2021.12.13（观察者模式c++）

观察者模式：股票提醒

当股票的价格上涨或下降5%时，会通知持有该股票的股民，当股民听到价格上涨的消息时会买股票，当价格下降时会大哭一场

c++源代码：

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

class MyObserver {
public:
	virtual void response(int rate) {};
};

class MySubject {
protected:
	list<MyObserver*>observers;
public:
	/*注册方法*/
	void attach(MyObserver*observer) {
		observers.push_back(observer);
	};
	/*注销方法*/
	void detach(MyObserver* observer) {
		observers.remove(observer);
	}

	/*抽象通知方法*/
	virtual void change(int rate) = 0;
};

class Stock : public MySubject {
public:
	void change(int rate) {
		list<MyObserver*>::iterator iter = observers.begin();
		for (; iter != observers.end(); iter++)
			(*iter)->response(rate);
	}
};

class Holders :public MyObserver {
public:
	void response(int rate) {
		if (rate >= 5) {
			cout << "股票上涨，买买买" << endl;
		}
		else if (rate <= -5) {
			cout << "股票下跌，大哭一场" << endl;
		}
		else {
			cout << "股票比较稳定，还好还好" << endl;
		}
	}
};

int main() {
	MySubject* subject = new Stock();
	MyObserver*obs1 = new Holders();
	subject->attach(obs1);
	cout << "****股票上涨****" << endl;
	subject->change(5);
	cout << endl;
	cout << "****股票下跌****" << endl;
	subject->change(-5);
	cout << endl;
	cout << "****股票稳定****" << endl;
	subject->change(4);
	cout << endl;
}

实现截图：