Mixed FORTRAN/C with OS/2 DLLs: Example, Restrictions

• Microsoft FORTRAN for OS/2, version 5.1

SUMMARY

It is not possible to link an OS/2 DLL (dynamic-link library) that contains both FORTRAN and C object code. All OS/2 DLLs must contain code in only one language.

From the same FORTRAN main program, it is possible to call a separate FORTRAN DLL and a C DLL, but only if the C DLL has the C run-time library statically-linked into the C DLL. If the C run-time library is linked-in dynamically, when linking the executable with both CRTEXE.OBJ and FRTEXE.OBJ, some "L2025: Multiply Defined Symbols" and one "L2029: Unresolved External" result.

From a FORTRAN statically linked executable, it is possible to call a FORTRAN DLL, which in turn calls a C DLL. This is possible only if the C DLL has the C run-time library statically-linked to the C DLL.

From a FORTRAN statically linked executable, it is not possible to call a C DLL that calls a FORTRAN DLL. This will result in a protection violation on entry into the FORTRAN DLL. It is also not possible to statically link in the FORTRAN run-time library to a FORTRAN DLL because the necessary libraries are not available.

Page 151 of the "Microsoft FORTRAN Advanced Topics Manual" for version 5.1 states that mixed language programming is not recommended in conjunction with multithread programs or dynamic-linked libraries. Any mixed language between OS/2 DLLs is not considered a feature of the product, and therefore is not generally supported.

MORE INFORMATION

The following project code example calls a FORTRAN DLL, which in turn calls a C DLL. Upon returning to the FORTRAN main program, the C DLL is called again.

Description of the Files that Make Up the Project

   File           Description
   ----           -----------

   CC.CMD         Command file to create C DLL, FORTRAN DLL, and MAIN.EXE
   MAIN.FOR       Main FORTRAN program
   MYSUB.FOR      FORTRAN source code for FORTRAN DLL
   MYFORT.DLL     FORTRAN DLL
   MYFORT.DEF     Definitions file containing exports for C DLL
   MYFORT.LIB     Import library resulting from MYC.DEF
   C.C            C source code for C DLL
   MYC.DLL        C DLL
   MYC.DEF        Definitions file containing exports for C DLL
   MYC.LIB        Import library resulting from MYC.DEF
   LLIBCDLL.LIB*  Import library for static-linked C run-time library
   LLIBCE.LIB*    Static C run-time library
   FRTEXE.OBJ*    Startup code to be linked with (for using FORTRAN DLLs)
   FRTDLL.OBJ*    Startup code to be linked in all user-written DLLs
   FRTLIB.DLL     FORTRAN run-time DLL (previously created by the user)
   FRTLIB.LIB     Imports library corresponding to FORTRAN run-time DLL
                  (previously created by the user)

Command File and Source Code for the Project

MAKEFILE     Makefile to create C DLL, FORTRAN DLL, and MAIN.EXE

myfort.lib: myfort.def

 implib myfort.lib myfort.def

 implib myc.lib myc.def

 fl /c /Zi /Od /MD mysub.for

 link mysub frtdll,myfort.dll,nul,/co /nod frtlib myc os2,myfort.def
 copy myfort.dll c:\os2\dll

 cl /c /Zi /Od /AL /MD c.c

 link c,myc.dll,nul,/co /nod llibcdll os2,myc.def
 copy myc.dll c:\os2\dll

 fl /c /Zi /Od /MD main.for

  link main frtexe,main,nul,/co /nod frtlib os2 myfort myc;


MAIN.FOR:   Main FORTRAN program:

      interface to subroutine subtest[c]
      end

      integer*4 ii
      write(*,*) 'this is from the main program'
      call dllsub(ii)
      write(*,*) 'this is after the call ',ii
      write(*,*) 'calling the c dll'
      call subtest
      write(*,*) 'back from the c dll'
      end

MYSUB.FOR: FORTRAN source code for FORTRAN DLL: c-----------------------------------

      interface to subroutine subtest [c] ()
      end

      subroutine dllsub [loadds] (ii)
      integer*4 ii

      ii = 2.0
      write(*,*) 'this is from myfort.dll'
      call subtest()
      end

MYFORT.DEF: Definitions file containing exports for C DLL: ;------------------------------------ LIBRARY MYFORT INITINSTANCE DATA MULTIPLE PROTMODE EXPORTS

   DLLSUB

C.C:        C source code for C DLL.
/*-----------------------------------*/
#include <stdio.h>
void _loadds _export subtest()

  int n,i;
  n = 6;
  i = 8;

  printf("\nthis is a test in c\n");
  printf("\n n is %d  i is %d",n,i);
 }
/*-----------------------------------*/


MYC.DEF:    Definitions file containing exports for C DLL.

      _subtest