Operator Overloading in C++

In this lesson: Overload operators in C++ — +, ==, <<, [] — member vs friend functions, with examples and output. In Hindi & English.

What is operator overloading?

Operator overloading lets you teach operators like +, == and << how to work with your own classes. Instead of c3 = add(c1, c2), you can write c3 = c1 + c2 — your class starts to feel like a built-in type. It is a form of compile-time polymorphism.

How it works

You define a function named operator followed by the symbol. It can be a member (left operand is the object) or a non-member/friend (both operands are parameters).

Overloading +

#include <iostream>
using namespace std;
class Complex {
public:
    double re, im;
    Complex(double r, double i) : re(r), im(i) {}
    Complex operator+(const Complex &o) const {   // member
        return Complex(re + o.re, im + o.im);
    }
};
int main() {
    Complex a(1, 2), b(3, 4);
    Complex c = a + b;               // uses operator+
    cout << c.re << " + " << c.im << "i\n";
    return 0;
}

Overloading ==

bool operator==(const Complex &o) const {
    return re == o.re && im == o.im;
}
// now: if (a == b) ...

Overloading <<

To print with cout << obj, the left operand is the stream — so this must be a non-member, usually a friend:

friend ostream& operator<<(ostream &os, const Complex &c) {
    os << c.re << " + " << c.im << "i";
    return os;                       // return stream for chaining
}
// now: cout << a << "\n";

Member vs friend

For a compact syntax reference and a full worked class, see the operator overloading syntax page.

Rules and limits

• You cannot invent new operators or change their precedence/arity.
• A few cannot be overloaded: ::, ., .*, ?:, sizeof.
• Keep the meaning intuitive — + should add, not subtract.

Common mistakes

• Making operator<< a member (the stream must be the left operand).
• Forgetting to return the stream from operator<<.
• Giving an operator a surprising meaning that confuses readers.
• Returning a reference to a local object from an operator.

Summary

• Operator overloading gives operators custom meaning for your classes.
• Define a function named operator plus the symbol.
• Members take the left operand as the object; friends take both.
• << must be a non-member/friend and return the stream.
• A few operators cannot be overloaded; keep meanings intuitive.