c++ - 错误 : overloaded 'operator<<' must be a binary operator (has 3 parameters)

Question

我知道有很多这样的问题，但我找不到适合我的解决方案。

我正在尝试制作简单的分数计算器，它可以添加或减去任意数量的函数并将答案写为缩减分数。

示例:输入=3/2 + 4/8, 输出 =2

我正在尝试重载运算符以完成此操作。

所以在我尝试开发的程序中，输入由一个表达式组成，该表达式由运算符 + 或 - 分隔的分数组成。

表达式中分数的数量是任意的。

以下 6 行中的每一行都是有效输入表达式的示例:

1/2 + 3/4
1/2 -5/7+3/5
355/113
3    /9-21/    -7
4/7-5/-8
-2/-3+7/5

***我遇到的问题是，当我运行我的程序时，它有一个重载操作错误:*错误:重载 'operator<<' must be a binary operator(有 3 个参数)****

  /Users/Spicycurryman/Desktop/ECS40/hw1/fraction.cpp:61:22: error: overloaded 'operator<<' must be a binary operator (has 3 parameters)
  ostream& Fraction::operator<<(ostream &os, Fraction& n)
                     ^
/Users/Spicycurryman/Desktop/ECS40/hw1/fraction.cpp:80:22: error: overloaded 'operator>>' must be a binary operator (has 3 parameters)
  istream& Fraction::operator>>(istream &os, Fraction& n)

我不明白为什么这是一个错误。

我的以下代码如下:

CPP 文件

#include "Fraction.h"

Fraction::Fraction(int a, int b)
{

}
int Fraction::find_gcd (int n1, int n2) 
{
  int gcd, remainder;

  remainder = n1 % n2; 
  while ( remainder != 0 )
  {
    n1 = n2;
    n2 = remainder; 
    remainder = n1 % n2; 
  } 
  gcd = n2; 

  return (gcd);
}

void Fraction::reduce_fraction(int nump,  int denomp) 
{
  this->nump = nump;
  this->denomp = denomp; 
  int gcd;   
  gcd = find_gcd(nump, denomp);
  nump = nump / gcd;
  denomp = denomp / gcd;

    if ((denomp<0 && nump < 0 ))
    {
        denomp*=-1;
        nump*=-1;
    }
    else if (denomp < 0 &&  nump >0){
        denomp*=-1;

    }
    if ( denomp ==0) {
        throw invalid_argument( "Error: zero denominator" );
    }   
}



Fraction& Fraction::operator+(const Fraction& n) {
    denom = denomp * n.denom;
    numera = (nump * n.numera) + (n.denom * n.nump);
    return (*this);

}

Fraction& Fraction::operator-(const Fraction& n) {
    denom = denomp * n.denom;
    numera = (nump * n.numera) - (n.denom* n.nump);
    return (*this);
}

  ostream& Fraction::operator<<(ostream &os, Fraction& n)
{
    if (n.numera == 0)
    {
        cout << 0 << endl;
        return os;
    }
    else if (n.numera == n.denom)
    {
        cout << 1 << endl;
        return os;
    }
    else
    {
        cout << n.numera << '/' << n.denom << endl;
        return os;
    }
}

  istream& Fraction::operator>>(istream &os, Fraction& n)
{
    char slash = 0;
    return os >> n.numera >> slash >> n.denom;

}

头文件

#ifndef FRACTION_H
#define FRACTION_H
#include <iostream>
#include <stdexcept>
using namespace std;


class Fraction{

    public: 
    Fraction(int a, int b);
    int fraction(int a,int b);
    int find_gcd(int n1, int n2); 
    void reduce_fraction(int nump,  int denomp);
    Fraction& operator+(const Fraction& n);
    Fraction& operator-(const Fraction& n);
    friend ostream& operator<<(ostream &os, const  Fraction& n);
    friend istream& operator>>(istream &is, const Fraction& n);
private:
    int denom;
    int numera;
    int denomp;
    int nump;



};

#endif

主 CPP 文件

#include "Fraction.h"
#include <iostream>
using namespace std;

int main()
{
  Fraction x(2,3);
  Fraction y(6,-2);

  cout << x << endl;
  cout << y << endl;

  cin >> y;
  cout << y << endl;
  Fraction z = x + y;
  cout << x << " + " << y << " = " << z << endl;
}

我知道运算符是成员函数，成员函数采用隐式第一个参数，这意味着我的运算符现在采用三个参数，它可能被固定为非成员函数；但是，这在该程序中不起作用。在我的情况下，我将如何修复它以使程序正常工作？

非常感谢!

Answer 1

问题是你声明了 operator>>和 operator<<作为非成员函数，但定义为成员函数。

这应该可以解决该问题(但会引发另一组问题)。所以不是

  ostream& Fraction::operator<<(ostream &os, Fraction& n)
  {
     ...


  istream& Fraction::operator>>(istream &os, Fraction& n)
  {
     ...

实现为:

  ostream& operator<<(ostream &os, Fraction& n)
{
...

  istream& operator>>(istream &os, Fraction& n)
{
...

---

另外，请注意您将函数声明为:

friend ostream& operator<<(ostream &os, const  Fraction& n);
friend istream& operator>>(istream &is, const Fraction& n);

但定义为(因此您更改了签名):

  ostream& Fraction::operator<<(ostream &os, Fraction& n)
  istream& Fraction::operator>>(istream &os, Fraction& n)

正确的方法是声明和定义为:

  ostream& Fraction::operator<<(ostream &os, const Fraction& n)
  istream& Fraction::operator>>(istream &os, Fraction& n)

---

我只是添加更改。其余与问题相同:

class Fraction{
    friend ostream& operator<<(ostream &os, const  Fraction& n);
    friend istream& operator>>(istream &is, Fraction& n);
  // the rest is the same
};

ostream& operator<<(ostream &os, const Fraction& n)
{
    if (n.numera == 0)
    {
        cout << 0 << endl;
        return os;
    }
    else if (n.numera == n.denom)
    {
        cout << 1 << endl;
        return os;
    }
    else
    {
        cout << n.numera << '/' << n.denom << endl;
        return os;
    }
}

  istream&  operator>>(istream &os, Fraction& n)
{
    char slash = 0;
    return os >> n.numera >> slash >> n.denom;

}