagated if Num is negative and Format is Unsigned.
72 function Valid (Item : in Packed_Decimal;
Format : in Packed_Format) return Boolean;
73 This function returns True if Item has a value consistent with
Format, and False otherwise. The rules for the formation of
Packed_Decimal values are implementation defined.
74 function Length (Format : in Packed_Format) return Natural;
75 This function returns the minimal length of a Packed_Decimal value
sufficient to hold any value of type Num when represented as
Format.
76 function To_Decimal (Item : in Packed_Decimal;
Format : in Packed_Format) return Num;
77 Produces a value of type Num corresponding to Item as represented
by Format. Num'Scale is the number of digits after the assumed
radix point in Item. Conversion_Error is propagated if the value
represented by Item is outside the range of Num.
78 function To_Packed (Item : in Num;
Format : in Packed_Format) return Packed_Decimal;
79/1 This function returns the Packed_Decimal value for Item,
represented in accordance with Format. The length of the returned
value is Length(Format), and the lower bound is 1.
Conversion_Error is propagated if Num is negative and Format is
Packed_Unsigned.
80 function Valid (Item : in Byte_Array;
Format : in Binary_Format) return Boolean;
81 This function returns True if Item has a value consistent with
Format, and False otherwise.
82 function Length (Format : in Binary_Format) return Natural;
83 This function returns the minimal length of a Byte_Array value
sufficient to hold any value of type Num when represented as
Format.
84 function To_Decimal (Item : in Byte_Array;
Format : in Binary_Format) return Num;
85 Produces a value of type Num corresponding to Item as represented
by Format. Num'Scale is the number of digits after the assumed
radix point in Item. Conversion_Error is propagated if the value
represented by Item is outside the range of Num.
86 function To_Binary (Item : in Num;
Format : in Binary_Format) return Byte_Array;
87/1 This function returns the Byte_Array value for Item, represented
in accordance with Format. The length of the returned value is
Length(Format), and the lower bound is 1.
88 function To_Decimal (Item : in Binary) return Num;
function To_Decimal (Item : in Long_Binary) return Num;
89 These functions convert from COBOL binary format to a
corresponding value of the decimal type Num. Conversion_Error is
propagated if Item is too large for Num.
90 function To_Binary (Item : in Num) return Binary;
function To_Long_Binary (Item : in Num) return Long_Binary;
91 These functions convert from Ada decimal to COBOL binary format.
Conversion_Error is propagated if the value of Item is too large
to be represented in the result type.
Implementation Requirements
92 An implementation shall support pragma Convention with a COBOL
convention_identifier for a COBOL-eligible type (see B.1).
Implementation Permissions
93 An implementation may provide additional constants of the private types
Display_Format, Binary_Format, or Packed_Format.
94 An implementation may provide further floating point and integer types in
Interfaces.COBOL to match additional native COBOL types, and may also supply
corresponding conversion functions in the generic package Decimal_Conversions.
Implementation Advice
95 An Ada implementation should support the following interface
correspondences between Ada and COBOL.
96 * An Ada access T parameter is passed as a "BY REFERENCE" data item of
the COBOL type corresponding to T.
97 * An Ada in scalar parameter is passed as a "BY CONTENT" data item of
the corresponding COBOL type.
98 * 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.
NOTES
99 14 An implementation is not required to support pragma Convention for
access types, nor is it required to support pragma Import, Export or
Convention for functions.
100 15 If an Ada subprogram is exported to COBOL, then a call from COBOL
call may specify either "BY CONTENT" or "BY REFERENCE".
Examples
101 Examples of Interfaces.COBOL:
102 with Interfaces.COBOL;
procedure Test_Call is
103 -- Calling a foreign COBOL program
-- Assume that a COBOL program PROG has the following declaration
-- in its LINKAGE section:
-- 01 Parameter-Area
-- 05 NAME PIC X(20).
-- 05 SSN PIC X(9).
-- 05 SALARY PIC 99999V99 USAGE COMP.
-- The effect of PROG is to update SALARY based on some algorithm
104 package COBOL renames Interfaces.COBOL;
105 type Salary_Type is delta 0.01 digits 7;
106 type COBOL_Record is
record
Name : COBOL.Numeric(1..20);
SSN : COBOL.Numeric(1..9);
Salary : COBOL.Binary; -- Assume Binary = 32 bits
end record;
pragma Convention (COBOL, COBOL_Record);
107 procedure Prog (Item : in out COBOL_Record);
pragma Import (COBOL, Prog, "PROG");
108 package Salary_Conversions is
new COBOL.Decimal_Conversions(Salary_Type);
109 Some_Salary : Salary_Type := 12_345.67;
Some_Record : COBOL_Record :=
(Name => "Johnson, John ",
SSN => "111223333",
Salary => Salary_Conversions.To_Binary(Some_Salary));
110 begin
Prog (Some_Record);
...
end Test_Call;
111 with Interfaces.COBOL;
with COBOL_Sequential_IO; -- Assumed to be supplied by implementation
procedure Test_External_Formats is
112 -- Using data created by a COBOL program
-- Assume that a COBOL program has created a sequential file with
-- the following record structure, and that we need to
-- process the records in an Ada program
-- 01 EMPLOYEE-RECORD
-- 05 NAME PIC X(20).
-- 05 SSN PIC X(9).
-- 05 SALARY PIC 99999V99 USAGE COMP.
-- 05 ADJUST PIC S999V999 SIGN LEADING SEPARATE.
-- The COMP data is binary (32 bits), high-order byte first
113 package COBOL renames Interfaces.COBOL;
114 type Salary_Type is delta 0.01 digits 7;
type Adjustments_Type is delta 0.001 digits 6;
115 type COBOL_Employee_Record_Type is -- External representation
record
Name : COBOL.Alphanumeric(1..20);
SSN : COBOL.Alphanumeric(1..9);
Salary : COBOL.Byte_Array(1..4);
Adjust : COBOL.Numeric(1..7); -- Sign and 6 digits
end record;
pragma Convention (COBOL, COBOL_Employee_Record_Type);
116 package COBOL_Employee_IO is
new COBOL_Sequential_IO(COBOL_Employee_Record_Type);
use COBOL_Employee_IO;
117 COBOL_File : File_Type;
118 type Ada_Employee_Record_Type is -- Internal representation
record
Name : String(1..20);
SSN : String(1..9);
Salary : Salary_Type;
Adjust : Adjustments_Type;
end record;
119 COBOL_Record : COBOL_Employee_Record_Type;
Ada_Record : Ada_Employee_Record_Type;
120 package Salary_Conversions is
new COBOL.Decimal_Conversions(Salary_Type);
use Salary_Conversions;
121 package Adjustments_Conversions is
new COBOL.Decimal_Conversions(Adjustments_Type);
use Adjustments_Conversions;
122 begin
Open (COBOL_File, Name => "Some_File");
123 loop
Read (COBOL_File, COBOL_Record);
124 Ada_Record.Name := To_Ada(COBOL_Record.Name);
Ada_Record.SSN := To_Ada(COBOL_Record.SSN);
Ada_Record.Salary :=
To_Decimal(COBOL_Record.Salary, COBOL.High_Order_First);
Ada_Record.Adjust :=
To_Decimal(COBOL_Record.Adjust, COBOL.Leading_Separate);
... -- Process Ada_Record
end loop;
exception
when End_Error => ...
end Test_External_Formats;
B.5 Interfacing with Fortran
1 The facilities relevant to interfacing with the Fortran language are the
package Interfaces.Fortran and support for the Import, Export and Convention
pragmas with convention_identifier Fortran.
2 The package Interfaces.Fortran defines Ada types whose representations are
identical to the default representations of the Fortran intrinsic types
Integer, Real, Double Precision, Complex, Logical, and Character in a
supported Fortran implementation. These Ada types can therefore be used to
pass objects between Ada and Fortran programs.
Static Semantics
3 The library package Interfaces.Fortran has the following declaration:
4 with Ada.Numerics.Generic_Complex_Types; -- see G.1.1
pragma Elaborate_All(Ada.Numerics.Generic_Complex_Types);
package Interfaces.Fortran is
pragma Pure(Fortran);
5 type Fortran_Integer is range implementation-defined;
6 type Real is digits implementation-defined;
type Double_Precision is digits implementation-defined;
7 type Logical is new Boolean;
8 package Single_Precision_Complex_Types is
new Ada.Numerics.Generic_Complex_Types (Real);
9 type Complex is new Single_Precision_Complex_Types.Complex;
10 subtype Imaginary is Single_Precision_Complex_Types.Imaginary;
i : Imaginary renames Single_Precision_Complex_Types.i;
j : Imaginary renames Single_Precision_Complex_Types.j;
11 type Character_Set is implementation-defined character type;
12 type Fortran_Character
is array (Positive range <>) of Character_Set;
pragma Pack (Fortran_Character);
13 function To_Fortran (Item : in Character) return Character_Set;
function To_Ada (Item : in Character_Set) return Character;
14 function To_Fortran (Item : in String) return Fortran_Character;
function To_Ada (Item : in Fortran_Character) return String;
15 procedure To_Fortran (Item : in String;
Target : out Fortran_Character;
Last : out Natural);
16 procedure To_Ada (Item : in Fortran_Character;
Target : out String;
Last : out Natural);
17 end Interfaces.Fortran;
18 The types Fortran_Integer, Real, Double_Precision, Logical, Complex, and
Fortran_Character are Fortran-compatible.
19 The To_Fortran and To_Ada functions map between the Ada type Character and
the Fortran type Character_Set, and also between the Ada type String and the
Fortran type Fortran_Character. The To_Fortran and To_Ada procedures have
analogous effects to the string conversion subprograms found in
Interfaces.COBOL.
Implementation Requirements
20 An implementation shall support pragma Convention with a Fortran
convention_identifier for a Fortran-eligible type (see B.1).
Implementation Permissions
21 An implementation may add additional declarations to the Fortran interface
packages. For example, the Fortran interface package for an implementation of
Fortran 77 (ANSI X3.9-1978) that defines types like Integer*n, Real*n,
Logical*n, and Complex*n may contain the declarations of types named Integer_-
Star_n, Real_Star_n, Logical_Star_n, and Complex_Star_n. (This convention
should not apply to Character*n, for which the Ada analog is the constrained
array subtype Fortran_Character (1..n).) Similarly, the Fortran interface
package for an implementation of Fortran 90 that provides multiple kinds of
intrinsic types, e.g. Integer (Kind=n), Real (Kind=n), Logical (Kind=n),
Complex (Kind=n), and Character (Kind=n), may contain the declarations of
types with the recommended names Integer_Kind_n, Real_Kind_n, Logical_Kind_n,
Complex_Kind_n, and Character_Kind_n.
Implementation Advice
22 An Ada implementation should support the following interface
correspondences between Ada and Fortran:
23 * An Ada procedure corresponds to a Fortran subroutine.
24 * An Ada function corresponds to a Fortran function.
25 * An Ada parameter of an elementary, array, or record type T is passed
as a T(F) argument to a Fortran procedure, where T(F) 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.
26 * 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.
NOTES
27 16 An object of a Fortran-compatible record type, declared in a
library package or subprogram, can correspond to a Fortran common
block; the type also corresponds to a Fortran "derived type".
Examples
28 Example of Interfaces.Fortran:
29 with Interfaces.Fortran;
use Interfaces.Fortran;
procedure Ada_Application is
30 type Fortran_Matrix is array (Integer range <>,
Integer range <>) of Double_Precision;
pragma Convention (Fortran, Fortran_Matrix); -- stored in Fortran's
-- column-major order
procedure Invert (Rank : in Fortran_Integer; X : in out Fortran_Matrix);
pragma Import (Fortran, Invert); -- a Fortran subroutine
31 Rank : constant Fortran_Integer := 100;
My_Matrix : Fortran_Matrix (1 .. Rank, 1 .. Rank);
32 begin
33 ...
My_Matrix := ...;
...
Invert (Rank, My_Matrix);
...
34 end Ada_Application;
Generated by dwww version 1.15 on Fri Jun 21 22:15:43 CEST 2024.