友元-----练习

#include<iostream>
using namespace std;
class Data;
class Time
{
public:
 Time(int,int,int);
 void display(Data &d);
private:
 int hour;
 int min;
 int secede;
};
class Data
{
public:
 friend void Time::display(Data &d);
 Data(int,int,int);
private:
 int year;
 int month;
 int day;
};
void Time::display(Data &d)
{
 cout<<d.year<<"/"<<d.month<<"/"<<d.day<<endl;
 cout<<hour<<":"<<min<<":"<<secede<<endl;
}
Time::Time(int h,int m,int s):hour(h),min(m),secede(s){}
Data::Data(int y,int m,int d):year(y),month(m),day(d){}
int main()
{
 Time t(12,0,0);
 Data d(2013,8,8);
 t.display(d);
 return 0;
}