26.3 A Phone Number Formatting Facet Class

Now that we have locales and facets in C++, we can encapsulate the locale-dependent parsing and formatting of telephone numbers into a new facet class. Let's focus on formatting in this example. We call the new facet class phone_put, analogous to time_put, money_put, etc.

The phone_put facet class serves solely as a base class for facet classes that actually implement the locale-dependent formatting. The relationship of class phone_put to the other facet classes is illustrated in Figure 13:

Figure 13: The relationship of the phone_put facet to the implementing facets

Here is a first tentative declaration of the new facet class phone_put:

class phone_put: public std::locale::facet {                 // 1
public:
  static std::locale::id id;                                 // 2
  typedef std::string string_type;

  phone_put (std::size_t refs = 0)
    : std::locale::facet (refs) { }                          // 3

  string_type put (const string_type &cntryName,
                   const string_type &areaCode,
                   const string_type &extension) const;      // 4
};