14.2.1.3 ATTRIBUTES Directive

 cDEC$ ATTRIBUTES att [,att]... :: object [,object]...

c

Is one of the following: C (or c), !, or * (see Section 14.2.1.1).

att

Is one of the following:

ALIAS	REFERENCE
C	STDCALL
DLLEXPORT [1]	VALUE
DLLIMPORT [1]	VARYING
EXTERN
[1] WNT, W95

object

Is the name of a data object or procedure.

The following table shows which properties can be used with various objects:

Property	Variable and Array Declarations	Common Block Names [1]	Subprogram Specification and EXTERNAL Statements
ALIAS	No	Yes	Yes
C	No	Yes	Yes
DLLEXPORT	No	Yes	Yes
DLLIMPORT	No	Yes	Yes
EXTERN	Yes	No	No
REFERENCE	Yes	No	No
STDCALL	No	Yes	Yes
VALUE	Yes	No	No
VARYING	No	No	Yes
[1] A common block name is specified as [/]common-block-name[/]

These 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

• 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 (see Section 14.2.1.2).

• C and STDCALL

  Specify how data is to be passed when you use routines written in C or assembler with FORTRAN or Fortran 90 routines.

  On Intel processors, C and STDCALL have slightly different meanings; on all other platforms, they are interpreted as synonyms.

  When applied to a subprogram, these properties define the subprogram as having a specific set of calling conventions.

  The following table summarizes the differences between the calling conventions:

  Convention	C [1]	STDCALL [1]	Default [2]
  Arguments passed by value	Yes	Yes	No
  Case of external subprogram names	VMS: Uppercase U*X: Lowercase WNT: Lowercase W95: Lowercase	VMS: Uppercase U*X: Lowercase WNT: Lowercase W95: Lowercase	VMS: Uppercase U*X: Lowercase WNT: Uppercase W95: Uppercase
  U*X only:
  Trailing underscore added	No	No	Yes
  WNT, W95:
  Leading underscore added	Yes	Yes	Yes
  Number of arguments added	No	Yes	Yes
  Caller stack cleanup	Yes	No	No
  Variable number of arguments	Yes	No	No
  [1] C and STDCALL are synonyms on OpenVMS and DIGITAL UNIX systems, and Windows NT systems on Alpha processors [2] The Fortran 90 calling convention

  If C or STDCALL is specified for a subprogram, arguments (except for arrays and characters) are passed by value. Subprograms using standard Fortran 90 conventions pass arguments by reference.

  On Intel processors, an underscore ( _ ) is placed at the beginning of the external name of a subprogram. If STDCALL is specified, an at sign (@) followed by the number of argument bytes being passed is placed at the end of the name. For example, a subprogram named SUB1 that has three INTEGER(4) arguments and is defined with STDCALL is assigned the external name _sub1@12.

  Character arguments are passed as follows:

  • By default:

    • On OpenVMS and DIGITAL UNIX Systems, hidden lengths are put at the end of the argument list.

    • On Windows NT and Windows 95 Systems, hidden lengths immediately follow the variable.

  • If C or STDCALL (only) are specified:

    On all systems, the first character of the string is passed (and padded with zeros out to INTEGER(4) length).

  • If C or STDCALL are specified with REFERENCE:

    On all systems, the string is passed with no length.

  See also the following description of REFERENCE.

• DLLEXPORT and DLLIMPORT (WNT, W95)

  Define a dynamic-link library's (DLL) interface for processes that use them. The properties can be assigned to data objects or procedures.

  DLLEXPORT specifies that procedures or data are being exported to other applications or DLLs. This causes the compiler to produce efficient code, eliminating the need for a module definition (.def) file to export symbols.

  If a procedure (or data) is declared with the DLLEXPORT property, it must be defined in the same module of the same program.

  Symbols defined in a DLL are imported by programs that use them. The program must link with the import DLL and use the DLLIMPORT property inside the program unit that imports the symbol. DLLIMPORT is specified in a declaration, not a definition, since you cannot define a symbol you are importing.

• 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.

• 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 or KIND=8) 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 following occurs:

  • On OpenVMS and DIGITAL UNIX systems, the string is passed with no length

  • On Windows NT and Windows 95 systems, hidden lengths immediately follow the variable

  If REFERENCE and C (or STDCALL) are specified for a character argument, the string is passed with no length.

  VALUE is the default if the C or STDCALL property is specified in the subprogram definition.

• 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.

For More Information:

• On syntax rules for all general directives, see Section 14.2.1.1.

• On using the cDEC$ ATTRIBUTES directive, see your user manual or programmer's guide.