面试：C++观察者模式实现

 #include <list>

 class Subject;

 class Observer{
 public:
     virtual ~Observer(){};
     virtual void update(Subject * sub){};
 protected:
     Observer(){};

 };

 class Subject {
 public:
     Subject() { };
     virtual ~Subject() { };
     virtual void attach(Observer* ob) {
         this->_observers.push_back(ob);
     }
     void detach(Observer* ob) {
         this->_observers.remove(ob);
     }

     void notify(){
         for(auto ob : _observers){
             ob->update(this);
         }
     }
 private:
     std::list<Observer*> _observers;
 };