看到书上的代码之后，产生了一些疑问，还请大佬指教一下程序如下：
#include<iostream>
using namespace std;
class Base1{
public:
virtual void display()const;
};
void Base1::display()const{
cout<<"Base1::display()"<<endl;
}
class Base2:public Base1{
public:
void display()const;
};
void Base2::display()const{
cout<<"Base2::display()"<<endl;
}
class Derived:public Base2{
public:
void display()const;
};
void Derived::display()const{
cout<<"Derived::display()"<<endl;
}
void fun(Base1 *ptr){
ptr->display();
}
int main()
{
Base1 base1;
Base2 base2;
Derived derived;
fun(&base1);
fun(&base2);
fun(&derived);
return 0;
}
#include<iost
