std::locale::id (3) - Linux Man Pages
Defined in header <locale>
The class std::locale::id provides implementation-specific identification of a locale facet. Each class derived from std::locale::facet must have a public static member named id of type std::locale::id and each std::locale object maintains a list of facets it implements, indexed by their ids.
Facets with the same id belong to the same facet category and replace each other when added to a locale object.
constructor (public member function)
operator= (public member function)
The following example shows how to construct a minimal custom facet.
// Run this code