Accessing Mixed-Language, External Variables in FORTRAN

• Microsoft FORTRAN for MS-DOS, versions 4.1, 5.0 and 5.1
• Microsoft FORTRAN for OS/2, versions 4.1, 5.0, and 5.1

SUMMARY

The following is a sample C and FORTRAN mixed-language program demonstrating how to access external variables from within Microsoft FORTRAN.

FORTRAN Code

      SUBROUTINE ASSIGN
      INTEGER*2 X [EXTERN, ALIAS:'_extrn']

      X = 2
      END

C Code

#include <stdio.h>

int extrn;

    extrn = 5;
    printf("Before call to FORTRAN:  %d\n",extrn);
    assign();
    printf(" After call to FORTRAN:  %d\n",extrn);

MORE INFORMATION

To use global variables exported from another language in FORTRAN, the EXTERN attribute must be used. EXTERN tells the FORTRAN compiler that the variable is not local to the FORTRAN subroutine or function. Variables declared EXTERN will instead be resolved by the linker. You can use the ALIAS attribute to assign a different name to the imported variable; in this example, it is required because the underscore prepended by the C compiler is invalid in the FORTRAN naming convention.

No modifications should be necessary for the exporting module to allow FORTRAN to import the global variable(s).