关于虚函数实现多态的原理及分析

class Person{
public:
	virtual void f(){cout << "use f()" << endl;}
	virtual void g(){cout << "use g()" << endl;}
	virtual void h(){cout << "use h()" << endl;}
};

class Bag:public Person{
public:
	virtual void i(){cout << "use i()" << endl;}
	virtual void j(){cout << "use j()" << endl;}
};

class Bag:public Person{
public:
	void f(){cout << "class Bag use fun" << endl;}
	virtual void i(){cout << "use i()" << endl;}
	virtual void j(){cout << "use j()" << endl;}
}; 

#include <iostream>
using namespace std;

class Person1{
public:
    virtual void f(){}
    virtual void g(){}
    virtual void h(){}
    virtual ~Person1(){}
};

class Person2{
public:
    virtual void f(){}
    virtual void g(){}
    virtual void h(){}
    void a(){           // 成员函数，不需要重载
        cout << "class Person2" << endl;
    }
    virtual ~Person2(){}
};

class Person3{
public:
    virtual void g(){}
    virtual void h(){}
    virtual ~Person3(){}
};

class Bag:public Person1, public Person2, public Person3{
public:
    void f(){
        cout << "Bag f()" << endl;
    }
    void g(){
        cout << "Bag g()" << endl;
    }
    void a(){
        cout << "Class Bag" << endl;
    }
};

int main(int argc, char const *argv[])
{
    Person3* p3 = new Bag;
    //p3->f();    // P3 没有成员函数f（）
                  // 多态首先得是 父类有虚函数，其次是子类要定义该函数的重载
                  // 如果父类的虚函数改为成员函数，则子类无法进行重载，即无法实现多态
    delete p3;
    p3 = NULL;

    Person1* p1 = new Bag;
    p1->f();
    delete p1;
    p1 = NULL;

    Person2* p2 = new Bag;
    p2->a();
    delete p2;
    p2 = NULL;
    
    return 0;
}