______________________________________________________________________

  22   Localization library                           [lib.localization]

  ______________________________________________________________________

1 This clause describes components that C++ programs may use to encapsu-
  late  (and  therefore be more portable when confronting) cultural dif-
  ferences.  The locale facility includes  internationalization  support
  for  character classification and string collation, numeric, monetary,
  and date/time formatting and parsing, and message retrieval.

2 The following subclauses describe components for  locales  themselves,
  the  standard facets, and facilities from the ISO C library, as summa-
  rized in Table 1:

                  Table 1--Localization library summary

     +---------------------------------------------------------------+
     |                    Subclause                        Header(s) |
     +---------------------------------------------------------------+
     |_lib.locales_ Locales                                <locale>  |
     |_lib.locale.categories_ Standard locale Categories             |
     +---------------------------------------------------------------+
     |_lib.c.locales_ C library locales                    <clocale> |
     +---------------------------------------------------------------+

  22.1  Locales                                            [lib.locales]

  Header <locale> synopsis

  namespace std {
  // subclause _lib.locale_, locale:
    class locale;
    template <class Facet> const Facet& use_facet(const locale&);
    template <class Facet> bool         has_facet(const locale&) throw();

  // subclause _lib.locale.convenience_, convenience interfaces:
    template <class charT> bool isspace (charT c, const locale& loc) const;
    template <class charT> bool isprint (charT c, const locale& loc) const;
    template <class charT> bool iscntrl (charT c, const locale& loc) const;
    template <class charT> bool isupper (charT c, const locale& loc) const;
    template <class charT> bool islower (charT c, const locale& loc) const;
    template <class charT> bool isalpha (charT c, const locale& loc) const;
    template <class charT> bool isdigit (charT c, const locale& loc) const;
    template <class charT> bool ispunct (charT c, const locale& loc) const;
    template <class charT> bool isxdigit(charT c, const locale& loc) const;
    template <class charT> bool isalnum (charT c, const locale& loc) const;
    template <class charT> bool isgraph (charT c, const locale& loc) const;
    template <class charT> charT toupper(charT c, const locale& loc) const;
    template <class charT> charT tolower(charT c, const locale& loc) const;
  // subclauses _lib.category.ctype_ and _lib.facet.ctype.special_, ctype:
    class ctype_base;
    template <class charT> class ctype;
    template <>            class ctype<char>;        // specialization
    template <class charT> class ctype_byname;
    template <>            class ctype_byname<char>; // specialization
    class codecvt_base;
    template <class internT, class externT, class stateT> class codecvt;
    template <class internT, class externT, class stateT> class codecvt_byname;
  // subclauses _lib.category.numeric_ and _lib.facet.numpunct_, numeric:
    template <class charT, class InputIterator>  class num_get;
    template <class charT, class OutputIterator> class num_put;
    template <class charT> class numpunct;
    template <class charT> class numpunct_byname;
  // subclause _lib.category.collate_, collation:
    template <class charT> class collate;
    template <class charT> class collate_byname;
  // subclause _lib.category.time_, date and time:
    class time_base;
    template <class charT, class InputIterator>  class time_get;
    template <class charT, class InputIterator>  class time_get_byname;
    template <class charT, class OutputIterator> class time_put;
    template <class charT, class OutputIterator> class time_put_byname;
  // subclauses _lib.category.monetary_, money:
    class money_base;
    template <class charT, class InputIterator>  class money_get;
    template <class charT, class OutputIterator> class money_put;
    template <class charT, bool Intl> class moneypunct;
    template <class charT, bool Intl> class moneypunct_byname;
  // subclause _lib.category.messages_, message retrieval:
    class messages_base;
    template <class charT> class messages;
    template <class charT> class messages_byname;
  }

1 The header <locale> defines classes and declares functions that encap-
  sulate and manipulate the information peculiar to a locale.1)
  _________________________
  1)  In  this  subclause, the type name struct tm is an incomplete type
  that is defined in <ctime>.

  22.1.1  Class locale                                      [lib.locale]
  namespace std {
    class locale {
    public:
    // types:
      class facet;
      class id;
      typedef int category;
      static const category   // values assigned here are for exposition only
        none     = 0,
        collate  = 0x010, ctype    = 0x020,
        monetary = 0x040, numeric  = 0x080,
        time     = 0x100, messages = 0x200,
        all = collate | ctype | monetary | numeric | time  | messages;
    // construct/copy/destroy:
      locale() throw()
      locale(const locale& other) throw()
      explicit locale(const char* std_name);
      locale(const locale& other, const char* std_name, category);
      template <class Facet> locale(const locale& other, Facet* f);
      template <class Facet> locale(const locale& other,
                                    const locale& one);
      locale(const locale& other, const locale& one, category);
     ~locale() throw();  // non-virtual
      const locale& operator=(const locale& other) throw();
    // locale operations:
      basic_string<char>                  name() const;
      bool operator==(const locale& other) const;
      bool operator!=(const locale& other) const;
      template <class charT, class Traits, class Allocator>
        bool operator()(const basic_string<charT,Traits,Allocator>& s1,
                        const basic_string<charT,Traits,Allocator>& s2) const;
    // global locale objects:
      static       locale  global(const locale&);
      static const locale& classic();
    };
  }

1 Class locale implements a type-safe polymorphic set of facets, indexed
  by facet type.  In other words, a facet has a dual role: in one sense,
  it's just a class interface; at the same time, it's an  index  into  a
  locale's set of facets.

2 Access to the facets of a locale is via two member function templates,
  use_facet<> and has_facet<>.

3 [Example: An iostream operator<< might be implemented as:2)

  _________________________
  2) Notice that, in the call to put, the stream is implicitly converted
  to an ostreambuf_iterator<charT,traits>.

    template <class charT, class traits>
      basic_ostream<charT,traits>&
      operator<< (basic_ostream<charT,traits>& s, Date d)
    {
      typename basic_ostream<charT,traits>::sentry cerberos;
      if (cerberos) {
        ios_base::iostate err = 0;
        tm tmbuf; d.extract(tmbuf);
        use_facet< time_put<charT,ostreambuf_iterator<charT,traits> > >(
          s.getloc()).put(s, s, s.fill(), err, &tmbuf, 'x');
        s.setstate(err);  // might throw
      }
      return s;
    }
   --end example]

4 In  the  call  to  use_facet<Facet>(loc),  the type argument chooses a
  facet, making available all members of the named type. If Facet is not
  present  in  a  locale  (or,  failing  that, in the global locale), it
  throws the standard exception bad_cast.  A C++ program can check if  a
  locale  implements  a  particular  facet  with  the  template function
  has_facet<Facet>().  User-defined facets may be installed in a locale,
  and used identically as may standard facets (_lib.facets.examples_).

5 [Note:   All   locale  semantics  are  accessed  via  use_facet<>  and
  has_facet<>, except that:

  --A   member   operator   template    operator()(basic_string<C,T,A>&,
    basic_string<C,T,A>&)  is provided so that a locale may be used as a
    predicate argument to the standard collections, to collate  strings.

  --Convenient  global  interfaces  are  provided  for traditional ctype
    functions such as isdigit() and isspace(), so that  given  a  locale
    object  loc  a  C++  program  can  call isspace(c,loc).  (This eases
    upgrading existing extractors  (_lib.istream.formatted_).)     --end
    note]

6 An instance of locale is immutable; once a facet reference is obtained
  from it, that reference remains usable as long  as  the  locale  value
  itself exists.

7 In successive calls to a locale facet member function during a call to
  an iostream inserter or extractor or a streambuf member function,  the
  returned  result  shall  be  identical.  [Note: This implies that such
  results may safely be reused without calling the locale  facet  member
  function  again,  and that member functions of iostream classes cannot
  safely call imbue() themselves, except as specified elsewhere.   --end
  note]

8 A  locale  constructed  from  a name string (such as "POSIX"), or from
  parts of two named locales, has a name;  all  others  do  not.   Named
  locales  may be compared for equality; an unnamed locale is equal only
  to (copies of) itself.  For an unnamed locale, locale::name()  returns
  the string *".

  22.1.1.1  locale types                              [lib.locale.types]

  22.1.1.1.1  Type locale::category                [lib.locale.category]

  typedef int category;

1 Valid category values include the locale member bitmask elements none,
  collate, ctype, monetary, numeric, time, and messages.   In  addition,
  locale member all is defined such that the expression
    (collate | ctype | monetary | numeric | time | messages | all) == all
  is true.  Further, the result of applying operators | and & to any two
  valid values is valid, and results in the setwise union and  intersec-
  tion, respectively, of the argument categories.

2 locale member functions expecting a category argument require either a
  valid category value or one of the constants LC_CTYPE etc., defined in
  <cctype>.   Such  a  category  value  identifies a set of locale cate-
  gories.  Each locale category, in turn, identifies  a  set  of  locale
  facets, including at least those shown in Table 2:

                     Table 2--Locale Category Facets

      +------------------------------------------------------------+
      |Category                   Includes Facets                  |
      +------------------------------------------------------------+
      |collate    collate<char>, collate<wchar_t>                  |
      +------------------------------------------------------------+
      |ctype      ctype<char>, ctype<wchar_t>                      |
      |           codecvt<char,char,mbstate_t>,                    |
      |           codecvt<wchar_t,char,mbstate_t>                  |
      +------------------------------------------------------------+
      |monetary   moneypunct<char>, moneypunct<wchar_t>            |
      |           moneypunct<char,true>, moneypunct<wchar_t,true>, |
      |           money_get<char>, money_get<wchar_t>              |
      |           money_put<char>, money_put<wchar_t>              |
      +------------------------------------------------------------+
      |numeric    numpunct<char>, numpunct<wchar_t>,               |
      |           num_get<char>, num_get<wchar_t>                  |
      |           num_put<char>, num_put<wchar_t>                  |
      +------------------------------------------------------------+
      |time       time_get<char>, time_put<wchar_t>,               |
      |           time_put<char>, time_put<wchar_t>                |
      +------------------------------------------------------------+
      |messages   messages<char>, messages<wchar_t>                |
      +------------------------------------------------------------+

3 For  any  locale  loc either constructed, or returned by locale::clas-
  sic(), and any facet Facet that is a member of  a  standard  category,
  has_facet<Facet>(loc)  is  true.   Each  locale  member function which

  takes a locale::category argument operates on the corresponding set of
  facets.

4 An  implementation  is  required  to  provide those instantiations for
  facet templates identified as members of a  category,  and  for  those
  shown in Table 3:

                     Table 3--Required Instantiations

     +---------------------------------------------------------------+
     |Category                     Includes Facets                   |
     +---------------------------------------------------------------+
     |collate    collate_byname<char>, collate_byname<wchar_t>       |
     +---------------------------------------------------------------+
     |ctype      ctype_byname<char>, ctype_byname<wchar_t>           |
     +---------------------------------------------------------------+
     |monetary   moneypunct_byname<char,International>,              |
     |           moneypunct_byname<wchar_t,International>,           |
     |           money_get<char,InputIterator>,                      |
     |           money_get<wchar_t,InputIterator>,                   |
     |           money_put<char,OutputIterator>,                     |
     |           money_put<wchar_t,OutputIterator>                   |
     +---------------------------------------------------------------+
     |numeric    numpunct_byname<char>, numpunct_byname<wchar_t>     |
     |           num_get<C,InputIterator>, num_put<C,OutputIterator> |
     +---------------------------------------------------------------+
     |time       time_get<char,InputIterator>,                       |
     |           time_get_byname<char,InputIterator>,                |
     |           time_get<wchar_t,OutputIterator>,                   |
     |           time_get_byname<wchar_t,OutputIterator>,            |
     |           time_put<char,OutputIterator>,                      |
     |           time_put_byname<char,OutputIterator>,               |
     |           time_put<wchar_t,OutputIterator>                    |
     |           time_put_byname<wchar_t,OutputIterator>             |
     +---------------------------------------------------------------+

5 For  the  facets  num_get<>  and num_put<> the implementation provided
  must depend only on the corresponding facets numpunct<>  and  ctype<>,
  instantiated  on the same character type.  Other facets are allowed to
  depend on any other facet that is part of a standard category.

6 In declarations of facets,  a  template  formal  parameter  with  name
  InputIterator  or  OutputIterator  indicates  the  set of all possible
  instantiations on parameters that satisfy the requirements of an Input
  Iterator  or  an Output Iterator, respectively (_lib.iterator.require-
  ments_).  A template formal parameter with name C represents  the  set
  of  all  possible  instantiations  on  a  parameter that satisfies the
  requirements for a character on which any of the  iostream  components
  can  be  instantiated.  A template formal parameter with name Interna-
  tional represents the set of all possible  instantiations  on  a  bool
  parameter.

  22.1.1.1.2  Class locale::facet                     [lib.locale.facet]
  namespace std {
    class locale::facet {
    protected:
      explicit facet(size_t refs = 0);
      virtual ~facet();
    private:
      facet(const facet&);          // not defined
      void operator=(const facet&); // not defined
    };
  }

1 Class  facet  is the base class for locale feature sets.  A class is a
  facet if it is publicly derived from another facet,  or  if  it  is  a
  class  derived from locale::facet and containing a declaration as fol-
  lows:
        static ::std::locale::id id;
  Template parameters in this Clause which  must  be  facets  are  those
  named Facet in declarations.  A program that passes a type that is not
  a facet, as an (explicit or deduced) template parameter  to  a  locale
  function expecting a facet, is ill-formed.

2 The  refs argument to the constructor is used for lifetime management.

  --If (refs == 0) the facet's lifetime is  managed  by  the  locale  or
    locales it is incorporated into;

  --if (refs == 1) its lifetime is until explicitly deleted.

3 Constructors  of  all facets defined in this Clause take such an argu-
  ment and pass it along to their facet  base  class  constructor.   All
  one-argument  constructors  defined  in this clause are explicit, pre-
  venting their participation in automatic conversions.

4 For some standard facets a standard _byname" class, derived  from  it,
  implements  the virtual function semantics equivalent to that facet of
  the locale constructed by locale(const  char*)  with  the  same  name.
  Each  such facet provides a constructor that takes a const char* argu-
  ment, which names the locale, and a refs argument, which is passed  to
  the  base  class  constructor.   If  there is no _byname" version of a
  facet, the base class implements named locale semantics itself by ref-
  erence to other facets.

  22.1.1.1.3  Class locale::id                           [lib.locale.id]
  namespace std {
    class locale::id {
    public:
      id();
    private:
      void operator=(const id&); // not defined
      id(const id&);             // not defined
    };
  }

1 The class locale::id provides identification of a locale facet  inter-
  faces,  used as an index for lookup and to encapsulate initialization.

2 [Note: Because facets are used by iostreams, potentially while  static
  constructors  are  running, their initialization cannot depend on pro-
  grammed static initialization.  One  initialization  strategy  is  for
  locale to initialize each facet's id member the first time an instance
  of the facet is installed into a locale.  This depends only on  static
  storage  being  zero  before  constructors run (_basic.start.init_).
  --end note]

  22.1.1.2  locale constructors and destructor         [lib.locale.cons]

  locale() throw();

1 Default constructor: a snapshot of the current global locale.
  Effects:
    Constructs   a   copy   of   the    argument    last    passed    to
    locale::global(locale&),  if it has been called; else, the resulting
    facets  have  virtual  function  semantics  identical  to  those  of
    locale::classic().   [Note: This constructor is commonly used as the
    default value for arguments of functions that take a  const  locale&
    argument.   --end note]

  locale(const locale& other) throw();

  Effects:
    Constructs a locale which is a copy of other.

  const locale& operator=(const locale& other) throw();

  Effects:
    Creates a copy of other, replacing the current value.
  Returns:
    *this

  explicit locale(const char* std_name);

  Effects:
    Constructs  a  locale  using  standard C locale names, e.g. "POSIX".
    The resulting locale implements semantics defined to  be  associated
    with that name.
  Throws:
    runtime_error if the argument is not valid, or is null.
  Notes:
    The  set  of valid string argument values is "C", "", and any imple-
    mentation-defined values.

  locale(const locale& other, const char* std_name, category);

  Effects:
    Constructs a locale as a copy of other except for the facets identi-
    fied  by  the  category  argument,  which instead implement the same
    semantics as locale(std_name).
  Throws:
    runtime_error if the argument is not valid, or is null.
  Notes:
    The locale has a name if and only if other has a name.

  template <class Facet> locale(const locale& other, Facet* f);

  Effects:
    Constructs a locale incorporating all facets from the first argument
    except  that  of type Facet, and installs the second argument as the
    remaining facet.  If f is null, the resulting object is  a  copy  of
    other.
  Notes:
    The resulting locale has no name.

  template <class Facet> locale(const locale& other, const locale& one);

  Effects:
    Constructs a locale incorporating all facets from the first argument
    except that identified by Facet, and  that  facet  from  the  second
    argument instead.
  Throws:
    runtime_error if has_facet<Facet>(one) is false.
  Notes:
    The resulting locale has no name.

  locale(const locale& other, const locale& one, category cats);

  Effects:
    Constructs a locale incorporating all facets from the first argument
    except those that implement cats,  which  are  instead  incorporated
    from the second argument.
  Notes:
    The  resulting  locale has a name if and only if the first two argu-
    ments have names.

  ~locale() throw();

2 A non-virtual destructor that throws no exceptions.

  22.1.1.3  locale members                          [lib.locale.members]

  basic_string<char>  name() const;

  Returns:
    The name of *this, if it has one; otherwise, the string "*".

  22.1.1.4  locale operators                      [lib.locale.operators]

  bool operator==(const locale& other) const;

  Returns:
    true if both arguments are the same locale, or one is a copy of  the
    other,  or each has a name and the names are identical; false other-
    wise.

  bool operator!=(const locale& other) const;

  Returns:
    The result of the expression: !(*this == other)

  template <class charT, class Traits, class Allocator>
    bool operator()(const basic_string<charT,Traits,Allocator>& s1,
                    const basic_string<charT,Traits,Allocator>& s2) const;

  Effects:
    Compares two strings according to the collate<charT> facet.
  Notes:
    This member operator template (and therefore locale  itself)  satis-
    fies  requirements  for  a  comparator  predicate  template argument
    (_lib.algorithms_) applied to strings.
  Returns:
    The result of the following expression:
      use_facet< collate<charT> >(*this).compare(s1.data(), s1.data()+s1.size(),
                                                 s2.data(), s2.data()+s2.size()) < 0;

1 [Example: A vector of strings v can be collated according to collation
  rules in locale loc simply by (_lib.alg.sort_, _lib.vector_):
    std::sort(v.begin(), v.end(), loc);
   --end example]

  22.1.1.5  locale static members                   [lib.locale.statics]

  static locale global(const locale& loc);

1 Sets the global locale to its argument.

  Effects:
    Causes  future calls to the constructor locale() to return a copy of
    the argument.  If the argument has a name, does
        std::setlocale(LC_ALL, loc.name().c_str());
    otherwise, the effect on the C locale, if  any,  is  implementation-
    defined.
  Returns:
    The previous value of locale().

  static const locale& classic();

2 The "C" locale.
  Returns:
    A  locale  that implements the classic "C" locale semantics, equiva-
    lent to the value locale("C").
  Notes:
    This locale, its facets, and their member functions, do  not  change
    with time.

  22.1.2  locale globals                   [lib.locale.global.templates]

  template <class Facet> const Facet& use_facet(const locale& loc);

1 Get a reference to a facet of a locale.
  Returns:
    a reference to the corresponding facet of loc, if present.
  Throws:
    bad_cast if has_facet<Facet>(*this) is false.
  Notes:
    The reference returned remains valid at least as long as any copy of
    loc exists.

  template <class Facet> bool has_facet(const locale& loc) throw();

  Returns:
    true if the facet requested is present in loc; otherwise false

  22.1.3  Convenience interfaces                [lib.locale.convenience]

  22.1.3.1  Character classification                [lib.classification]

  template <class charT> bool isspace (charT c, const locale& loc) const;
  template <class charT> bool isprint (charT c, const locale& loc) const;
  template <class charT> bool iscntrl (charT c, const locale& loc) const;
  template <class charT> bool isupper (charT c, const locale& loc) const;
  template <class charT> bool islower (charT c, const locale& loc) const;
  template <class charT> bool isalpha (charT c, const locale& loc) const;
  template <class charT> bool isdigit (charT c, const locale& loc) const;
  template <class charT> bool ispunct (charT c, const locale& loc) const;
  template <class charT> bool isxdigit(charT c, const locale& loc) const;
  template <class charT> bool isalnum (charT c, const locale& loc) const;
  template <class charT> bool isgraph (charT c, const locale& loc) const;

1 Each of these functions isF returns the result of the expression:
    use_facet< ctype<charT> >(loc).is(ctype_base::F, c)
  where F is the ctype_base::mask value corresponding to  that  function
  (_lib.category.ctype_).3)

  22.1.3.2  Character conversions                      [lib.conversions]

  template <class charT> charT toupper(charT c, const locale& loc) const;

  Returns:
    use_facet<ctype<charT> >(loc).toupper(c).

  template <class charT> charT tolower(charT c, const locale& loc) const;

  Returns:
    use_facet<ctype<charT> >(loc).tolower(c).

  22.2  Standard locale categories               [lib.locale.categories]

1 Each of the standard categories includes a family of facets.  Some  of
  these  implement formatting or parsing of a datum, for use by standard
  or users' iostream operators << and >>, as members  put()  and  get(),
  respectively.   Each  such member function takes an ios_base& argument
  whose members flags(), precision(), and width(), specify the format of
  the  corresponding  datum.   (_lib.ios.base_).   Those functions which
  need to use other facets call its  member  getloc()  to  retrieve  the
  locale  imbued  there.   Formatting  facets use the character argument
  fill to fill out the specified width where necessary.

2 The put() members make no provision for error reporting.   (Any  fail-
  ures  of  the  OutputIterator  argument  must  be  extracted  from the
  returned iterator.)  The  get()  members  take  an  ios_base::iostate&
  argument whose value they ignore, but set to ios_base::failbit in case
  of a parse error.
  _________________________
  3)  When  used  in a loop, it is faster to cache the ctype<> facet and
  use it directly, or use the vector form of ctype<>::is.

  22.2.1  The ctype category                        [lib.category.ctype]
  namespace std {
    class ctype_base {
    public:
      enum mask {  // numeric values are for exposition only.
        space=1<<0, print=1<<1, cntrl=1<<2, upper=1<<3, lower=1<<4,
        alpha=1<<5, digit=1<<6, punct=1<<7, xdigit=1<<8,
        alnum=alpha|digit, graph=alnum|punct
      };
    };
  }

1 The type mask is a bitmask type.

  22.2.1.1  Template class ctype                      [lib.locale.ctype]
    template <class charT>
    class ctype : public locale::facet, public ctype_base {
    public:
      typedef charT char_type;
      explicit ctype(size_t refs = 0);
      bool         is(mask m, charT c) const;
      const charT* is(const charT* low, const charT* high, mask* vec) const;
      const charT* scan_is(mask m,
                           const charT* low, const charT* high) const;
      const charT* scan_not(mask m,
                            const charT* low, const charT* high) const;
      charT        toupper(charT) const;
      const charT* toupper(charT* low, const charT* high) const;
      charT        tolower(charT c) const;
      const charT* tolower(charT* low, const charT* high) const;
      charT        widen(char c) const;
      const char*  widen(const char* low, const char* high, charT* to) const;
      char         narrow(charT c, char dfault) const;
      const charT* narrow(const charT* low, const charT*, char dfault,
                          char* to) const;
      static locale::id id;

    protected:
     ~ctype();  // virtual
      virtual bool         do_is(mask m, charT c) const;
      virtual const charT* do_is(const charT* low, const charT* high,
                                 mask* vec) const;
      virtual const charT* do_scan_is(mask m,
                                      const charT* low, const charT* high) const;
      virtual const charT* do_scan_not(mask m,
                                       const charT* low, const charT* high) const;
      virtual charT        do_toupper(charT) const;
      virtual const charT* do_toupper(charT* low, const charT* high) const;
      virtual charT        do_tolower(charT) const;
      virtual const charT* do_tolower(charT* low, const charT* high) const;
      virtual charT        do_widen(char) const;
      virtual const char*  do_widen(const char* low, const char* high,
                                    charT* dest) const;
      virtual char         do_narrow(charT, char dfault) const;
      virtual const charT* do_narrow(const charT* low, const charT* high,
                                     char dfault, char* dest) const;
    };

1 Class ctype encapsulates the C  library  <cctype>  features.   istream
  members  are  required  to  use  ctype<> for character classing during
  input parsing.

2 The base class implementation implements character classing  appropri-
  ate to the implementation's native character set.

  22.2.1.1.1  ctype members                   [lib.locale.ctype.members]

  bool         is(mask m, charT c) const;
  const charT* is(const charT* low, const charT* high,
                  mask* vec) const;

  Returns:
    do_is(m,c) or do_is(low,high,vec)

  const charT* scan_is(mask m,
                       const charT* low, const charT* high) const;

  Returns:
    do_scan_is(m,low,high)

  const charT* scan_not(mask m,
                        const charT* low, const charT* high) const;

  Returns:
    do_scan_not(m,low,high)

  charT        toupper(charT) const;
  const charT* toupper(charT* low, const charT* high) const;

  Returns:
    do_toupper(c) or do_toupper(low,high)

  charT        tolower(charT c) const;
  const charT* tolower(charT* low, const charT* high) const;

  Returns:
    do_tolower(c) or do_tolower(low,high)

  charT       widen(char c) const;
  const char* widen(const char* low, const char* high, charT* to) const;

  Returns:
    do_widen(c) or do_widen(low,high,to)

  char         narrow(charT c, char dfault) const;
  const charT* narrow(const charT* low, const charT*, char dfault,
                      char* to) const;

  Returns:
    do_narrow(c,dfault) or do_narrow(low,high,dfault,to)

  22.2.1.1.2  ctype virtual functions        [lib.locale.ctype.virtuals]

  bool         do_is(mask m, charT c) const;
  const charT* do_is(const charT* low, const charT* high,
                     mask* vec) const;

  Effects:
    Classifies a character or sequence of characters.  For each argument
    character, identifies a value M of type ctype_base::mask.  The  sec-
    ond  form  places M for all *p where (low<=p && p<high), into vec[p-
    low].
  Returns:
    The first form returns the result of the expression (M &  m)  !=  0;
    i.e.,  true if the character has the characteristics specified.  The
    second form returns high.

  const charT* do_scan_is(mask m,
                         const charT* low, const charT* high) const;

  Effects:
    Locates a character in a buffer that conforms to a classification m.
  Returns:
    The  smallest  pointer  p  in the range [low, high) such that is(*p)

    would return true; otherwise, returns high.

  const charT* do_scan_not(mask m,
                          const charT* low, const charT* high) const;

  Effects:
    Locates a character in a buffer that fails to conform to a classifi-
    cation m.
  Returns:
    The  smallest  pointer p, if any, in the range [low, high) such that
    is(*p) would return false; otherwise, returns high.

  charT        do_toupper(charT c) const;
  const charT* do_toupper(charT* low, const charT* high) const;

  Effects:
    Converts a character or characters to upper case.  The  second  form
    replaces each character *p in the range [low, high) for which a cor-
    responding upper-case character exists, with that character.
  Returns:
    The first form returns the corresponding upper-case character if  it
    is  known to exist, or its argument if not.  The second form returns
    high.

  charT        do_tolower(charT c) const;
  const charT* do_tolower(charT* low, const charT* high) const;

  Effects:
    Converts a character or characters to lower case.  The  second  form
    replaces  each character *p in the range [low, high) and for which a
    corresponding lower-case character exists, with that character.
  Returns:
    The first form returns the corresponding lower-case character if  it
    is  known to exist, or its argument if not.  The second form returns
    high.

  charT        do_widen(char c) const;
  const char*  do_widen(const char* low, const char* high,
                        charT* dest) const;

  Effects:
    Applies the simplest reasonable transformation from a char value  or
    sequence  of  char  values  to  the  corresponding  charT  value  or
    values.4)  The  only characters for which unique transformations are
    required   are   those   in   the   basic   source   character   set
  _________________________
  4) The char argument of do_widen is intended to accept values  derived
  from character literals for conversion the locale's encoding.

    (_lex.charset_).
    For any named ctype category with a ctype<charT> facet ctw and valid
    ctype_base::mask value M (is(M, c) || !ctw.is(M, do_widen(c))  )  is
    true.5)
    The second form transforms each character  *p  in  the  range  [low,
    high), placing the result in dest[p-low].
  Returns:
    The  first  form  returns  the  transformed  value.  The second form
    returns high.

  char         do_narrow(charT c, char dfault) const;
  const charT* do_narrow(const charT* low, const charT* high,
                         char dfault, char* dest) const;

  Effects:
    Applies the simplest reasonable transformation from a charT value or
    sequence  of charT values to the corresponding char value or values.
    For any character c in the basic source character set(_lex.charset_)
    the transformation is such that
      do_widen(do_narrow(c),0) == c
    For  any  named ctype category with a ctype<char> facet ctc however,
    and ctype_base::mask value M,
        (is(M,c) || !ctc.is(M, do_narrow(c),dfault) )"
    is true (unless do_narrow returns dfault).   In  addition,  for  any
    digit  character  c, the expression (do_narrow(c,dfault)-'0') evalu-
    ates to the digit value of the character.  The  second  form  trans-
    forms each character *p in the range [low, high), placing the result
    (or dfault if no  simple  transformation  is  readly  available)  in
    dest[p-low].
  Returns:
    The  first  form returns the transformed value; or dfault if no map-
    ping is readily available.  The second form returns high.

  22.2.1.2  Template class ctype_byname        [lib.locale.ctype.byname]

  _________________________
  5)  In  other  words, the transformed character is not a member of any
  character classification that c is not also a member of.

    template <class charT>
    class ctype_byname : public ctype<charT> {
    public:
      explicit ctype_byname(const char*, size_t refs = 0);
    protected:
     ~ctype_byname();  // virtual
      virtual bool         do_is(mask m, charT c) const;
      virtual const charT* do_is(const charT* low, const charT* high,
                                 mask* vec) const;
      virtual const char*  do_scan_is(mask m,
                                      const charT* low, const charT* high) const;
      virtual const char*  do_scan_not(mask m,
                                       const charT* low, const charT* high) const;
      virtual charT        do_toupper(charT) const;
      virtual const charT* do_toupper(charT* low, const charT* high) const;
      virtual charT        do_tolower(charT) const;
      virtual const charT* do_tolower(charT* low, const charT* high) const;
      virtual charT        do_widen(char) const;
      virtual const char*  do_widen(const char* low, const char* high,
                                    charT* dest) const;
      virtual char         do_narrow(charT, char dfault) const;
      virtual const charT* do_narrow(const charT* low, const charT* high,
                                     char dfault, char* dest) const;
    };
  }

  22.2.1.3  ctype specializations              [lib.facet.ctype.special]
  namespace std {
    template <> class ctype<char>
      : public locale::facet, public ctype_base {
    public:
      typedef char char_type;
      explicit ctype(const mask* tab = 0, bool del = false,
                     size_t refs = 0);
      bool is(mask m, char c) const;
      const char* is(const char* low, const char* high, mask* vec) const;
      const char* scan_is (mask m,
                           const char* low, const char* high) const;
      const char* scan_not(mask m,
                           const char* low, const char* high) const;
      char        toupper(char c) const;
      const char* toupper(char* low, const char* high) const;
      char        tolower(char c) const;
      const char* tolower(char* low, const char* high) const;
      char  widen(char c) const;
      const char* widen(const char* low, const char* high, char* to) const;
      char  narrow(char c, char dfault) const;
      const char* narrow(const char* low, const char* high, char dfault,
                         char* to) const;
      static locale::id id;
      static const size_t table_size = IMPLEMENTATION_DEFINED;
    protected:
      const mask* table() const throw();
      static const mask* classic_table() throw();

     ~ctype();  // virtual
      virtual char        do_toupper(char) const;
      virtual const char* do_toupper(char* low, const char* high) const;
      virtual char        do_tolower(char) const;
      virtual const char* do_tolower(char* low, const char* high) const;
    };
  }

1 A specialization ctype<char> is provided so that the member  functions
  on type char can be implemented inline.6)  The  implementation-defined
  value of member table_size is at least 256.

  22.2.1.3.1  ctype<char> destructor         [lib.facet.ctype.char.dtor]

  ~ctype();

  Effects:
    If  the  constructor's  first  argument  was nonzero, and its second
    argument was true, does delete [] table().

  22.2.1.3.2  ctype<char> members         [lib.facet.ctype.char.members]

1 In the following member descriptions, for unsigned char values v where
  (v  >=  table_size),  table()[v] is assumed to have an implementation-
  defined value (possibly different for each such value v) without  per-
  forming the array lookup.

  explicit ctype(const mask* tbl = 0, bool del = false,
                 size_t refs = 0);

  Precondition:
    tbl either 0 or an array of at least table_size elements.
  Effects:
    Passes its refs argument to its base class constructor.

  bool        is(mask m, char c) const;
  const char* is(const char* low, const char* high,
                 mask* vec) const;

  Effects:
    The second form, for all *p in the range [low, high), assigns vec[p-
    low] to table()[(unsigned char)*p].
  Returns:
    The first form returns table()[(unsigned char)c]  &  m;  the  second
  _________________________
  6) Only the char (not unsigned char and signed char) form is provided.
  The specialization is specified in the standard, and not  left  as  an
  implementation detail, because it affects the derivation interface for
  ctype<char>.

    form returns high.

  const char* scan_is(mask m,
                      const char* low, const char* high) const;

  Returns:
    The smallest p in the range [low, high) such that
      table()[(unsigned char) *p] & m
    is true.

  const char* scan_not(mask m,
                       const char* low, const char* high) const;

  Returns:
    The smallest p in the range [low, high) such that
      table()[(unsigned char) *p] & m
    is false.

  char        toupper(char c) const;
  const char* toupper(char* low, const char* high) const;

  Returns:
    do_toupper(c) or do_toupper(low,high)

  char        tolower(char c) const;
  const char* tolower(char* low, const char* high) const;

  Returns:
    do_tolower(c) or do_tolower(low,high)

  char  widen(char c) const;
  const char* widen(const char* low, const char* high,
      char* to) const;

  Effects:
    ::memcpy(to, low, high-low)
  Returns:
    c or hi

  char        narrow(char c, char /*dfault*/) const;
  const char* narrow(const char* low, const char* high,
                     char /*dfault*/, char* to) const;

  Effects:
    ::memcpy(to, low, high-low)
  Returns:
    c or high.

  +-------                      BEGIN BOX 1                     -------+
  The library WG feels that the members widen and narrow should delegate
  to virtual members do_widen and do_narrow, as in the ctype<> template,
  to  permit char encodings that differ from the basic execution charac-
  ter encoding.
  +-------                       END BOX 1                      -------+

  const mask* table() const throw();

  Returns:
    The first constructor argument, if it was non-zero, otherwise  clas-
    sic_table().

  22.2.1.3.3  ctype<char> static          [lib.facet.ctype.char.statics]
       members

  static const mask* classic_table() throw();

  Returns:
    A pointer to the initial element of  an  array  of  size  table_size
    which  represents  the  classifications  of  characters  in  the "C"
    locale.

  22.2.1.3.4  ctype<char> virtual        [lib.facet.ctype.char.virtuals]
       functions

  char        do_toupper(char) const;
  const char* do_toupper(char* low, const char* high) const;
  char        do_tolower(char) const;
  const char* do_tolower(char* low, const char* high) const;

  These functions are described identically as those members of the same
  name in the ctype class template (_lib.locale.ctype.members_).

  22.2.1.4  Class                      [lib.locale.ctype.byname.special]
       ctype_byname<char>
    template <> class ctype_byname<char> : public ctype<charT> {
    public:
      explicit ctype_byname(const char*, size_t refs = 0);
    protected:
     ~ctype_byname();  // virtual
      virtual char        do_toupper(char) const;
      virtual const char* do_toupper(char* low, const char* high) const;
      virtual char        do_tolower(char) const;
      virtual const char* do_tolower(char* low, const char* high) const;
    };
  }

1
  22.2.1.5  Template class codecvt                  [lib.locale.codecvt]
  namespace std {
    class codecvt_base {
    public:
      enum result { ok, partial, error, noconv };
    };
    template <class internT, class externT, class stateT>
    class codecvt : public locale::facet, public codecvt_base {
    public:
      typedef internT  intern_type;
      typedef externT  extern_type;
      typedef stateT state_type;
      explicit codecvt(size_t refs = 0)
      result out(stateT& state,
        const internT* from, const internT* from_end, const internT*& from_next,
              externT*   to,       externT* to_limit,       externT*& to_next) const;
      result unshift(stateT& state,
             externT*   to,        externT* to_limit,       externT*& to_next) const;
      result in(stateT& state,
        const externT* from, const externT* from_end, const externT*& from_next,
              internT*   to,       internT* to_limit,       internT*& to_next) const;
      int encoding() const throw();
      bool always_noconv() const throw();
      int length(const stateT&, const externT* from, const externT* end,
                 size_t max) const;
      int max_length() const throw();
      static locale::id id;
    protected:
     ~codecvt();  // virtual
      virtual result do_out(stateT& state,
        const internT* from, const internT* from_end, const internT*& from_next,
              externT* to,         externT* to_limit,       externT*& to_next) const;
      virtual result do_unshift(stateT& state,
              externT* to,         externT* to_limit,       externT*& to_next) const;
      virtual result do_in(stateT& state,
        const externT* from, const externT* from_end, const externT*& from_next,
              internT* to,         internT* to_limit,       internT*& to_next) const;
      virtual int do_encoding() const throw();
      virtual bool do_always_noconv() const throw();
      virtual int do_length(const stateT&, const externT* from, const externT* end,
                            size_t max) const;
      virtual int do_max_length() const throw();
    };
  }

1 The  class  codecvt<internT,externT,stateT> is for use when converting
  from one codeset to another, such as from wide characters to multibyte
  characters,  between wide character encodings such as Unicode and EUC.

2 The stateT argument selects the pair of codesets being mapped between.

3 Implementations   are   required   to   provide   instantiations   for
  <wchar_t,char,mbstate_t> and <char,char,mbstate_t>.   The  base  class

  instance  of the latter implements a degenerate conversion: its member
  always_noconv() returns true and max_length() returns  1.   Instantia-
  tions  on  mbstate_t perform conversion between encodings known to the
  library implementor.  Other encodings can be converted by specializing
  on  a  user-defined  stateT  type.   The stateT object can contain any
  state that is useful to communicate to or from the specialized do_con-
  vert  member.   The base class implementations convert the implementa-
  tion-defined native execution codeset.

  22.2.1.5.1  codecvt members               [lib.locale.codecvt.members]

  result out(stateT& state,
    const internT* from, const internT* from_end, const internT*& from_next,
          externT* to, externT* to_limit, externT*& to_next) const;

  Returns:
    do_out(state, from, from_end, from_next, to,to_limit, to_next)

  result unshift(stateT& state,
          externT* to, externT* to_limit, externT*& to_next) const;

  Returns:
    do_unshift(state, to, to_limit, to_next)

  result in(stateT& state,
    const externT* from, const externT* from_end, const externT*& from_next,
          internT* to, internT* to_limit, internT*& to_next) const;

  Returns:
    do_in(state, from,from_end,from_next, to,to_limit,to_next)

  int encoding() const throw();

  Returns:
    do_encoding()

  bool always_noconv() const throw();

  Returns:
    do_always_noconv()

  int length(stateT& state, const externT* from, const externT* from_end,
             size_t max) const;

  Returns:
    do_length(state, from,from_end,max)

  int max_length() const throw();

  Returns:
    do_max_length()

  22.2.1.5.2  codecvt virtual              [lib.locale.codecvt.virtuals]
       functions

  result do_out(stateT& state,
    const internT* from, const internT* from_end, const internT*& from_next,
    externT* to, externT* to_limit, externT*& to_next) const;

  result do_in(stateT& state,
    const externT* from, const externT* from_end, const externT*& from_next,
          internT* to, internT* to_limit, internT*& to_next) const;

  Preconditions:
    (from<=from_end && to<=to_end) well-defined and true; state initial-
    ized, if at the beginning of a sequence, or else equal to the result
    of converting the preceding characters in the sequence.
  Effects:
    Translates  characters  in the source range [from,from_end), placing
    the results in sequential  positions  starting  at  destination  to.
    Converts no more than (from_end-from) source elements, and stores no
    more than (to_limit-to) destination elements.
    Stops if it encounters a character it  cannot  convert.   It  always
    leaves  the  from_next  and to_next pointers pointing one beyond the
    last element successfully converted.  [Note: If  no  translation  is
    needed  (returns  noconv),  sets  to_next  equal to argument to, and
    from_next equal to argument from.   --end note]
  Notes:
    Its operations on state are unspecified.
    [Note: This argument can be used, for  example,  to  maintain  shift
    state,  to  specify  conversion  options (such as count only), or to
    identify a cache of seek offsets.   --end note]
  Returns:
    An enumeration value, as summarized in Table 4:

                       Table 4--convert result values

     +-----------------------------------------------------------------+
     | Value                           Meaning                         |
     +-----------------------------------------------------------------+
     |ok        completed the conversion                               |
     |partial   not all source characters converted                    |
     |error     encountered a from_type character it could not convert |
     |noconv    no conversion was needed                               |
     +-----------------------------------------------------------------+
    A return value of partial, if (from_next==from_end), indicates  that

    either  the  destination sequence has not absorbed all the available
    destination elements, or that additional source elements are  needed
    before another destination element can be produced.

  result do_unshift(stateT& state,
    externT* to, externT* to_limit, externT*& to_next) const;

  Effects
    Places  characters  starting at to that should be appended to termi-
    nate a sequence when the current stateT is  given  by  state.7)  The
    base class implementation stores no characters.
  Returns
    An enumeration value, as summarized in Table 5:

                       Table 5--convert result values

   +----------------------------------------------------------------------+
   | Value                              Meaning                           |
   +----------------------------------------------------------------------+
   |ok        completed the sequence                                      |
   |partial   more characters need to be supplied to complete termination |
   |error     state has invalid value.                                    |
   |noconv    no termination is needed for this state_type                |
   +----------------------------------------------------------------------+
    The base class implementation returns noconv.

  int do_encoding() const throw();

  Returns:
    -1  if the encoding of the externT sequence is state-dependent; else
    the constant number of  externT  characters  needed  to  produce  an
    internal character; or 0 if this number is not a constant8).

  bool do_always_noconv() const throw();

  Returns:
    true if do_convert() returns noconv for all valid  argument  values.
    The    base    class    implementation    for    the   instantiation
    <char,char,mbstate_t> returns true; others return false.

  _________________________
  7) Typically these will be characters to return the state to stateT()
  8)  If  encoding() yields -1, then more than max_length() externT ele-
  ments may be consumed when producing a single internT  character,  and
  additional  externT elements may appear at the end of a sequence after
  those that yield the final internT character.

  int do_length(stateT& state, const externT* from, const externT* from_end,
                size_t max) const;

  Preconditions:
    (from<=from_end) well-defined and true; state initialized, if at the
    beginning  of  a sequence, or else equal to the result of converting
    the preceding characters in the sequence.
  Returns:
    (from_next-from) where from_next is the largest value in  the  range
    [from,from_end]  such  that  the  sequence  of  values  in the range
    [from,from_next) represents max or fewer valid  complete  characters
    of  type  internT.  The base class implementation returns the lesser
    of max and (from_end-from).

  int do_max_length() const throw();

  Returns:
    The maximum value that do_length(state,from,from_end,1)  can  return
    for any valid range [from,from_end) and stateT value state.

  22.2.1.6  Template class                   [lib.locale.codecvt.byname]
       codecvt_byname
  namespace std {
    template <class internT, class externT, class stateT>
    class codecvt_byname : public codecvt<internT, externT, stateT> {
    public:
      explicit codecvt_byname(const char*, size_t refs = 0);
    protected:
     ~codecvt_byname();  // virtual
      virtual result do_out(stateT& state,
        const internT* from, const internT* from_end, const internT*& from_next,
              externT* to,         externT* to_limit,       externT*& to_next) const;
      virtual result do_in(stateT& state,
        const externT* from, const externT* from_end, const externT*& from_next,
              internT* to,         internT* to_limit,       internT*& to_next) const;
      virtual int do_encoding() const throw();
      virtual bool do_always_noconv() const throw();
      virtual int do_length(const stateT&, const externT* from, const externT* end,
                            size_t max) const;
      virtual int do_max_length() const throw();
    };
  }

  22.2.2  The numeric category                    [lib.category.numeric]

1 The classes num_get<> and  num_put<>  handle  numeric  formatting  and
  parsing.   Virtual  functions  are provided for several numeric types.
  Implementations may (but are not required to) delegate  extraction  of
  smaller types to extractors for larger types.9)
  _________________________
  9)  Parsing "-1" correctly into (e.g.) an unsigned short requires that
  the corresponding member get() at least extract the sign before  dele-

2 The  base  class  implementation  refers to the ios_base& argument for
  formatting specifications (_lib.locale.categories_), and to its imbued
  locale  for  the  numpunct<> facet to identify all numeric punctuation
  preferences, and also for the ctype<> facet to perform character clas-
  sification.

3 Extractor and inserter members of the standard iostreams use num_get<>
  and num_put<> member functions for formatting and parsing numeric val-
  ues  (_lib.istream.formatted.reqmts_, _lib.ostream.formatted.reqmts_).

  22.2.2.1  Template class num_get                  [lib.locale.num.get]
  namespace std {
    template <class charT, class InputIterator = istreambuf_iterator<charT> >
    class num_get : public locale::facet {
    public:
      typedef charT            char_type;
      typedef InputIterator    iter_type;
      explicit num_get(size_t refs = 0);
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, bool& v)          const;
      iter_type get(iter_type in, iter_type end, ios_base& ,
                    ios_base::iostate& err, long& v)          const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned short& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned int& v)  const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, float& v)         const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, double& v)        const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long double& v)   const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, void*& v)   const;
      static locale::id id;

  _________________________
  gating.

    protected:
     ~num_get();  // virtual
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, bool& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned short& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned int& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, float& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, void*& v) const;
    };
  }

1 The facet num_get is used  to  parse  numeric  values  from  an  input
  sequence such as an istream.

  22.2.2.1.1  num_get members                [lib.facet.num.get.members]

  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, long& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, unsigned short& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, unsigned int& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, unsigned long& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, short& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, double& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, long double& val) const;
  iter_type get(iter_type in, iter_type end, ios_base& str,
                ios_base::iostate& err, void*& val) const;

  Returns:
    do_get(in, end, str, err, val).

  22.2.2.1.2  num_get virtual               [lib.facet.num.get.virtuals]
       functions

  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, long& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, unsigned short& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, unsigned int& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, unsigned long& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, float& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, double& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, long double& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, void*& val) const;

  Effects:
    Reads  characters  from   in,   interpreting   them   according   to
    str.flags(),   use_facet<   ctype<charT>   >(loc),   and  use_facet<
    numpunct<charT> >(loc).  If an error occurs, val is unchanged;  oth-
    erwise it is set to the resulting value.

1 The details of this operation occur in two stages

  --Stage 1: Determine a conversion specifier

  --Stage  2: Extract characters from in and transform them into char's,
    converting the value transformed characters according to the conver-
    sion specification determined in stage 1.

  --Stage 3: Store results
    The details of the stages are presented below.
  Stage 1:
    The function initializes local variables via
          fmtflags flags = str.flags();
          fmtflags basefield = (flags & ios_base::basefield);
          fmtflags uppercase = (flags & ios_base::uppercase);
          fmtflags basefield = (flags & ios_base::basefield);
          fmtflags boolalpha = (flags & ios_base::boolalpha);
     For  conversion  to  an  integral type, the function determines the
    integral conversion specifier as indicated in Table 6:

                        Table 6--Integer conversions

            +--------------------------------------------------+
            |            State                stdio equivalent |
            +--------------------------------------------------+
            |basefield == oct                        %o        |
            +--------------------------------------------------+
            |basefield == hex && !uppercase          %x        |
            +--------------------------------------------------+
            |basefield == hex                        %X        |
            +--------------------------------------------------+
            |basefield == 0                          %i        |
            +--------------------------------------------------+
            |signed integral type                    %d        |
            +--------------------------------------------------+
            |unsigned integral type                  %u        |
            +--------------------------------------------------+
    For conversions to a  floating type the specifier is %g.
    For conversions to void* the specifier is %p.
    A length specifier is added  to  the  conversion  specification,  if
    needed, as indicated in Table  7.

                          Table 7--Length Modifier

                     +---------------------------------+
                     |     type        length modifier |
                     +---------------------------------+
                     |short                   h        |
                     +---------------------------------+
                     |unsigned short          h        |
                     +---------------------------------+
                     |long                    l        |
                     +---------------------------------+
                     |unsigned long           l        |
                     +---------------------------------+
                     |long double             L        |
                     +---------------------------------+
  Stage 2:
    If in==end then stage 2 terminates.  Otherwise a charT is taken from
    in and local variables are initialized as if by
          char_type ct = *in ;
          char c = use_facet<ctype<charT> >(loc).narrow(ct,' ');
          if ( ct ==  use_facet<numpunct<charT> >(loc).decimal_point() )
              c = '.';
          bool discard =
              ( ct == use_facet<numpunct<charT> >(loc).thousands_sep()
                  &&
               use_facet<numpunct<charT> >(loc).grouping().length() != 0 );

    If discard is true then the position of the character is remembered,
    but  the  character  is  otherwise ignored.  If it is not discarded,
    then a check is made to determine if c is allowed as the next  char-
    acter  of  an  input  field  of the conversion specifier returned by
    stage 1. If so it is accumulated.
    If the character is neither discarded nor  accumulated  then  in  is
    advanced by ++in and processing returns to the beginning of stage 2.
  Stage 3:
    The result of stage 2 processing can be one of

  --A sequence of chars has been accumulated in stage  2  that  is  con-
    verted (according to the rules of std::scanf) to a value of the type
    of val.  This value is stored in val and ios_base::goodbit is stored
    in err.

  --The sequence of chars accumulated in stage 2 would have caused scanf
    to report an input failure.  ios_base::failbit is assigned to
    Digit grouping is checked.  That is, the positions of discarded sep-
    arators  is  examined for consistency with use_facet<numpunct<charT>
    >(loc).grouping()

  +-------                      BEGIN BOX 2                     -------+
  Is the treatment of separators here clear?
  +-------                       END BOX 2                      -------+

  If they are not consistent then ios_base::failbit is assigned to  err.

2 In  any  case,  if  stage  2 processing was terminated by the test for
  in==end then err|=ios_base::eofbit is performed.

  iter_type do_get(iter_type in, iter_type end, ios_base& str,
                   ios_base::iostate& err, bool& val) const;

  Effects:
    If (str.flags()&&ios_base::boolalpha)==0 then input proceeds  as  it
    would  for  an  int except that if a value is being stored into val,
    the value is determined according to the following: If the value  to
    be stored is 0 then false is stored.  If the value is 1 then true is
    stored.  Otherwise err|=ios_base::failbit is performed and no  value
    is stored.

3 Otherwise  a  target  string  to  be  matched is determined by calling
  either       use_facet<ctype<charT>        >(loc).truename()        or
  use_facet<ctype<charT>  >(loc).falsename() depending on whether val is
  true or false (respectively).

4 As long as in!=end and characters continue to match the target  string
  charT's  are  obtained  by doing *in++.  A value is assigned to err as
  follows

  --If the target string was matched completely, then goodbit.

  --If input was terminated because in!=end, then eofbit

  --Otherwise, failbit.
  Returns:
    in.

  22.2.2.2  Template class num_put                  [lib.locale.num.put]
  namespace std {
    template <class charT, class OutputIterator = ostreambuf_iterator<charT> >
    class num_put : public locale::facet {
    public:
      typedef charT            char_type;
      typedef OutputIterator   iter_type;
      explicit num_put(size_t refs = 0);
      iter_type put(iter_type s, ios_base& f, char_type fill, bool v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, long v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill,
                    unsigned long v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill,
                    double v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill,
                    long double v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill,
                    void* v) const;
      static locale::id id;
    protected:
     ~num_put();  // virtual
      virtual iter_type do_put(iter_type, ios_base&, char_type fill,
                               bool v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill,
                               long v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill,
                               unsigned long) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill,
                               double v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill,
                               long double v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill,
                               void* v) const;
    };
  }

1 The facet num_put is used to format  numeric  values  to  a  character
  sequence such as an ostream.

  22.2.2.2.1  num_put members                [lib.facet.num.put.members]

  iter_type put(iter_type out, ios_base& str, char_type fill,
                long val) const;
  iter_type put(iter_type out, ios_base& str, char_type fill,
                unsigned long val) const;
  iter_type put(iter_type out, ios_base& str, char_type fill,
                double val) const;
  iter_type put(iter_type out, ios_base& str, char_type fill,
                long double val) const;
  iter_type put(iter_type out, ios_base& str, char_type fill,
                void* val) const;

  Returns:
    do_put(out, str, fill, val).

  22.2.2.2.2  num_put virtual               [lib.facet.num.put.virtuals]
       functions

  iter_type do_put(iter_type out, ios_base& str, char_type fill,
                   bool val) const;
  iter_type do_put(iter_type out, ios_base& str, char_type fill,
                   long val) const;
  iter_type do_put(iter_type out, ios_base& str, char_type fill,
                   unsigned long val) const;
  iter_type do_put(iter_type out, ios_base& str, char_type fill,
                   double val) const;
  iter_type do_put(iter_type out, ios_base& str, char_type fill,
                   long double val) const;
  iter_type do_put(iter_type out, ios_base& str, char_type fill,
                   void* val) const;

  Effects:
    Writes characters to the sequence out, formatting val as desired. In
    the following description, a local variable initialized with
          locale loc = str.getloc();
    The base class implementation is described in several stages

  --Stage  1: Determine a printf conversion specifier spec and determin-
    ing the characters that would be  printed  by  printf(_lib.c.files_)
    given this conversion specifier for
          std::printf(spec, val)
    assuming that the current locale is the "C" locale.

  --Stage  2:  Adjust  the representation by converting each char deter-
    mined by stage 1 to a charT using a conversion and  values  returned
    by members of use_facet< numpunct<charT> >(str.getloc())

  --Stage 3: Determine where padding is required.

  --Stage 4: Insert the sequence into the out.
    Detailed descriptions of each stage follow.
  Returns:
    out.

  Stage 1:
    The  first action of stage 1 is to determine a conversion specifier.
    The tables that describe this determination use the following  local
    variables
          fmtflags flags = this->flags() ;
          fmtflags basefield =  (flags & (ios_base::basefield));
          fmtflags uppercase =  (flags & (ios_base::uppercase));
          fmtflags floatfield = (flags & (ios_base::floatfield));
          fmtflags showpos =    (flags & (ios_base::showpos));
          fmtflags showbase =   (flags & (ios_base::showbase));
     All  tables  used  in describing stage 1 are ordered.  That is. the
    first line whose condition is true applies.  A line without a condi-
    tion is the default behavior when none of the earlier lines apply.
     For  conversion  from an integral type other than a character type,
    the function determines the integral conversion specifier  as  indi-
    cated in Table 8.

                        Table 8--Integer conversions

      +---------------------------------------------------------------+
      |                   State                      stdio equivalent |
      +---------------------------------------------------------------+
      |basefield == ios_base::oct                           %o        |
      +---------------------------------------------------------------+
      |(basefield == ios_base::hex) && !uppercase           %x        |
      +---------------------------------------------------------------+
      |(basefield == ios_base::hex)                         %X        |
      +---------------------------------------------------------------+
      |for a signed integral type                           %d        |
      +---------------------------------------------------------------+
      |for an unsigned integral type                        %u        |
      +---------------------------------------------------------------+
     For  conversion from a floating-point type, the function determines
    the floating-point conversion specifier as indicated in Table 9:

                    Table 9--Floating-point conversions

    +--------------------------------------------------------------------+
    |                     State                         stdio equivalent |
    +--------------------------------------------------------------------+
    |floatfield == ios_base::fixed                             %f        |
    +--------------------------------------------------------------------+
    |floatfield == ios_base::scientific && !uppercase          %e        |
    +--------------------------------------------------------------------+
    |floatfield == ios_base::scientific                        %E        |
    +--------------------------------------------------------------------+
    |!uppercase                                                %g        |
    +--------------------------------------------------------------------+
    |otherwise                                                 %G        |
    +--------------------------------------------------------------------+
    For conversions from an integral or floating type a length  modifier
    is added to the conversion specifier as indicated in  Table 10.

                         Table 10--Length modifier

                     +---------------------------------+
                     |     type        length modifier |
                     +---------------------------------+
                     |short                   h        |
                     +---------------------------------+
                     |unsigned short          h        |
                     +---------------------------------+
                     |long                    l        |
                     +---------------------------------+
                     |unsigned long           l        |
                     +---------------------------------+
                     |long double             L        |
                     +---------------------------------+
                     |otherwise             none       |
                     +---------------------------------+
    The conversion specifier has the following optional additional qual-
    ifiers prepended as indicated in Table 11:

                       Table 11--Numeric conversions

      +--------------------------------------------------------------+
      |       Type(s)                State          stdio equivalent |
      +--------------------------------------------------------------+
      |an integral type oth-   flags & showpos             +         |
      |er than a character     flags & showbase            #         |
      |type                                                          |
      +--------------------------------------------------------------+
      |a floating-point type   flags & showpos             +         |
      |                        flags & showpoint           #         |
      +--------------------------------------------------------------+
    For conversion from a floating-point type, if (flags() & fixed) != 0
    or  if precision() > 0, then precision() is specified in the conver-
    sion specification.
    For conversion from void* the specifier is %p.
    The representations at the end of stage 1  consists  of  the  char's
    that  would  be  printed  by a call of printf(s, val) where s is the
    conversion specifier determined above.

  Stage 2:
    Any character c other than a decimal  point(.)  is  converted  to  a
    charT via charT(c)

1 A local variable punct is initialized via
      numpunct<charT> punct = use_facet< numpunct<charT> >(str.getloc())
     For  integral  types, punct.thousands_sep() characters are inserted
    into  the  sequence  as  determined  by  the   value   returned   by
    punct.do_grouping()     using     the     method     described    in
    _lib.facet.numpunct.virtuals_
    Decimal point characters(.) are replaced by punct.decimal_point()

  Stage 3:
    A local variable is initialized as
          fmtflags adjustfield=   (flags & (ios_base::adjustfield));
    The location of any padding is determined according to Table 12:

                           Table 12--Fill padding

       +-------------------------------------------------------------+
       |            State                         Location           |
       +-------------------------------------------------------------+
       |adjustfield == ios_base::left    pad after                   |
       +-------------------------------------------------------------+
       |adjustfield == ios_base::right   pad before                  |
       +-------------------------------------------------------------+
       |adjustfield == internal and a    pad after the sign          |
       |sign occurs in the representa-                               |
       |tion                                                         |
       +-------------------------------------------------------------+
       |adjustfield == internal and      pad after x or X            |
       |representation after stage 1                                 |
       |began with 0x 1or 0X                                         |
       +-------------------------------------------------------------+
       |otherwise                        pad before stage 2 sequence |
       +-------------------------------------------------------------+
     width()  is nonzero and the number of charT's in the sequence after
    stage 3 is less than width(), then enough fill characters are  added
    to  the  sequence at the position indicated for padding to bring the
    length of the sequence to width().
    width(0) is called.

  Stage 4:
    The sequence of charT's at the end of stage 3 are output via
          *out++ = c
    If at any point out.failed() becomes true,  then  output  is  termi-
    nated.

  iter_type put(iter_type out, ios_base& str, char_type fill,
                bool val) const;

  Effects:
    If (str.flags()&ios_base::boolalpha)==0 then do
          out = put(out, str, fill, (int)val)
    Otherwise do
          string_type s =
              val ? use_facet<ctype<charT> >(loc).truename()
                        : use_facet<ctype<charT> >(loc).falsename() ;
    and then insert the characters of s into out.

  _________________________
  10) The conversion specification #o generates a leading 0 which is not
  a padding character.

  22.2.3  The numeric punctuation facet             [lib.facet.numpunct]

  22.2.3.1  Template class numpunct                [lib.locale.numpunct]
  namespace std {
    template <class charT>
    class numpunct : public locale::facet {
    public:
      typedef charT               char_type;
      typedef basic_string<charT> string_type;
      explicit numpunct(size_t refs = 0);
      char_type    decimal_point()   const;
      char_type    thousands_sep()   const;
      string       grouping()        const;
      string_type  truename()        const;
      string_type  falsename()       const;
      static locale::id id;
    protected:
     ~numpunct();  // virtual
      virtual char_type    do_decimal_point() const;
      virtual char_type    do_thousands_sep() const;
      virtual string       do_grouping()      const;
      virtual string_type  do_truename()      const;  // for bool
      virtual string_type  do_falsename()     const;  // for bool
    };
  }

1 numpunct<>  specifies  numeric  punctuation.   The base class provides
  classic C" numeric formats, while the _byname" version supports  named
  locale (e.g. POSIX, X/Open) numeric formatting semantics.

2 The  syntax  for  number formats is as follows, where digit represents
  the radix set specified by the fmtflags argument value, whitespace  is
  as  determined  by  the  facet  ctype<charT> (_lib.locale.ctype_), and
  thousands-sep and  decimal-point  are  the  results  of  corresponding
  numpunct<charT> members.  Integer values have the format:
    integer   ::= [sign] units
    sign      ::= plusminus [whitespace]
    plusminus ::= '+' | '-'
    units     ::= digits [thousands-sep units]
    digits    ::= digit [digits]
  and floating-point values have:
    floatval ::= [sign] units [decimal-point [digits]] [e [sign] digits] |
                 [sign]        decimal-point  digits   [e [sign] digits]
    e        ::= 'e' | 'E'
  where  the  number of digits between thousands-seps is as specified by
  do_grouping().  For parsing, if the digits portion contains  no  thou-
  sands-separators, no grouping constraint is applied.

  +-------                      BEGIN BOX 3                     -------+
  Note:  The above text does not describe any behavior of numpunct<> and
  is not referred to anywhere else in the Draft, and should be  deleted.
  +-------                       END BOX 3                      -------+

  22.2.3.1.1  numpunct members              [lib.facet.numpunct.members]

  char_type decimal_point() const;

  Returns:
    do_decimal_point()

  char_type thousands_sep() const;

  Returns:
    do_thousands_sep()

  string grouping()  const;

  Returns:
    do_grouping()

  string_type truename()  const;
  string_type falsename() const;

  Returns:
    do_truename() or do_falsename(), respectively.

  22.2.3.1.2  numpunct virtual             [lib.facet.numpunct.virtuals]
       functions

  char_type do_decimal_point() const;

  Returns:
    A character for use as the decimal radix separator.  The base  class
    implementation returns '.'.

  string_type do_thousands_sep() const;

  Returns:
    A  character  for  use as the digit group separator.  The base class
    implementation returns ','.

  string do_grouping() const;

  Returns:
    A basic_string<char> vec used as a  vector  of  integer  values,  in
    which each element vec[i] represents the number of digits11) in  the
  _________________________
  11) Thus, the string "\003" specifies groups of 3 digits each, and "3"
  probably indicates groups of 51 (!) digits each.

    group  at  position  i,  starting  with  position 0 as the rightmost
    group.  If vec.size() <= i, the number is the same as  group  (i-1);
    if  (i<0  ||  vec[i]<=0  || vec[i]==CHAR_MAX), the size of the digit
    group is unlimited.
    The base class implementation returns the empty  string,  indicating
    no grouping.

  string_type do_truename()  const;
  string_type do_falsename() const;

  Returns:
    A  string  representing the name of the boolean value true or false,
    respectively.
    In the base class implementation these names are "true" and "false".

  22.2.3.2  Template class                  [lib.locale.numpunct.byname]
       numpunct_byname
  namespace std {
    template <class charT>
    class numpunct_byname : public numpunct<charT> {
      // this class is specialized for char and wchar_t.
    public:
      explicit numpunct_byname(const char*, size_t refs = 0);
    protected:
     ~numpunct_byname();  // virtual
      virtual char_type    do_decimal_point() const;
      virtual char_type    do_thousands_sep() const;
      virtual string       do_grouping()      const;
      virtual string_type  do_truename()      const;  // for bool
      virtual string_type  do_falsename()     const;  // for bool
    };
  }

  22.2.4  The collate category                    [lib.category.collate]

  22.2.4.1  Template class collate                  [lib.locale.collate]
  namespace std {
    template <class charT>
    class collate : public locale::facet {
    public:
      typedef charT               char_type;
      typedef basic_string<charT> string_type;
      explicit collate(size_t refs = 0);
      int compare(const charT* low1, const charT* high1,
                  const charT* low2, const charT* high2) const;
      string_type transform(const charT* low, const charT* high) const;
      long hash(const charT* low, const charT* high) const;
      static locale::id id;

    protected:
     ~collate();  // virtual
      virtual int    do_compare(const charT* low1, const charT* high1,
                                const charT* low2, const charT* high2) const;
      virtual string_type do_transform(const charT* low, const charT* high) const;
      virtual long   do_hash     (const charT* low, const charT* high) const;
    };
  }

1 The class collate<charT> provides features for use  in  the  collation
  (comparison)  and  hashing  of strings.  A locale member function tem-
  plate, operator(), uses the collate facet to allow  a  locale  to  act
  directly as the predicate argument for standard algorithms (_lib.algo-
  rithms_) and containers operating on strings.  The base  class  imple-
  mentation applies lexicographic ordering (_lib.alg.lex.comparison_).

2 Each  function  compares  a  string  of  characters  *p  in  the range
  [low,high).

  22.2.4.1.1  collate members               [lib.locale.collate.members]

  int compare(const charT* low1, const charT* high1,
              const charT* low2, const charT* high2) const;

  Returns:
    do_compare(low1, high1, low2, high2)

  string_type transform(const charT* low, const charT* high) const;

  Returns:
    do_transform(low, high)

  long hash(const charT* low, const charT* high) const;

  Returns:
    do_hash(low, high)

  22.2.4.1.2  collate virtual              [lib.locale.collate.virtuals]
       functions

  int do_compare(const charT* low1, const charT* high1,
                 const charT* low2, const charT* high2) const;

  Returns:
    1  if  the first string is greater than the second, -1 if less, zero
    otherwise.  The base class implementation implements a lexicographi-
    cal comparison (_lib.alg.lex.comparison_).

  string_type do_transform(const charT* low, const charT* high) const;

  Returns:
    A  basic_string<charT>  value  that, compared lexicographically with
    the result of calling transform() on another string, yields the same
    result as calling do_compare() on the same two strings.12)

  long do_hash(const charT* low, const charT* high) const;

  Returns:
    An integer value equal to the result of calling hash() on any  other
    string  for which do_compare() returns 0 (equal) when passed the two
    strings.  [Note: The probability that the  result  equals  that  for
    another  string  which  does not compare equal should be very small,
    approaching  (1.0/numeric_limits<unsigned  long>::max()).      --end
    note]

  22.2.4.2  Template class                   [lib.locale.collate.byname]
       collate_byname
  namespace std {
    template <class charT>
    class collate_byname : public collate<charT> {
    public:
      explicit collate_byname(const char*, size_t refs = 0);
    protected:
     ~collate_byname();  // virtual
      virtual int    do_compare(const charT* low1, const charT* high1,
                                const charT* low2, const charT* high2) const;
      virtual string_type do_transform(const charT* low, const charT* high) const;
      virtual long   do_hash(     const charT* low, const charT* high) const;
    };

  22.2.5  The time category                          [lib.category.time]

1 Templates time_get<charT,InputIterator> and time_put<charT,OutputIter-
  ator> provide date and time formatting and parsing.  Their members use
  their ios_base&, ios_base::iostate&, and fill arguments  as  described
  in (_lib.locale.categories_), and the ctype<> facet, to determine for-
  matting details.

  22.2.5.1  Template class time_get                [lib.locale.time.get]

  _________________________
  12)  This function is useful when one string is being compared to many
  other strings.

  namespace std {
    class time_base {
    public:
      enum dateorder { no_order, dmy, mdy, ymd, ydm };
    };

    template <class charT, class InputIterator = istreambuf_iterator<charT> >
    class time_get : public locale::facet, public time_base {
    public:
      typedef charT            char_type;
      typedef InputIterator    iter_type;
      explicit time_get(size_t refs = 0);
      dateorder date_order()  const { return do_date_order(); }
      iter_type get_time(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t)  const;
      iter_type get_date(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t)  const;
      iter_type get_weekday(iter_type s, iter_type end, ios_base& f,
                            ios_base::iostate& err, tm* t) const;
      iter_type get_monthname(iter_type s, iter_type end, ios_base& f,
                              ios_base::iostate& err, tm* t) const;
      iter_type get_year(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t\fP) const;
      static locale::id id;
    protected:
     ~time_get();  // virtual
      virtual dateorder do_date_order()  const;
      virtual iter_type do_get_time(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_date(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_weekday(iter_type s, iter_type end, ios_base&,
                                       ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_monthname(iter_type s, ios_base&,
                                         ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_year(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
    };
  }

1 time_get is used to parse a character sequence, extracting  components
  of  a  time or date into a struct tm record.  Each get member parses a
  format  as  produced  by   a   corresponding   format   specifier   to
  time_put<>::put.   If  the  sequence  being parsed matches the correct
  format, the corresponding members of the struct tm argument are set to
  the  values used to produce the sequence; otherwise either an error is
  reported or unspecified values are assigned.13)

  _________________________
  13) In other words, user confirmation is required for reliable parsing
  of  user-entered dates and times, but machine-generated formats can be
  parsed reliably.  This allows parsers to be  aggressive  about  inter-
  preting user variations on standard formats.

  22.2.5.1.1  time_get members             [lib.locale.time.get.members]

  dateorder date_order() const;

  Returns:
    do_date_order()

  iter_type get_time(iter_type s, iter_type end, ios_base& str,
                     ios_base::iostate& err, tm* t) const;

  Returns:
    do_get_time(s, end, str, err, t)

  iter_type get_date(iter_type s, iter_type end, ios_base& str,
                     ios_base::iostate& err, tm* t) const;

  Returns:
    do_get_date(s, end, str, err, t)

  iter_type get_weekday(iter_type s, iter_type end, ios_base& str,
                        ios_base::iostate& err, tm* t) const;
  iter_type get_monthname(iter_type s, iter_type end, ios_base& str,
                          ios_base::iostate& err, tm* t) const;

  Returns:
    do_get_weekday(s, end, str, err, t) or do_get_monthname(s, end, str,
    err, t)

  iter_type get_year(iter_type s, iter_type end, ios_base& str,
                     ios_base::iostate& err, tm* t) const;

  Returns:
    do_get_year(s, end, str, err, t)

  22.2.5.1.2  time_get virtual            [lib.locale.time.get.virtuals]
       functions

  dateorder do_date_order() const;

  Returns:
    An  enumeration  value  indicating the preferred order of components
    for those date formats that are composed of day, month, and year.14)
    Returns no_order if the date format specified by 'x' contains  other
  _________________________
  14) This function is intended as a convenience only, for  common  for-
  mats, and may return no_order in valid locales.

    variable components (e.g. Julian day, week number, week day).

  iter_type do_get_time(iter_type s, iter_type end, ios_base& str,
                        ios_base::iostate& err, tm* t) const;

  Effects:
    Reads  characters  starting at s until it has extracted those struct
    tm members, and remaining format characters, used by time_put<>::put
    to  produce  the  format specified by 'X', or until it encounters an
    error or end of sequence.
  Returns:
    An iterator pointing immediately beyond the  last  character  recog-
    nized as possibly part of a valid time.

  iter_type do_get_date(iter_type s, iter_type end, ios_base& str,
                        ios_base::iostate& err, tm* t) const;

  Effects:
    Reads  characters  starting at s until it has extracted those struct
    tm members, and remaining format characters, used by time_put<>::put
    to  produce  the  format specified by 'x', or until it encounters an
    error.
  Returns:
    An iterator pointing immediately beyond the  last  character  recog-
    nized as possibly part of a valid date.

  iter_type do_get_weekday(iter_type s, iter_type end, ios_base& str,
                           ios_base::iostate& err, tm* t) const;
  iter_type do_get_monthname(iter_type s, iter_type end, ios_base& str,
                             ios_base::iostate& err, tm* t) const;

  Effects:
    Reads  characters  starting at s until it has extracted the (perhaps
    abbreviated) name of a weekday or month.  If it finds  an  abbrevia-
    tion that is followed by characters that could match a full name, it
    continues reading until it matches the full name or fails.  It  sets
    the appropriate struct tm member accordingly.
  Returns:
    An  iterator  pointing  immediately beyond the last character recog-
    nized as part of a valid name.

  iter_type do_get_year(iter_type s, iter_type end, ios_base& str,
                        ios_base::iostate& err, tm* t) const;

  Effects:
    Reads characters starting at s until it has extracted an unambiguous
    year  identifier.   It  is  implementation-defined whether two-digit
    year numbers are accepted, and (if so) what century they are assumed
    to lie in.  Sets the t->tm_year member accordingly.

  Returns:
    An  iterator  pointing  immediately beyond the last character recog-
    nized as part of a valid year identifier.

  22.2.5.2  Template class                  [lib.locale.time.get.byname]
       time_get_byname
  namespace std {
    template <class charT, class InputIterator = istreambuf_iterator<charT> >
    class time_get_byname : public time_get<charT, InputIterator> {
    public:
      explicit time_get_byname(const char*, size_t refs = 0);
    protected:
     ~time_get_byname();  // virtual
      virtual dateorder do_date_order()  const;
      virtual iter_type do_get_time(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_date(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_weekday(iter_type s, iter_type end, ios_base&,
                                       ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_monthname(iter_type s, iter_type end, ios_base&,
                                         ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_year(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
    };
  }

  22.2.5.3  Template class time_put                [lib.locale.time.put]
  namespace std {
    template <class charT, class OutputIterator = ostreambuf_iterator<charT> >
    class time_put : public locale::facet {
    public:
      typedef charT            char_type;
      typedef OutputIterator   iter_type;
      explicit time_put(size_t refs = 0);
        // the following is implemented in terms of other member functions.
      iter_type put(iter_type s, ios_base& f, char_type fill, const tm* tmb,
                    const charT* pattern, const charT* pat_end) const;
      iter_type put(iter_type s, ios_base& f, char_type fill,
                    const tm* tmb, char format, char modifier = 0) const;
      static locale::id id;
    protected:
     ~time_put();  // virtual
      virtual iter_type do_put(iter_type s, ios_base&, char_type, const tm* t,
                               char format, char modifier) const;
    };
  }

  22.2.5.3.1  time_put members             [lib.locale.time.put.members]

  iter_type put(iter_type s, ios_base&, char_type fill, const tm* t,
                const charT* pattern, const charT* pat_end) const;
  iter_type put(iter_type s, ios_base&, char_type fill, const tm* t,
                char format, char modifier = 0) const;

  Effects:
    The  first  form interprets the characters immediately following a %
    in the sequence between pattern and pat_end  as  format  specifiers,
    according  to the mapping used by the function strftime() Characters
    are converted using ctype<>::narrow() to identify format specifiers.
    [Note:  This implies that if narrow() has no mapping for the charac-
    ter %, no format specifiers are identified.   --end note]
    The second form calls do_put() once, simply passing along its  argu-
    ments.
  Returns:
    An  iterator pointing immediately after the last character produced.

  22.2.5.3.2  time_put virtual            [lib.locale.time.put.virtuals]
       functions

  iter_type do_put(iter_type s, ios_base&, char_type fill, const tm* t,
                   char format, char modifier) const;

  Effects:
    Formats  the  contents  of the parameter t into characters placed on
    the output sequence s.  Formatting is controlled by  the  parameters
    format  and  modifier,  interpreted identically as the format speci-
    fiers in the  string  argument  to  the  standard  library  function
    strftime().15)
  Returns:
    An iterator pointing immediately after the last character  produced.

  22.2.5.4  Template class                  [lib.locale.time.put.byname]
       time_put_byname
  namespace std {
    template <class charT, class OutputIterator = ostreambuf_iterator<charT> >
    class time_put_byname : public time_put<charT, OutputIterator>
    {
    public:
      explicit time_put_byname(const char*, size_t refs = 0);
    protected:
     ~time_put_byname();  // virtual
      virtual iter_type do_put(iter_type s, ios_base&, char_type, const tm* t,
                               char format, char modifier) const;
    };
  }

  _________________________
  15) Interpretation of the modifier argument is implementation-defined,
  but should follow POSIX conventions.

  22.2.6  The monetary category                  [lib.category.monetary]

1 These templates handle monetary formats.  A template  parameter  indi-
  cates  whether local or international monetary formats are to be used.

2 money_get<>   and   money_put<>   members   use    their    ios_base&,
  ios_base::iostate&,    and    fill    arguments    as   described   in
  (_lib.locale.categories_), and the moneypunct<> and ctype<> facets, to
  determine formatting details.

  22.2.6.1  Template class money_get              [lib.locale.money.get]
  namespace std {
    template <class charT,
              class InputIterator = istreambuf_iterator<charT> >
    class money_get : public locale::facet {
    public:
      typedef charT               char_type;
      typedef InputIterator       iter_type;
      typedef basic_string<charT> string_type;
      explicit money_get(size_t refs = 0);
      iter_type get(iter_type s, iter_type end, bool intl,
                    ios_base& f, ios_base::iostate& err,
                    long double& units) const;
      iter_type get(iter_type s, iter_type end, bool intl,
                    ios_base& f, ios_base::iostate& err,
                    string_type& digits) const;
      static const bool intl = Intl;
      static locale::id id;
    protected:
     ~money_get();  // virtual
      virtual iter_type do_get(iter_type, bool, iter_type, ios_base&,
                               ios_base::iostate& err, long double& units) const;
      virtual iter_type do_get(iter_type, bool, iter_type, ios_base&,
                               ios_base::iostate& err, string_type& digits) const;
    };
  }

  22.2.6.1.1  money_get members           [lib.locale.money.get.members]

  iter_type get(iter_type s, iter_type end, bool intl,
                ios_base& f, ios_base::iostate& err,
                long double& quant) const;
  iter_type get(s, iter_type end, bool intl, ios_base&f,
                ios_base::iostate& err, string_type& quant) const;

  Returns:
    do_get(s, end, intl, f, err, quant)

  22.2.6.1.2  money_get virtual          [lib.locale.money.get.virtuals]
       functions

  iter_type do_get(iter_type s, iter_type end, bool intl,
                   ios_base& str, ios_base::iostate& err,
                   long double& units) const;
  iter_type do_get(iter_type s, iter_type end, bool intl,
                   ios_base& strfP, ios_base::iostate& err,
                   string_type& digits) const;

  Effects:
    Reads characters from s until it has constructed a  monetary  value,
    as specified in str.flags() and the moneypunct<charT,true> or money-
    punct<charT,false> facet of str.getloc(), (depending on whether intl
    is  true  or  false respectively) or until it encounters an error or
    runs out of characters.  It parses the format sequence specified  by
    moneypunct<>::neg_format() for all monetary values.  The result is a
    pure sequence of digits, representing a count of the  smallest  unit
    of currency representable.16)
    Digit group separators are optional; if present, digit  grouping  is
    checked after all syntactic elements have been read.  If no grouping
    is specified, any thousands separator characters encountered in  the
    input sequence are not considered part of the numeric format.
    Where space or none appear in the format pattern, except at the end,
    optional whitespace is consumed.  If (str.flags() &  ios_base::show-
    base)  is  false, the currency symbol is optional, and if it appears
    after all other required syntactic elements it is not consumed.   If
    the  expression  above is true, the currency symbol is required, and
    is always consumed.  If the first character of the a sign appears in
    its  correct  position,  any remaining sign characters are required,
    and consumed.  [Example: If showbase is off, then when the  sign  is
    "()"  and  the  currency symbol is "L", in "(100 L)" the "L" is con-
    sumed; but in "-100 L" it is not.   --end example] Sets the argument
    units  or  digits  from  the  sequence  of  digits  found.  units is
    negated, or digits is preceded by '-', for  a  negative  value.   On
    error, the units or digits argument is unchanged.
  Returns:
    An  iterator  pointing  immediately beyond the last character recog-
    nized as part of a valid monetary quantity.

  +-------                      BEGIN BOX 4                     -------+
  The description above needs further review.
  +-------                       END BOX 4                      -------+

  _________________________
  16) For  example, the sequence $1,056.23 in a common U.S. locale would
  yield, for units, 105623, or for digits, 105623".

  22.2.6.2  Template class money_put              [lib.locale.money.put]
  namespace std {
    template <class charT, bool Intl = false,
              class OutputIterator = ostreambuf_iterator<charT> >
    class money_put : public locale::facet {
    public:
      typedef charT               char_type;
      typedef OutputIterator      iter_type;
      typedef basic_string<charT> string_type;
      explicit money_put(size_t refs = 0);
      iter_type put(iter_type s, bool intl, ios_base& f,
                    char_type fill, long double units) const;
      iter_type put(iter_type s, bool intl, ios_base& f,
                    char_type fill, const string_type& digits) const;
      static locale::id id;
    protected:
     ~money_put();  // virtual
      virtual iter_type
        do_put(iter_type, bool, ios_base&, char_type fill,
               long double units) const;
      virtual iter_type
        do_put(iter_type, bool, ios_base&, char_type fill,
               const string_type& digits) const;
    };
  }

  22.2.6.2.1  money_put members           [lib.locale.money.put.members]

  iter_type put(iter_type s, bool intl, ios_base& f, char_type fill,
                long double quant) const;
  iter_type put(iter_type s, bool intl, ios_base& f, char_type fill,
                const string_type& quant) const;

  Returns:
    do_put(s, intl, f, loc, quant)

  22.2.6.2.2  money_put virtual          [lib.locale.money.put.virtuals]
       functions

  iter_type do_put(iter_type s, bool intl, ios_base& str,
                   char_type fill, long double units) const;
  iter_type do_put(iter_type s, bool intl, ios_base& str,
                   char_type fill, const string_type& digits) const;

  Effects:
    Writes  characters  to  s,  according to the format specified by the
    moneypunct<charT,true>  or  moneypunch<charT,false>  facet  of   loc
    (depending  on  whether  intl  is  true  or false respectively), and
    str.flags().  Ignores any fractional part of units, or  any  charac-
    ters  in  digits  beyond  the (optional) leading '-' and immediately
    subsequent digits.

  Notes:
    The  currency  symbol  is   generated   only   if   (str.flags()   &
    ios_type::showbase)  is  true.  If ((str.flags() & ios_type::adjust-
    field) == ios_type::internal) the fill characters are  placed  where
    none or space appears in the formatting pattern (_lib.money.get.vir-
    tuals_).
  Returns:
    An iterator pointing immediately after the last character  produced.

  22.2.6.3  Template class moneypunct            [lib.locale.moneypunct]
  namespace std {
    class money_base {
    public:
      enum part { none, space, symbol, sign, value };
      struct pattern { char field[4]; };
    };

    template <class charT, bool International = false>
    class moneypunct : public locale::facet, public money_base {
    public:
      typedef charT char_type;
      typedef basic_string<charT> string_type;
      explicit moneypunct(size_t refs = 0);
      charT        decimal_point() const;
      charT        thousands_sep() const;
      string       grouping()      const;
      string_type  curr_symbol()   const;
      string_type  positive_sign() const;
      string_type  negative_sign() const;
      int          frac_digits()   const;
      pattern      pos_format()    const;
      pattern      neg_format()    const;
      static locale::id id;
      static const bool intl = International;
    protected:
     ~moneypunct();  // virtual
      virtual charT        do_decimal_point() const;
      virtual charT        do_thousands_sep() const;
      virtual string       do_grouping()      const;
      virtual string_type  do_curr_symbol()   const;
      virtual string_type  do_positive_sign() const;
      virtual string_type  do_negative_sign() const;
      virtual int          do_frac_digits()   const;
      virtual pattern      do_pos_format()    const;
      virtual pattern      do_neg_format()    const;
    };
  }

1 This   provides   money   punctuation,  similar  to  numpunct<>  above
  (_lib.locale.numpunct_).  In particular, the value portion of the for-
  mat is:
    value ::= units [decimal-point [digits]] |
              decimal-point digits
  if frac_digits returns a positive value, or just

    value ::= units
  otherwise.   In these forms, the decimal-point and thousands-separator
  are as determined below and the number of  digits  after  the  decimal
  point is exactly the value returned by frac_digits.

  22.2.6.3.1  moneypunct members         [lib.locale.moneypunct.members]

      charT        decimal_point() const;
      charT        thousands_sep() const;
      string       grouping()      const;
      string_type  curr_symbol()   const;
      string_type  positive_sign() const;
      string_type  negative_sign() const;
      int          frac_digits()   const;
      pattern      pos_format()    const;
      pattern      neg_format()    const;

1 Each  of  these  functions  F returns the result of calling the corre-
  sponding virtual member function do_F().

  22.2.6.3.2  moneypunct virtual        [lib.locale.moneypunct.virtuals]
       functions

  charT do_decimal_point() const;

  Returns:
    The  radix separator to use in case do_frac_digits() is greater than
    zero.17)

  charT do_thousands_sep() const;

  Returns:
    The digit group separator to use in case do_grouping()  specifies  a
    digit grouping pattern.18)

  string       do_grouping() const;

  Returns:
    A     pattern    defined    identically    as    the    result    of
    numpunct<charT>::do_grouping().19)

  string_type do_curr_symbol() const;
  _________________________
  17) In common U.S. locales this is '.'.
  18) In common U.S. locales this is ','.
  19) This is most commonly the value "\003" not "3").

  Returns:
    A string to use as the currency identifier symbol.20)

  string_type do_positive_sign() const;
  string_type do_negative_sign() const;

  Returns:
    do_positive_sign() returns the string to use to indicate a  positive
    monetary  value;21)  do_negative_sign() returns the string to use to
    indicate a negative value.  The first character of  the  string  (if
    any)  is placed in the position indicated for the sign in the format
    pattern, and any remaining characters are  placed  after  all  other
    format elements.

  int do_frac_digits() const;

  Returns:
    The number of digits after the decimal radix separator, if any.22)

  pattern do_pos_format() const;
  pattern do_neg_format() const;

  Returns:
    A  pattern,  a four-element array specifying the order in which syn-
    tactic elements appear in the monetary format.  In this  array  each
    enumeration  value  symbol,  sign,  value,  and either space or none
    appears exactly once.  none, if present, is  not  first;  space,  if
    present,  is  neither  first  nor last.  Otherwise, the elements may
    appear in any order.   The  base  class  implementation  returns  an
    object of type pattern initialized to { symbol, sign, none, value };
    this value is also returned for all international instantiations.23)

  22.2.6.4  Template class                [lib.locale.moneypunct.byname]
       moneypunct_byname

  _________________________
  20) For international instantiations (second template parameter  true)
  this  is  always  four  characters  long,  usually three letters and a
  space.
  21) This is usually the empty string.
  22) In common U.S. locales, this is 2.
  23) Note that the international symbol returned by do_curr_sym()  usu-
  ally contains a space, itself; for example, "USD ".

  namespace std {
    template <class charT, bool Intl = false>
    class moneypunct_byname : public moneypunct<charT, Intl> {
    public:
      explicit moneypunct_byname(const char*, size_t refs = 0);
    protected:
     ~moneypunct_byname();  // virtual
      virtual charT        do_decimal_point() const;
      virtual charT        do_thousands_sep() const;
      virtual string       do_grouping()      const;
      virtual string_type  do_curr_symbol()   const;
      virtual string_type  do_positive_sign() const;
      virtual string_type  do_negative_sign() const;
      virtual int          do_frac_digits()   const;
      virtual pattern      do_pos_format()    const;
      virtual pattern      do_neg_format()    const;
    };
  }

  22.2.7  The message retrieval category         [lib.category.messages]

1 Class  messages<charT>  implements  retrieval  of strings from message
  catalogs.

  22.2.7.1  Template class messages                [lib.locale.messages]
  namespace std {
    class messages_base {
    public:
      typedef int catalog;
    };

    template <class charT>
    class messages : public locale::facet, public messages_base {
    public:
      typedef charT char_type;
      typedef basic_string<charT> string_type;
      explicit messages(size_t refs = 0);
      catalog open(const basic_string<char>& fn, const locale&) const;
      string_type  get(catalog c, int set, int msgid,
                       const string_type& dfault) const;
      void    close(catalog c) const;
      static locale::id id;
    protected:
     ~messages();  // virtual
      virtual catalog do_open(const basic_string<char>&, const locale&) const;
      virtual string_type  do_get(catalog, int set, int msgid,
                             const string_type& dfault) const;
      virtual void    do_close(catalog) const;
    };
  }

1 Values of type messages_base::catalog usable as arguments  to  members
  get and close can be obtained only by calling member open.

  22.2.7.1.1  messages members             [lib.locale.messages.members]

  catalog open(const basic_string<char>& name, const locale& loc) const;

  Returns:
    do_open(name, loc).

  string_type get(catalog cat, int set, int msgid,
                  const string_type& dfault) const;

  Returns:
    do_get(cat, set, msgid, dfault).

  void  close(catalog cat) const;

  Effects:
    Calls do_close(cat).

  22.2.7.1.2  messages virtual            [lib.locale.messages.virtuals]
       functions

  catalog do_open(const basic_string<char>& name,
                  const locale& loc) const;

  Returns:
    A value that may be passed to get() to retrieve a message, from  the
    message catalog identified by the string name according to an imple-
    mentation-defined mapping.  The result  can  be  used  until  it  is
    passed to close().
    Returns a value less than 0 if no such catalog can be opened.
  Notes:
    The  locale  argument  loc is used for character set code conversion
    when retrieving messages, if needed.

  string_type do_get(catalog cat, int set, int msgid,
                const string_type& dfault) const;

  Requires:
    A catalog cat obtained from open() and not yet closed.
  Returns:
    A message identified by arguments set, msgid, and dfault,  according
    to  an  implementation-defined  mapping.   If no such message can be
    found, returns dfault.

  void do_close(catalog cat) const;

  Requires:
    A catalog cat obtained from open() and not yet closed.
  Effects:
    Releases unspecified resources associated with  cat.
  Notes:
    The limit on such resources, if any, is implementation-defined.

  22.2.7.2  Template class                  [lib.locale.messages.byname]
       messages_byname
  namespace std {
    template <class charT>
    class messages_byname : public messages<charT> {
    public:
      explicit messages_byname(const char*, size_t refs = 0);
    protected:
     ~messages_byname();  // virtual
      virtual catalog do_open(const basic_string<char>&, const locale&) const;
      virtual string_type  do_get(catalog, int set, int msgid,
                             const string_type& dfault) const;
      virtual void    do_close(catalog) const;
    };
  }

  22.2.8  Program-defined facets                   [lib.facets.examples]

1 A C++ program may define facets to be added to a locale and used iden-
  tically as the built-in facets.  To create a new facet interface,  C++
  programs  simply derive from locale::facet a class containing a static
  member: static locale::id id.

2 [Note: The locale member function templates verify its type and  stor-
  age class.   --end note]

3 This initialization/identification system depends only on the initial-
  ization to 0 of static objects, before static constructors are called.
  When  an  instance  of  a  facet  is installed in a locale, the locale
  checks whether an id has been  assigned,  and  if  not,  assigns  one.
  Before  this  occurs,  any  attempted  use of its interface causes the
  bad_cast exception to be thrown.

4 [Example: Here is a program that just calls C functions:
    #include <locale>
    extern "C" void c_function();
    int main()
    {
      using namespace std;
      locale::global(locale(""));  // same as setlocale(LC_ALL, "");
      c_function();
      return 0;
    }
  In other words, C library localization is unaffected.   --end example]

5 [Example: Traditional global localization is still easy:

    #include <iostream>
    #include <locale>
    int main(int argc, char** argv)
    {
      using namespace std;
      locale::global(locale(""));  // set the global locale
        // imbue it on all the std streams
      cin.imbue(locale());
      cout.imbue(locale());
      cerr.imbue(locale());
      wcin.imbue(locale());
      wcout.imbue(locale());
      wcerr.imbue(locale());

      return MyObject(argc, argv).doit();
    }
   --end example]

6 [Example: Greater flexibility is possible:
    #include <iostream>
    #include <locale>
    int main()
    {
      using namespace std;
      cin.imbue(locale(""));  // the user's preferred locale
      cout.imbue(locale::classic());
      double f;
      while (cin >> f) cout << f << endl;
      return (cin.fail() != 0);
    }
  In  a European locale, with input 3.456,78, output is 3456.78.   --end
  example]

7 This can be important even for simple  programs,  which  may  need  to
  write  a  data  file in a fixed format, regardless of a user's prefer-
  ence.

8 [Example: Here is an example of the use of locales in a library inter-
  face.
    // file: Date.h
    #include <iosfwd>
    #include <string>
    #include <locale>
       ...
    class Date {
      ...
     public:
      Date(unsigned day, unsigned month, unsigned year);
      std::string asString(const std::locale& = std::locale());
    };
    istream& operator>>(istream& s, Date& d);
    ostream& operator<<(ostream& s, Date d);
    ...
  This example illustrates two architectural uses of class locale.

9 The  first  is  as  a  default argument in Date::asString(), where the
  default is the global (presumably user-preferred) locale.

10The second is in the operators << and >>, where a locale  "hitchhikes"
  on  another  object,  in  this case a stream, to the point where it is
  needed.
    // file: Date.C
    #include "Date"  // includes <ctime>
    #include <sstream>
    std::string Date::asString(const std::locale& l)
    {
      using namespace std;
      ostringstream s; s.imbue(l);
      s << *this; return s.str();
    }
    std::istream& operator>>(std::istream& s, Date& d)
    {
      using namespace std;
      istream::sentry cerberos;
      if (cerberos) {
        ios_base::iostate err = goodbit;
        struct tm t;
        use_facet< time_get<char> >(s.getloc()).get_date(s, 0, s, err, &t);
        if (!err) d = Date(t.tm_day, t.tm_mon + 1, t.tm_year + 1900);
        s.setstate(err);
      }
      return s;
    }
   --end example]

11A locale object may be extended with a new facet simply by  construct-
  ing  it  with  an instance of a class derived from locale::facet.  The
  only member a C++ program must define is the static member  id,  which
  identifies your class interface as a new facet.

12[Example: Classifying Japanese characters:
    // file: <jctype>
    #include <locale>
    namespace My {
      using namespace std;
      class JCtype : public locale::facet {
      public:
        static locale::id id;  // required for use as a new locale facet
        bool is_kanji(wchar_t c);
        JCtype() {}
      protected:
       ~JCtype() {}
      };
    }

    // file: filt.C
    #include <iostream>
    #include <locale>
    #include "jctype" // above
    std::locale::id JCtype::id;  // the static JCtype member declared above.
    int main()
    {
      using namespace std;
      typedef ctype<wchar_t> wctype;
      locale loc(locale(""),       // the user's preferred locale ...
                 new My::JCType);  // and a new feature ...
      wchar_t c = use_facet<wctype>(loc).widen('!');
      if (use_facet<My::JCType>(loc).is_kanji(c))
        cout << "no it isn't!" << endl;
      return 0;
    }

13The  new facet is used exactly like the built-in facets.   --end exam-
  ple]

14[Example: Replacing an existing facet is even easier.  Here we do  not
  define  a  member  id because we are reusing the numpunct<charT> facet
  interface:
    // my_bool.C
    #include <iostream>
    #include <locale>
    #include <string>
    namespace My {
      using namespace std;
      typedef numpunct_byname<char> cnumpunct;
      class BoolNames : public cnumpunct {
       protected:
        string do_truename()  { return "Oui Oui!"; }
        string do_falsename() { return "Mais Non!"; }
       ~BoolNames() {}
      public:
        BoolNames(const char* name) : cnumpunct(name) {}
      };
    }
    int main(int argc, char** argv)
    {
      using namespace std;
      // make the user's preferred locale, except for...
      locale loc(locale(""), new My::BoolNames(""));
      cout.imbue(loc);
      cout << boolalpha << "Any arguments today? " << (argc > 1) << endl;
      return 0;
    }
   --end example]

  22.3  C Library Locales                                [lib.c.locales]

1 Header <clocale> (Table 13):

                   Table 13--Header <clocale> synopsis

            +-------------------------------------------------+
            |   Type                    Name(s)               |
            +-------------------------------------------------+
            |Macros:                                          |
            |             LC_ALL        LC_COLLATE   LC_CTYPE |
            |             LC_MONETARY   LC_NUMERIC   LC_TIME  |
            |             NULL                                |
            +-------------------------------------------------+
            |Struct:      lconv                               |
            +-------------------------------------------------+
            |Functions:   localeconv    setlocale             |
            +-------------------------------------------------+

2 The contents are the same as the Standard C library header <locale.h>.

  SEE ALSO: ISO C clause 7.4.