friend函数

/*
* Time.h
*
*  Created on: 2010-10-17
*/
#include<iostream>
using namespace std;

#ifndef TIME_H_
#define TIME_H_

class Time {
public:
Time();
Time(int,int,int);
friend void display(Time&);
virtual ~Time();
private:
int hour;
int min;
int sec;
};
#endif /* TIME_H_ */

/*
* Time.cpp
*
*  Created on: 2010-10-17
*/

#include "Time.h"
#include<iostream>
using namespace std;

Time::Time():hour(0),min(0),sec(0) {
// TODO Auto-generated constructor stub
cout<<"Time constructed!......"<<endl;

}

Time::Time(int h,int m,int s):hour(h),min(m),sec(s){
cout<<"U have design hour, min, sec......"<<endl;
}

Time::~Time() {
// TODO Auto-generated destructor stub
cout<<"Time deconstructed!......"<<endl;
}

void display(Time& t)
{
cout<<t.hour<<":"<<t.min<<":"<<t.sec<<endl;
}

~~TimeTest.cpp~~

#include<iostream>
#include"Time.h"
using namespace std;

int main()
{
Time firstTime;/*若写成Time firstTime();是不对的。默认构造函数的调用就是
Class class;*/
Time secondTime(10,20,30);
display(secondTime);
return  0;
}

Eclipse C++ IDE for Linux编译器的输出结果：
Time constructed!......
U have design hour, min, sec......
10:20:30
Time deconstructed!......
Time deconstructed!......