C++ using keyword

Question

What is the difference between these two usage of using keyword:

using boost::shared_ptr;

and

using namespace boo         


        

Answer 1

The first is called using declaration;

The second is called using directive.

Quoting MSDN:

Note the difference between the using directive and the using declaration:

the using declaration allows an individual name to be used without qualification,

the using directive allows all the names in a namespace to be used without qualification.