C++ 设计模式： 观察者模式

#ifndef H_OBSERVER_H
#define H_OBSERVER_H


#include <iostream>
#include <list>
using namespace std;

class Observer
{
public:
    virtual void Update(int) = 0;
};

class Subject
{
public:
    virtual void Attach(Observer*) = 0;
    virtual void Detach(Observer*) = 0;
    virtual void Notify() = 0;
};

class ConcreteObserver : public Observer
{
public:
    ConcreteObserver(Subject* pSubject) : m_pSubject(pSubject) {}

    void Update(int value)
    {
        cout << "ConcreteObserver get the update. New State:" << value << endl;
    }

private:
    Subject* m_pSubject;
};

class ConcreteObserver2 : public Observer
{
public:
    ConcreteObserver2(Subject* pSubject) : m_pSubject(pSubject) {}

    void Update(int value)
    {
        cout << "ConcreteObserver2 get the update. New State:" << value << endl;
    }

private:
    Subject* m_pSubject;
};

class ConcreteSubject : publ