课程设计__友元

///友元
///友元有利于数据共享，但是破坏了类的封装性

#include <iostream>

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<<t.hour<<" "<<t.minute<<" "<<t.sec<<endl;
}

int main() {
    Time t(12,13,14);
    display(t);
    return 0;
}

///友元
///友元有利于数据共享，但是破坏了类的封装性

#include <iostream>

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<<d.month<<" "<<d.day<<" "<<d.year<<endl;
    cout<<hour<<" "<<minute<<" "<<sec<<endl;
}

int main() {
    Time t(10,13,56);
    Date d(12,25,2016);
    t.display(d);
    return 0;
}