///友元///友元有利于数据共享，但是破坏了类的封装性#include 
      
       using namespace std;class Time {public:    Time (int h=10,int m=10,int s=10):hour(h),minute(m),sec(s) {}    ///将普通函数放到类中，普通函数可以访问私有成员    friend void display(Time &t);private:    int hour;    int minute;    int sec;};void display(Time &t) {    cout<
       
        <<" "<
        
         <<" "<
         
          <
         
        
       
      

 

///友元///友元有利于数据共享，但是破坏了类的封装性#include 
      
       using namespace std;class Date;    ///对Date类提前声明class Time {public:    Time (int h,int m,int s):hour(h),minute(m),sec(s) {};    void display(Date &d);private:    int hour;    int minute;    int sec;};class Date {public:    Date(int m,int d,int y):month(m),day(d),year(y) {}    ///声明Time中display函数为本类的友元成员函数，可以访问本类的私有成员    friend void Time::display(Date &d);private:    int month;    int day;    int year;};void Time::display(Date &d) {    cout<
       
        <<" "<
        
         <<" "<
         
          <