cDEC$ ATTRIBUTES
Lets you specify properties for data objects and procedures. It
takes the following form:
cDEC$ ATTRIBUTES att [,att]... :: object [,object]...
c Is one of the following: C (or c), !, or *.
att Is one of the following properties:
ADDRESS64
ALIAS EXTERN
ALLOW_NULL IGNORE_LOC
NO_ARG_CHECK
C NOMIXED_STR_LEN_ARG
DECORATE REFERENCE
DEFAULT REFERENCE32
DESCRIPTOR REFERENCE64
DESCRIPTOR32 STDCALL
DESCRIPTOR64 VALUE
VARYING
object Is the name of a data object or procedure.
The properties can be used in function and subroutine definitions,
in type declarations, and with the INTERFACE and ENTRY statements.
Properties applied to entities available through use or host
association are in effect during the association. For example,
consider the following:
MODULE MOD1
INTERFACE
SUBROUTINE SUB1
!DEC$ ATTRIBUTES C, ALIAS:'othername' :: NEW_SUB
END SUBROUTINE
END INTERFACE
CONTAINS
SUBROUTINE SUB2
CALL NEW_SUB
END SUBROUTINE
END MODULE
In this case, the call to NEW_SUB within SUB2 uses the C and ALIAS
properties specified in the interface block.
Options C, STDCALL, REFERENCE, VALUE, and VARYING affect the
calling conventions of routines:
o You can specify C, STDCALL, REFERENCE, and VARYING for an
entire routine.
o You can specify VALUE and REFERENCE for individual arguments.
For compatibility, !MS$ATTRIBUTES can be used in place of cDEC$
ATTRIBUTES.
The properties are described in the following sections.
1 – ADDRESS64
Specifies that the data object has a 64-bit address. This property can be specified for any variable or dummy argument, including ALLOCATABLE and deferred-shape arrays. However, variables with this property cannot be data-initialized. It can also be specified for COMMON blocks or for variables in a COMMON block. If specified for a COMMON block variable, the COMMON block implicitly has the ADDRESS64 property. ADDRESS64 is not compatible with the AUTOMATIC attribute.
2 – ALIAS
Specifies an alternate external name to be used when referring to
external subprograms. Its form is:
ALIAS:external-name
external-name Is a character constant delimited by apostrophes
or quotation marks. The character constant is
used as is; the string is not changed to uppercase,
nor are blanks removed.
The ALIAS property overrides the C (and STDCALL) property. If both
C and ALIAS are specified for a subprogram, the subprogram is given
the C calling convention, but not the C naming convention. It
instead receives the name given for ALIAS, with no modifications.
ALIAS cannot be used with internal procedures, and it cannot be
applied to dummy arguments.
cDEC$ ATTRIBUTES ALIAS has the same effect as the cDEC$ ALIAS
directive.
3 – ALLOW_NULL
Enables a corresponding dummy argument to pass a NULL pointer (defined by a zero or the NULL intrinsic function) by value for the argument. ALLOW_NULL is only valid if the REFERENCE property is also specified; otherwise, it has no effect.
4 – C and STDCALL
Specify how data is to be passed when you use routines written in C
or assembler with FORTRAN or Fortran 95/90 routines.
C and STDCALL are interpreted as synonyms.
When applied to a subprogram, these properties define the
subprogram as having a specific set of calling conventions.
The difference between the calling conventions is this: If C or
STDCALL is specified for a subprogram, arguments (except for
arrays and characters) are passed by value. Subprograms using
standard Fortran 95/90 conventions pass arguments by reference.
Character arguments are passed as follows:
o By default, hidden lengths are put at the end of the argument
list.
o If C or STDCALL (only) is specified:
On all systems, the first character of the string is passed
(and padded with zeros out to INTEGER(4) length).
o If C or STDCALL is specified, and REFERENCE is specified for
the argument:
On all systems, the string is passed with no length.
o If C or STDCALL is specified, and REFERENCE is specified for
the routine (but REFERENCE is not specified for the argument,
if any):
On all systems, the string is passed with the length.
5 – DECORATE
Specifies that the external name used in cDEC$ ALIAS or cDEC$ ATTRIBUTES ALIAS should have the prefix and postfix decorations performed on it that are associated with the calling mechanism that is in effect. These are the same decorations performed on the procedure name when ALIAS is not specified. The case of the external name is not modified. If ALIAS is not specified, this property has no effect.
6 – DEFAULT
Overrides certain compiler options that can affect external routine and COMMON block declarations. It specifies that the compiler should ignore compiler options that change the default conventions for external symbol naming and argument passing for routines and COMMON blocks (/iface, /names, and /assume:underscore). This option can be combined with other cDEC$ ATTRIBUTES options, such as STDCALL, C, REFERENCE, ALIAS, etc. to specify attributes different from the compiler defaults. This option is useful when declaring INTERFACE blocks for external routines, since it prevents compiler options from changing calling or naming conventions.
7 – DESCRIPTOR
Specifies that the argument is passed by VMS descriptor. This property can be specified only for dummy arguments in an INTERFACE block (NOT for a routine itself).
8 – DESCRIPTOR32
Specifies that the argument is passed as a 32-bit descriptor.
9 – DESCRIPTOR64
Specifies that the argument is passed as a 64-bit descriptor.
10 – EXTERN
Specifies that a variable is allocated in another source file. EXTERN can be used in global variable declarations, but it must not be applied to dummy arguments. EXTERN must be used when accessing variables declared in other languages.
11 – IGNORE_LOC
Enables %LOC to be stripped from an argument. IGNORE_LOC is only valid if the REFERENCE property is also specified; otherwise, it has no effect.
12 – NO_ARG_CHECK
Specifies that type and shape matching rules related to explicit interfaces are to be ignored. This permits the construction of an INTERFACE block for an external procedure or a module procedure that accepts an argument of any type or shape; for example, a memory copying routine. NO_ARG_CHECK can appear only in an INTERFACE block for a non-generic procedure or in a module procedure. It can be applied to an individual dummy argument name or to the routine name, in which case the property is applied to all dummy arguments in that interface. NO_ARG_CHECK cannot be used for procedures with the PURE or ELEMENTAL prefix. If an argument has an INTENT or OPTIONAL attribute, any NO_ARG_CHECK specification is ignored.
13 – NOMIXED_STR_LEN_ARG
Specifies that hidden lengths be placed in sequential order at the end of the argument list.
14 – REFERENCE and VALUE
Specify how a dummy argument is to be passed. REFERENCE specifies a dummy argument's memory location is to be passed instead of the argument's value. VALUE specifies a dummy argument's value is to be passed instead of the argument's memory location. When a dummy argument has the VALUE property, the actual argument passed to it can be of a different type. If necessary, type conversion is performed before the subprogram is called. When a complex (KIND=4, KIND=8, or KIND=16) argument is passed by value, two floating-point arguments (one containing the real part, the other containing the imaginary part) are passed by immediate value. Character values, substrings, assumed-size arrays, and adjustable arrays cannot be passed by value. If REFERENCE (only) is specified for a character argument, the string is passed but the length is not passed. If REFERENCE is specified for a character argument, and C (or STDCALL) has been specified for the routine, the string is passed but the length is not passed. This is true even if REFERENCE is also specified for the routine. If REFERENCE and C (or STDCALL) are specified for a routine, but REFERENCE has not been specified for the argument, the string is passed with the length. VALUE is the default if the C or STDCALL property is specified in the subprogram definition.
15 – REFERENCE32
Specifies that the argument is accepted only by 32-bit address.
16 – REFERENCE64
Specifies that the argument is accepted only by 64-bit address.
17 – VARYING
Allows a variable number of calling arguments. If VARYING is specified, the C property must also be specified. Either the first argument must be a number indicating how many arguments to process, or the last argument must be a special marker (such as -1) indicating it is the final argument. The sequence of the arguments, and types and kinds must be compatible with the called procedure.