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

Wow, that's evil.

Is this portable across compilers?

Most definitely not. Consider the following:

foo* x = new bar();
delete x;

In order for this to work, foo's destructor must be virtual which it clearly isn't. As long as you don't use new and as long as the derived objectd don't have custom destructors, though, you could be lucky.

/EDIT: On the other hand, if the code is only used as in the question, inheritance has no advantage over composition. Just follow the advice given by m_pGladiator.