1 #include <list> 2  3 class Subject; 4  5 class Observer{ 6 public: 7     virtual ~Observer(){}; 8     virtual void update(Subject * sub){}; 9 protected:10     Observer(){};11 12 };13 14 class Subject {15 public:16     Subject() { };17     virtual ~Subject() { };18     virtual void attach(Observer* ob) {19         this->_observers.push_back(ob);20     }21     void detach(Observer* ob) {22         this->_observers.remove(ob);23     }24 25     void notify(){26         for(auto ob : _observers){27             ob->update(this);28         }29     }30 private:31     std::list<Observer*> _observers;32 };