Q6. Demonstrate Friend Function and Friend Class

Question:
Write program to demonstrate use of friend function and friend class.

My Approach

C++ me friend function aur friend class ek special feature hai jo encapsulation ke principle ko tod kar private/protected data ko access karne dete hain.

• Friend Function: Ek normal function jo kisi class ka friend declare hone par uske private/protected members ko directly access kar sakta hai.
• Friend Class: Agar ek class ko friend declare kar diya jaye, to wo dusri class ke private/protected members ko access kar sakti hai.

Ye real-world scenario me useful hota hai jab hume closely related classes ke beech data share karna ho bina unnecessary getter-setter banaye.

Program Code

File Name: friend_demo.cpp

#include <iostream>
using namespace std;
 
// ================= Friend Function Demo =================
class Box {
private:
    int length;
 
public:
    Box(int l) : length(l) {}
 
    // Friend Function declaration
    friend void printLength(Box b);
};
 
// Friend Function Definition
void printLength(Box b) {
    cout << "Length of the box: " << b.length << endl;
}
 
// ================= Friend Class Demo =================
class Engine {
private:
    int horsepower;
 
public:
    Engine(int hp) : horsepower(hp) {}
 
    // Declaring Car as a friend class
    friend class Car;
};
 
class Car {
public:
    void showEnginePower(Engine e) {
        cout << "Car engine horsepower: " << e.horsepower << " HP" << endl;
    }
};
 
// ================= Main Function =================
int main() {
    cout << "=== Friend Function Demo ===" << endl;
    Box b1(15);
    printLength(b1);  // Friend function accessing private member
 
    cout << "\n=== Friend Class Demo ===" << endl;
    Engine e1(120);
    Car c1;
    c1.showEnginePower(e1);  // Friend class accessing private member
 
    return 0;
}

Sample Input / Output

Output:

=== Friend Function Demo ===
Length of the box: 15

=== Friend Class Demo ===
Car engine horsepower: 120 HP

Explanation

1. Friend Function Example

   • printLength() ek normal function hai lekin Box class me friend declare kiya gaya hai.
   • Isliye wo Box ke private data member length ko directly access kar sakta hai.

2. Friend Class Example

   • Car class ko Engine class ke andar friend declare kiya gaya hai.
   • Is wajah se Car directly Engine ke private data member horsepower ko access kar pa rahi hai.

Real-Time Relevance

• Friend Function: Example – Agar ek class ke private members ko ek external utility function (like logger or printer) ko access karna ho bina getters banaye.
• Friend Class: Example – Car manufacturing system me Car aur Engine closely linked classes hain. Car ko engine ki internal details chahiye hoti hain, isliye Car ko Engine ka friend declare kiya jata hai.

Conclusion

Is program me dono concepts clearly demonstrate hote hain:

• Friend Function → private data access karne ke liye ek function.
• Friend Class → ek class ko dusri class ke private/protected data access karne ka adhikar.

Submitted by:
Intesab Ansari
MCA Student, NMU University
Portfolio: intesab.live