C++ 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.
Declaration of friend function in C++
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.
C++ friend function Example
Let’s see the simple example of C++ friend function used to print the length of a box.
Output:
Length of box: 10
Let’s see a simple example when the function is friendly to two classes.
Output:
10
In the above example, min() function is friendly to two classes, i.e., the min() function can access the private members of both the classes A and B.
C++ Friend class
A friend class can access both private and protected members of the class in which it has been declared as friend.
Let’s see a simple example of a friend class.
Output:
value of x is : 5
In the above example, class B is declared as a friend inside the class A. Therefore, B is a friend of class A. Class B can access the private members of class A.