observer 观察者模式

#include <iostream>
#include <string>
#include <list>
using namespace std;
// subject notify中调用 observer 的update 更新状态
typedef string State;

class subject;
class observer
{
public:
    virtual ~observer(){}
    virtual void update(subject *sub) =0;
    virtual void printInfo() =0;
protected:
    observer(){}
    State _st;
};

class subject
{
public:
    virtual ~subject(){ delete _obvs; }
    virtual void attach(observer *obv){ _obvs->push_back(obv); }
    virtual void detach(observer *obv){ if (obv != NULL) _obvs->remove(obv); }
    virtual void notify(){
        for (list<observer*>::iterator it = _obvs->begin(); it != _obvs->end(); ++it){
            (*it)->update(this);
        }
    }
    virtual void setState(const State &st) =0;
    virtual State getState() =0;

protected:
    subject():_obvs(new list<observer*>){}

private:
    list<observer*>* _obvs;        
};

class concrete_subject : public subject
{
public:
    concrete_subject(){}
    ~concrete_subject(){}
    void setState(const State &st){ _st = st; }
    State getState(){ return _st; }
private:
    State _st;
};

class concrete_observera : public observer
{
public:
    concrete_observera(subject *sub):_sub(sub){ _sub->attach(this); } 
    virtual ~concrete_observera(){ _sub->detach(this); }
    virtual subject* getSubject(){ return _sub; }
    void update(subject *sub){ _st = sub->getState(); printInfo();}
    void printInfo(){ cout << "obvA: " << _st <<endl; }
private:
    subject *_sub;
};

class concrete_observerb : public observer
{
public:
    concrete_observerb(subject *sub):_sub(sub){ _sub->attach(this); } 
    virtual ~concrete_observerb(){ _sub->detach(this); cout << "B Destructor"<<endl; }
    virtual subject* getSubject(){ return _sub; }
    void update(subject *sub){ _st = sub->getState(); printInfo();}
    void printInfo(){ cout << "obvB: " << _st <<endl; }
private:
    subject *_sub;
};

int main()
{
    subject *sub = new concrete_subject();
    observer *obv1 = new concrete_observera(sub);
    observer *obv2 = new concrete_observerb(sub);
    sub->setState("state1");
    sub->notify();
    sub->setState("state2");
    sub->notify();
    delete obv1;
    delete obv2;
    delete sub;
    return 0;
}