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.