The ATTRIBUTES directive options C and STDCALL specify procedure calling, naming, and argument passing conventions. They take the following forms:
cDEC$ ATTRIBUTES C :: object[, object] ...
cDEC$ ATTRIBUTES STDCALL :: object[, object] ...
c |
Is one of the following: C (or c), !, or *. (See Syntax Rules for Compiler Directives.) |
object |
Is the name of a data object or procedure. |
On W*32 only (see Conventions, Platform labels), C and STDCALL have slightly different meanings; on all other platforms, they are interpreted as synonyms.
When applied to a subprogram, these options 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 |
L*X, M*X: Lowercase W*32, W*64: Lowercase |
L*X, M*X: Lowercase W*32, W*64: Lowercase |
L*X, M*X: Lowercase W*32, W*64: Uppercase |
L*X, M*X only: |
|||
Trailing underscore added |
No |
No |
Yes3 |
M*X only: |
|||
Leading underscore added |
No |
No |
Yes |
W*32 only: |
|||
Leading underscore added |
Yes |
Yes |
Yes4 |
Number of argument bytes added to name |
No |
Yes |
No |
Caller stack cleanup |
Yes |
No |
Yes |
Variable number of arguments |
Yes |
No |
Yes |
1C and STDCALL are synonyms on Linux systems. 2The Intel Fortran calling convention 3On Linux systems, if there are one or more underscores in the external name, two trailing underscores are added; if there are no underscores, one is added. 4W*32 only |
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If C or STDCALL is specified for a subprogram, arguments (except for arrays and characters) are passed by value. Subprograms using standard Fortran conventions pass arguments by reference.
On IA-32 architecture, 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, hidden lengths are put at the end of the argument list.
On Windows* systems using IA-32 architecture, you can get Compaq* Visual Fortran default behavior by specifying compiler option iface.
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).
If C or STDCALL is specified, and REFERENCE is specified for the argument:
On all systems, the string is passed with no length.
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.
Building Applications: Adjusting Calling Conventions in Mixed-Language Programming Overview