Can I undo the effect of “using namespace” in C++?

Question

With using namespace I make the whole contents of that namespace directly visible without using the namespace qualifier. This can cause problems if using

Answer 1

No, C++ Standard doesn't say anything about "undo". The best you are allowed to do is to limit scope of using:

#include 

namespace Ximpl {

using namespace std;    
vector x;

}

vector z; // error. should be std::vector

But unfortunately using namespace Ximpl will bring all names from std namespace as well.