using keyword — Looks up names in alternate classes or namespaces
block-decl := using-decl | using-directive using-decl ::= using [typename] [::] nested-name :: unqualified-id ; | using [::] unqualified-id ; using-directive ::= using namespace [::] [nested-name ::] namespace-name ;
The using
keyword starts a
using
declaration or using
directive.
A using
declaration
imports a name from another namespace into the current namespace. It
can also be used to introduce a name into a class scope; this is most
often used to promote the access level of an inherited member or bring
an inherited member into the derived class for overload
resolution.
A using
directive
tells the compiler to search an additional namespace when looking up
unqualified names.