C++ Operator Overloading

In this C++ tutorial, you will learn about Operator Overloading, how to use Operator Overloading in custom classes to overload a builtin operator and specify your own custom code of operation, with examples.

C++ Operator Overloading in C++

Operator Overloading in C++ is the process of defining a custom logic for an operator to work for user defined classes.

We are already familiar with Operator Overloading, but are not conscious about it. For example, we use + operator to concatenate two strings. Here, + operator is overloaded with a definition to concatenate strings when + is used with two string type objects.

Another example would be complex numbers. When we use + operator to add two complex numbers, only the respective real and complex parts are added.

Syntax

The syntax to overload operator + for class A, where + operator returns nothing, is

class A {
public:
    void operator + (A const &a) {
        // logic
    }
};

The syntax to overload operator + for class A, where + operator returns an object of type A, is

class A {
public:
    A operator + (A const &a) {
        A result;
        // logic
        return result;
    }
};

The definition for Operator Overloading starts with return type, followed by operator keyword, then the operator symbol, then the right operand. The logic is enclosed in flower braces just like a member function.

Examples

1. Overload single operator

In the following example, we define a class A. For this class, we overload operator + for objects of type A using Operator Overloading.

C++ Program

#include <iostream>
using namespace std;

class A {
public:
    int x;
    A(int _x = 0) {
        x = _x;
    }
    A operator + (A const &a) {
        A result;
        result.x = x + a.x;
        return result;
    }
};

int main() {
    A a1(4);
    A a2(5);
    A result = a1 + a2;
    cout << "Result : " << result.x << endl;
}

Output

Result : 9
Program ended with exit code: 0

2. Overload Multiple Operators

In the following example, we define a class Log for logarithmic objects. For this class, we overload operator + and -.

C++ Program

#include <iostream>
using namespace std;

class Log {
public:
    double x;
    Log(int _x = 0) {
        x = _x;
    }
    Log operator + (Log const &a) {
        Log result;
        result.x = x * a.x;
        return result;
    }
    Log operator - (Log const &a) {
        Log result;
        result.x = x / a.x;
        return result;
    }
};

int main() {
    Log a1(4);
    Log a2(5);
    Log logAdd = a1 + a2;
    cout << "log 4 + log 5 = log " << logAdd.x << endl;
    Log logSub = a1 - a2;
    cout << "log 4 - log 5 = log " << logSub.x << endl;
}

Output

log 4 + log 5 = log 20
log 4 - log 5 = log 0.8
Program ended with exit code: 0

Conclusion

In this C++ Tutorial, we learned what Operator Overloading is, and how to use Operator Overloading to define custom logic for operations on user defined class objects, with the help of examples.