多态性6

#include<iostream>
using namespace std;
class Base1{
public:
virtual void display() const=0;
};
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()
{
Base2 base2;
Derived derived;
fun(&base2);
fun(&derived);
return 0;
}