When should you use 'friend' in C++?

Question

I have been reading through the C++ FAQ and was curious about the friend declaration. I personally have never used it, however I am interested in exploring the language.

Answer 1

The canonical example is to overload operator<<. Another common use is to allow a helper or admin class access to your internals.

Here are a couple of guidelines I heard about C++ friends. The last one is particularly memorable.

• Your friends are not your child's friends.
• Your child's friends are not your friends.
• Only friends can touch your private parts.