Calling C++ function from Fortran in Visual Studio 2010

Question

I want to call a C++ function from Fortran. To do that, I make a FORTRAN project in Visual Studio 2010. After that I add a Cpp project to that FORTRAN project. The following err

Answer 1

Your problem is that since you compile with a C++ compiler, print_C is not a C function, but a C++ function. Since the Fortran code tries to call a C function, it cannot find the C++ function.

The solution to your problem therefore is

• either compile with a C compiler, so you get actual C code,
• or tell the C++ compiler that you actually want to declare a C function.

The latter is done with extern "C", like this:

extern "C" void print_C(char *text)
{
  printf("%s\n", text);
}

If you want to be able to compile your code both as C and as C++, you can use

#ifdef __cplusplus
extern "C"
#endif
void print_C(char *text)
{
  printf("%s\n", text);
}

The symbol __cplusplus is defined for C++, but not for C, so your code will work in both (of course only as long as the rest of your code also remains in that subset).