“using namespace” in c++ headers

Question

In all our c++ courses, all the teachers always put using namespace std; right after the #includes in their .h files. This seems to me

Answer 1

I believe you can use 'using' in C++ headers safely if you write your declarations in a nested namespace like this:

namespace DECLARATIONS_WITH_NAMESPACES_USED_INCLUDED
{
    /*using statements*/

    namespace DECLARATIONS_WITH_NO_NAMESPACES_USED_INCLUDED
    {
        /*declarations*/
    }
}

using namespace DECLARATIONS_WITH_NAMESPACES_USED_INCLUDED::DECLARATIONS_WITH_NO_NAMESPACES_USED_INCLUDED;

This should include only the things declared in 'DECLARATIONS_WITH_NO_NAMESPACES_USED_INCLUDED' without the namespaces used. I have tested it on mingw64 compiler.