How to Overload the Less-Than (<) Operator in C++?

In C++ we have an operator called less than operator (<) which checks if the left side operand is smaller than the right side operand or not. In this article, we will learn how to overload the less-than operator in C++.

Overloading Less-Than Operator in C++

In C++, we can overload the less-than operator using the operator function declared as shown:

Syntax to Overload Less-Than Operator

bool operator<(const className& right) const;

Here, className is the name of the class and right is the name of the right-hand side operand.

C++ Program to Overload Less-Than Operator

The below program demonstrates how we can overload less-than operators using operator overloading in C++.

C++

// C++ program to overload the less than < operator
#include <iostream>
using namespace std;

// creating class Coordinates
class Coordinates {
public:
    // constructor
    Coordinates(int x, int y)
        : x(x)
        , y(y)
    {
    }

    // Overloading the less-than operator for the Point
    // objects
    bool operator<(const Coordinates& other) const
    {
        return (x < other.x)
               || ((x == other.x) && (y < other.y));
    }

private:
    int x, y;
};

int main()
{

    // initializing two coordinates p1 and p2
    Coordinates p1(1, 2);
    Coordinates p2(3, 4);

    // checking if p1 is less than p2
    if (p1 < p2) {
        cout << "p1 is less than p2." << endl;
    }
    else {
        cout << "p1 is not less than p2." << endl;
    }
    return 0;
}

Output

p1 is less than p2.

Explanation: In the above example, we are overloading the less than (<) operator to compare between the given points for that we first compare the x coordinates of two Points p1 and p2 and if they are equal then we compare the y coordinates, and return the smaller one.