C++ - Difference Between Functors and Functions

In C++, we have multiple options to operate over the data like in the case where we can use functions and functors. Although both seem to be similar in a few ways but have multiple differences between them. Let's check the differences between functions and functors in C++.

What are functions?

Functions are pieces of code that can be called from any other part of a program. They are a way of organizing code so that it is reusable, and can be used to perform a specific set of operations. Functions can be defined in any programming language and are typically used to encapsulate a set of instructions that can be called multiple times.

Example:

#include <iostream>
using namespace std;
  
// Function definition
int add(int a, int b) 
{ 
   int c = a + b; 
   return c; 
} 
   
// Driver code 
int main() 
{ 
   int a = 5, b = 6; 
   int c = add(a, b); 
   cout << c; 
   return 0; 
}

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What are functors?

Functors, also known as function objects, are objects that behave like functions. They are a type of object that can be treated like a function and can be used to encapsulate a set of instructions. They are similar to functions in that they can be used to encapsulate a set of operations, but they are different in that they can store states and can be used in more complex ways.

Example:

#include <iostream>
using namespace std;

// Functor definition
struct Add {
    // Data members
    int a;

    // Constructor
    Add(int a)
        : a(a)
    {
    }

    // Function call operator
    int operator()(int b) { return a + b; }
};

// Driver code
int main()
{
    Add add(5);
    int c = add(6);
    cout << c;
    return 0;
}

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Difference between functions and functors