虚函数

class A{
public:
    void print(){ cout<<"This is A"<<endl;}
};
class B:public A{
public:
    void print(){ cout<<"This is B"<<endl;}
};
int main(){ //为了在以后便于区分，我这段main()代码叫做main1
    A a;
    B b;
    a.print();
    b.print();
}

int main(){ //main2
    A a;
    B b;
    A* p1=&a;
    A* p2=&b;
    p1->print();
    p2->print();
}

class A{
public:
    virtual void print(){ cout<<"This is A"<<endl;} //现在成了虚函数了
};
class B:public A{
public:
    void print(){ cout<<"This is B"<<endl;} //这里需要在前面加上关键字virtual吗？
};