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What Is A Function Object Functor In C++?

What Is A Function Object Functor In C++

In modern C++ programming we can use many different ways to call functions. One of the features from C11 is functor, an early function object in C++. The functor function objects are callable objects. A functor or function object is any object for which the function call operator is defined. Let’s learn what a functor is and how we can use a functor in C++.

What is a functor in C++?

A functor is an object that can be used as a function or function pointer by using operator(), this term is not same as function term in programming. We can pass many arguments with them; thus, we don’t need to define many global variables, we can use these kinds of variables in the scope that we use.

Here is the syntax how we can use define a functor by using function call operator operator(),

Is there a simple example of how to run a functor object with std::thread in C++?

We can create operators as shown below in our simple functor example. This simple rectangle example function object returns its area as below.

in this example, we can use its initial values to calculate its area by using our functor like so:

Is there a full example of how to run a functor object with std::thread in C++?

Here is a full example of how to run a functor object with std::thread in C++.

and the output will be as follows,

The function objects are callable objects, and they are enhanced by the new standard library features in C++17 (std::invoke), C++20 (jthread), C++23 (invoke_r, move_only_function) , and in the next C++26 (copyable_function).

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About author

Dr. Yilmaz Yoru has 35+ years of coding with more than 30+ programming languages, mostly C++ on Windows, Android, Mac-OS, iOS, Linux, and some other operating systems. He graduated and received his MSc and PhD degrees from the Department of Mechanical Engineering of Eskisehir Osmangazi University. He is the founder and CEO of ESENJA LLC Company. His interests are Programming, Thermodynamics, Fluid Mechanics, Artificial Intelligence, 2D & 3D Designs, and high-end innovations.
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