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c++namespacesstdusing

C++ using namespace declaration

So for a while I've been using...

using namespace::std;

and recently I realized that's supposed to be

using namespace std;

Can somebody explain to me why what I was doing worked, and how it differs from the correct way of declaring the usage of a certain namespace?

Solution

  • The first version works because the compiler sees it as

    using namespace ::std;
// Notice space^

    That is simply telling the compiler to look for the name-space std in the global scope.

    The scope operator :: without anything on the left-hand side is the same as the global scope.