订阅者模式（观察者模式）

#include <memory>
#include <list>
#include <iostream>

struct Notification
{
	virtual ~Notification()
	{
	}
	virtual void process() = 0;
};

class SubscriberA: public Notification
{
public:
	//Notification
	virtual void process()
	{
		std::cout << "A\n";
	}
};

class SubscriberB: public Notification
{
public:
	//Notification
	virtual void process()
	{
		std::cout << "B\n";
	}
};

class Publisher
{
	std::list<std::shared_ptr<Notification>> _listSubscribers;
public:
	void subscribeForNotification(std::shared_ptr<Notification> subscriber)
	{
		if (!subscriber)
		{
			return;
		}
		auto it = _listSubscribers.begin();
		while (it != _listSubscribers.end())
		{
			if (*it == subscriber)
			{
				return;
			}
			++it;
		}
		_listSubscribers.push_back(subscriber);
	}
	void start()
	{
		notifySubscribers();
	}
private:
	void notifySubscribers()
	{
		for (auto it = _listSubscribers.begin(); it != _listSubscribers.end(); ++it)
		{
			(*it)->process();
		}
	}
};

int main()
{
	Publisher p;
	p.subscribeForNotification(std::shared_ptr<Notification>(new SubscriberA()));
	p.subscribeForNotification(std::shared_ptr<Notification>(new SubscriberB()));
	p.start();
	return 0;
}