Overloaded 'operator++' must be a unary or binary operator (has 3 parameters)

Question

I have a header file and a .cpp file. I am trying to implement a prefix and postfix operator overload but I keep getting this error when setting up the overload.

fraction.h

#ifndef FRACTION_H
#define FRACTION_H

#include <iostream>

using namespace std;

class Fraction 
{
   public:
      Fraction();
      Fraction(int, int);
      int getTop() {return m_top;}
      int getBottom() {return m_bottom;}
      void set(int t, int b) {m_top=t; m_bottom=b; reduce();
      }

   protected:
   private:
      void reduce();
      int gcf(int, int);

      int m_top;
      int m_bottom;
};

Fraction& operator ++ (Fraction);
Fraction operator++(Fraction, int);

#endif

Main.cpp

#include <iostream>

using namespace std;
#include "fraction.h"

int main {
   cout << "The fraction is" << f;
   cout << "The output of ++f is " << (++f) << endl;
   cout << "The fraction is" << f;
   cout << "The output of f++ is " << (f++) << endl;
   cout << "The fraction is" << f;

   return 0;
}

Fraction& Fraction::operator ++ (Fraction){
   // Increment prefix
   m_top += m_bottom;
   return *this;
}

Fraction Fraction::operator ++ (Fraction, int){
   //Increment postfix
}

These are the two errors I get:

 prefix error: "Parameter of overloaded post-increment operator must have type 'int' (not 'Fraction')"

postfix error: "Overloaded 'Operator++' must be a unary or binary operator (has 3 parameters)"

Is the prefix error actually an error with my ide? I know it must be 'int' for post-increment, but I am trying to do a pre-increment. I use xcode.

Answer 1

You declared the operators outside the class as non-class functions

Fraction& operator ++ (Fraction);
Fraction operator++(Fraction, int);

however then you are trying to define them like class member functions

Fraction& Fraction::operator ++ (Fraction){
   // Increment prefix
   m_top += m_bottom;
   return *this;
}

Fraction Fraction::operator ++ (Fraction, int){
   //Increment postfix
}

Either declare them as class member functions the following way

class Fraction
{
public:
    Fraction & operator ++();
    Fraction operator ++( int );
    //...

And in this case the definition for example of the preincrement operator can look like

Fraction & Fraction::operator ++(){
   // Increment prefix
   m_top += m_bottom;
   return *this;
}

Or declare them as non-class function that are friends of the class because they need to have access to private data members of the class

class Fraction
{
public:
    friend Fraction & operator ++( Fraction & );
    friend Fraction operator ++( Fraction &, int );
    //...

And in this case the definition for example of the preincrement operator can look like

Fraction & operator ++( Fraction &f ){
   // Increment prefix
   f.m_top += f.m_bottom;
   return f;
}