C++ allows you to over-load existing operator as along as it involves at least one object.

For example, if a Complex class if defined to represent complex, numbers, it will be possible to give meaning to expressions such as:

• a+b
• a-b
• a * b
• a/b where a,b are Complex objects

Over-definition of Operators

Let's consider a Point class, and suppose that we want to define the operator + in order to give meaning to an expression such as a + b, when a and b are Point type. The agreement adopted by C++ to over-define this operator is to define a function named: operator +.

• This function must haver two Point type arguments and provide a return vale of the same type.
• This function may be a member of the class or an independent function (a friendly function)

In general, when multiple operators are combined within the same expression (whether they are over defined or not), they retain relative priority and association. All operators can be over-defined except '.', '::', '?:'.

Over-definition with a friendly function

Operator over-definition with a friendly function is based on:

• prototype of the operator + function: Point operator + (Point, Point) ;
• a declaration of friendship within the Point class;
• definition of the function

#include <iostream>
using namespace std ;
class Point {
    int x, y ;
    public :
    Point (int abs=0, int ord=0) { x=abs ; y=ord ;} // constructor
    friend Point operator+ (Point, Point) ;
    void display() { cout << " Coordinates : " << x << " " << y << "\n" ; }
} ;
Point operator + (Point a, Point b) {
    Point p ;
    p.x = a.x + b.x ; p.y = a.y + b.y ;
    return p ;
}
int main() {
    Point a(1,2) ; a.display() ;
    Point b(2,5) ; b.display() ;
    Point c ;
    c = a+b ; c.display() ;
    c = a+b+c ; c.display() ;
    return 0;
}
// ----------------------------Code Output--------------------------------------
// Coordinates : 1 2
// Coordinates : 2 5
// Coordinates : 3 7
// Coordinates : 6 14