FRIEND FUNCTIONS IN C++

 FRIEND FUNCTIONS IN C++

 A friend function is a non-member function that is given special permission to access the private and protected members of a class.

Normally, only member functions of a class can access private data.
But a friend function breaks this rule safely for special cases.

---

Syntax

A friend function is declared inside the class using the keyword friend, but its definition is outside the class.

 class ClassName {

private:

    int a;

public:

    friend void showData(ClassName obj);  // Declaration

};

Outside class:

void showData(ClassName obj) {

    cout << obj.a;

}

---

 

Key Properties

Property	Explanation
Not a member	Friend function is NOT a member of class.
Can access private/protected	But it is allowed to access private and protected data.
Called normally	It is NOT called using objectName.function().
Uses objects as parameters	It uses object(s) as arguments to access data.
Can belong to multiple classes	A single friend function can be friend of many classes.

 

Example

#include <iostream>

using namespace std;

 

class Sample {

private:

    int x;

public:

    Sample(int val) { x = val; }

 

    friend void show(Sample s);   // friend declaration

};

 

void show(Sample s) {

    cout << "Value of x = " << s.x;  // Accessing private data

}

 

int main() {

    Sample obj(10);

    show(obj);

}

 

Output:

Value of x = 10

---

Use Cases of Friend Functions

1. When operator overloading requires access to private members

2. When two different classes need to share private data

3. When we need non-member functions that still work closely with a class

4. To increase performance

 

---

Friend Function vs Member Function

Member Function	Friend Function
Always belongs to class	Not part of class
Called using object	Called normally like a normal function
Can access private data	Can access private data
Has this pointer	No this pointer
Needs object to call	Needs object only if required as parameter

---

 

Advantages of Friend Functions

Access private data

Useful for debugging, comparison, or complex logic.

More flexibility

Can operate across two or more classes.

Useful in operator overloading

Especially stream operators.

---

 

Disadvantages of Friend Functions

Breaks encapsulation

Allows external functions to access private data.

Hard to maintain

Excessive use reduces object-oriented design.

Cannot be inherited

Friendship is not inherited.

---