template<class Facet>
const Facet& use_facet(const locale& loc,
const Facet *fac, bool make_it);The template function returns a reference to the locale facet of class Facet listed within the locale object loc. If no
such object is listed, the function throws an object of class bad_cast.
In this implementation, make_it instructs the function to generate the locale facet on demand. But you should write
_USE(loc, Facet), or _USEFAC(loc, Facet) in place of use_facet(loc, (Facet *)0, make_it), because
the second and third parameters are a nonstandard extension. The former is strongly preferred when looking up a facet
that should always be present -- it generates the requested facet on demand, if necessary. The latter will report that the
locale initially constructed by locale() has no facets.