#include "iostream"
#include "cstring"
#include "string"
#include "cstdio"
using namespace std;
class base{
public:
    virtual void display() const{
        cout<<"I come from base"<<endl;
    }
};

class base1:public base{
public:
    virtual void display() const{
        cout<<"I come from base1"<<endl;
    }
};

class base2:public base1{            //這里寫base或者base1都是一樣的效果。
    virtual void display() const{
        cout<<"I come from base2"<<endl;
    }
};

void fun(base *ptr){
    ptr->display();
}
int main(){
    base Base;
    base1 Base1;
    base2 Base2;
    fun(&Base);
    fun(&Base1);
    fun(&Base2);
    return 0;
}