Computer Science Canada :: View topic - Strange behavior when compiling C++ for Fortran

Computer Science Canada

Strange behavior when compiling C++ for Fortran

Author:

jomarin [ Fri Dec 05, 2008 8:09 am ]

Post subject:

Strange behavior when compiling C++ for Fortran

Hi everybody,

I need to call a C++ routine from a Fortran code. After some research on the internet, I found a solution using g++ and g77.
The problem is that I get some strange behavior, concerning the memory managment. The code of the small example is attached to this topic. Here is the contents :

file testmac.f :

code:

C
INTEGER*4 sum
INTEGER*4 im0,im1, im2, im3, im4, im5

C
im0=41
im1=42
im2=43
im3=44
im4=45
im5=46

WRITE(*,*) im0,im1,im2,im3,im4,im5

CALL MAC(im0,im1,im2,im3,im4,im5)

C
sum=im0+im1+im2+im3+im4+im5

WRITE(*,*) sum

WRITE(*,*) im0,im1,im2,im3,im4,im5
WRITE(*,*) sum

C
STOP
END

File mac.cpp

code:

#include "mac.h"

#include <iostream>

using namespace std;

// ##################################################################
// Getting MAC Address via popen() within C++-program in Windows 2000
// ##################################################################

#define MAC_ADDRESS_SIZE 17

// =====================================
void __stdcall mac_(int *v1,int *v2,int *v3,int *v4,int *v5,int *v6)
{

cout << *v1 << " " << *v2 << " " << *v3 << " " << *v4 << " " << *v5 << " " << *v6 << endl;

*v1=1;
*v2=2;
*v3=3;
*v4=4;
*v5=5;
*v6=6;

cout << *v1 << " " << *v2 << " " << *v3 << " " << *v4 << " " << *v5 << " " << *v6 << endl;

}

File mac.h

code:

#ifndef _MAC_H
#define _MAC_H

extern "C"
{
void __stdcall mac_(int *,int *,int *,int *,int *,int *);
}

#endif

To compile, I use :
g77 -g -c testmac.f
g++ -g -c mac.cpp
g77 mac.o testmac.o -o testmac.exe -lstdc++

I get following warning message :
Warning: resolving _mac_ by linking to _mac_@24
Use --enable-stdcall-fixup to disable these warnings
Use --disable-stdcall-fixup to disable these fixups

And now the output with my comments :
41 42 43 44 45 46 // OK printing integer values in the fortran
41 42 43 44 45 46 // OK printing parameters values in the C++ function
1 2 3 4 5 6 // OK variables correctly set in the C++ function
21 // OK the sum is correct (with ddd I checked that the variable values are correct)
1 2 3 4 2289728 4199088 // WRONG, the two last variables have been overwritten
21 // OK the sum variable did'nt change

In fact, using ddd, it seems that the WRITE(*,*) sum command modifies variables im4 and im5.
That is the to last that I declared (I changed the declaration order and the problem is always on the two last declared variables).

I'm using g++ and g77 on cygwin.
I have no idea what I am doing wrong.

Thanks in advance,

Joel.

Author:

btiffin [ Fri Dec 05, 2008 6:35 pm ]

Post subject:

Re: Strange behavior when compiling C++ for Fortran

jomarin;

I had to remove the two occurrences of the __stdcall prototype modifiers, but everything worked.

So I can only guess that you are not doing anything wrong...

code:

~/lang/g77$ g++ -g -c mac.cpp
~/lang/g77$ gfortran -g -c testmac.f
~/lang/g77$ gfortran -o testmac testmac.o mac.o -lstdc++
~/lang/g77$ ./testmac
41 42 43 44 45 46
41 42 43 44 45 46
1 2 3 4 5 6
21
1 2 3 4 5 6
21
~/lang/g77$ gfortran --version
GNU Fortran (Debian 4.3.2-1) 4.3.2
Copyright (C) 2008 Free Software Foundation, Inc.

GNU Fortran comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Fortran
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING

~/lang/g77$ g++ --version
g++ (Debian 4.3.2-1) 4.3.2
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

~/lang/g77$ uname -a
Linux home 2.6.26-1-686 #1 SMP Sat Nov 8 19:00:26 UTC 2008 i686 GNU/Linux

Cheers

Author:	OneOffDriveByPoster [ Sun Dec 07, 2008 5:49 pm ]
Post subject:	Re: Strange behavior when compiling C++ for Fortran
btiffin @ Fri Dec 05, 2008 6:35 pm wrote: I had to remove the two occurrences of the __stdcall prototype modifiers, but everything worked. So I can only guess that you are not doing anything wrong... Actually, having the __stdcall seems to be what the OP is doing wrong. It works fine on Cygwin if you take the __stdcall out.

Author:	jomarin [ Mon Dec 08, 2008 3:01 am ]
Post subject:	Re: Strange behavior when compiling C++ for Fortran
Thanks a lot for your answers. I deleted the __stdcall and it works fine now, with no more warning message at compilation . However, It is a little bit strange because all sites concening linking C++ from fortran I have seen indicated to add __stdcall in the declaration ... For example : http://www.physiology.wisc.edu/comp/docs/notes/not017.html#ccall Joel.

You can syndicate this boards posts using the file backend.php or view the topic map using sitemap.php.

Terms of Use | Privacy Policy