C++ Operator Overloading

C++ compiler can use operators on basic types such as int, float and string. When you create a custom class and try to use an operator, the compiler does not know how to deal with provided information. Here is where operator overloading comes in. C++ allows operator overloading for specific types - effectively you can define custom behaviors for a wide range of operators.

In this example, I use a custom Point class which has x and y values. Shown operators (+,-,*,/,>,<,>>,<<) are altered to exhibit a particular behavior as to compare those values.

//overloading operators

#include "stdafx.h" //-- for Visual Studio only
#include <iostream>
#include <string>

using namespace std;

class Point {

 int _x, _y;

public:
 Point(int x, int y) :
  _x(x), _y(y) {
 }

 int x() const {
  return _x;
 }

 int y() const {
  return _y;
 }
 
 bool operator > (const Point &p)const {
  return (_x + _y) > (p._y + p._y);
 }

 bool operator < (const Point &p)const {
  return (_x + _y) < (p._x + p._y);
 }

 bool operator == (const Point &p)const {
  return (_x == p._x) && ( _x == p._y);
 }

 friend ostream& operator << (ostream& os,const Point &p) {
  os << "(" << p._x << "," << p._y << ")";
  return (os);
 }
 
 friend istream& operator >> (istream &input, Point &p)
 {
  input >> p._x;
  input >> p._y;
  return input;
 }

 Point operator = (Point &p) {
  _x=p._x;
  _y=p._y;
  return *this;  
 }

 Point operator + (const Point &p) const {
  return Point(_x+p._x, _y+p._y);
 }

 Point operator - (const Point &p)const {
  return Point(_x-p._x, _y-p._y);
 }

 Point operator * (const Point &p)const {
  return Point(_x * p._x, _y * p._y);
 }

 Point operator / (const Point &p)const {
  //---check for denominator - 0
  if (p._y == 0)return Point(0, 0);
  return Point(_x / p._x, _y / p._y);
 }
};

int main()
{

 Point alpha(2,2), beta(4,4), gamma(8,8);
 cout << "3 points (custom class)" << endl;
 cout << endl;
 cout << alpha << " alpha" << endl;
 cout << beta << " beta" << endl;
 cout << gamma << " gamma" << endl;
 cout << endl;
 cout << "overloaded operators (+,-,*,/,>,<,>>,<<)" << endl;
 cout << endl;
 cout << (alpha + beta) << " alpha + beta" << endl;
 cout << (alpha + beta + gamma) << " alpha + beta + gamma" << endl;
 cout << (alpha - beta) << " alpha - beta" << endl;
 cout << (alpha * beta) << " alpha * beta" << endl;
 cout << (beta / alpha) << " alpha / beta" << endl;
 cout << (alpha > beta) << "  is alpha bigger than beta (0=false)" << endl;
 cout << (alpha < beta) << "  is alpha smaller than beta (1=true)" << endl;
 cout << endl;
 cout << "3 Points (unaltered after using operators)" << endl;
 cout << endl;
 cout << alpha << " alpha" << endl;
 cout << beta << " beta" << endl;
 cout << gamma << " gamma" << endl;

 cin.get();

    return 0;
}