Why does everybody use unanchored namespace declarations (i.e. std:: not ::std::)?

Question

It seems to me that using unanchored namespaces is just asking for trouble later when someone puts in a new namespace that happens to have the same name as a root level name

Answer 1

A lot of code is written in the global namespace. If someone really redefines ::std::, it won't matter how you refer to it in that kind of code.

Also, your scenario is both unlikely and easy to work around. Firstly, the convention since there was a 'std' was that you don't use that name. Secondly, if you were to encounter a package that defined the 'std' namespace, you just do this:

#include 

namespace package_name {
  using namespace std;
}

namespace my_app {
  class my_class : public package_name::class_of_something {};
}

Or something similar. You might have to explicitly name ::std as std. My point is this: people go about using the un-anchored 'std::' all the time because even the worst-case consequences aren't a big deal, and unlikely at that.