Operator Overloading

You have probably heard the word operator before when talking about programming.

If you haven’t heard of it, don’t worry, you have used operators! Here are some examples of operators:

+ - * / % & || ~ -- ++ += >= <= < > [] -> new ! << >>

I would not be surprised if some of these are new to you! In this course, we have not used operators like ~ or -> yet!

Here are the general types of operators:

1. Arithmetic Operators -> used to perform arithmetic operations on variables and data (+ - * /).
2. Assignment Operators -> used to assign values to variables (= += *=).
3. Relational Operators -> used to check the relationship between two operands (== != > <).
4. Logical Operators -> used to check whether an expression is true or false (&& || !).
5. Bitwise Operators -> used to perform operations on individual bits. They can only be used alongside char and int data types. & | ^ ~ << >>
6. Misc. Operators -> sizeof ?: . & -> << >>

That’s all good and fun, but what if we want to change the way these operators behave or define operators for our custom types/classes/structs? Well, we do this with Operator Overloading.

IBM defines overloading operators as such:

“You can redefine or overload the function of most built-in operators in C++. These operators can be overloaded globally or on a class-by-class basis. Overloaded operators are implemented as functions and can be member functions or global functions.

An overloaded operator is called an operator function. You declare an operator function with the keyword operator preceding the operator. Overloaded operators are distinct from overloaded functions, but like overloaded functions, they are distinguished by the number and types of operands used with the operator.”

-IBM’s Website

Here’s an example of how to overload an operator that compares the sum of our CustomList type:

1. sum() is a member function defined in the CustomList class.

operator==(const CustomList &that) const {
	return this->sum() == that.sum() ? true : false;
}

operator!=(const CustomList &that) const {
	return this->sum() != that.sum() ? true : false;
}

We haven’t covered arrow syntax with pointers yet and most likely will not cover it in this course. But essentially, the code is comparing the sums of 2 CustomLists using the this keyword and another CustomList defined as that. These operators return a boolean value!

You can overload any type of operator even ++ or ~!