Question

新手入门，求大神指导c++指导友元函数重载运算符问题。

#include<iostream.h>
class clock
{
int hour,minute,second;
public:
clock(int nh=0,int nm=0,int ns=0)
{ hour=nh;minute=nm;second=ns;}
void display();
friend void operator ++(clock c1);
friend void operator ++(clock c1,int);
};
void clock::display()
{
cout<<hour<<"-"<<minute<<"-"<<second<<endl;
}
void operator ++(clock c1)
{
second++;
if(second>=60)
{
second=0;
minute++;
if(minute>=60)
{ minute=0;
hour++;
hour=hour%24;
}
}
cout<<"++clock:";
}
void operator ++(clock c1,int)
{
second++;
if(second>=60)
{
second=0;
minute++;
if(minute>=60)
{ minute=0;
hour++;
hour=hour%24;
}
}
cout<<"clock++:";
}
void main()
{
clock myclock(23,59,59);
myclock.display();
++myclock;
myclock.display();
myclock++;
myclock.display();
}
D:\c++\Cpp1.cpp(20) : error C2065: 'second' : undeclared identifier
D:\c++\Cpp1.cpp(24) : error C2065: 'minute' : undeclared identifier
D:\c++\Cpp1.cpp(27) : error C2065: 'hour' : undeclared identifier

Answer 1

void operator ++(clock c1)
{
c1.second++;
if(c1.second>=60)
{
c1.second=0;
c1.minute++;
if(c1.minute>=60)
{ c1.minute=0;
c1.hour++;
c1.hour=c1.hour%24;
}
}
cout<<"++clock:";
}
这样就行了
都少了 对象名和一个点
即 c1.

Answer 2

不知道是不是因为你的second, minute, hour 都是private. 试试这个：
class clock
{
public:
int hour,minute,second;
clock(int nh=0,int nm=0,int ns=0)
{ hour=nh;minute=nm;second=ns;}
void display();
friend void operator ++(clock c1);
friend void operator ++(clock c1,int);
};