Friend Function

If a function is defined as a friend function in C++, then the protected and private data of a class can be accessed using the function.

By using the keyword friend compiler knows the given function is a friend function.

For accessing the data, the declaration of a friend function should be done inside the body of a class starting with the keyword friend.

Syntax:

class class_name

{

friend data_type function_name(arguments);

};

In the above declaration, the friend function is preceded by the keyword friend. The function can be defined anywhere in the program like a normal C++ function. The function definition does not use either the keyword friend or scope resolution operator.

Characteristics of a Friend function:

• The function is not in the scope of the class to which it has been declared as a friend.

• It cannot be called using the object as it is not in the scope of that class.

• It can be invoked like a normal function without using the object.

• It cannot access the member names directly and has to use an object name and dot membership operator with the member name.

• It can be declared either in the private or the public part.

#include <iostream>

#include <conio.h>

using namespace std;

class Calculator {

private:

    int num1, num2;

public:

    // Constructor to initialize numbers

    Calculator(int n1, int n2) {

        num1 = n1;

        num2 = n2;

    }

    // Declare friend function

    friend int addNumbers(Calculator calc);

};

int addNumbers(Calculator calc) {

    // Accessing private members directly

    return calc.num1 + calc.num2;

}

int main() {

  Calculator calc(60, 40); // Create an object of Calculator class

    // Call friend function to add numbers

    cout << "The sum is: " << addNumbers(calc) << endl;

    getch();

    return 0;

}

Output:

The sum is : 100

Friend Class