Pointers to virtual member functions. How does it work?

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It works because the Standard says that’s how it should happen. I did some tests with GCC, and it turns out for virtual functions, GCC stores the virtual table offset of the function in question, in bytes.

struct A { virtual void f() { } virtual void g() { } }; 
int main() { 
  union insp { 
    void (A::*pf)();
    ptrdiff_t pd[2]; 
  }; 
  insp p[] = { { &A::f }, { &A::g } }; 
  std::cout << p[0].pd[0] << " "
            << p[1].pd[0] << std::endl;
}

That program outputs 1 5 – the byte offsets of the virtual table entries of those two functions. It follows the Itanium C++ ABI, which specifies that.

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