友元三例

//例1：一个普通函数是友元函数。可以访问类的私有成员变量

#include <iostream>

 

using namespace std;

 

class Time

{

public:

       Time(int h=20,int m=25,int s=30):m_iHour(h),m_iMinute(m),m_iSecond(s){}

       void Show()

       {

              cout<< m_iHour<<":"<< m_iMinute<<":"<<m_iSecond<<endl;

       }

    friend void display(Time& t);//友元函数,display()是一个普通的函数

 

private:

       int m_iHour;

       int m_iMinute;

       int m_iSecond;

};

 

void display(Time& t)

{

       cout<<t.m_iHour<<":"<<t.m_iMinute<<":"<<t.m_iSecond<<endl;

}

 

void main()

{

       Time time1(5,6);

       //time1.Show();

      

       display(time1);

}

 

//例2：一个类中函数访问另一个类的私有成员变量

#include <iostream>

using namespace std;

 

class Date;//不完全声明

 

class Time

{

public:

       Time(int h=20,int m=25,int s=30):m_iHour(h),m_iMinute(m),m_iSecond(s){}

       void Show()

       {

              cout<< m_iHour<<":"<< m_iMinute<<":"<<m_iSecond<<endl;

       }

    void display(Date &d);

      

private:

       int m_iHour;

       int m_iMinute;

       int m_iSecond;

};

 

class Date{

public:

       Date(int y=2007,int m=12,int d=25)

       {

              m_iYear=y;m_iMonth=m,m_iDay=d;

       }

       friend void Time::display(Date &d);

      

private:

       int m_iYear;

       int m_iMonth;

       int m_iDay;

};

void Time::display(Date &d)

{

       cout<<d.m_iYear<<"/"<<d.m_iMonth<<"/"<<d.m_iDay<<endl;

       cout<<m_iHour<<":"<< m_iMinute<<":"<<m_iSecond<<endl;

}

 

void main()

{

       Time time1(5,6);

       //time1.Show();

      

       Date date1;

       time1.display(date1);

}

 

//例3：一个类是另一个类的友元类

#include <iostream>

using namespace std;

 

class Date;

 

class Time

{

public:

       Time(int h=20,int m=25,int s=30):m_iHour(h),m_iMinute(m),m_iSecond(s){}

       void Show()

       {

              cout<< m_iHour<<":"<< m_iMinute<<":"<<m_iSecond<<endl;

       }

    void display(Date &);

      

private:

       int m_iHour;

       int m_iMinute;

       int m_iSecond;

};

 

class Date

{

public:

       Date(int y=2007,int m=12,int d=25)

       {

              m_iYear=y;m_iMonth=m,m_iDay=d;

       }

       friend Time;//类Time中所有的函数都可以访问类Date中的私有成员

      

private:

       int m_iYear;

       int m_iMonth;

       int m_iDay;

};

 

void Time::display(Date &d)

{

       cout<<d.m_iYear<<"/"<<d.m_iMonth<<"/"<<d.m_iDay<<endl;

       cout<<m_iHour<<":"<< m_iMinute<<":"<<m_iSecond<<endl;

}

 

void main()

{

       Time time1(5,6);

       //time1.Show();

      

       Date date1;

       time1.display(date1);

}