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Why can fail Mingw to reuse a C++ struct in a COMMON in FORTRAN?

From: Pedro567
Subject: Why can fail Mingw to reuse a C++ struct in a COMMON in FORTRAN?
Date: Tue, 04 May 2010 15:46:40 -0000
User-agent: G2/1.0

We are having a problem to match properly a  C++ struct exported as
dll using GNU g++ 4.4.0 with a COMMON block in Fortran using GNU
gfortran 4.4.0. Tt works properly in Linux version, but not with
Mingw. Probably we are missing something in this platform. Any help
will be welcomme.

Code in C++ (compiled as a dll):
extern "C"
extern struct {
  int   n;
  int   k;

}  area_ ;

extern "C" __declspec(dllexport) void view_() { area_.n= 83;
++, n=%d , k=%d \n",area_.n,area_.k); return; }

Code in FORTRAN (main program calling the previous dll):
      BLOCK DATA t

        PROGRAM P456
       COMMON /AREA/ N,K
        N = 3
        K = 6
        WRITE(*,*) N,K
        CALL view
        WRITE(*,*) N,K

We add an extra C file to the dll for compiling independly of
__declspec(dllexport) struct {
  int   n;
  int   k;

}  area_ ;

Using GNU g++ and gfortran in Mingw the area_ struct is not properly
shared and two
copies are used in memory, the output is wrong:
3   6
83 0
3  6
But using GNU g++ and gfortran 4.4 in Linux Debian and Microsoft C++
6.0, 2003 and 2008 we
obtain a correct result:
3  6
83  6
83  6

The AREA common block in FORTRAN does not point to the same struct
area in C++ dll, why?

Why fails only in Windows platform using GNU C++ compiler?

Thanks for any help

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