Question

Given the following C++ code,

#ifdef __cplusplus
extern "C" {
#endif
        struct foo {
                void getNum() { 
                }
        };
#ifdef __cplusplus
}
#endif

int main (int argc, char * const argv[]) {
        return 0 ;
}

Is it possible to call getNum() from C?

Answer 1

No, since getNum is a member function, which C doesn’t have.

A possible solution to that problem is to write a C++ function to return a foo instance as a foo* (where foo is changed to be an empty struct) to C (I assume this is binary compiled as C++ to which C is linking), then have a free function in C++ called foo_getNum or something, which takes a foo* (whose definition is modified for the C version to be empty) which calls getNum on it. It wouldn’t be type safe though, obviously, (but taking a foo* even when foo is empty would be better than void* – thanks David).