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;
};