#include<iostream>using namespace std; class base{public:virtual void fn(int x){cout<<"in base class,int x="<<x<<endl;}（1）}; class sub:public base{public:virtual void fn(int x){cout<<"in sub class,int x="<<x<<endl;}（2）virtual void fn(double x){cout<<"in sub class,double x="<<x<<endl;}（3）}; ...