我该如何清除错误 [英] How can I clear the error

问题描述

当我在下面运行代码时，我收到'class fraction'没有名为'inc'的成员

我想以朋友的身份运行所有功能。

请建议



我尝试过：

When I run the code on below, I recieve 'class fraction' has no member named 'inc'
I want to run all functions as friend.
Please advice

What I have tried:

#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)const;
long getDen (void)const;
void print  (void);
friend fraction add (const fraction &, const fraction &);
friend fraction sub (const fraction &, const fraction &);
friend fraction mult(const fraction &, const fraction &);
friend fraction div (const fraction &, const fraction &);
friend fraction inc (const 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) const
{
  return den ;
}
long fraction::getnum (void) const
{
  return num ;
}
void fraction:: print (void)
{
    if(den==0)
       den=1L;
    cout<<num<<"/"<<den <<endl;
}
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);
}
fraction sub ( 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);
}
fraction mult ( const fraction &f1,  const fraction &f2)
{
 long num = (f1.getnum ( ) * f2.getnum ( ));
 long den = (f1.getDen ( ) * f2.getDen ( ));
 return fraction(num, den);
}
fraction div( const fraction &f1,  const fraction &f2)
{
long num = (f1.getnum ( ) * f2.getDen ( ));
long den = (f1.getDen ( ) * f2.getnum ( ));
return fraction(num, den);
}
fraction inc (const fraction &f1)
{
return add(f1,fraction(1,1));
}
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;
}

推荐答案

您已为操作声明了成员函数，但未提供定义（实现）。您现有的实现是全局函数，而不是 fraction 类的成员函数（全局函数在定义时声明）。



如果您只有 inc，那么您在没有参数的情况下调用 inc（） （const fraction&）。所以你必须使用 inc（f1）而不是 f1.inc（）。



但是为了连接操作，必须在对象上执行它们并更改内容。因此，添加缺少的成员函数定义，省略一个参数：

You have declared member functions for the operations but did not provide definitions (implementations). Your exiting implementations are global functions and not member functions of the fraction class (the global functions are declared when defined).

Also you are calling inc() without parameter while you only have a inc(const fraction &). So you would have to use inc(f1) instead of f1.inc().

But to concatenate operations they must be performed on the object and change the content. So add the missing member function definition(s) omitting one parameter:

class fraction
{
    // ...
    fraction inc();
};

fraction fraction::inc()
{ 
    *this = inc(*this);
    return *this; 
}

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