How to overload operator<< in cpp ?

Question

How to overload operator<< function in cpp of a class for desired output ?

Answer 1

I have an example in this:
https://code.sololearn.com/cStdw0OPtPxG

Answer 2

Does the operator<< really need to be a friend function or there is a way we can define it inside the class

Answer 3

I believe it must be a friend because cout will not call via a method invocation.