error private within this context c++

Question

I think I have been working on this code too long. Anyway here is whats happening.

header file (scope of the project forbids changing public)

#ifndef FRACTION_
#define FRACTION_

using namespace std;

#include <iostream>

class Fraction
{
  private:

    int num,denom;


  public:

    // Construct fraction from numerator and denominator
    //
    Fraction( int = 0, int = 1 );

    // Construct fraction by copying existing fraction
    //
    Fraction( const Fraction& );

    // Assign into fraction by copying existing fraction
    //
    Fraction& operator=( const Fraction& );

    // Return true if fraction is valid (non-zero denominator)
    //
    bool IsValid() const;

    // Return value of numerator
    //
    int Numerator() const;

    // Return value of denominator
    //
    int Denominator() const;

    // Input/Output operations
    //
    friend istream& operator>>( istream&, Fraction& );
    friend ostream& operator<<( ostream&, const Fraction& );
};

// Comparative operations
//
bool operator==( const Fraction&, const Fraction& );
bool operator!=( const Fraction&, const Fraction& );
bool operator< ( const Fraction&, const Fraction& );
bool operator<=( const Fraction&, const Fraction& );
bool operator> ( const Fraction&, const Fraction& );
bool operator>=( const Fraction&, const Fraction& );

// Arithmetic operations
//
Fraction operator+( const Fraction&, const Fraction& );
Fraction operator-( const Fraction&, const Fraction& );
Fraction operator*( const Fraction&, const Fraction& );
Fraction operator/( const Fraction&, const Fraction& );

#endif

I am trying to overload the + operator, here is my code for that:

Fraction operator+(const Fraction &f1, const Fraction &f2)
{
    return(((f1.num*f2.denom)+(f1.denom*f2.num)),(f1.denom*f2.denom));
}

I get an error about referencing num and denom as private variable, I am just having a hard time figuring out how to correct that problem.

Answer 1

Use Numerator() instead of num and Denominator() instead of denom. Your operator is not a member, nor a friend, so it can't access private members.

The other option would be to

• make it a member (but making an operator that can be a free function a member has several disadvantages, including that you can't say 5 + frac, only frac + 5)
• make it a friend, (but making it a friend when it doesn't have to be increases the number of things that have access to the class not through its interface, leading to increased code maintenance)