C++ Friend Functions

A friend function in C++ is a function that is not a member of a class, but has the ability to access the private and protected members of that class. It is declared inside the class using the keyword friend.

About Friend Functions

1. A friend function is not a member of the class.

2. It can access private and protected members of the class.

3. It is often used when a function needs to operate on multiple classes or interact with private members of a class, but doesn’t belong to the class itself.

Example:


#include <iostream>
using namespace std;

class Employee {
private:
    string name;
    int age;

public:
    // Constructor to initialize values
    Employee(string n, int a) : name(n), age(a) {}

    // Friend function declaration
    friend void displayEmployeeInfo(Employee emp);
};

// Friend function definition
void displayEmployeeInfo(Employee emp) {
    cout << "Name: " << emp.name << endl;  // Accessing private member 'name'
    cout << "Age: " << emp.age << endl;    // Accessing private member 'age'
}

int main() {
    // Creating a Employee object
    Employee employee("John", 35);

    // Calling the Employee function
    displayEmployeeInfo(employee);  // This can access the private members of 'Employee'

    return 0;
}

Output:

Name: John
Age: 35

Explanation:

1. Employee Class:

It has two private data members: name and age.
It has a constructor to initialize these members.

2. Friend Function displayEmployeeInfo():

This function is declared as a friend of the Employee class, meaning it can access the private members (name and age) of any Employee object.
It prints the private information of the Employee object passed to it.

3. In main():

A Employee object employee is created.
The friend function displayEmployeeInfo() is called, and it can access the private members of the employee object.

C++ Friend Functions – Interview Questions

Q 1: What is a friend function?

Ans: A function that can access private members of a class.

Q 2: How is a friend function declared?

Ans: Using the friend keyword.

Q 3: Is a friend function a class member?

Ans: No.

Q 4: Can a friend function access private data?

Ans: Yes..

Q 5: Can one function be friend of multiple classes?

Ans: Yes.