It is used to access facet of locale and returns a reference to facet Facet of locale loc. The function has_facet can be used to check if a locale has a particular facet present before attempting to use it with this function.
Following is the declaration for std::use_facet.
template <class Facet> const Facet& use_facet (const locale& loc);
loc − It is a locale object.
It returns a reference to facet Facet of locale loc.
Strong guarantee − if an exception is thrown, there are no changes in loc.
It has accessed by Argument loc, and the returned object may be used to access facet object.