Friend Function and Class in C++

In C++, classes are created to package data and functions, protecting internal information from external interference. However, there are situations in which it is essential to have access to private members to improve functionality. This is when the Friend Function is utilised in C++. A Friend Function in C++ offers a means to bypass conventional access restrictions, enabling external functions or other classes to directly access private and protected members.  

Friend Functions are crucial for intricate operations as they improve the adaptability and interaction among classes due to their distinctive capability. Let's learn more about Friend Functions in C++ in depth to enhance your Programming skills. Are you ready to write more efficient and adaptable code in different scenarios?  

Table of Contents

1) Syntax of Friend Function in C++ 

2) Types of Friend Functions in C++ 

3) Friend Class in C++ 

4) Example of a Friend Function in C++ 

5) Advantages of Using Friend Functions 

6) Disadvantages of Using Friend Functions 

7) Conclusion 

Syntax of Friend Function in C++ 

In C++, a Friend Function's syntax begins with the ‘friend’ keyword within the class requiring access. It is stated as follows:
 

A friend function in C++ is defined outside the class, similar to a typical function. The friend keyword allows this function to access the private and protected members of the class. It’s important to note that a friend function is not considered a member of the class it operates on, and it can be invoked without creating an object of that class. Understanding this syntax is crucial for effectively utilising friend functions in your C++ code. 

The structure of a friend function in C++ allows it to bypass the usual access restrictions of a class. Declaring a function as a friend grants it specific permission to access the class’s private and protected members. 

This declaration is placed within the class but does not make the function a member of the class. Instead, it permits external functions or separate classes to access data that would otherwise be inaccessible. This mechanism is particularly useful when multiple classes need to work closely together, facilitating smooth communication and cooperation.
 

Types of Friend Functions in C++ 

Different types of Friend Functions in C++ offer unique ways for functions to access private class members, boosting flexibility and inter-class communication. Let’s discuss two main types:  

1) Global Function as a Friend Function 

A standalone function outside any class can access private members of a class by using Global Function as a Friend Function. This kind is useful for operations that involve various classes, allowing for data manipulation without restrictions from classes. 

2) Member Function of Another Class as a Friend Function 

Allowing a member function from a different class to access private members is achieved by declaring it as a friend function. This category promotes intimate connections among classes, improving adaptability and teamwork. It supports encapsulation while enabling targeted access, simplifying communication and ensuring seamless operation among interconnected classes in C++. 

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Friend Class in C++ 

A Friend Class can reach the private and protected members of another class if declared as a friend. This is especially helpful when a certain class requires direct access to the private and protected members of other classes. In the case of a LinkedList class, it might require access to the private members of a Node class. In C++, to define a ‘Friend Class’, you can use the friend keyword followed by the class name.
 

This declaration enables seamless interaction between classes while keeping encapsulation when needed. 

Example of a Friend Function in C++ 

Here's an example showcasing the use of a Friend Function in C++ to add the private values of two classes:
 

Output: 

In this example, the ‘addValues()’ function is a friend to both 'ClassA' and 'ClassB', allowing it to go into their private members and perform the addition. 

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Advantages of Using Friend Functions 

The Friend Function allows access to private data within classes, although it does come with certain drawbacks. Below are the main benefits of Friend Functions in C++: 

a) Direct Access: Friend Functions can access private members even without inheriting the class 

b) Bridge Classes: They act as a link between two groups by directly accessing their confidential information  

c) Operator Flexibility: They improve the versatility of overloaded operators  

d) Versatile Declaration: They may be defined within the public, private, or protected parts of a class 

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Disadvantages of Using Friend Functions 

While Friend Functions facilitate unique access capabilities in C++, they also come with notable cons that impact class design and security. Let's discuss them here: 

a) Data Breach: Friend Functions breach data hiding by gaining access to private members external to the class.  

b) No Polymorphism: Their lack of support for run-time polymorphism restricts their dynamic behaviour. 

Conclusion 

We hope this blog has provided you with a thorough understanding of the Friend Function and how it enables informed decisions. It serves as a powerful tool that facilitates interaction between classes by granting way into private members without inheritance. By mastering this concept, you can enhance the flexibility and efficiency of your code. 

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