Calling a function from a FORTRAN DLL using C++ code

Question

I want to load a fortran dll in C++ code and call a function in the fortran dll.

Following is the code

  SUBROUTINE SUB1()
  PRINT *, 'I am a function '
  END

After creation of the foo.dll [fotran dll ] this is the folowing C++ code in visual studio 2012 that I have written to load the fortran dll . and call the function SUB1 in the fortran code

#include <iostream>
#include <fstream>
#include <Windows.h>

using namespace std;  
extern "C" void SUB1();
typedef void (WINAPI *PGNSI)(LPSYSTEM_INFO);

int main(void)
{
                LoadLibrary(L"foo.dll");

                PGNSI pGNSI = (PGNSI) GetProcAddress(GetModuleHandle(TEXT("foo.dll")),"SUB1");

                return 0;

}

While running the I am getting the following error:

The program can't start because libgcc_s_dw2-1.dll is missing from your computer. Try reinstalling the program to fix this problem.

Is this the correct way of calling the dll from C++ ? I am very new to this fortran dll . Please help me regarding this.

Answer 1

First of all you need to export the function like this...

!fortcall.f90
subroutine Dll1() BIND(C,NAME="Dll1")
implicit none
!DEC$ ATTRIBUTES DLLEXPORT :: Dll1
PRINT *, 'I am a function'
return
end !subroutine Dll1

Create the dll using following command

gfortran.exe -c fortcall.f90
gfortran.exe -shared -static -o foo.dll fortcall.o

After that, place the libgcc_s_dw2-1.dll, libgfortran-3.dll and libquadmath-0.dll in the application path of VS. OR you can add the PATH to environment.

After that, you can call the FORTRAN exposed function from VS like below...

#include <iostream>
#include <Windows.h>

using namespace std;
extern "C" void Dll1();
typedef void(* LPFNDLLFUNC1)();

int main(void)
{
    HINSTANCE hDLL;
    LPFNDLLFUNC1 lpfnDllFunc1;    // Function pointer

    hDLL = LoadLibrary(L"foo.dll");

    if (hDLL != NULL)
    {
        lpfnDllFunc1 = (LPFNDLLFUNC1)GetProcAddress(hDLL,"Dll1");
        if (!lpfnDllFunc1)
        {
            // handle the error
            FreeLibrary(hDLL);
            return -1;
        }
        else
        {
            // call the function
            lpfnDllFunc1();
        }
    }
    return 0;
}