c++虚函数和虚继承

关键字virtual用于父类方法，如果传了一个子类对象，并且子类重写了父类的这个virtual方法，就会调用子类的方法。传谁就调用谁，这个就是多态。
#include<iostream> 
using namespace std;

class Biological{
public:
    virtual void range(){
        cout<<"widely"<<endl;
    }

    void name(){
        cout<<"biological"<<endl;
    }
};

class Animal:public Biological{
public:
    virtual void range(){
        cout<<"medium"<<endl;
    }

    void name(){
        cout<<"animal"<<endl;
    }
};

class Person:public Animal{
public:
    virtual void range(){
        cout<<"small"<<endl;
    }

    void name(){
        cout<<"person"<<endl;
    }
};

void Display(Biological *p){
    p->range();
    p->name();
    delete p;
}

int main(){
    Display(new Biological);
    Display(new Animal);
    Display(new Person);
    return 0;
}

#include<iostream> 
using namespace std;

class Biological{
public:
    Biological(){
        cout<<"Biological构造"<<endl; 
    }

    ~Biological(){
        cout<<"Biological析构"<<endl; 
    }
};

class Animal:virtual public Biological{
public:
    Animal(){
        cout<<"Animal构造"<<endl; 
    }

    ~Animal(){
        cout<<"Animal析构"<<endl; 
    }
};

class Plant:virtual public Biological{
public:
    Plant(){
        cout<<"Plant构造"<<endl; 
    }

    ~Plant(){
        cout<<"Plant析构"<<endl; 
    }
};

class SeaAnemone:public Animal,public Plant{
public:
    SeaAnemone(){
        cout<<"SeaAnemone构造"<<endl; 
    }

    ~SeaAnemone(){
        cout<<"SeaAnemone析构"<<endl; 
    }
};


int main(){
    SeaAnemone sea_anemone;
    return 0;
}

#include<iostream> 
using namespace std;

class Biological{
public:
    Biological(){
        cout<<"Biological构造"<<endl; 
    }

    virtual ~Biological(){
        cout<<"Biological析构"<<endl; 
    }
private:
    char *name;
};

class Animal:virtual public Biological{
public:
    Animal(){
        cout<<"Animal构造"<<endl; 
    }

    ~Animal(){
        cout<<"Animal析构"<<endl; 
    }
};

class Plant:virtual public Biological{
public:
    Plant(){
        cout<<"Plant构造"<<endl; 
    }

    ~Plant(){
        cout<<"Plant析构"<<endl; 
    }
};

class SeaAnemone:public Animal,public Plant{
public:
    SeaAnemone(){
        cout<<"SeaAnemone构造"<<endl; 
    }

    ~SeaAnemone(){
        cout<<"SeaAnemone析构"<<endl; 
    }
};


int main(){
    Biological *sea_anemone = new SeaAnemone;
    delete sea_anemone;
    return 0;
}

注意：如果将~Biological()函数前的virtual去掉那么函数会出错。

总结：我们一定要注意在基类的析构函数前面加上virtual，使其变成虚析构在C++程序中使用虚函数，虚继承和虚析构是很好的习惯 可以避免许多的问题。