I need a good explain for ( ::) in this code

Question

This code is:

https://code.sololearn.com/cmKA9Q2J4uLs/?ref=app

Answer 1

It just tells the compiler in which scope to look, thats why it's called the scope resolution operator.

A means that A is in the current scope.
A::B means that the compiler should look for B inside A
A::B::C would mean that the compiler should look for C inside B which is inside A.
std::string means that the compiler should look inside std for string.

Answer 2

Thanks Dennis.