What is the default namespace

Question

what is the default namespace in c++？

#include<iostream>
class B{
 .....
}
int main(){
.....
}

so what namespace is class B in?

Answer 1

B is in the global namespace. It can be referred to unambiguously as ::B.

Eric Z provides an excerpt from C++03 here: https://stackoverflow.com/a/10269085