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Learn the Friend Function in C++ Syntax with Examples

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C++ is a cross-platform language that is used to create high-performance applications. Edureify, the best AI Learning App has already provided an informative article on the C++ Programming Language.

In this article, Edureify brings the details of the Friend Function of C++, an essential component that enables C++ to be such a user-friendly programming language.

Read on to know more about the Friend Function of C++.

The Friend Function in C++

The Friend Function in C++ is defined as the function that authorizes access to all the protected and private members of the class. A Friend Function can be either a member of another class or a global function.

Some of the features of the Friend Function are-

It is a special function in C++ that has access to private and protected data of a class without even being a member function of a class.
It is a non-member function or ordinary function of a class. When a function is declared as a Friend, it gets permission to all the access.
The keyword Friend is placed in the function declaration and not in the function definition
This function uses the dot operator and the name of the object with the member name to access the names of the members.
The Friend Function can be declared in any section of the class, i.e., either the public or private or protected sector of the class.
The scope of the class does not declare the Friend Function

Friend Function Syntax

The following is the syntax of the Friend Function in C++ –

class Box {
  double width;
public:
  double length;
  friend void printWidth (Box Box) ;
   void setWidth (double wid) ;
};

Advantages of Friend Function

The following are the advantages of the Friend Function-

The programmer can generate more efficient codes
Permits the sharing of private class information by a non-member function
Non-public members of a class can be easily accessed
The friend function is used more when interrelated members relative to other parts of the program are contained in two or more classes
Permits addition functionality that is not commonly used by the class

Declaring a Friend Function in C++

When a class is declared as a friend class, all the friend class members become friend functions. The Friend Function in C++ can be declared in the following ways-

Class class_name
{
Friend data_type function_name(argument/s);
};

Another way of declaring the function is-

class classB;
class classA {
           //ClassB is a friend class of ClassA
           friend class ClassB;
….
}
class ClassB {
….
}

Here, the members of class A can be accessed from class B. But the members of class A cannot access the members of class B.

Example of the Friend Function-

The following is a simple program that shows the working of the Friend Function-

#include <iostream>
using namespace std;
class Distance {
           private:
             int meter;
             // friend function
             friend int addFive(Distance);
           public:
             Distance() : meter(0) {}
};
//friend function definition
int addFive(Distance d) {
           //accessing private members from the friend function
           d.meter += 5;
           return d.meter;
}
int main() {
           Distance D;
           cout << “Distance:” <<addFive(D);
           return 0;
}

Output:  Distance: 5

The following is another example of adding members of two different classes using the friend function-

#include <iostream>
using namespace std;
// forward declaration
class ClassB;
class ClassA {
           public:
             // constructor to initialize numA to 12
             ClassA() : numA(12) {}
           private:
             int numA;
             // friend function declaration
             friend int add(ClassA. ClassB);
};
class ClassB {
           public:
             // constructor to initialize numB to 1
             ClassB() : numb(1) {}
           private:
             int numB;
             // friend function declaration
             friend int add(ClassA, ClassB);
};
// access members of both classes
int add(ClassA objectA, ClassB object) {
           return (objectA.numA + objectB.objectB);
}
int main() {
           ClassA objectA;
           ClassB objectB;
           cout << “Sum:” << add(objectA, objectB);
           return 0;
}

Output: Sum: 13

C++ Friend Class

When class B is the friend of class A, class B has access to all the members of class A. The add() function is created in class B. The add() function returns the sum of numA and numb. It is simple to create objects of class A inside class B for the latter is a friend class.

Here is a program that showcases the working of C++ friend class-

#include <iostream>
using namespace std;
// forward declaration
class ClassB;
class ClassA {
           private:
             //int numA;
             // friend class declaration
             friend class ClassB;
           public:
             // constructor to initialize numA to 12
             ClassA() : numA(12) {}
};
class ClassB {
           private:
             int numb;
           private:
             int numB;
           public:
             // constructor to initialize numB to 1
             ClassB() : numb(1) {}
           // member function to add numA
           // from ClassA and numB from ClassB
           int add() {
            ClassA objectA;
           return (objectA.numA + objectB.objectB);
    }
};
int main() {
           ClassB objectB;
           cout << “Sum:” << object.add();
           return 0;
}

Output: Sum: 13

Here were the examples and details of the Friend Function in C++. Edureify with its coding Bootcamp job-ready courses aims to provide its students with all the knowledge that will help them understand these programming languages and develop their desired applications.

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Some FAQs on Friend Function in C++ –

1. What is the Friend Function in C++?

2. Mention 4 features of the Friend Function in C++?

The 4 features of the Friend Function in C++ are-

The scope of the class does not declare the Friend Function
It is a special function in C++ that has access to private and protected data of a class without even being a member function of a class.
It is a non-member function or ordinary function of a class. When a function is declared as a Friend, it gets permission to all the access.
The keyword Friend is placed in the function declaration and not in the function definition

3. What is the C++ Friend Class?

4. Provide the syntax for Friend Function in C++.

The syntax of the Friend Function in C++ is-

class Box {
  double width;
public:
     double length;
     friend void printWidth (Box Box) ;
     void setWidth (double wid) ;
};
5. From where can I learn more about C++ and other programming languages?

Edureify with its coding Bootcamp job-ready courses will provide all the important courses and study materials that students who would like to know more about programming languages can avail of.

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