观察者模式，有时我们又称为发布模式，当一个基类的状态（如某个属性）改变后，将会通知所有继承它的类的状态进行改变。
#include <iostream>
#include <list>
#include <numeric>
#include <algorithm>
using namespace std;
class ObserBase;
//base class of earth
class EarthBase
{
public:
virtual void attach(ObserBase *o)=0;
virtual void change()=0;
virtual void setWeather(string str)=0;
virtual string getWeather()=0;
};
//base class of observer
class ObserBase
{
public:
virtual string getName()=0;
virtual void update(EarthBase *s)=0;
virtual void changeWeather(string weather)=0;
};
//earth class
class Earth:public EarthBase
{
private:
string weather;
std::list<ObserBase*> l;
public:
Earth()
{
};
void attach(ObserBase *o)
{
this->l.push_back(o);
};
void change()
{
for(std::list<ObserBase*>::iterator it=l.begin();it!=l.end();++it)
{
(*it)->update(this);
}
};
void setWeather(string str)
{
this->weather=str;
change();
};
string getWeather()
{
return this->weather;
};
};
//oberver class, or satellite
class Observer:public ObserBase
{
private:
string name;
EarthBase* sub;
public:
Observer(string str)
{
name=str;
};
Observer(string str,EarthBase* sub_)
{
name=str;
sub = sub_;
sub->attach(this);
};
string getName()
{
return name;
};
void update(EarthBase *s)
{
cout<<this->getName()+ " " + s->getWeather()<<endl;
};
void changeWeather(string weather)
{
sub->setWeather(weather);
}
};
int main(int argc, char *argv[])
{
Earth e;
Observer *s1 = new Observer("风云一号");
Observer *s2 = new Observer("风云二号");
Observer *s3 = new Observer("风云三号");
Observer *s4 = new Observer("风云四号");
Observer *s5 = new Observer("风云五号",&e);
e.attach(s1);
e.attach(s2);
e.attach(s3);
e.attach(s4);
e.setWeather("fine");
s5->changeWeather("bad weather!!");
return 0;
}