Overloading The Comparison Operators

Introduction

The comparison operators are all binary operators that do not modify their operands so we can make our overloaded comparison operators friend functions.

Examples

Example 1

class Point
{
private:
    double m_dX, m_dY, m_dZ;
 
public:
    Point(double dX=0.0, double dY=0.0, double dZ=0.0)
    {
    m_dX = dX;
    m_dY = dY;
    m_dZ = dZ;
    }
 
    friend ostream& operator<< (ostream &out, Point &cPoint);
    friend istream& operator>> (istream &in, Point &cPoint);
 
    double GetX() { return m_dX; }
    double GetY() { return m_dY; }
    double GetZ() { return m_dZ; }
};
 
ostream& operator<< (ostream &out, Point &cPoint)
{
    // Since operator<< is a friend of the Point class, we can access
    // Point's members directly.
    out << "(" << cPoint.m_dX << ", " <<
        cPoint.m_dY << ", " <<
        cPoint.m_dZ << ")";
    return out;
}
 
istream& operator>> (istream &in, Point &cPoint)
{
    in >> cPoint.m_dX;
    in >> cPoint.m_dY;
    in >> cPoint.m_dZ;
    return in;
}

Example 2

class Cents
{
private:
    int m_nCents;
 
public:
    Cents(int nCents) { m_nCents = nCents; }
 
    friend bool operator> (Cents &cC1, Cents &cC2);
    friend bool operator<= (Cents &cC1, Cents &cC2);
 
    friend bool operator< (Cents &cC1, Cents &cC2);
    friend bool operator>= (Cents &cC1, Cents &cC2);
};
 
bool operator> (Cents &cC1, Cents &cC2)
{
    return cC1.m_nCents > cC2.m_nCents;
}
 
bool operator<= (Cents &cC1, Cents &cC2)
{
    return cC1.m_nCents <= cC2.m_nCents;
}
 
bool operator< (Cents &cC1, Cents &cC2)
{
    return cC1.m_nCents < cC2.m_nCents;
}
 
bool operator>= (Cents &cC1, Cents &cC2)
{
    return cC1.m_nCents >= cC2.m_nCents;
}