🟣 OOP · Lesson 44

Friend Function and Friend Class

What is Friend Function and Friend Class?

Friend Function and Friend Class
A friend function or class can access private and protected members of another class. It should be used carefully because it reduces strict encapsulation.

Level
🟣 Object-Oriented Programming

Example File
friend-functions.cpp

Main Focus
Concept + syntax + practical C++ program

Why should you learn this?

It helps you write correct and readable C++ programs.
It is used repeatedly in school practicals, projects and competitive programming.
It builds the base for advanced topics such as OOP, STL and data structures.

Important Terms

Term	Meaning / Use
friend	Friend used in Friend Function and Friend Class programming.
private access	Private access used in Friend Function and Friend Class programming.
non-member function	Non-member function used in Friend Function and Friend Class programming.
controlled access	Controlled access used in Friend Function and Friend Class programming.

Syntax / Pattern

friend return_type functionName(ClassName obj);

Example Program

#include <iostream>
using namespace std;
class Box{
    int length = 10;
    friend void show(Box b);
};
void show(Box b){ cout << b.length; }
int main(){ Box b; show(b); }

Expected Output

Program Explanation

show() is not a member function.
Because it is friend, it can access private length.

Exam Tip: In C++ practical answers, write the logic first, then the program, then expected output. For theory, always include one suitable example.

Where will you use it?

operator overloading
closely related classes
utility functions

Common Mistakes

Using friend everywhere.
Thinking friend is inherited automatically.

Practice Tasks

Create friend function to add private values of two objects.
Explain why friend should be limited.

Summary

Friend Function and Friend Class is an important C++ topic. Learn the definition, understand the syntax, run the example program and then solve the practice tasks to make the concept strong.