How can I call a C++ function from C?

c, c++

Solution

Unfortunately, my first attempt answered the wrong question....

For the question you did ask...

You can, as someone point out, pass around `void *`'s. And that's what I would also recommend. As far as C is concerned, pointers to C++ objects should be totally opaque.

C++ functions can be labeled `extern "C"` as well if they are in the global namespace. Here is an example:

myfunc.hpp:

#ifdef __cplusplus
extern "C" {
#endif

extern int myfunction(int, void *ob);

#ifdef __cplusplus
}
#endif

myfunc.cpp:

#include "myfunc.hpp"

void myfunction(int x, void *vobptr)
{
    ClassType *ob = static_cast<ClassType *>(vobptr);
}

afoofile.c

#include "myfunc.hpp"

void frobble(int x, void *opaque_classtype_ptr) {
    myfunction(x, opaque_classtype_ptr);
    /* do stuff with buf */
}

The other option is to do basically the same thing with creative use of `typedef`s in C. This, IMHO, is quite ugly, but here is an example anyway:

myfunc.hpp:

#ifdef __cplusplus
extern "C" {
#else
typedef void ClassType;  /* This is incredibly ugly. */
#endif

extern int myfunction(int, ClassType *ob);

#ifdef __cplusplus
}
#endif

myfunc.cpp:

#include "myfunc.hpp"

void myfunction(int x, ClassType *ob)
{
    // Do stuff with ob
}

afoofile.c

#include "myfunc.hpp"

void frobble(int x, ClassType *opaque_classtype_ptr) {
    myfunction(x, opaque_classtype_ptr);
    /* do stuff with buf */
}

Problem

I have a header declaring functions that take pointers to C++ objects as parameters. The implementaton is in a seperate C++ file. How can I include this header in C and use the functions in C even though the arguments need to be C++ object pointers?

Original source

Related problems