C++ friend function

In this post, you will learn everything there is to know about the friend function in C++, including an example program and a step-by-step explanation of the code.

What exactly is the friend function?

A friend function is a class function that has the same access as a class's member functions. The friend function, however, is not a member function. If the keyword "friend" is used before any function declared within the class, that function will be referred to as the "friend" function.

Where is the friend function declared?

Inside the class where a member function of the same class is declared, a friend function is declared. However, the friend function is not a member of the class to which it belongs (or where it is declared).

To declare a function as a friend function, use the friend keyword. Alternatively, use this keyword before the function name. As an example,

friend void myFun();

The friend function is defined outside the class (where it is declared). To define a friend function, the friend keyword is not required. This keyword is required only while declaring the function inside the class.

Why is the keyword "friend" used?

It is used to tell the compiler that it is not a member function of the class. Rather, it is a friend function. Because if you remove the keyword "friend," then this function gets processed by the compiler as a member function of the class.

How to call the "Friend" function

The friend function cannot be called on any object, or the friend function has no caller object. because it is not a member function of the class where it is declared. And, when defining the function, there is no membership label attached. Therefore, to call this function from the main() function, just call it as a normal function call.

Why would you use the friend function?

In a big project, there are a lot of programmers who work for the same project. Therefore, using the friend function, one programmer can access the private data of members of the class defined by another programmer.

For example, suppose a programmer named James wants to access the private data of a member of a class that is defined by another programmer named Ricky. So, Ricky declares a friend function inside the class defined by him and tells the name of this function to his friend James, who works for the same project. Now James can use this function to access private data for members of the class defined by Ricky.

Step-by-Step Explanation of the C++ Friend Function

Now let's take an example that multiplies any two numbers entered by the user. There is a friend function in this program. Let's have a look at the program; later, I'll explain each and everything that goes inside the program in a step-by-step manner.

using namespace std;

class CodesCracker
      int m, n, res;
      void getData()
         cout<<"Enter two numbers: ";
      void showResult()
         cout<<"\nResult = "<<res;
      friend void mulFun(CodesCracker &c);
int main()
   CodesCracker ob;
   return 0;
void mulFun(CodesCracker &x)
   x.res = (x.m) * (x.n);

This program was built and runs under the Code::Blocks IDE. The snapshot given below shows a sample run of the above program:

CPP friend function example

Now supply two numbers, say 5 and 6. Press the ENTER key to see the output as shown in the following snapshot:

CPP friend function program

Here is a step-by-step explanation of the previous program:

C++ Quiz

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