返回信息流在一个类中，我已经定义了友元函数，可在编译时确出错，说该函数无法使用该类的私有变量，这是怎么回事？
这是一条镜像帖。来源：北邮人论坛 / cpp / #29923同步于 2009/10/14
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CPP机器人发帖
[求助]友元函数无法调用私有变量，问题出在哪里？
zmw
2009/10/14镜像同步16 回复
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9 条回复
【 在 zmw 的大作中提到: 】
: 在一个类中，我已经定义了友元函数，可在编译时确出错，说该函数无法使用该类的私有变量，这是怎么回事？
代码拿出来，真相马上就有了
【 在 LOVEBABY 的大作中提到: 】
: 代码拿出来，真相马上就有了
#include <iostream>
using namespace std;
class DigitalTime
{
public:
friend bool operator == (const DigitalTime& time1, const DigitalTime& time2);
//bool operator == (const DigitalTime& time1);
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;
};
#include <iostream>
#include <cctype>
#include <cstdlib>
#include "dtime.h"
using namespace std;
void read_hour(istream& ins, int& the_hour);
void read_minute(istream& ins, int& the_mintue);
int digit_to_int(char c);
bool operator ==(const DigitalTime& time1, const DigitalTime& time2)
{
return (time1.hour == time2.hour && time1.minute == time2.minute);
}
DigitalTime::DigitalTime(int the_hour, int the_minute)
{
if (the_hour < 0 || the_hour > 23 || the_minute < 0 || the_minute > 59)
{
cout << "Illegal input.";
exit(1);
}
else
{
hour = the_hour;
minute = the_minute;
}
}
DigitalTime::DigitalTime() : hour(0), minute(0)
{
}
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;
}
void DigitalTime::advance(int hours_added, int minutes_added)
{
hour = (hour + hours_added)%24;
advance(minutes_added);
}
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 ( int(c) - int('0') );
}
void read_minute(istream& ins, int& the_minute)
{
char c1, c2;
ins >> c1 >> c2;
if (!(isdigit(c1) && isdigit(c2)))
{
cout << "Error illegal input\n";
exit(1);
}
the_minute = digit_to_int(c1)*10 + digit_to_int(c2);
if (the_minute < 0 || the_minute > 59)
{
cout << "Error illegal input\n";
exit(1);
}
}
void read_hour(istream& ins, int& the_hour)
{
char c1, c2;
ins >> c1 >> c2;
if (!(isdigit(c1) && (isdigit(c2) || c2 == ':') ) )
{
cout << "Error illegal input\n";
exit(1);
}
if (isdigit(c1) && 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\n";
exit(1);
}
}
if ( the_hour < 0 || the_hour > 23 )
{
cout << "Error illegal input\n";
exit(1);
}
}
【 在 zmw 的大作中提到: 】
: #include <iostream>
: using namespace std;
: class DigitalTime
: ...................
我能编译通过啊