______________________________________________________________________

  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

  #include <limits>
  #include <string>
  #include <iosfwd>
  #include <stdexcept>    // for runtime_error
  #include <vector>       // for vector<char>

  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();
    template <class charT, class Traits>
      basic_ostream<charT,Traits>&
        operator<<(basic_ostream<charT,Traits>& s, const locale& loc);
    template <class charT, class Traits>
      basic_istream<charT,Traits>&
        operator>>(basic_istream<charT,Traits>& s, locale& loc);
  // 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;
                           class ctype<char>;        // specialization
    template <class charT> class ctype_byname;
                           class ctype_byname<char>; // specialization
    class codecvt_base;
    template <class fromT, class toT, class stateT> class codecvt;
    template <class fromT, class toT, 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> class moneypunct;
    template <class charT> 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)

  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, category);
      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,Traits>
        bool operator()(const basic_string<charT,Traits>& s1,
                        const basic_string<charT,Traits>& s2) const;

  _________________________
  1)  In  this  subclause, the type name struct tm is an incomplete type
  that is defined in <ctime>.

    // global locale objects:
      static       locale  global(const locale&);
      static const locale& classic();
      static       locale  transparent();
    };
  }

  +-------                 BEGIN BOX 1                -------+
  Change: Added a third argument, category, to  the  second  constructor
  template    above    for    consistency   with   the   definition   in
  [lib.locale.cons]
  +-------                  END BOX 1                 -------+

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  (and  special­
  ized, for simplicity of exposition) as:2)
    ostream& operator<<(ostream& s, double f)
    {
      if (s.opfx()) {
        locale loc = s.getloc();
        use_facet< num_put<char> >(loc).put(s, s, loc, f);
      }
      s.osfx();
      return s;
    }
   --end example]

  +-------                 BEGIN BOX 2                -------+
  Error handling must be added to the example above, once it is  decided
  what to do.
  +-------                  END BOX 2                 -------+

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_).

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

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

  --A   member    operator    template    operator()(basic_string<C,T>&,
    basic_string<C,T>&)  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 A  locale  which  does  not  implement a facet delegates to the global
  locale in effect at the time  that  instantiation  of  use_facet<>  is
  first called on that facet (_lib.locale.statics_).

7 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.   The  effect  of imbuing on a stream (_lib.ios.base_,
  _lib.ios_), or installing as the global locale, the result  of  static
  member  locale::transparent() (or any locale with similar behavior) is
  unspecified.

8 Caching results from calls to locale  facet  member  functions  during
  calls  to iostream inserters and extractors, and in streambufs between
  calls   to    basic_streambuf::imbue,    is    explicitly    supported
  (_lib.streambuf_).3)

9 A locale constructed from a name string (such  as  "POSIX"),  or  from
  parts  of  two  named  locales, or read from a stream, 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 unsigned category;

1 Valid category values include 0 and the locale member bitmask elements
  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.
  _________________________
  3) This implies that member functions of iostream classes cannot safe­
  ly call imbue() themselves, except as specified elsewhere.

  +-------                 BEGIN BOX 3                -------+
  Change: The proposal (N0699,22-003), specified that "&" meant "union",
  and "|" intersection.  This was seen as a typo.
  +-------                  END BOX 3                 -------+

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,wchar_t,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>                |
      +------------------------------------------------------------+

  +-------                 BEGIN BOX 4                -------+
  Editorial Proposal: Add money_get<char,true>, money_get<wchar_t,true>,
  money_put<char,true>, and money_put<wchar_t,true>,  or  eliminate  the
  bool  template  parameter  and  add a parameter to the get() and put()
  members to choose at runtime which moneypunct<> facet to use.
  +-------                  END BOX 4                 -------+

3 For   any   locale   loc   either   constructed,   or   returned    by
  locale::classic(),  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,International,InputIterator>,        |
     |           money_get<wchar_t,International,InputIterator>,     |
     |           money_put<char,International,OutputIterator>,       |
     |           money_put<wchar_t,International,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>             |
     +---------------------------------------------------------------+

  +-------                 BEGIN BOX 5                -------+
  Change: In the money_get<> and money_put<> facets of the table  above,
  a template argument International has been added to be consistent with
  the definition of those facets.
  +-------                  END BOX 5                 -------+

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.requirements_).   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.

  +-------                 BEGIN BOX 6                -------+
  Editorial Proposal Those facets represented with a template  parameter
  International represent the set of all possible instantiations on both
  true and false.  [Alternatively, remove the bool parameter from  those
  templates,  and  add  a bool argument to their get() and put() members
  instead.]
  +-------                  END BOX 6                 -------+

  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

  reference 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 Identification of a locale facet  interface,  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  locale instance whose value is a snapshot of the cur­
    rent global locale state as set by locale::global(locale&) or the  C
    function  setlocale().   This  constructor  is  commonly used as the
    default value for arguments of functions that take  a  locale  argu­
    ment.

  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.
  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).
  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.
  Notes:
    The resulting locale has no name.

  +-------                 BEGIN BOX 7                -------+
  Editorial  proposal:  What  if the pointer parameter is 0?  Recommend:
  Throw runtime_error.
  +-------                  END BOX 7                 -------+

  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>
    bool operator()(const basic_string<charT,Traits>& s1,
                    const basic_string<charT,Traits>& 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 Replaces ::setlocale().
  Effects:
    Sets the global locale to its argument.   Subsequent  calls  to  the
    default  constructor, and of other library functions affected by the
    function setlocale(), use the locale loc until the next call to this
    member or setlocale().
  Returns:
    The previous global 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.

  static locale transparent();

3 The continuously updated global locale.
  Returns:
    A  locale  which  implements  semantics that vary dynamically as the
    global locale is changed.
  Notes:
    The effect of imbuing this locale into  an  iostreams  component  is
    unspecified (_lib.ios.members_).

  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.
  Effects:
    If  the requested Facet is not present in loc, but is present in the

    current global locale,  returns  the  global  locale's  instance  of
    Facet.   Because  locale  objects are immutable, subsequent calls to
    use_facet<Facet>(loc) return the same object, regardless  of  subse­
    quent calls to setlocale or locale::global.
  Notes:
    The  only  exception  to  this  rule  is  for the locale returned by
    locale::transparent(); it always returns  the  facet  found  in  the
    global locale at the time of each call.
  Throws:
    bad_cast  if (has_facet<Facet>(*this) || has_facet<Facet>(locale()))
    is false, or other unspecified objects catchable as exception.
  Returns:
    A reference to the requested facet.
  Notes:
    The result is guaranteed by locale's value semantics to last as long
    as the value of locP.

  +-------                 BEGIN BOX 8                -------+
  Is bad_cast the best choice of exceptions to throw?
  +-------                  END BOX 8                 -------+

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

  Returns:
    An  indication  whether  the  facet requested is present in loc.  If
    use_facet<Facet>(loc) has already been called successfully,  returns
    true.
  Notes:
    has_facet<Facet>(locale::transparent()) always returns false.

  template <class charT, class Traits>
    basic_ostream<charT,Traits>&
      operator<<(basic_ostream<charT,Traits>& s, const locale& loc);

2 The     regular     stream     output     operator     for     locales
  (_lib.ostream.formatted_).
  Effects:
    s << loc.name() << endl.
  Returns:
    The output stream argument s.

  template <class charT, class Traits>
    basic_istream<charT,Traits>&
      operator>>(basic_istream<charT,Traits>& s, loc& loc);

3 The     regular     stream     input     operator     for      locales
  (_lib.istream.formatted_).

  Effects:
    Read a line into a string and construct a locale from it.  If either
    operation    fails,    indicates    a     failure     by     calling
    s.setstate(ios_base::failbit)  (which  may  throw  ios_base::failure
    (_lib.iostate.flags_), otherwise,  assigns  the  constructed  locale
    object into the argument loc.
  Returns:
    s.

  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_).4)

  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:
    loc.template use<ctype<charT> >().tolower(c).

  _________________________
  4) When used loop, it is faster to cache the ctype<> facet and use  it
  directly, or use the vector form of ctype<>::is.

  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, intended for use by standard or
  users' operators << and >>.  Those that take a basic_ios<charT>& argu­
  ment obey all formatting conventions specified  for  members  of  that
  class, including width() and fill() (_lib.ios.base_).

  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 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;
    };

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 first
    form returns the result of the expression (M & m) != 0.  The  second
    form  simply  places  M  for  all  *p where (low<=p && p<high), into
    vec[p-low].
  Returns:
    The first form returns true if the character has the characteristics
    specified.  The second form returns high.

  const char* 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 char* 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.
  Effects:
    The  second form replaces each character *p in the range [low, high)
    for which a corresponding 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 upper case.
  Effects:
    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.
    The  only  characters  for which unique transformations are required
    are the digits, alphabetic characters, '-', '+', newline, and space.

    For any named ctype category with a ctype<charT> facet ctw and valid
    ctype_base::mask  value  M,  however,  (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.
    The only characters for which unique  transformations  are  required
    are the digits, alphabetic characters, '-', '+', newline, and space.
    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;
    };
  }

  +-------                 BEGIN BOX 9                -------+
  Change:  In  the previous Draft, the above class definition mistakenly
  described the specialization ctype_byname<char>.  That definition  has
  been  moved  to its proper section, and this one fleshed out according
  to the original proposal.
  +-------                  END BOX 9                 -------+

  22.2.1.3  ctype specializations              [lib.facet.ctype.special]
  namespace std {
    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;
    protected:
      const mask* table() const;
      static const mask* classic_table();
     ~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)

  +-------                BEGIN BOX 10                -------+
  Editorial Proposal: Members  table()  and  classic_table()  should  be
  marked throw().
  +-------                 END BOX 10                 -------+

  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]

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

  Effects:
    Passes its refs argument to its base class constructor.

  _________________________
  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>.

  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
    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.

  const mask* table() const;

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

  +-------                BEGIN BOX 11                -------+
  Editorial proposal: table() should be marked throw().
  +-------                 END BOX 11                 -------+

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

  static const mask* classic_table();

  Returns:
    A   pointer   the   initial   element   of   an   array   of    size
    numeric_limits<unsigned  char>::max() + 1 which represents the clas­
    sifications of characters in the "C" locale.

  +-------                BEGIN BOX 12                -------+
  Editorial proposal: classic_table() should be marked throw().
  +-------                 END BOX 12                 -------+

  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>
    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 fromT, class toT, class stateT>
    class codecvt : public locale::facet, public codecvt_base {
    public:
      typedef fromT  from_type;
      typedef toT    to_type;
      typedef stateT state_type;
      explicit codecvt(size_t refs = 0)
      result convert(stateT& state,
          const fromT* from, const fromT* from_end, const fromT*& from_next,
                toT*   to,         toT*   to_limit,         toT*& to_next) const;
      static locale::id id;
    protected:
     ~codecvt();  // virtual
      virtual result do_convert(stateT& state,
          const fromT* from, const fromT* from_end, const fromT*& from_next,
                toT*   to,   toT*         to_limit,       toT*&   to_next) const;
    };
  }

1 The  class  codecvt<fromT,toT,stateT>  is for use when converting from
  one codeset to another, such as  from  wide  characters  to  multibyte
  characters,  or  between  wide character sets such as Unicode and EUC.
  Instances of this facet are typically used in pairs instantiated oppo­
  sitely.

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

3 Implementations   are   required   to   provide   instantiations   for
  <char,wchar_t,mbstate_t> and <wchar_t,char,mbstate_t>.  Instantiations
  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_convert
  member.  The base class implementations  convert  the  implementation-
  defined native execution codeset.

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

  result convert(stateT& state,
    const fromT* from, const fromT* from_end, const fromT*& from_next,
            toT* to, toT* to_limit, toT*& to_next) const;

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

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

  result do_convert(stateT& state,
    const fromT* from, const fromT* from_end, const fromT*& from_next,
            toT* to, toT* to_limit, toT*& 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  range  [from,from_end),  placing  the
    results  in  sequential positions starting at *to.  Converts no more
    than  (from_end-from)  fromT  elements,  and  stores  no  more  than
    (to_limit-to) toT 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 character successfully converted.
    If  no translation is needed (returns noconv), sets to_next equal to
    argument to.
  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   ran out of space in the destination                    |
     |error     encountered a from_type character it could not convert |
     |noconv    no conversion was needed                               |
     +-----------------------------------------------------------------+

  22.2.1.6  Template class                   [lib.locale.codecvt.byname]
       codecvt_byname
  namespace std {
    template <class fromT, class toT, class stateT>
    class codecvt_byname : public codecvt<fromT, toT, stateT> {
    public:
      explicit codecvt_byname(const char*, size_t refs = 0);
    protected:
     ~codecvt_byname();  // virtual
      virtual result do_convert(stateT& state,
        const fromT* from, const fromT* from_end, const fromT*& from_next,
              toT*   to,   toT*         to_limit,       toT*&   to_next) const;
    };
  }

  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 are allowed to delegate extraction of smaller types to
  extractors for larger types, but are not required to do so.

2 The functions take a locale argument because their base  class  imple­
  mentation relies on numpunct<> members to identify all numeric punctu­
  ation preferences, and on ctype<> members to perform character classi­
  fication.

3 Extractor  and inserter members of the standard iostreams are required
  to use num_get<> and num_put<> member  functions  for  formatting  and
  parsing                               (_lib.istream.formatted.reqmts_,
  _lib.ostream.formatted.reqmts_).  The ios_type& argument is used  both
  for  format  control, and to report errors, as described in subclauses
  _lib.iostate.flags_ and _lib.fmtflags.state_.

  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;
      typedef basic_ios<charT> ios_type;
      explicit num_get(size_t refs = 0);
      iter_type get(iter_type in, iter_type end, ios_type&,
                    const locale&, bool& v)          const;
      iter_type get(iter_type in, iter_type end, ios_type& ,
                    const locale&, long& v)          const;
      iter_type get(iter_type in, iter_type end, ios_type&,
                    const locale&, unsigned long& v) const;
      iter_type get(iter_type in, iter_type end, ios_type&,
                    const locale&, double& v)        const;
      iter_type get(iter_type in, iter_type end, ios_type&,
                    const locale&, long double& v)   const;
      static locale::id id;
    protected:
     ~num_get();  // virtual
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               bool& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               unsigned long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               long double& 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_type& str
                const locale& loc, bool& val) const;
  iter_type get(iter_type in, iter_type end, ios_type& str
                const locale& loc, long& val) const;
  iter_type get(iter_type in, iter_type end, ios_type& str
                const locale& loc, unsigned long& val) const;
  iter_type get(iter_type in, iter_type end, ios_type& str
                const locale& loc, double& val) const;
  iter_type get(iter_type in, iter_type end, ios_type& str
                const locale& loc, long double& val) const;

  Returns:
    do_get(in, end, str, loc, 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_type& str
                   const locale& loc, bool& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_type& str
                   const locale& loc, long& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_type& str
                   const locale& loc, unsigned long& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_type& str
                   const locale& loc, double& val) const;
  iter_type do_get(iter_type in, iter_type end, ios_type& str
                   const locale& loc, long double& val) const;

  Effects:
    Reads  characters  from   in,   interpreting   them   according   to
    str.flags(), loc.use template< ctype<charT> >, and loc.use template<
    numpunct<charT> >.  do_get() ignores  the  value  of  str.rdstate();
    however,  indicates  failure by calling str.setstate(failbit) (which
    may throw ios_base::failure (_lib.iostate.flags_)).
    If an error occurs, val is unchanged; otherwise it  is  set  to  the
    resulting value.
  Notes:
    Digit  group  separators are optional; if present, digit grouping is
    checked after the entire number is read.  When reading a non-numeric
    boolean value, the names are compared exactly.
  Returns:
    An iterator pointing one past the last character consumed as part of
    the converted field.

  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;
      typedef basic_ios<charT> ios_type;
      explicit num_put(size_t refs = 0);
      iter_type put(iter_type s, ios_type& f, const locale& loc, bool v) const;
      iter_type put(iter_type s, ios_type& f, const locale& loc, long v) const;
      iter_type put(iter_type s, ios_type& f, const locale& loc,
                    unsigned long v) const;
      iter_type put(iter_type s, ios_type& f, const locale& loc, double v) const;
      iter_type put(iter_type s, ios_type& f, const locale& loc,
                    long double v) const;
      static locale::id id;

    protected:
     ~num_put();  // virtual
      virtual iter_type do_put(iter_type, ios_type&, const locale&, bool v) const;
      virtual iter_type do_put(iter_type, ios_type&, const locale&, long v) const;
      virtual iter_type do_put(iter_type, ios_type&, const locale&,
                               unsigned long) const;
      virtual iter_type do_put(iter_type, ios_type&, const locale&, double v) const;
      virtual iter_type do_put(iter_type, ios_type&, const locale&,
                               long double 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_type& str
                const locale& loc, bool val) const;
  iter_type put(iter_type out, ios_type& str
                const locale& loc, long val) const;
  iter_type put(iter_type out, ios_type& str
                const locale& loc, unsigned long val) const;
  iter_type put(iter_type out, ios_type& str
                const locale& loc, double val) const;
  iter_type put(iter_type out, ios_type& str
                const locale& loc, long double val) const;

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

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

  iter_type do_put(iter_type out, ios_type& str
                   const locale& loc, bool val) const;
  iter_type do_put(iter_type out, ios_type& str
                   const locale& loc, long val) const;
  iter_type do_put(iter_type out, ios_type& str
                   const locale& loc, unsigned long val) const;
  iter_type do_put(iter_type out, ios_type& str
                   const locale& loc, double val) const;
  iter_type do_put(iter_type out, ios_type& str
                   const locale& loc, long double val) const;

  Effects:
    Writes characters to the sequence out, formatting val  according  to
    str.flags(), loc.use template< ctype<charT> >, and loc.use template<
    numpunct<charT> >.  Inserts digit group separators as  specified  by
    numpunct<charT>::do_grouping.

  Notes:
    do_put()  ignores  and  does  not change the result of str.rdstate()
    (_lib.ios.base_).
  Returns:
    An iterator pointing immediately after the last character  produced.

  +-------                BEGIN BOX 13                -------+
  What  if do_put cannot produce all the characters requested?  Is there
  a way to bound how much storage do_put will consume?  If we don't know
  if  the puts fail, how can ostream member functions set badbit as they
  are required to do?  The same questions apply  to  the  put  functions
  later in this clause.
  +-------                 END BOX 13                 -------+

  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);
      string_type  decimal_point()   const;
      string_type  thousands_sep()   const;
      vector<char> grouping()        const;
      string_type  truename()        const;
      string_type  falsename()       const;
      static locale::id id;
    protected:
     ~numpunct();  // virtual
      virtual string_type  do_decimal_point() const;
      virtual string_type  do_thousands_sep() const;
      virtual vector<char> 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 14                -------+
  Is  support for syntax like "0xFF" required for iostreams support?  If
  so, we need to add language describing it.
  +-------                 END BOX 14                 -------+

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

  string_type decimal_point() const;

  Returns:
    do_decimal_point()

  string_type thousands_sep() const;

  Returns:
    thousands_sep()

  vector<char> 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

  string_type do_decimal_point() const;

  Returns:
    A  basic_string<charT>  for  use as the decimal radix separator.  If
    this is not a one-character string, num_get<charT,InputIterator>  is
    not required to recognize numbers formatted using it.
    The base class implementation returns ".".

  string_type do_thousands_sep() const;

  Returns:
    A basic_string<charT> for use as the digit group separator.  If this
    is longer than one character,  num_get<charT,InputIterator>  is  not
    required to recognize numbers formatted with it.
    The base class implementation returns the empty string.

  vector<char> do_grouping() const;

  Returns:
    A  vector  vec in which each element vec[i] represents the number of
    digits in the group at position i starting with 0 as  the  rightmost
    group.   If  vec.size() <= i, the number is the same as group (i-1);
    if (i<0 || vec[i]<=0), the size of the digit group is unlimited.
    The base class implementation returns the empty vector.

  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 string_type  do_decimal_point() const;
      virtual string_type  do_thousands_sep() const;
      virtual vector<char> 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.algorithms_)  and  containers  operating  on  strings.  The base
  class     implementation      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.7)

  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<unsignedlong>::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;
    };

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

  22.2.5  The time category                          [lib.category.time]

1 The          classes         time_get<charT,InputIterator>         and
  time_put<charT,OutputIterator> provide date and  time  formatting  and
  parsing.   The ios_type& argument is used both for format control, and
  to report errors, as described in subclauses  _lib.ios::fmtflags_  and
  _lib.ios::iostate_.

  22.2.5.1  Template class time_get                [lib.locale.time.get]
  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;
      typedef basic_ios<charT> ios_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_type& f,
                         const locale& loc, tm* t)  const;
      iter_type get_date(iter_type s, iter_type end, ios_type& f,
                         const locale& loc, tm* t)  const;
      iter_type get_weekday(iter_type s, iter_type end, ios_type& f,
                            const locale& loc, tm* t) const;
      iter_type get_monthname(iter_type s, iter_type end, ios_type& f,
                              const locale& loc, tm* t) const;
      iter_type get_year(iter_type s, iter_type end, ios_type& f,
                         const locale& loc, 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_type&,
                                    const locale&, tm* t) const;
      virtual iter_type do_get_date(iter_type s, iter_type end, ios_type&,
                                    const locale&, tm* t) const;
      virtual iter_type do_get_weekday(iter_type s, iter_type end, ios_type&,
                                       const locale&, tm* t) const;
      virtual iter_type do_get_monthname(iter_type s, ios_type&,
                                         const locale&, tm* t) const;
      virtual iter_type do_get_year(iter_type s, iter_type end, ios_type&,
                                    const locale&, 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.8)

  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_type& str,
                     const locale& loc, tm* t) const;

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

  iter_type get_date(iter_type s, iter_type end, ios_type& str,
                     const locale& loc, tm* t) const;

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

  iter_type get_weekday(iter_type s, iter_type end, ios_type& str,
                        const locale&loc, tm* t) const;
  iter_type get_monthname(iter_type s, iter_type end, ios_type& str,
                          const locale& loc, tm* t) const;

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

  iter_type get_year(iter_type s, iter_type end, ios_type& str,
                     const locale& loc, tm* t) const;

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

  _________________________
  8)  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.

  22.2.5.1.2  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 dates composed of day, month, and year.
    Returns  no_order if the date format specified by 'X' contains other
    variable components (e.g Julian day, week number, week day).

  iter_type do_get_time(iter_type s, iter_type end, ios_type& str,
                        const locale&, 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.
    Indicates  an  error  by  calling,  str.setstate(failbit), which may
    throw ios_base::failure (_lib.iostate.flags_)).
  Returns:
    An iterator pointing immediately beyond the  last  character  recog­
    nized as part of the time, if no error occurred.

  iter_type do_get_date(iter_type s, iter_type end, ios_type& str,
                        const locale&, 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.
    Indicates failure by calling str.setstate(failbit) (which may  throw
    ios_base::failure (_lib.iostate.flags_)).
  Returns:
    An  iterator  pointing  immediately beyond the last character recog­
    nized as part of the date, if no error occurred.

  iter_type do_get_weekday(iter_type s, iter_type end, ios_type& str,
                           const locale&, tm* t) const;
  iter_type do_get_monthname(iter_type s, iter_type end, ios_type& str,
                             const locale&, 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.
    Indicates failure by calling str.setstate(failbit) (which may  throw
    ios_base::failure (_lib.iostate.flags_)).
  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_type& str,
                        const locale&, tm* t) const;

  Effects:
    Reads characters starting at s until it has extracted an unambiguous
    year  identifier.   It is unspecified whether two-digit year numbers
    are accepted, or what century they are assumed to lie in.  Sets  the
    t->tm_year member accordingly.
    Indicates  failure by calling str.setstate(failbit) (which may throw
    ios_base::failure (_lib.iostate.flags_)).
  Returns:
    An iterator pointing immediately beyond the  last  character  recog­
    nized as part of a valid year identifier.

  +-------                BEGIN BOX 15                -------+
  Editorial  proposal:  Should  this say "implementation-defined" rather
  than "unspecified"?
  +-------                 END BOX 15                 -------+

  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_type&,
                                    const locale&, tm* t) const;
      virtual iter_type do_get_date(iter_type s, iter_type end, ios_type&,
                                    const locale&, tm* t) const;
      virtual iter_type do_get_weekday(iter_type s, iter_type end, ios_type&,
                                       const locale&, tm* t) const;
      virtual iter_type do_get_monthname(iter_type s, iter_type end, ios_type&,
                                         const locale&, tm* t) const;
      virtual iter_type do_get_year(iter_type s, iter_type end, ios_type&,
                                    const locale&, 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;
      typedef basic_ios<charT> ios_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_type& f, const locale& loc, const tm* tmb,
                    const charT* pattern, const charT* pat_end) const;
      iter_type put(iter_type s, ios_type& f, const locale& loc,
                    const tm* t, char format, char modifier = 0) const;
      static locale::id id;
    protected:
     ~time_put();  // virtual
      virtual iter_type do_put(iter_type s, ios_type&, const locale&, 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_type&, const locale&, const tm* t,
                const charT* pattern, const charT* pat_end) const;
  iter_type put(iter_type s, ios_type&, const locale&, 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_type&, const locale&, 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

    specifiers in the string argument to the standard  library  function
    strftime().9)
  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_type&, const locale&, const tm* t,
                               char format, char modifier) const;
    };
  }

  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.
  money_get<> and money_put<> use moneypunct<> members to determine  all
  formatting  details.   moneypunct<>  provides basic format information
  for money processing.  The ios_type& argument is used both for  format
  control,   and   to   report   errors,   as  described  in  subclauses
  _lib.ios::fmtflags_ and _lib.ios::iostate_.

  22.2.6.1  Template class money_get              [lib.locale.money.get]
  namespace std {
    template <class charT, bool Intl = false,
              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;
      typedef basic_ios<charT>    ios_type;
      explicit money_get(size_t refs = 0);
      iter_type get(iter_type s, iter_type end, ios_type& f,
                    const locale& loc, double& units) const;
      iter_type get(iter_type s, iter_type end, ios_type& f,
                    const locale& loc, string_type& digits) const;
      static const bool intl = Intl;
      static locale::id id;

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

    protected:
     ~money_get();  // virtual
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               double& units) const;
      virtual iter_type do_get(iter_type, iter_type, ios_type&, const locale&,
                               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, ios_type& f,
                const locale& loc, double& quant) const;
  iter_type get(s, iter_type end, ios_type&f,
                const locale& loc, string_type& quant) const;

  Returns:
    do_get(s, end, f, loc, 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, ios_type& str,
                   const locale& loc, double& units) const;
  iter_type do_get(iter_type s, iter_type end, ios_type& strfP,
                   const locale& loc, 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> facet of  loc,
    or  until  it  encounters  an  error or runs out of characters.  The
    result is a pure sequence of digits, representing  a  count  of  the
    smallest unit of currency representable.10) Digit  group  separators
    are  optional;  if present, digit grouping is checked after all syn­
    tactic elements have been read.  Where space or none appear  in  the
    format  pattern, except at the end, optional whitespace is consumed.
    If (str.flags() & ios_type::showbase) 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 remain­
    ing  sign characters are required, and consumed.  [Example: If show­
    base is off, then when the sign is "()" and the currency  symbol  is
    "L",  in "(100 L)" the "L" is consumed; 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.
  _________________________
  10) For  example, the sequence $1,056.23 in a common U.S. locale would
  yield, for units, 105623, or for digits, 105623".

    Indicates failure by calling str.setstate(failbit) (which may  throw
    ios_base::failure (_lib.iostate.flags_)).
    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 16                -------+
  The description above needs further review.
  +-------                 END BOX 16                 -------+

  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;
      typedef basic_ios<charT>    ios_type;
      explicit money_put(size_t refs = 0);
      iter_type put(iter_type s, ios_type& f, const locale& loc,
                    double units) const;
      iter_type put(iter_type s, ios_type& f, const locale& loc,
                    const string_type& digits) const;
      static const bool intl = Intl;
      static locale::id id;
    protected:
     ~money_put();  // virtual
      virtual iter_type
        do_put(iter_type, ios_type&, const locale&, double units) const;
      virtual iter_type
        do_put(iter_type, ios_type&, const locale&,
               const string_type& digits) const;
    };
  }

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

  iter_type put(iter_type s, ios_type& f, const locale& loc,
                double quant) const;
  iter_type put(iter_type s, ios_type& f, const locale& loc,
                const string_type& quant) const;

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

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

  iter_type do_put(iter_type s, ios_type& str, const locale& loc,
                   double units) const;
  iter_type do_put(iter_type s, ios_type& str, const locale& loc,
                   const string_type& digits) const;

  Effects:
    Writes  characters  to  s,  according to the format specified by the
    moneypunct<charT> facet of loc, and str.flags().  Ignores any  frac­
    tional  part  of  units,  or  any  characters  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::adjustfield) == ios_type::internal)  the  fill  characters
    are  placed  where  none  or space appears in the formatting pattern
    (_lib.money.get.virtuals_).
  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;
      vector<char> 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 vector<char> 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;
      vector<char> 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.11)
  _________________________
  11) In common U.S. locales this is '.'.

  charT do_thousands_sep() const;

  Returns:
    The digit group separator to use in case do_grouping()  specifies  a
    digit grouping pattern.12)

  vector<char> do_grouping() const;

  Returns:
    A     pattern    defined    identically    as    the    result    of
    numpunct<charT>::do_grouping().13)

  string_type do_curr_symbol() const;

  Returns:
    A string to use as the currency identifier symbol.14)

  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;15)  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.16)

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

  Returns:
    A  pattern,  a  four-element  array  specifying  the  order in which
  _________________________
  12) In common U.S. locales this is ','.
  13) This is most commonly the vector "{ 3 }"
  14) For international instantiations (second template parameter  true)
  this  is  always  four  characters  long,  usually three letters and a
  space.
  15) This is usually the empty string.
  16) In common U.S. locales, this is 2.

    syntactic elements appear in the monetary format.
  Notes:
    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  ele­
    ments may appear in any order.  In international instantiations, the
    result is always { symbol, sign, none, value }.17)

  22.2.6.4  Template class                [lib.locale.moneypunct.byname]
       moneypunct_byname
  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 vector<char> 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 T1 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);

  _________________________
  17) Note that the international symbol usually contains a  space,  it­
  self; for example, "USD ".

      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 The  type  of messages_base::catalog is implementation-defined.  Valid
  values of this type can be obtained only by default construction or by
  calling  member do_open.  Default construction, copy construction, and
  assignment operations on this type must be well-formed and  not  throw
  exceptions,  although  the  effect  of copying invalid values is unde­
  fined.

  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
       cin.imbue(locale());        // imbue it on the std streams
      cout.imbue(locale());
      cerr.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 <stringstream>
    std::string Date::asString(const std::locale& l)
    {
      using namespace std;
      stringstream s; s.imbue(l);
      s << *this; return s.data();
    }
    std::istream& operator>>(std::istream& s, Date& d)
    {
      using namespace std;
      if (!s.ipfx(0)) return s;
      locale loc = s.getloc();
      struct tm t;
      use_facet< time_get<char> >(loc).get_date(s, s, 0, loc, &t);
      if (s) d = Date(t.tm_day, t.tm_mon + 1, t.tm_year + 1900);
      s.isfx();
      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 << "Any arguments today? " << (argc > 1) << endl;
      return 0;
    }
   --end example]

  22.3  C Library Locales                                [lib.c.locales]

1 Header <clocale> (Table 5):

                    Table 5--Header <clocale> synopsis

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

2 The contents are the same as the Standard C library.

  SEE ALSO: ISO C subclause 7.10.4.