C++ Fortran integration in Linux

[kdurgarao]

Hello,
I have a difficulty in Mixed language programming. There are many global variables in a fortran module, which have to be accessed from C++ main program. Although the compiler is giving no errors with the following simple structure, but, linker gives errors with - 'undefined reference to the common variable in C++ object'.

fortran module:

MODULE EXAMP
SAVE

REAL, X(4), Y(4), Z(4)
REAL, PARAMETER :: Pi =3.14159

END MODULE EXAMP

C++:
#include<iostream>

extern "C" float EXAMP_mp_X[4];
extern "C" float EXAMP_mp_Y[4];
extern "C" float EXAMP_mp_Z[4];
extern "C" float EXAMP_mp_Pi;
using namespace std;
int main()
{
.....
....
}
I am using Linux...g++ and gfortran compiler in the following way
gfortran -c mod.f
g++ -c testc.cpp
g++ -o test mod.o testc.o -llapack

Could anyone please share their experience in handling the similar problem. Thanking you,

[drl]

Hi.

I looked through the man pages for gfortran and g++, and there are a lot of references to symbols, I didn't see any that would help solve this problem.

I used nm to list the symbols from both compiled sources. Here are the Fortran and cc that I used:

% cat mymod.f90 
	MODULE EXAMP
	SAVE

	REAL X(4), Y(4), Z(4)
	REAL, PARAMETER :: Pi =3.14159
	real mypi
	data mypi / pi /

	END MODULE EXAMP

and the main:

% cat main.cc
#include<iostream>

extern "C" float EXAMP_mp_X[4];
extern "C" float __examp_MOD_x[4];
extern "C" float EXAMP_mp_Y[4];
extern "C" float EXAMP_mp_Z[4];
// extern "C" float EXAMP_mp_Pi;
extern "C" float __examp_MOD_mypi;

using namespace std;

int main()
{

  cout << " Hello, world from c++\n";
  // cout << EXAMP_mp_X[0];
  cout << " x[0] is " << __examp_MOD_x[0] << endl;
  cout << " mypi is " << __examp_MOD_mypi << endl;
  cout << " Goodbye.\n";
}

I compiled, linked and executed with this:

% cat doit
#!/bin/bash

# Abort on any error.

set -o errexit

# Compile.

g++ -c main.cc
gfortran -c mymod.f90

# Link.

g++ *.o

# Look at symbols.

echo
nm *.o

# Execute.

echo
./a.out

Which produced:

% ./doit


main.o:
00000000000000d4 t _GLOBAL__I_main
0000000000000097 t _Z41__static_initialization_and_destruction_0ii
                 U _ZNSolsEPFRSoS_E
                 U _ZNSolsEf
                 U _ZNSt8ios_base4InitC1Ev
                 U _ZNSt8ios_base4InitD1Ev
                 U _ZSt4cout
                 U _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
0000000000000000 b _ZStL8__ioinit
                 U _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
                 U __cxa_atexit
                 U __dso_handle
                 U __examp_MOD_mypi
                 U __examp_MOD_x
                 U __gxx_personality_v0
0000000000000000 T main

mymod.o:
0000000000000000 D __examp_MOD_mypi
0000000000000000 B __examp_MOD_x
0000000000000010 B __examp_MOD_y
0000000000000020 B __examp_MOD_z

 Hello, world from c++
 x[0] is 0
 mypi is 3.14159
 Goodbye.

This shows that the symbols in the original sources did not match. When they are changed as in the new version, the code runs.

Someone may be able to suggest a better solution, but this seems to work in the meantime.

Best wishes ... cheers, drl

[kdurgarao]

Thank you very much Mr. drl. Your approach seems to work for my problem.
Best Regards,