On namespace 'names': ::std:: vs std::


I have been looking over some posts here on Stackoverflow, and I have noticed that most people use std:: but some people uses ::std::

I think i have read something about a <em>global scope</em> or something like that in namespaces as a reason to use ::std:: (but i can't find it now, because it was in a comment to an unrelated question)

Is there any reason to prefer one way versus the other?


It's a bad idea to write code like this, but you <em>could</em>:

namespace foo { namespace std { int bar; } std::string s; }

In that case, the std::string refers to the ::foo::std namespace, not the ::std namespace. So, using ::std::string is just being a little bit more unambiguously careful.


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