将普通函数声明为友元函数

#include <iostream>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std;
class Time
{
    public:
        Time(int,int,int);
        friend void display(Time&);
    private:
        int hour;
        int minute;
        int sec;
};

Time::Time(int h,int m,int s)
{
    hour=h;
    minute=m;
    sec=s;
}

void display(Time&t)
{
    cout<<t.hour<<":"<<t.minute<<":"<<t.sec<<endl;
}
int main(int argc, char** argv) {
    Time t1(10,13,56);
    display(t1);
    return 0;
}