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在读《大话设计模式》，在此记录有关C++实现备忘录模式。

场景引入：游戏中的存档，比如打boss之前记录人物的血量等状态。

下面代码是自己根据理解实现的存档人物血量功能。

#include <iostream>using namespace std;//声明玩家类
class GamePlayer {
public:GamePlayer(int volume = 100) :bloodVolume(volume) {};void setBloodVolume(int volume) {bloodVolume = volume;};void decreaseBloodVolume(int volume) {if (bloodVolume < volume){bloodVolume = 0;}else {bloodVolume = bloodVolume - volume;}}int getBloodVolume() {return bloodVolume;};void showBloodVolume() {std::cout << "当前角色血量为" << bloodVolume << std::endl;}private:int bloodVolume;	//血量
};//声明备忘录类
class memorandum {
public:void setMemor(GamePlayer& setPlayer){std::cout << "正在存档..." << std::endl;this->player.setBloodVolume(setPlayer.getBloodVolume());}void getMemor(GamePlayer& getPlayer){std::cout << "正在读档..." << std::endl;getPlayer.setBloodVolume(player.getBloodVolume());}private:GamePlayer player;
};int main()
{GamePlayer player(60);	player.showBloodVolume();memorandum playerMemory;//存档playerMemory.setMemor(player);//模拟玩家受到攻击player.decreaseBloodVolume(20);player.showBloodVolume();//回档playerMemory.getMemor(player);player.showBloodVolume();return 0;
}

上面这段代码，声明了一个备忘录类，传入要存档的对象，获取其数据，临时存储在private的成员变量中。读档的时候引用传入玩家类，根据需要拷贝原先存储的数据。但是如果这时候需要添加蓝量相关的数据存储，需要修改的代码很多，首先是备忘录类中函数获取的数据要修改。然后玩家类中要新添加操作蓝量对应的接口。将备忘录类放在玩家类中，可以避免这些接口的声明

代码如下：

#include <iostream>
#include <memory>using namespace std;//声明玩家类
class GamePlayer {
public:GamePlayer(int volume = 100) :bloodVolume(volume) {};//声明备忘录类class memorandum {public:int bloodVolume;memorandum(int bloodNum) :bloodVolume(bloodNum) {};};void setBloodVolume(int volume) {bloodVolume = volume;};void decreaseBloodVolume(int volume) {if (bloodVolume < volume){bloodVolume = 0;}else {bloodVolume = bloodVolume - volume;}}int getBloodVolume() {return bloodVolume;};void showPlayerState() {std::cout << "当前角色血量为" << bloodVolume << std::endl;}//存档void savePlayerState() {std::cout << "存档中..." << std::endl;memor = std::make_shared<memorandum>(bloodVolume);}void readPlayerState() {std::cout << "读档中..." << std::endl;bloodVolume = memor->bloodVolume;		//读取人物血量}private:int bloodVolume;	//血量std::shared_ptr<memorandum> memor;
};int main()
{GamePlayer player(60);	player.showPlayerState();player.savePlayerState();//模拟玩家受到攻击player.decreaseBloodVolume(20);player.showPlayerState();//读档档player.readPlayerState();player.showPlayerState();//再次受到攻击player.decreaseBloodVolume(10);player.savePlayerState();player.readPlayerState();	//读档player.showPlayerState();	//展示当前数据return 0;
}

这时，如果存档和读档更多的数据比如蓝量，怒气值，经验等，客户端代码不需要修改，仅需要修改玩家类中的代码。