观察者模式又叫做发布-订阅模式。观察者模式定义了一种一对多的依赖关系，让多个观察者对象（公司楼上员工）同时监听某一个主题对象（公司1楼前台秘书）。这个主题对象在状态发生变化时，会通知所有观察者对象，使它们能够自动更新自己。
1: #include <string>
2: #include <iostream>
3: #include <vector>
4: using namespace std;
5: 6: class SecretaryBase;
7: //抽象观察者
8: class CObserverBase
9: { 10: protected:
11: string name;
12: SecretaryBase* sub;
13: public:
14: CObserverBase(string strname,SecretaryBase* strsub)
15: { 16: name=strname;
17: sub=strsub;
18: } 19: virtual void Update()=0;
20: }; 21: //具体的观察者，看股票的
22: class StockObserver : public CObserverBase
23: { 24: public:
25: StockObserver(string strname,SecretaryBase* strsub) : CObserverBase(strname,strsub)
26: { 27: } 28: virtual void Update();
29: }; 30: 31: //具体观察者，看NBA的
32: class NBAObserver : public CObserverBase
33: { 34: public:
35: NBAObserver(string strname,SecretaryBase* strsub) : CObserverBase(strname,strsub){}
36: virtual void Update();
37: }; 38: 39: 40: //抽象通知者
41: class SecretaryBase
42: { 43: public:
44: string action;
45: vector<CObserverBase*> observers;
46: public:
47: virtual void Attach(CObserverBase* observer)=0;
48: virtual void Notify()=0;
49: }; 50: 51: //具体通知者
52: class Secretary :public SecretaryBase
53: { 54: public:
55: void Attach(CObserverBase* ob)
56: { 57: observers.push_back(ob);
58: } 59: void Notify()
60: { 61: vector<CObserverBase*>::iterator p = observers.begin();
62: while (p!=observers.end())
63: { 64: (*p)->Update();
65: p++;
66: } 67: } 68: }; 69: 70: void StockObserver::Update()
71: { 72: cout<<name<<":"<<sub->action<<",不要玩股票了，要开始工作了" << endl;
73: } 74: void NBAObserver::Update()
75: { 76: cout<<name<<":"<<sub->action<<",不要玩股票了，要开始工作了" << endl;
77: } 78: 79: 80: 客户端
81: int main()
82: { 83: SecretaryBase *p=new Secretary(); //创建观察者
84: //被观察的对象
85: CObserverBase *s1= new NBAObserver("小李",p);
86: CObserverBase *s2 = new StockObserver("小赵",p);
87: //加入观察队列
88: p->Attach(s1);
89: p->Attach(s2);
90: //事件
91: p->action="老板来了";
92: //通知
93: p->Notify();
94: return 0;
95: }