Calling C++ from C

hello.cpp

using namespace std;
#include <iostream>

extern "C" void hello(int repeatCount) {
    for (int i=0; i<repeatCount; i++) {
        cout << "hello from C++" << endl;
    }
}

main.c

#include "hello.h"

int main(int argc, char** argv) {
    hello(3);
}

To be callable by C, the C++ function needs to be declared as extern "C" to prevent name mangling.

Note that without name mangling, C not only can't support function overloading (two or more functions with same name but different argument types), but if the convention of putting function prototypes in header files that are checked against both points of use and point of definition isn't followed, there is no way to make sure types match. K&R C didn't provide for prototypes, but the later ANSI C required them at point of use. However, even with ANSI C, different prototypes might be provided in different files if convention of putting prototypes in a single header file is not followed.