C + + polymorphic

Polymorphic 1. polymorphic use

The interface does not need to be modified in order for the code to be reused easily and to add a feature.

#include <iostream>using namespace std;class A{public:  virtual void eat(){}  virtual void sleep(){}};class Human : public A{public:  void eat(){    cout << "Human eat" << endl;  }  void sleep(){    cout << "Human sleep" << endl;  }};class Pig : public A{public:  void eat(){    cout << "Pig eat" << endl;  }  void sleep(){    cout << "Pig sleep" << endl;    }};//这个fun方法是个对外的接口，当需要增加新功能时，新的功能只需要继承class A，就可以使用这个接口。void fun(A& a){  a.eat();  a.sleep();}int main(){  Human h;  Pig p;  fun(h);//调用的是Human的eat和sleep  fun(p);//调用的是Pig的eat和sleep}

2. Conditions necessary for polymorphic formation

• Virtual functions
• Method with the same name
• Method parameter numbers are the same, method parameters are of the same type
• Return value type is the same
• You must use a pointer or reference from the parent class, and the object of the parent class cannot form a polymorphic

However, there is one exception, although the return value type is different, but the return value of the parent class's method is a pointer to the parent class, and the return value of the method of the subclass is a pointer to the subclass, and can also form polymorphism.

#include <iostream>using namespace std;class Base{public:  virtual Base* show(){    cout << "Base show" << endl;  }};class D : public Base{  D* show(){//返回值和父类不一样，但因为是父子关系，所以也可以形成多态    cout << "D show" << endl;  }};int main(){  D d;  Base* pb = &d;  pb->show();//调用的是子类的show方法}

C + + polymorphic