这是咋回事啊?友元函数和私有变量问题

[selooloo]

代码如下:

#include <iostream>
#include <cctype>
#include <cstdlib>
//#include "dtime.h"
using namespace std;

class DigitalTime
{
    public:
        friend bool operator ==(const DigitalTime &time1,const DigitalTime& time2);
        DigitalTime(int the_hour,int the_minute);
        DigitalTime();
        void advance(int minutes_added);
        void advance(int hours_added,int minutes_added);
        friend istream& operator >>(istream& ins,DigitalTime the_object);
        friend ostream& operator <<(ostream& outs,const DigitalTime the_object);
    private:
        int hour;
        int minute;
};

void read_hour(istream& ins,int& the_hour);
void read_minute(istream& ins,int& the_minute);
bool operator ==(const DigitalTime& time1,const DigitalTime& time2)
{
    return (time1.hour==time2.hour && time2.minute==time2.minute);
}

DigitalTime::DigitalTime(int the_hour,int the_minute)
{
    if(the_hour<0 || the_minute<0)
    {
        cout<<"Illegal time!\n";
        system("pause");
        exit(1);
    }
    hour=the_hour;
    minute=the_minute;
}

DigitalTime::DigitalTime():hour(0),minute(0)
{}

void DigitalTime::advance(int hours_added,int minutes_added)
{
    int new_hours,new_minutes;
    new_minutes=minute+minutes_added;
    minute=new_minutes%60;
    new_hours=hour+hours_added+new_minutes/60;
    hour=new_hours%24;
}

void DigitalTime::advance(int minutes_added)
{
    int gross_minutes=minute+minutes_added;
    minute=gross_minutes%60;
    int hour_adjustment=gross_minutes/60+hour;
    hour=hour_adjustment%24;
}

ostream& operator <<(ostream& outs,const DigitalTime& the_object)
{
    outs<<the_object.hour<<":";
    if(the_object.minute<10)
    outs<<'0';
    outs<<the_object.minute;
    return outs;
}

istream& operator >>(istream& ins,DigitalTime& the_object)
{
    read_hour(ins,the_object.hour);
    read_minute(ins,the_object.minute);
    return ins;
}

int digit_to_int(char c)
{
    return (c-'0');
}

void read_hour(istream& ins,int& the_hour)
{
    char c1,c2;
    ins>> c1>>c2;
    if(!(isdigit(c1) && isdigit(c2) || c2==':'))
    {
        cout<<"Error illegal input to read_hour.\n";
        system("pause");
        exit(1);
    }
    if(c2==':')
    the_hour=digit_to_int(c1);
    else
    {
        the_hour=digit_to_int(c1)*10 + digit_to_int(c2);
        ins>>c2;
        if(c2!=':')
        {
        cout<<"Error illegal input to read_minute.\n";
        system("pause");
        exit(1);
        }
    }
    if(the_hour>24 || the_hour<0)
    {
        cout<<"Error illegal input to read_hour.\n";
        system("pause");
        exit(1);
    }
}

void read_minute(istream& ins,int& the_minute)
{
    char c1,c2;
    if(!isdigit(c1) || !isdigit(c2))
    {
        cout<<"Error illegal input to read_minute.\n";
        system("pause");
        exit(1);
    }
    the_minute=digit_to_int(c1)*10 + digit_to_int(c2);
    if(the_minute<0 || the_minute>60)
    {
        cout<<"Error illegal input to read_minute.\n";
        system("pause");
        exit(1);
    }
}
    

错误如下：

15 D:\dev\c++\dtime.h
`int DigitalTime::hour' is private
16 D:\dev\c++\dtime.h
`int DigitalTime::minute' is private

别的函数都可以访问私有变量，就
friend istream& operator >>(istream& ins,DigitalTime the_object);
friend ostream& operator <<(ostream& outs,const DigitalTime the_object);
这两个函数不行，实在是蹊跷，眼睛快看爆掉了也没看有出啥错误，各位帮帮忙

[pengzhixi]

const DigitalTime &//这个必须的

[pur_e]

你声明的时候没用引用，实现的时候用了
声明：friend istream& operator >>(istream& ins,DigitalTime the_object);
实现：istream& operator >>(istream& ins,DigitalTime& the_object)


被编译器认为是两个不同的函数吧，应该是，实现的那个函数不是友元

[hlyces]

friend istream& operator >>(istream& ins,DigitalTime the_object);
friend ostream& operator < <(ostream& outs,const DigitalTime the_object);

///没错才怪了，你改变的是DigitalTime the_object

[Vegertar]

观察两个重载的第二参数，声明与定义不一致

[kim_jinye]

up

[tanleihexinxin]

friend istream& operator >>(istream& ins,DigitalTime &the_object);
friend ostream& operator <<(ostream& outs,const DigitalTime &the_object);

[selooloo]

晕，老眼昏花了，结贴