c++中虚函数的简单应用

作者:baihacker
来源:http://hi.baidu.com/feixue http://hi.youkuaiyun.com/baihacker

本来是题目是:无聊时写了一点c++代码
后来发现都和虚函数有关,于是就把题目名字改了
其实我也不知道为什么要写这个，就随便写写吧。

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> using namespace std; 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 o; IHello& ih = o; IWorld& iw = o; 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，处理类是平行的 //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 o; 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结点分开了。 #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; }