四个角色类：
flyweight享元类：所有具体享元类的超类或接口，通过这个接口，flyweight可以接受并作用于外部状态。
flyweight享元工厂类：一个享元工厂，用来创建并管理flyweight，当用户请求一个flyweight时，flyweightfactory对象提供一个已创建的实例或者创建一个（如果不存在的话）。
concreteflyweight具体享元类：继承flyweight超类或实现flyweight接口，并为内部状态增加存储空间。
unsharedconcreteflyweight不需共享的具体flyweight子类、指那些不需要共享的flyweight子类。因为flyweight接口类共享成为可能，但并不强制共享。
模式实现：
[code]//享元类 class flyweight{ public: virtual void operation(int extrinsicstate){} }; //具体享元类 class concreteflyweight: public flyweight{ public: virtual void operation(int extrinsicstate)override{ std::cout << "concreteflyweight: " << extrinsicstate << std::endl; } }; //不需共享的flyweight子类 class unsharedconcreteflyweight: public flyweight{ public: virtual void operation(int extrinsicstate){ std::cout << "unsharedconcreteflyweight: " << extrinsicstate << std::endl; } }; //享元工厂，用来创建并管理flyweight对象 class flyweightfactory{ private: std::map<std::string, flyweight*> flyweights; public: flyweightfactory(){ flyweights["x"] = new concreteflyweight; flyweights["y"] = new concreteflyweight; flyweights["z"] = new concreteflyweight; } flyweight* getflyweight(std::string key){ return (flyweight*)flyweights[key]; } };
客户端：
[code]//client int main(){ //外部状态 int extrinsicstate = 22; //工厂 flyweightfactory *f = new flyweightfactory; flyweight* fx = f->getflyweight("x"); fx->operation(--extrinsicstate); //output: concreteflyweight: 21 flyweight* fy = f->getflyweight("y"); fy->operation(--extrinsicstate); //output: concreteflyweight: 20 flyweight* fz = f->getflyweight("z"); fz->operation(--extrinsicstate); //output: concreteflyweight: 19 flyweight *uf = new unsharedconcreteflyweight; //output: unsharedconcreteflyweight: 18 uf->operation(--extrinsicstate); return 0; }
享元模式好处：
如果一个应用程序使用了大量的对象，而大量的这些对象造成了很大的存储开销时就应该考虑使用。
对象的大多数状态可以使用外部状态，如果删除对象的外部状态，那么可以用相对较少的共享对象取代很多组对象，此时可以考虑使用享元模式。
以上就是c++设计模式浅识享元模式的内容。