1.定义

在GOF的《设计模式:可复用面向对象软件的基础》一书中对观察者模式是这样说的：定义对象间的一种一对多的依赖关系，当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。

2.代码简单实现

1 #include
     
       2 #include
      
        3 #include
       
         4 using namespace std; 5 class AbObserver 6 { 7 public: 8     virtual void getMessage(string message) = 0; 9 };10 11 class AbSecretary12 {13 public:14     virtual void senfMessage(string message) = 0;15     virtual void addObserver(AbObserver * observer) = 0;16 };17 //开小差的同事类（观察者）18 class Observer:public AbObserver19 {20 public:21     void getMessage(string message)22     {23         cout << message << endl;24     }25 };26 //秘书类（主题对象，通知者）27 class Secretary:public AbSecretary28 {29 public:30     void senfMessage(string message)31     {32         for (list
        
         ::iterator it = observers.begin(); it != observers.end(); it++)33         {34             (*it)->getMessage(message);35         }36     }37     void addObserver(AbObserver * observer)38     {39         observers.push_back(observer);40     }41 private:42     list
         
           observers;43 };44 45 int main()46 {47     Observer *observer1 = new Observer;48     Observer *observer2 = new Observer;49     Secretary * secretary = new Secretary;50     secretary->addObserver(observer1);51     secretary->addObserver(observer2);52     secretary->senfMessage("老板来了");53     secretary->senfMessage("老板走了");54     system("pause");55     return 0;56 }