Dynamic Link Library, Compaq Visual Fortran 6.6 & Module

[Bakhbergen]

Dear Forum Members,
I need to create and use dynamic-link library (DLL) for Fortran application using Compaq Visual Fortran 6.6. The following code works just fine:

########################################$# PROGRAM AMAIN1 IMPLICIT NONE REAL(8):: A,B,S A = 1D0 B = 2D0 CALL SUBRO1(A,B,S) PRINT*, 'S = ', S END PROGRAM AMAIN1$######################################$# SUBROUTINE SUBRO1(A,B,S) !DEC ATTRIBUTES DLLEXPORT :: SUBRO1 IMPLICIT NONE REAL(8):: A,B,S S = A + B RETURN END SUBROUTINE SUBRO1$######################################$# The result is correct: S = 3.00000000000000 Press any key to continue$######################################$# However, if I implement the same algorithm using the module, I get inconsistent result (i.e. zero):$######################################$# PROGRAM AMAIN2 USE MODUL2 IMPLICIT NONE A = 1D0 B = 2D0 CALL SUBRO2 PRINT*, 'S = ', S END PROGRAM AMAIN2$######################################$# MODULE MODUL2 IMPLICIT NONE REAL(8):: A,B,S END MODULE MODUL2$######################################$# SUBROUTINE SUBRO2 !DEC ATTRIBUTES DLLEXPORT :: SUBRO2 USE MODUL2 IMPLICIT NONE S = A + B RETURN END SUBROUTINE SUBRO2$######################################$# The result is incorrect: S = 0.000000000000000E+000 Press any key to continue$#########################################

As can be seen above, DLL contains only subprogram in both cases (SUBRO1 and SUBRO2, respectively). I have built DLL and LIB files from the visual development environment. The second case (with the use of module) represents the structure of my large source-code so I need to resolve this issue. Any advice would be greatly appreciated.

 

[BvU]

Hallo Bakhbergen, $\qquad$

Modul2 is only a declaration of local variables. You need something like COMMON to make them global is what I would suspect.

(old hand, more fortran 77 than f90, but who knows this helps)

 

[BvU]

However, https://www.tutorialspoint.com/fortran/fortran_modules.htm claims global character.
Your result does not reflect that. Still worth investigating (ask for the addresses of the variables in debug or something ?)

 

[Bakhbergen]

However, https://www.tutorialspoint.com/fortran/fortran_modules.htm claims global character.
Your result does not reflect that. Still worth investigating (ask for the addresses of the variables in debug or something ?)

Hello BvU! I appreciate your intention to help with this. There weren't any error / warning during the debugging. Just gives incorrect result.

 

[BvU]

I don't expect any errors reported, just diffferent address spaces assigned in the DLL and the main EXE

 

[Bakhbergen]

BTW, the same algorithm without using the DLL works well and gives correct result:

PROGRAM AMAIN3
USE MODUL3
IMPLICIT NONE
A = 1D0
B = 2D0
CALL SUBRO3
PRINT*, 'S = ', S
END PROGRAM AMAIN3

MODULE MODUL3
IMPLICIT NONE
REAL(8):: A,B,S
END MODULE MODUL3

SUBROUTINE SUBRO3
USE MODUL3
IMPLICIT NONE
S = A + B
RETURN
END SUBROUTINE SUBRO3

S = 3.00000000000000
Press any key to continue