C++多态的实现条件

#include <iostream>
class Person{
public:
virtual void say(){
std::cout<<"person"<<std::endl;
}
};
class Student:public Person{
public:
void say(){
std::cout<<"student"<<std::endl;
}
};
int main(){
Person per;
Student stud;
per.say();
stud.say();
//传递对象
per = stud;
per.say();
//指针
Person *pPtr = &stud;
pPtr->say();
//引用
Person &pRef = stud;
pRef.say();
}