源代码：

#include<iostream>

using namespace std;

class Timer;

class TimerFriend

{

public:

void PrintTimer(Timer & t);

void ModifyTimer(Timer & t);

};

class Timer

{

public:

Timer(int hour = 0, int minute = 0, int second = 0)

{

m_hour = hour;

m_minute = minute;

m_second = second;

}

int GetHour()const{ return m_hour; }

int GetMinute()const{ return m_minute; }

int GetSecond()const{ return m_second; }

friend void TimerFriend::PrintTimer(Timer & t);

friend void TimerFriend::ModifyTimer(Timer & t);//加类的限定    TimerFriend::  

private:

int m_hour;

int m_minute;

int m_second;

};

void TimerFriend::PrintTimer(Timer & t)

{

cout << t.m_hour << ":" << t.m_minute << ":" << t.m_second << endl;

}

void TimerFriend::ModifyTimer(Timer & t)

{

cout << "时，分，秒" << endl;

cin >> t.m_hour >> t.m_minute >> t.m_second;

cout << "修改完毕！" << endl;

}

int main()

{

Timer t0(1, 10, 20);

TimerFriend tf;

tf.PrintTimer(t0);

tf.ModifyTimer(t0);

tf.PrintTimer(t0);

system("pause");

return 0;

}

报错：如图