Question

我一直在尝试为分数类的私有成员分配一个值，但是我被卡在ADD函数（友谊过程）并且每次都得到以下错误。

错误：＆＃39; num＆＃39;未在此范围内声明

#include <iostream>
#include <string.h>
using namespace std;

class fraction
{
 long num;
 long den;

 public:
 fraction ();
 fraction(long,long);
 fraction(const fraction&);
~fraction();
long getnum (void);
long getDen (void);
void print  (void);
friend void add (const fraction &, const fraction &);
void sub  (fraction, fraction);
void mult (fraction, fraction);
void div  (fraction, fraction);
void inc  (fraction);
};
fraction::fraction(long l_num,long l_den )
{
  num = l_num ;
  den = l_den ;
}
fraction::fraction( )
{
  num = 0L ;
  den = 1L ;
}
fraction::fraction(const fraction& F)
{
    num=F.num;
    den=F.den;
}
fraction:: ~fraction ( )
{
//  cout<<"Destructor"<<endl;
}
long fraction::getDen (void)
{
  return den ;
}
long fraction::getnum (void)
{
  return num ;
}
void fraction:: print (void)
{
    if(den==0)
       den=1L;
    cout<<num<<"/"<<den <<endl;
}
void add( fraction &f1,  fraction &f2)
{
  num = (f1.getnum ( ) * f2.getDen ( )) + ( f1.getDen ( ) * f2.getnum ( ) );
  den = (f1.getDen ( ) * f2.getDen ( ));
}
void fraction::sub (fraction f1, fraction f2)
{
  num = (f1.getnum ( ) * f2.getDen ( )) - ( f1.getDen ( ) * f2.getnum ( ) );
  den = (f1.getDen ( ) * f2.getDen ( ));
}
void fraction::mult (fraction f1, fraction f2)
{
  num = (f1.getnum ( ) * f2.getnum ( ));
  den = (f1.getDen ( ) * f2.getDen ( ));
}
void fraction::div(fraction f1, fraction f2)
{
num = (f1.getnum ( ) * f2.getDen ( ));
den = (f1.getDen ( ) * f2.getnum ( ));
}
void fraction::inc (fraction f1)
{
  num = (f1.getnum ( )) + ( f1.getDen ( ) );
  den = (f1.getDen ( ) );
}
int main()
{
fraction f1,f2(5L,0L);
fraction f3(f2);
f1.print();
f2.print();
f3.print();

f3 = add(f3 , fraction (-7,8) );
f1 = add(f2,f3);
f1.print ();

f1 = sub(f2 , f3);
f1.print();

f1 = mult(f2, f3);
f1.print();

f1.inc ().inc().print();
f1=div(f2 , f3 );
f1.print();

return 0;
}

Answer 1

C ++中的成员函数可以访问成员变量，而无需在它们之前显式指定this.。您可以在代码中利用这一点。但是，朋友的功能不能。在朋友函数中，您需要指定f1.num或f2.num（或您要更改的任何分数实例），而不仅仅是num。

Answer 2

您可以这样设计[root@ip-172-31-60-222 system]# systemctl daemon-reload [root@ip-172-31-60-222 system]# systemctl restart celery [root@ip-172-31-60-222 system]# systemctl status celery.service -l ● celery.service - datasidekick celery service Loaded: loaded (/etc/systemd/system/celery.service; enabled; vendor preset: disabled) Active: failed (Result: start-limit) since Wed 2017-03-01 04:16:33 UTC; 900ms ago Process: 22969 ExecStart=/home/datasidekick/datasidekick/newrelic.ini newrelic-admin run-program /home/datasidekick/datasidekick/venv/bin/celery -A datasidekick worker -l info -c 4 (code=exited, status=203/EXEC) Main PID: 22969 (code=exited, status=203/EXEC) Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: Unit celery.service entered failed state. Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: celery.service failed. Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: celery.service holdoff time over, scheduling restart. Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: start request repeated too quickly for celery.service Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: Failed to start datasidekick celery service. Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: Unit celery.service entered failed state. Mar 01 04:16:33 ip-172-31-60-222.ec2.internal systemd[1]: celery.service failed.功能：

add

fraction add( const fraction &f1, const fraction &f2) { long num = (f1.getnum ( ) * f2.getDen ( )) + ( f1.getDen ( ) * f2.getnum ( ) ); long den = (f1.getDen ( ) * f2.getDen ( )); return fraction(num, den); }如果以这种方式使用，则不再需要add函数。

您必须对getter函数进行更多编辑：

friend

请注意，您以这种方式使用long fraction::getDen (void) const { return den ; } long fraction::getnum (void) const { return num ; }：

add

因此，从f1 = add(f2,f3);返回空格对你没有帮助。

话虽如此，您应该在代码中看到其他错误

将值赋给类的私有成员变量

2 个答案: