代码只是示例了虚函数的一些应用,并不是说在该场景下这样用最好,甚至于说,几乎不会出现这样的用法。但这可以让初学者加深对虚函数的理解。
//继承多个接口,但是有相同的方法 #include <iostream> class IHello { public: virtual void Say()=0; }; class IWorld { public: virtual void Say()=0; }; class MHello:public IHello { public: void Say(){cout<<"Hello";} }; class MWorld:public IWorld { public: void Say(){cout<<"World"<<endl;} }; class CObject:public MHello,public MWorld { }; int main() { CObject 0; IHello& ih=0; IWorld& iw=0; ih.Say(); iw.Say(); return 0; }//两个平行类,通过被继承,虚函数,将下一个动作传到另一个类,V形转发 #include <iostream> using namespace std; class Hello { public: void Say(){cout<<"Hello";nextH();} virtual void nextH(){} }; class World { public: void Say(){cout<<"World";nextW();} virtual void nextW(){} }; class CObject:public Hello,public World { public: void nextH() { World::Say(); } void nextW() { ; } }; int main() { CObject o; o.Hello::Say(); return 0; }//受到上面平行类的启发,利用菱形继承,提供数据,实现一个switch,处理类似平行的 //但是对每个平行类要有不同签名的调用下一个的虚函数,并且在CObject中对这个处理过程进行编码 #include <iostream> using namespace std; class Data { public: int value; }; class Case1:public virtual Data { public: void process(){if(value==1){cout<<1<<endl;} else next1();} virtual void next1(){} }; class Case2:public virtual Data { public: void process(){if(value==2){cout<<2<<endl;} else next2();} virtual void next2(){} }; class Default:public virtual Data { public: void process(){cout<<"default"<<endl;} }; class CObject:public Case1,public Case2,public Default { public: void next1() { Case2::process(); } void next2() { Default::process(); } }; int main() { CObject 0; for(int i=0;i<4;++i) { o.value=i; o.Case1::process(); } return 0; }//想到责任链模式,也实现了一个 //但是一个处理者知道下一个处理者 #include <iostream> using namespace std; class MsgProcessor { public: MsgProcessor(MsgProcessor* next=NULL):next_(next){} virtual void process(int msg)=0; virtual void dispatch(int msg) { if(next_) next_->process(msg); } MsgProcessor* next_; }; class Handler1:public MsgProcessor { public: Handler1(MsgProcessor* next=NULL):MsgProcessor(next) { } void process(int msg) { if(msg==1) { cout<<1<<endl; } else { dispatch(msg); } } }; class Handler2:public MsgProcessor { public: Handler2(MsgProcessor* next=NULL):MsgProcessor(next) { } void process(int msg) { if(msg==2) { cout<<2<<endl; } else { dispatch(msg); } } }; class HandlerDefault:public MsgProcessor { public: HandlerDefault(MsgProcessor* next=NULL):MsgProcessor(next) { } void process(int msg) { cout<<"default"<<endl; } }; int main() { HandlerDefault dft; Handler2 h2(&dft); Handler1 h1(&h2); for(int i=0;i<4;i++) { h1.process(i); } return 0; }
//修饰器模式,好看一点,把终止结点和非终止节点分开了 #include <iostream> using namespace std; class Component { public: virtual void process(int msg)=0; }; class CaseDefault:public Component { public: void process(int msg) { cout<<"default"<<endl; } }; class CaseNormal:public Component { public: CaseNormal(Component* next=NULL):next_(next) { } virtual void process(int msg) { if(next_) next_->process(msg); } Component* next_; }; class Case1:public CaseNormal { public: Case1(Component* next=NULL):CaseNormal(next) { } void process(int msg) { if(msg==1) { cout<<1<<endl; } else { CaseNormal::process(msg); } } }; class Case2:public CaseNormal { public: Case2(Component* next=NULL):CaseNormal(next) { } void process(int msg) { if(msg==2) { cout<<2<<endl; } else { CaseNormal::process(msg); } } }; int main() { CaseDefault dft; Case2 c2(&dft); Case1 c1(&c2); for(int i=0;i<4;++i) { c1.process(i); } return 0; }