C++ In a Nutshell

Name

locale::facet class — Base class for locale facets

Synopsis

class locale::facet{
protected:
  explicit facet(size_t refs = 0);
  virtual ~facet(  );
private:
  facet(const facet&);          // Not defined
  void operator=(const facet&); // Not defined
};

The facet class is the base class for all facets. A derived class must also declare a public, static data member of type locale::id whose name is id. Even a derived class must declare its own id member because it must have an identifier that is distinct from that of the base-class facet. Any other members for a custom facet are entirely up to the programmer; the derived class does not need to provide a copy or default constructor or an assignment operator.

The locale class assigns a value to id when the facet object is added to a locale. You never need to examine or alter the id member; it is managed entirely by locale.

The explicit constructor for facet takes a single argument, ref. If ref == 0, the facet object is not deleted until the last locale that uses the facet is destroyed. If ref == 1, the facet object is never destroyed. The standard facet classes (ctype, etc.) also take a ref parameter and pass it directly to the inherited facet constructor. Custom facets can do whatever the programmer wants, such as relying on the default value of 0 to manage the facet’s lifetime automatically.

For example, suppose you want to define a facet that captures the locale-specific preferences for units of measure, such as length and weight. A program can store ...