Is it possible to subclass a C struct in C++ and use pointers to the struct in C code?

Question

Is there a side effect in doing this:

C code:

struct foo {
      int k;
};

int ret_foo(const struct foo* f){ 
    return f.k; 
}

C++ c

Answer 1

It will work, and portably BUT you cannot use any virtual functions (which includes destructors).

I would recommend that instead of doing this you have Bar contain a Foo.

class Bar
{
private:
   Foo  mFoo;
};