Friend Class in C++

 

Friend Class in C++

Definition

A friend class in C++ is a class that has access to the private and protected members of another class. Normally, private and protected members of a class are only accessible to the class's own methods or friends. To make a class a friend of another class, we use the keyword friend inside the class definition.

 

Why Do We Use Friend Classes?

We use a friend class to allow another class access to private or protected members of a class without making it a subclass or adding numerous getter and setter functions.

 

Need for Friend Classes

1.      Access Private Data: A friend class can work directly with private or protected members of another class.

2.      Convenience: Eliminates the need for additional public methods to expose private data.

3.      Specialized Use: Useful in scenarios where two or more classes need close collaboration and data sharing.

 

Advantages of Friend Classes

1.      Direct Access: The friend class has direct access to private and protected members of the other class.

2.      Simplifies Design: Reduces the need for additional public functions to share data between classes.

3.      Improves Collaboration: Facilitates close interaction between two tightly coupled classes.

  

Disadvantages of Friend Classes

1.      Breaks Encapsulation: It violates the principle of data hiding by allowing private data to be accessed directly.

2.      Tight Coupling: Increases dependency between classes, making the design harder to maintain.

3.      Not Inherited: Friendship is not inherited, so derived classes do not automatically gain access.

 

Example of a Friend Class

#include <iostream>

using namespace std;

 

class abc {

private:

    int sal = 40000;

protected:

    int pm = 5000;

public:

    friend class AjaySir;

};

 

class AjaySir {

public:

    void show(abc &obj) {

        cout << "Salary is " << obj.sal << endl;

                   cout<<"Pocket Money is " << obj.pm << endl;

    }

};

 

int main() {

    abc o1;

    AjaySir f1;

    f1.show(o1);

    return 0;

}

 

 

How Friend Classes Work?

• Declared as a friend inside the class definition.
• The friend class gains access to all private and protected members of the class.
• Methods of the friend class use the object of the original class to interact with private data.

 

Key in mind at the time of interview:

• Friendship is not mutual: If Class A declares Class B as a friend, Class B does not automatically make Class A its friend.
• Friendship is not transitive: If Class A is a friend of Class B and Class B is a friend of Class C, it doesn’t mean Class A is a friend of Class C.
• Friendship is not inherited: A derived class of a friend class does not automatically gain friendship.

 

Real-Life Example

A house with locked rooms (private data) is accessible only to the owner (class methods). However, the owner can give a trusted family (friend class) complete access to the house. Members of the family can then access the private areas directly.

For instance, AjaSir (friend class) has access to your private and protected data to manage tasks efficiently.

 

When to Avoid Friend Classes?

1.      When getters and setters can achieve the same functionality.

2.      When excessive use of friend classes complicates the design and violates the principle of encapsulation

 

 

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