gistfile1.cpp

class Broker {
public:
  void subscribe(void (*f)()) {
    _f = f;
  }

  void notify() {
    (_f)();
  }

private:
  void (*_f)();
};

class B {
public:
  B(Broker* b) {
    _b = b;
    // error: ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to member function.  Say '&B::c'
    // error: no matching function for call to 'Broker::subscribe(void (B::*)())'
    //  note: candidates are: void Broker::subscribe(void (*)())
    _b->subscribe(&c);
  }
  
  void c() {}

private:
  Broker* _b;
};