callback with member function pointer

//
//  main.cpp
//  callbackWithMemberPointer
//
//  Created by Rizky Herucakra on 7/5/13.
//  Copyright (c) 2013 Rizky Herucakra. All rights reserved.
//

#include <iostream>

class A{
public:
    void a_callback();

};

void A::a_callback(){
    using namespace std;
    cout << "A::a_callback is called";
}

typedef void (A::*callback_func)();

class B{
    callback_func callback;
    A* obj;
public:
    void do_something();
    void register_callback(A* ob,callback_func c);

    B();
};

B::B():obj(nullptr),callback(nullptr){}

void B::register_callback(A* ob,callback_func c){
    obj = ob;
    callback = c;
}

void B::do_something(){
    using namespace std;
    cout << "B::do_something called" << endl;
    if (callback != nullptr) (obj->*callback)();
}



int main(int argc, const char * argv[])
{

    A a;
    B b;
    b.register_callback(&a, &A::a_callback);
    b.do_something();
}