Calling a function from a DLL which is developed in C++ from C

Question

The function in dll has the prototype below

void Foo(int arg1, int& arg2);

The question is, how to declare the function prototype in C?

Is the declaration legal?

void Foo(int, int*);

Answer 1

Is the declaration legal?

It is, but it doesn't declare the same function. If you need a C API, you cannot use a reference. Stick to a pointer, and make sure the function has C linkage:

extern "C" void Foo(int, int*) {
   // Function body
}

If you cannot modify the DLL code, you need to write a C++ wrapper for it that exposes a proper C API.