C++virtual 虚函数详解

#include<iostream>
using namespace std;

class Animal
{
public:
    Animal(int height,int weight)
    {
        cout<<"Animal construct"<<endl;
    }
    ~Animal()
    {
        cout<<"Animal destruct"<<endl;
    }

    void eat()
    {
        cout<<"Animal's eat"<<endl;
    }
protected:
    void sleep() //在子类中可以访问 ，子类的sleep方法也是protected，不能被外部访问
    {
        cout<<"Animal's sleep"<<endl;
    }

public:
     void breathe() //c++多态性。
    {
        
        cout<<"Animal's breathe"<<endl;
    }

};

class Fish :public Animal //按照public继承
{
public:
 
    Fish():Animal(400,300) //在子类中向父类的构造函数传递参数，成功构造了animal对象
    {
        cout<<"fish construct"<<endl;
    }
    ~Fish()
    {
        cout<<"fish destruct"<<endl;
    }
    void breathe()
    {
        Animal::breathe(); //::作用域标识符
        cout<<"fish breath"<<endl;
    }

};

 void fn(Animal *pAn)
 {
     pAn->breathe();
 }
 

void main()
{
    //Animal an;
    //an.eat();
    Fish fh;
    //fh.breathe();
    //fh.test();
    Animal *pAn;
    pAn=&fh;
    fn(pAn);
//两个对象的转换要内存模型匹配.pAn是animal和fish的首地址,
  
}