Friend Function in C++

In C++, a friend function is a feature that plays an important role in programming, especially when we want to access the private and protected data of a class while following the principle of data security (Encapsulation). Using a friend function, we can grant an external function or class permission to access the private and protected data of another class.

A friend function in C++ is a function that is declared inside a class with the `friend` keyword. This function is not part of that class, but it is allowed to access the private and protected data of that class.

Not a member function, defined outside the class, can be a friend to any class, and is not called through an object of the class.

Needed for data security when external functions need access, for data access between multiple classes, and often for operator overloading.

Access to private data, external implementation, useful for operator overloading, and can access data from multiple classes.

Reduces data security by violating encapsulation, can increase code complexity, and is not a member function so it cannot be called using an object.

A class can also be declared as a friend, which means it can access all the private and protected members of the class that befriended it.