calling C++ function from fortran not C

Question

is it possible to call a C++ function from FORTRAN such as

#include <iostream.h>
extern "C"
{
    void single_cell(void)
    {
        cout<<"Hi from C++";
    }
}

So when I am using C it is working fine but with the C++ function it gives errors like Undefined error to cout etc

You would need using namespace std; or std::cout but i dont think this will work in an extern "C" — user181351
– user181351, Commented Aug 31, 2011 at 10:11
I'a not sure but maybe you must include<iostream> and use std::cout, but I don't know it will be working — nirmus
– nirmus, Commented Aug 31, 2011 at 10:12
You will need to edit the question to explain which C++ and fortran compilers you are using and how you are doing the linking before anyone can give you a definitive answer. — talonmies
– talonmies, Commented Aug 31, 2011 at 11:12

Community · Accepted Answer · 2017-05-23 11:43:19Z

3

Both g++ and gfortran, used as linkers, bring in extra libraries. That is why the Fortran/C++ combination is trickier than the Fortran/C combination ... just using the correct compiler as the linker won't work, you need to add a libary. Already suggested is to link with gfortran and specify the C++ runtime libraries. You can also link with g++ and specify the Fortran runtime libraries. See Linking fortran and c++ binaries using gcc for the details of both approaches.

edited May 23, 2017 at 11:43

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answered Aug 31, 2011 at 14:30

M. S. B.

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1 Comment

Zahur Over a year ago

g++ main.o print_hi.o -o main -lgfortran after using this command it gives the error as /cygnus/cygwin-b20/H-i586-cygwin32/i586-cygwin32/bin/1d cannot open -lgfortran: no such a file or director what is the exact procedure to include the path because i think the gfortran is installed in some other directory

mah · Accepted Answer · 2011-08-31 10:14:44Z

1

Assuming you could have your Fortran code call into a C function, the problem is not the code but rather how you are linking. When you're linking C++ objects you need to also pull in the C++ runtime. If using GCC, link with the g++ command and it will pull in the parts you need.

answered Aug 31, 2011 at 10:14

mah

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3 Comments

talonmies Over a year ago

Linking with g++ (and doing nothing else) will just result in the fortran runtime libraries not being found. The solution is either to link with the fortran compiler and add the C++ runtime libraries to the link statement, or link with the C++ compiler and add the fortran runtime libraries to the link statement. Both will work.

Zahur Over a year ago

@ talonmies yes you are right. The prblem is in the linking phase and i am uisng the gfortran commands so it is gives problem with the C++ cout. can you please give detail how i include the libraries in the linking command

Zahur Over a year ago

I am using Iso_c_binding in fortran for calling this C++ funciton, which works fine in the case of C but not in the C++

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