The class that describes a locale object that encapsulates culture-specific information as a set of facets that collectively define a specific localized environment.
For a list of all members of this type, see locale Members.
A facet is a pointer to an object of a class derived from class facet that has a public object of the form:
static locale::id id;
You can define an open-ended set of these facets. You can also construct a locale object that designates an arbitrary number of facets.
Predefined groups of these facets represent the locale categories traditionally managed in the Standard C Library by the function setlocale.
Category collate (LC_COLLATE) includes the facets:
Category ctype (LC_CTYPE) includes the facets:
ctype<char> ctype<wchar_t> codecvt<char, char, mbstate_t> codecvt<wchar_t, char, mbstate_t>
Category monetary (LC_MONETARY) includes the facets:
moneypunct<char, false> moneypunct<wchar_t, false> moneypunct<char, true> moneypunct<wchar_t, true> money_get<char, istreambuf_iterator<char> > money_get<wchar_t, istreambuf_iterator<wchar_t> > money_put<char, ostreambuf_iterator<char> > money_put<wchar_t, ostreambuf_iterator<wchar_t> >
Category numeric (LC_NUMERIC) includes the facets:
num_get<char, istreambuf_iterator<char> > num_get<wchar_t, istreambuf_iterator<wchar_t> > num_put<char, ostreambuf_iterator<char> > num_put<wchar_t, ostreambuf_iterator<wchar_t> > numpunct<char> numpunct<wchar_t>
Category time (LC_TIME) includes the facets:
time_get<char, istreambuf_iterator<char> > time_get<wchar_t, istreambuf_iterator<wchar_t> > time_put<char, ostreambuf_iterator<char> > time_put<wchar_t, ostreambuf_iterator<wchar_t> >
Category messages (LC_MESSAGES) includes the facets:
(The last category is required by Posix, but not the C Standard.)
Some of these predefined facets are used by the iostreams classes, to control the conversion of numeric values to and from text sequences.
An object of class locale also stores a locale name as an object of class string. Using an invalid locale name to construct a locale facet or a locale object throws an object of class runtime_error. The stored locale name is "*" if the locale object cannot be certain that a C-style locale corresponds exactly to that represented by the object. Otherwise, you can establish a matching locale within the Standard C Library, for the locale object loc, by calling setlocale(LC_ALL, loc.name().c_str()).
In this implementation, you can also call the static member function:
static locale empty( );
to construct a locale object that has no facets. It is also a transparent locale; if the template functions has_facet and use_facet cannot find the requested facet in a transparent locale, they consult first the global locale and then, if that is transparent, the classic locale. Thus, you can write:
Subsequent insertions to cout are mediated by the current state of the global locale. You can even write:
locale loc(locale::empty( ), locale::classic( ), locale::numeric); cout.imbue(loc);
Numeric formatting rules for subsequent insertions to cout remain the same as in the C locale, even as the global locale supplies changing rules for inserting dates and monetary amounts.