Question

Given Microsoft FORTRAN 5.1 and Microsoft C/C++ 14.0, along with the linker that comes with that version of FORTRAN (that must be used for other dependencies) how do I create a C function and call it from the FORTRAN application?

Answer 1

You have two choices.
1) I can show with example

FORTRAN

program ftest use iso_c_bindings implicit none interface function saythis(a) ! should be subroutine if saythis returns void import :: c_ptr type(c_ptr), value :: a end function saythis end interface  character(len=80), target :: str type(c_ptr) cstr integer :: r  str='Hello World From Fortran' // C_NULL_CHAR cstr=c_loc(str(1:1)) r=saythis(cstr) 

C/C++

#ifdef __cpluscplus #include &ltl;cstdio> using namespace std; #else #inlcude <stdio.h> #endif  #ifdef __GNUC__ #define FORT(func) func ## _ #else #define FORT(func) __stdcall func ## _ #endif  #ifdef __cpluscplus extern 'C' { #endif __declspec(dllexport) int FORT(sayit)(char* c) { return printf('%s\n',c); }  #ifdef __cpluscplus } #endif 

This works w/gcc toolchain. You’ll have to dumpbin on the DLL and fortran object code to see if the names match up correctly.
The other way is similar:

//This is for gcc toolchain //you'll have to find the symbol conversion yourself //I think that Visual Studio converts fortran names //to ALL CAPS so instead of func => _func you'll need func => FUNC 

FORTRAN

program ftest integer aa,bb,cc common/vari/aa,bb,cc  aa=7 bb=11 cc=0 call dosomething call dosomethingelse(aa,bb,cc) 

C/C++

#ifdef __cplusplus extern 'C' { #endif int _dosomething(); int _dosomethingelse(int*,int*,int*); //all fortran is pass by reference struct { int aa,bb,cc; } vari; #ifdef __cplusplus } #endif  //function def's go here //struct vari should be the same memory as common/vari block 

COMPILE COMMAND

$>g++ -c ctest.c <br/> $>gfortran -c ftest.f90 <br/> $>gfortran *.o -lstdc++ -o test_prog <br/> 

Hope this helps