What does friend function means? How to use it?

Question

found this topic in C++

Answer 1

C++ Friend Functions. A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.
Source - https://www.tutorialspoint.com/cplusplus/cpp_friend_functions.htm

Answer 2

You can also read about it in C++ Tutorial → More on Classes → The Friend Keyword