      ______________________________________________________________________

      27   Input/output library                           [lib.input.output]

      ______________________________________________________________________

    1 This clause describes components that C++ programs may use to  perform
      input/output operations.

    2 The  following subclauses describe requirements for stream parameters,
      and components  for  forward  declarations  of  iostreams,  predefined
      iostreams  objects,  base  iostreams classes, stream buffering, stream
      formatting and manipulators, string streams, and file streams, as sum-
      marized in Table 1:

                      Table 1--Input/output library summary

        +----------------------------------------------------------------+
        |                    Subclause                        Header(s)  |
        +----------------------------------------------------------------+
        |_lib.iostreams.requirements_ Requirements                       |
        +----------------------------------------------------------------+
        |_lib.iostream.forward_ Forward declarations         <iosfwd>    |
        +----------------------------------------------------------------+
        |_lib.iostream.objects_ Standard iostream objects    <iostream>  |
        +----------------------------------------------------------------+
        |_lib.iostreams.base_ Iostreams base classes         <ios>       |
        +----------------------------------------------------------------+
        |_lib.stream.buffers_ Stream buffers                 <streambuf> |
        +----------------------------------------------------------------+
        |                                                    <istream>   |
        |_lib.iostream.format_ Formatting and manipulators   <ostream>   |
        |                                                    <iomanip>   |
        +----------------------------------------------------------------+
        |_lib.string.streams_ String streams                 <sstream>   |
        |                                                    <cstdlib>   |
        +----------------------------------------------------------------+
        |                                                    <fstream>   |
        |_lib.file.streams_ File streams                     <cstdio>    |
        |                                                    <cwchar>    |
        +----------------------------------------------------------------+

      27.1  Iostreams requirements              [lib.iostreams.requirements]

      27.1.1  Definitions                        [lib.iostreams.definitions]

    1 For  character-related definitions, see _lib.char.traits.defs_.  Addi-
      tional iostreams definitions:

      --iostream class templates The iostream class templates are  templates
        defined  in  this clause that take two template arguments: charT and
        traits.  The argument charT is a character container class, and  the
        argument traits is a structure which defines additional characteris-
        tics and functions of the character type represented by charT neces-
        sary to implement the iostream class templates.

      --narrow-oriented   iostream   classes  The  narrow-oriented  iostream
        classes are the instantiations of the iostream  class  templates  on
        the  character  container  class  char  and the default value of the
        traits parameter.  The traditional iostream classes are regarded  as
        the  narrow-oriented iostream classes (_lib.narrow.stream.objects_).

      --wide-oriented iostream classes The  wide-oriented  iostream  classes
        are  the instantiations of the iostream class templates on the char-
        acter container class wchar_t and the default value  of  the  traits
        parameter.  (_lib.wide.stream.objects_).

      --repositional streams and arbitrary-positional streams A repositional
        stream, can seek to only the position where  we  previously  encoun-
        tered.   On  the other hand, an arbitrary-positional stream can seek
        to any integral position within the length  of  the  stream.   Every
        arbitrary-positional stream is repositional.

      27.1.2  Limitations                              [lib.iostream.limits]

      27.1.2.1  Imbue Limitations                [lib.iostream.limits.imbue]
      No function described in _lib.input.output_ except for ios_base::imbue
      causes any instance of basic_ios::imbue or  basic_streambuf::imbue  to
      be  called.   If  any user function called from a function declared in
      _lib.input.output_ or as an overriding virtual function of  any  class
      declared  in _lib.input.output_ calls imbue the behavior is undefined.

      27.1.2.2  Positioning Type Limitations      [lib.iostreams.limits.pos]
      The classes of clause _lib.input.output_ with template arguments charT
      and   traits   behave   as   described   if    traits::pos_type    and
      traits::off_type  are streampos and streamoff respectively.  Except as
      noted  explicitly  below  their  behavior  when  traits::pos_type  and
      traits::off_type are other types are implementation-defined.

      27.2  Forward declarations                      [lib.iostream.forward]

      Header <iosfwd> synopsis

      namespace std {
        template<> class char_traits<char>;
        template<> class char_traits<wchar_t>;

        template <class charT, class traits = char_traits<charT> >
          class basic_ios;

        template <class charT, class traits = char_traits<charT> >
          class basic_streambuf;

        template <class charT, class traits = char_traits<charT> >
          class basic_istream;

        template <class charT, class traits = char_traits<charT> >
          class basic_ostream;

        template <class charT, class traits = char_traits<charT> >
          class basic_iostream;

        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
          class basic_stringbuf;

        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
          class basic_istringstream;

        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
          class basic_ostringstream;

        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
          class basic_stringstream;

        template <class charT, class traits = char_traits<charT> >
          class basic_filebuf;

        template <class charT, class traits = char_traits<charT> >
          class basic_ifstream;

        template <class charT, class traits = char_traits<charT> >
          class basic_ofstream;

        template <class charT, class traits = char_traits<charT> >
          class basic_fstream;

        template <class charT, class traits = char_traits<charT> >
          class basic_istreambuf_iterator;

        template <class charT, class traits = char_traits<charT> >
          class basic_ostreambuf_iterator;
        typedef basic_ios<char>       ios;
        typedef basic_ios<wchar_t>    wios;

        typedef basic_streambuf<char> streambuf;
        typedef basic_istream<char>   istream;
        typedef basic_ostream<char>   ostream;
        typedef basic_iostream<char>  iostream;

        typedef basic_stringbuf<char>     stringbuf;
        typedef basic_istringstream<char> istringstream;
        typedef basic_ostringstream<char> ostringstream;
        typedef basic_stringstream<char>  stringstream;

        typedef basic_filebuf<char>  filebuf;
        typedef basic_ifstream<char> ifstream;
        typedef basic_ofstream<char> ofstream;
        typedef basic_fstream<char>  fstream;
        typedef basic_streambuf<wchar_t> wstreambuf;
        typedef basic_istream<wchar_t>   wistream;
        typedef basic_ostream<wchar_t>   wostream;
        typedef basic_iostream<wchar_t>  wiostream;

        typedef basic_stringbuf<wchar_t>     wstringbuf;
        typedef basic_istringstream<wchar_t> wistringstream;
        typedef basic_ostringstream<wchar_t> wostringstream;
        typedef basic_stringstream<wchar_t>  wstringstream;

        typedef basic_filebuf<wchar_t>  wfilebuf;
        typedef basic_ifstream<wchar_t> wifstream;
        typedef basic_ofstream<wchar_t> wofstream;
        typedef basic_fstream<wchar_t>  wfstream;
        template <class state> class fpos;
        typedef fpos<char_traits<char>::state_type>    streampos;
        typedef fpos<char_traits<wchar_t>::state_type> wstreampos;
      }
      [Note:

    1 The  template  class  basic_ios<charT,traits> serves as a virtual base
      class      for      the      classes      basic_istream<charT,traits>,
      basic_ostream<charT,traits>,    and   classes   derived   from   them.
      basic_iostream<charT,traits>   is   a   class   derived   from    both
      basic_istream and basic_ostream.

    2 The  template  class  basic_streambuf<charT,traits>  serves  as a base
      class for template classes basic_stringbuf, and basic_filebuf.

    3 The template class basic_istream serves as a base class  for  template
      classes basic_istringstream, and basic_ifstream

    4 The  template  class basic_ostream serves as a base class for template
      classes basic_ostringstream, and basic_ofstream

    5 The template class basic_iostream serves as a base class for  template
      classes basic_stringstream, and basic_fstream.

    6 Other  typedefs  define  instances of template classes specialized for
      char or wchar_t types.

    7 The template class fpos<charT> is a class  used  for  specifying  file
      position information.

    8 The  types  streampos  and wstreampos are used for positioning streams
      specialized on char and wchar_t respectively.

    9 This  synopsis  suggests   a   circularity   between   streampos   and
      char_traits<char>.   An  implementation  can avoid this circularity by
      substituting equivalent types. One way to do this might be
              template<class stateT> class fpos { ... }; // depends on nothing
              typedef ... _STATE; // implementation private declaration of stateT

              typedef fpos<_STATE> streampos;

              template<> struct char_traits<char> {
                 typedef streampos pos_type;
                 // ....
              }
       --end note]

      27.3  Standard iostream objects                 [lib.iostream.objects]

      Header <iostream> synopsis

      namespace std {
        extern istream cin;
        extern ostream cout;
        extern ostream cerr;
        extern ostream clog;

        extern wistream wcin;
        extern wostream wcout;
        extern wostream wcerr;
        extern wostream wclog;
      }

    1 The header <iostream> declares objects that associate objects with the
      standard  C streams provided for by the functions declared in <cstdio>
      (_lib.c.files_).

    2 Mixing operations on corresponding wide- and narrow-character  streams
      follows  the  same  semantics  as  mixing such operations on FILEs, as
      specified in Amendment 1 of the ISO C standard.  The objects are  con-
      structed,  and  the associations are established at some time prior to
      or during first time an object of class  basic_ios<charT,traits>::Init
      is  constructed,  and  in  any  case  before  the  body of main begins
      execution.1) The objects are not destroyed during program execution.2)
      _________________________
      1) If it is possible for them to do so, implementations are encouraged

      27.3.1  Narrow stream objects              [lib.narrow.stream.objects]

      istream cin;

    1 The object cin controls input from a stream buffer associated with the
      object stdin, declared in <cstdio>.

    2 After the object cin is initialized, cin.tie() returns &cout.

      ostream cout;

    3 The object cout controls output to a stream buffer associated with the
      object stdout, declared in <cstdio> (_lib.c.files_).

      ostream cerr;

    4 The object cerr controls output to a stream buffer associated with the
      object stderr, declared in <cstdio> (_lib.c.files_).

    5 After  the  object  cerr  is  initialized,  cerr.flags()  & unitbuf is
      nonzero.

      ostream clog;

    6 The object clog controls output to a stream buffer associated with the
      object stderr, declared in <cstdio> (_lib.c.files_).

      27.3.2  Wide stream objects                  [lib.wide.stream.objects]

      wistream wcin;

    1 The  object  wcin  controls input from a stream buffer associated with
      the object stdin, declared in <cstdio>.

    2 After the object wcin is initialized, wcin.tie() returns &wcout.

      wostream wcout;
      _________________________
      to initialize the objects earlier than required.
      2)  Constructors  and  destructors for static objects can access these
      objects to read input from stdin or write output to stdout or  stderr.

    3 The object wcout controls output to a stream  buffer  associated  with
      the object stdout, declared in <cstdio> (_lib.c.files_).

      wostream wcerr;

    4 The  object  wcerr  controls output to a stream buffer associated with
      the object stderr, declared in <cstdio> (_lib.c.files_).

    5 After the object wcerr is  initialized,  wcerr.flags()  &  unitbuf  is
      nonzero.

      wostream wclog;

    6 The  object  wclog  controls output to a stream buffer associated with
      the object stderr, declared in <cstdio> (_lib.c.files_).

      27.4  Iostreams base classes                      [lib.iostreams.base]

      Header <ios> synopsis

      #include <iosfwd>
      namespace std {
        typedef OFF_T  streamoff;
        typedef SZ_T streamsize;
        template <class stateT> class fpos;

        class ios_base;
        template <class charT, class traits = char_traits<charT> >
          class basic_ios;
      // _lib.std.ios.manip_, manipulators:
        ios_base& boolalpha  (ios_base& str);
        ios_base& noboolalpha(ios_base& str);
        ios_base& showbase   (ios_base& str);
        ios_base& noshowbase (ios_base& str);
        ios_base& showpoint  (ios_base& str);
        ios_base& noshowpoint(ios_base& str);
        ios_base& showpos    (ios_base& str);
        ios_base& noshowpos  (ios_base& str);
        ios_base& skipws     (ios_base& str);
        ios_base& noskipws   (ios_base& str);
        ios_base& uppercase  (ios_base& str);
        ios_base& nouppercase(ios_base& str);
      // _lib.adjustfield.manip_ adjustfield:
        ios_base& internal   (ios_base& str);
        ios_base& left       (ios_base& str);
        ios_base& right      (ios_base& str);
      // _lib.basefield.manip_ basefield:
        ios_base& dec        (ios_base& str);
        ios_base& hex        (ios_base& str);
        ios_base& oct        (ios_base& str);

      // _lib.floatfield.manip_ floatfield:
        ios_base& fixed      (ios_base& str);
        ios_base& scientific (ios_base& str);
      }

      27.4.1  Types                                       [lib.stream.types]

      typedef OFF_T streamoff;

    1 The type streamoff is an implementation-defined  type  that  satisfies
      the requirements of _lib.fpos.operations_.

      typedef SZ_T streamsize;

    2 The  type streamsize is a synonym for one of the signed basic integral
      types.  It is used to represent the number of  characters  transferred
      in an I/O operation, or the size of I/O buffers.3)

      27.4.2  Class ios_base                                  [lib.ios.base]
      namespace std {
        class ios_base {
        public:
          class failure;
          typedef T1 fmtflags;
          static const fmtflags boolalpha;
          static const fmtflags dec;
          static const fmtflags fixed;
          static const fmtflags hex;
          static const fmtflags internal;
          static const fmtflags left;
          static const fmtflags oct;
          static const fmtflags right;
          static const fmtflags scientific;
          static const fmtflags showbase;
          static const fmtflags showpoint;
          static const fmtflags showpos;
          static const fmtflags skipws;
          static const fmtflags unitbuf;
          static const fmtflags uppercase;
          static const fmtflags adjustfield;
          static const fmtflags basefield;
          static const fmtflags floatfield;
      _________________________
      3)  streamsize  is  used  in most places where ISO C would use size_t.
      Most of the uses of  streamsize  could  use  size_t,  except  for  the
      strstreambuf  constructors,  which require negative values.  It should
      probably be the signed type corresponding to  size_t  (which  is  what
      Posix.2 calls ssize_t).

          typedef T2 iostate;
          static const iostate badbit;
          static const iostate eofbit;
          static const iostate failbit;
          static const iostate goodbit;
          typedef T3 openmode;
          static const openmode app;
          static const openmode ate;
          static const openmode binary;
          static const openmode in;
          static const openmode out;
          static const openmode trunc;
          typedef T4 seekdir;
          static const seekdir beg;
          static const seekdir cur;
          static const seekdir end;
          class Init;
        // _lib.fmtflags.state_ fmtflags state:
          fmtflags flags() const;
          fmtflags flags(fmtflags fmtfl);
          fmtflags setf(fmtflags fmtfl);
          fmtflags setf(fmtflags fmtfl, fmtflags mask);
          void unsetf(fmtflags mask);
          streamsize precision() const;
          streamsize precision(streamsize prec);
          streamsize width() const;
          streamsize width(streamsize wide);
        // _lib.ios.base.locales_ locales:
          locale imbue(const locale& loc);
          locale getloc() const;
        // _lib.ios.base.storage_ storage:
          static int xalloc();
          long&  iword(int index);
          void*& pword(int index);
          // destructor
          ~ios_base();
         // _lib.ios.base.callback_ callbacks;
          enum event { erase_event, imbue_event, copyfmt_event };
          typedef void (*event_callback)(event, ios_base&, int index);
          void register_callback(event_call_back fn, int index);
          static bool sync_with_stdio(bool sync = true);
        protected:
          ios_base();
        private:
      //  static int index;  exposition only
      //  long* iarray;      exposition only
      //  void** parray;     exposition only
        };
      }

    1 ios_base defines several member types:

      --a class failure derived from exception;

      --a class Init;

      --three bitmask types, fmtflags, iostate, and openmode;

      --an enumerated type, seekdir.

    2 It maintains several kinds of data:

      --state information that reflects the integrity of the stream buffer;

      --control  information that influences how to interpret (format) input
        sequences and how to generate (format) output sequences;

      --additional information that is stored by the program for its private
        use.

    3 [Note:  For  the  sake of exposition, the maintained data is presented
      here as:

      --static int index, specifies the next available unique index for  the
        integer or pointer arrays maintained for the private use of the pro-
        gram, initialized to an unspecified value;

      --long* iarray, points to the first  element  of  an  arbitrary-length
        long array maintained for the private use of the program;

      --void**  parray,  points  to the first element of an arbitrary-length
        pointer array maintained for the private use of the program.   --end
        note]

      27.4.2.1  Types                                        [lib.ios.types]

      27.4.2.1.1  Class ios_base::failure                 [lib.ios::failure]

      namespace std {
        class ios_base::failure : public exception {
        public:
          explicit failure(const string& msg);
          virtual ~failure();
          virtual const char* what() const;
        };
      }

    1 The  class failure defines the base class for the types of all objects
      thrown as exceptions, by functions in the iostreams library, to report
      errors detected during stream buffer operations.

      explicit failure(const string& msg);

      Effects:
        Constructs  an  object of class failure, initializing the base class
        with exception(msg).
      Postcondition:
        what() == msg.str()

      const char* what() const;

      Returns:
        The message msg with which the exception was created.

      27.4.2.1.2  Type ios_base::fmtflags                [lib.ios::fmtflags]

      typedef T1 fmtflags;

    1 The type fmtflags is a bitmask  type  (_lib.bitmask.types_).   Setting
      its elements has the effects indicated in Table 2:

                            Table 2--fmtflags effects

           +-----------------------------------------------------------+
           | Element                   Effect(s) if set                |
           +-----------------------------------------------------------+
           |boolalpha    insert  and  extract  bool type in alphabetic |
           |             format                                        |
           |dec          converts integer input or  generates  integer |
           |             output in decimal base                        |
           |fixed        generate floating-point output in fixed-point |
           |             notation;                                     |
           |hex          converts integer input or  generates  integer |
           |             output in hexadecimal base;                   |
           |internal     adds fill characters at a designated internal |
           |             point in certain generated output, or identi- |
           |             cal to right if no such point is designated;  |
           |left         adds  fill characters on the right (final po- |
           |             sitions) of certain generated output;         |
           |oct          converts integer input or  generates  integer |
           |             output in octal base;                         |
           |right        adds fill characters on the left (initial po- |
           |             sitions) of certain generated output;         |
           |scientific   generates floating-point output in scientific |
           |             notation;                                     |
           |showbase     generates  a  prefix  indicating  the numeric |
           |             base of generated integer output;             |
           |showpoint    generates a decimal-point character  uncondi- |
           |             tionally in generated floating-point output;  |
           |showpos      generates  a + sign in non-negative generated |
           |             numeric output;                               |
           |skipws       skips leading white space before certain  in- |
           |             put operations;                               |
           |unitbuf      flushes output after each output operation;   |
           |uppercase    replaces certain lowercase letters with their |
           |             uppercase equivalents in generated output.    |
           +-----------------------------------------------------------+

    2 Type fmtflags also defines the constants indicated in Table 3:

                           Table 3--fmtflags constants

                     ----------------------------------------
                       Constant        Allowable values
                     ----------------------------------------
                      adjustfield   left | right | internal
                      basefield     dec | oct | hex
                      floatfield    scientific | fixed
                     ----------------------------------------

                     |                                      |
                     |                                      |
                     |                                      |
                     |                                      |
                     |                                      |

      27.4.2.1.3  Type ios_base::iostate                  [lib.ios::iostate]

      typedef T2 iostate;

    1 The type iostate is a bitmask type (_lib.bitmask.types_) that contains
      the elements indicated in Table 4:

                             Table 4--iostate effects

            +--------------------------------------------------------+
            |Element                 Effect(s) if set                |
            +--------------------------------------------------------+
            |badbit    indicates  a loss of integrity in an input or |
            |          output sequence  (such  as  an  irrecoverable |
            |          read error from a file);                      |
            |eofbit    indicates that an input operation reached the |
            |          end of an input sequence;                     |
            |failbit   indicates that an input operation  failed  to |
            |          read the expected characters, or that an out- |
            |          put operation failed to generate the  desired |
            |          characters.                                   |
            +--------------------------------------------------------+

    2 Type iostate also defines the constant:

      --goodbit, the value zero.

      27.4.2.1.4  Type ios_base::openmode                [lib.ios::openmode]

      typedef T3 openmode;

    1 The  type  openmode  is a bitmask type (_lib.bitmask.types_).  It con-
      tains the elements indicated in Table 5:

                            Table 5--openmode effects

               +---------------------------------------------------+
               |Element               Effect(s) if set             |
               +---------------------------------------------------+
               |app       seek to end before each write            |
               |ate       open and seek to end immediately after   |
               |          opening                                  |
               |binary    perform input and output in binary mode  |
               |          (as opposed to text mode)                |
               |in        open for input                           |
               |out       open for output                          |
               |trunc     truncate an existing stream when opening |
               +---------------------------------------------------+

      27.4.2.1.5  Type ios_base::seekdir                  [lib.ios::seekdir]

      typedef T4 seekdir;

    1 The  type  seekdir is an enumerated type (_lib.enumerated.types_) that
      contains the elements indicated in Table 6:

                             Table 6--seekdir effects

           +----------------------------------------------------------+
           |Element                       Meaning                     |
           +----------------------------------------------------------+
           |beg       request a seek (for subsequent input or output) |
           |          relative to the beginning of the stream         |
           |cur       request a seek relative to the current position |
           |          within the sequence                             |
           |end       request a seek relative to the current end of   |
           |          the sequence                                    |
           +----------------------------------------------------------+

      27.4.2.1.6  Class ios_base::Init                       [lib.ios::Init]

      namespace std {
        class ios_base::Init {
        public:
          Init();
         ~Init();
        private:
      //  static int init_cnt;  exposition only
        };
      }

    1 The class Init describes an object whose construction ensures the con-
      struction   of   the   eight   objects    declared    in    <iostream>
      (_lib.iostream.objects_)  that  associate file stream buffers with the
      standard C streams provided for by the functions declared in  <cstdio>
      (_lib.c.files_).

    2 For the sake of exposition, the maintained data is presented here as:

      --static int init_cnt, counts the number of constructor and destructor
        calls for class Init, initialized to zero.

      Init();

      Effects:
        Constructs an object of class Init.  If init_cnt is zero, the  func-
        tion  stores the value one in init_cnt, then constructs and initial-
        izes   the   objects    cin,    cout,    cerr,    clog    (_lib.nar-
        row.stream.objects_),     wcin,     wcout,    wcerr,    and    wclog
        (_lib.wide.stream.objects_).  In any case, the  function  then  adds
        one to the value stored in init_cnt.

      ~Init();

      Effects:
        Destroys  an  object of class Init.  The function subtracts one from
        the value stored in init_cnt and, if the resulting stored  value  is
        one,  calls cout.flush(), cerr.flush(), clog.flush(), wcout.flush(),
        wcerr.flush(), wclog.flush().

      27.4.2.2  ios_base fmtflags state functions       [lib.fmtflags.state]

      fmtflags flags() const;

      Returns:
        The format control information for both input and output.

      fmtflags flags(fmtflags fmtfl);

      Postcondition:
        fmtfl == flags().
      Returns:
        The previous value of flags().

      fmtflags setf(fmtflags fmtfl);

      Effects:
        Sets fmtfl in flags().
      Returns:
        The previous value of flags().

      fmtflags setf(fmtflags fmtfl, fmtflags mask);

      Effects:
        Clears mask in flags(), sets fmtfl & mask in flags().
      Returns:
        The previous value of flags().

      void unsetf(fmtflags mask);

      Effects:
        Clears mask in flags().

      streamsize precision() const;

      Returns:
        The precision (number of digits after the decimal point) to generate
        on certain output conversions.

      streamsize precision(streamsize prec);

      Postcondition:
        prec == precision().
      Returns:
        The previous value of precision().

      streamsize width() const;

      Returns:
        The  minimum  field width (number of characters) to generate on cer-
        tain output conversions.

      streamsize width(streamsize wide);

      Postcondition:
        wide == width().
      Returns:
        The previous value of width().

      27.4.2.3  ios_base locale functions             [lib.ios.base.locales]

      locale imbue(const locale loc);

      Effects:
        Calls each registered callback pair (fn,index)  (_lib.ios.base.call-
        back_)  as (*fn)(imbue_event,*this,index) at such a time that a call
        to ios_base::getloc() from within fn returns the  new  locale  value
        loc.
      Returns:
        If  no  locale  has  been  imbued,  a copy of the global C++ locale,
        locale(), in effect at the time of construction.  Otherwise, returns
        the  imbued locale, to be used to perform locale-dependent input and
        output operations.La Postcondition: loc == getloc().

      locale getloc() const;

      Returns:
        The previous value of getloc()..

      27.4.2.4  ios_base static members             [lib.ios.members.static]

      bool sync_with_stdio(bool sync = true);

      Returns:
        true, the first time it is called; otherwise, returns  true  if  the
        standard  iostream  objects(_lib.iostream.objects_) are synchronized
        and otherwise returns false.
      Effects:
        If any input or output operation has  occurred  using  the  standard
        streams prior to the call, the effect is implementation-defined Oth-
        erwise, called with a false argument, it allows the standard streams
        to operate independently of the standard C streams.

      27.4.2.5  ios_base storage functions            [lib.ios.base.storage]

      static int xalloc();

      Returns:
        index ++.

      long& iword(int idx);

      Effects:
        If  iarray is a null pointer, allocates an array of long of unspeci-
        fied size and stores a pointer to its first element in iarray.   The
        function then extends the array pointed at by iarray as necessary to
        include the element iarray[idx].  Each newly  allocated  element  of
        the array is initialized to zero.  The reference returned may become
        invalid after another call to the object's iword member with a  dif-
        ferent index, after a call to its copyfmt member, or when the object
        is destroyed.4) If the function fails5) it sets  badbit,  which  may
        throw an exception.
      Returns:
        On  success iarray[idx].  On failure, a valid int& initialized to 0.

      void* & pword(int idx);

      Effects:
        If parray is a null pointer, allocates an array of pointers to  void
        of  unspecified  size  and  stores a pointer to its first element in
        parray.  The function then extends the array pointed at by parray as
        necessary  to include the element parray[idx].  Each newly allocated
        element of the array is initialized to a null pointer.   The  refer-
        ence  returned may become invalid after another call to the object's
        pword member with a different index, after call to its copyfmt  mem-
        ber,  or  when  the object is destroyed.  If the function fails6) it
        sets badbit, which may throw an exception.
      Returns:
        On success parray[idx].  On failure a valid void*& initialized to 0.
      Notes:
        After  a subsequent call to pword(int) for the same object, the ear-
        lier return value may no longer be valid.

      27.4.2.6  ios_base callbacks                   [lib.ios.base.callback]

      void register_callback(event_callback fn, int index);

      Effects:
        Registers the pair (fn,index) such  that  during  calls  to  imbue()
        (_lib.ios.base.locales_),       copyfmt(),       or      ~ios_base()
        (_lib.ios.base.cons_), the  function  fn  is  called  with  argument
        index.   Functions  registered  are  called when an event occurs, in
        opposite order of registration.  Functions registered while a  call-
        back function is active are not called until the next event.
      Notes:
        Identical pairs are not merged.  A function registered twice will be
      _________________________
      4) An implementation is free  to  implement  both  the  integer  array
      pointed  at  by  iarray  and the pointer array pointed at by parray as
      sparse data structures, possibly with a one-element cache for each.
      5) for example, because it cannot allocate space.
      6) for example, because it cannot allocate space.

        called twice.

      27.4.2.7  ios_base constructors/destructors        [lib.ios.base.cons]

      ios_base();

      Effects:
        The ios_base members are have an indeterminate value after construc-
        tion.

      ~ios_base()

      Effects:
        Destroys  an  object of class ios_base.  Calls each registered call-
        back     pair      (fn,index)      (_lib.ios.base.callback_)      as
        (*fn)(erase_event,*this,index) at such time that any ios_base member
        function called from within fn has well defined results.

      27.4.3  Template class fpos                                 [lib.fpos]
      namespace std {
        template <class stateT> class fpos {
        public:
        // _lib.fpos.cons_ Constructors
          fpos(stateT);
        // _lib.fpos.members_ Members
          stateT state() const;
          void state(stateT);
        private;
          stateT st; // exposition only
        };
      }

      27.4.3.1  fpos Constructor                             [lib.fpos.cons]

      fpos(stateT s)

      Effects:
        Constructs an object and assigns s to st An fpos will  also  contain
        private  information needed to position a file.  This information is
        initialized in an unspecified fashion.

      27.4.3.2  fpos Members                              [lib.fpos.members]

      void state(stateT s);

      Effects:
        Assign s to st.

      stateT state();

      Returns:
        Current value of st.

      27.4.4  fpos requirements                        [lib.fpos.operations]

    1 Operations specified in Table 7 are permitted.  In that table,

      --P refers to an instance of fpos,

      --p and q refer to an values of type P,

      --O refers to type streamoff,

      --o refers to a value of type streamoff, and

      --i refers to a value of type int.

                        Table 7--Position type requirements

      +-----------------------------------------------------------------------------------------+
      |expression       return type           operational                assertion/note         |
      |                                        semantics               pre/post-condition       |
      +-----------------------------------------------------------------------------------------+
      |P(i)                                                      p == P(i)                      |
      |                                                          note: a destructor is assumed. |
      +-----------------------------------------------------------------------------------------+
      |P p(i);                                                                                  |
      |P p = i;                                                  post: p == P(i).               |
      +-----------------------------------------------------------------------------------------+
      |P(o)         POS_T                 converts from offset                                  |
      +-----------------------------------------------------------------------------------------+
      |O(p)         OFF_T                 converts to offset     P(O(p)) == p                   |
      +-----------------------------------------------------------------------------------------+
      |p == q       convertible to bool                          == is an equivalence relation  |
      +-----------------------------------------------------------------------------------------+
      |p != q       convertible to bool   !(p==q)                                               |
      +-----------------------------------------------------------------------------------------+
      |q = p + o    POS_T                 + offset               q-o == p                       |
      |p += o                                                                                   |
      +-----------------------------------------------------------------------------------------+
      |q = p - o    POS_T                 - offset               q+o == p                       |
      |p -= o                                                                                   |
      +-----------------------------------------------------------------------------------------+
      |o = p - q    OFF_T                 distance               q+o == p                       |
      +-----------------------------------------------------------------------------------------+
        [Note: Every implementation is required to supply overloaded  opera-
        tors on fpos objects to satisfy the requirements of _lib.fpos.opera-
        tions_.  It is unspecified whether these operators  are  members  of

        fpos, global operators, or provided in some other way.   --end note]

    2 Stream operations that return a value of type traits::pos_type  return
      P(O(-1))  as  an  invalid  value to signal an error.  If this value is
      used as an argument to any istream, ostream, or  streambufmember  that
      accepts  a  value  of  type traits::pos_type then the behavior of that
      function is undefined.

      27.4.5  Template class basic_ios                             [lib.ios]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_ios : public ios_base {
        public:
        // Types:
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
          typedef traits                    traits_type;
          operator void*() const
          bool operator!() const
          iostate rdstate() const;
          void clear(iostate state = goodbit);
          void setstate(iostate state);
          bool good() const;
          bool eof()  const;
          bool fail() const;
          bool bad()  const;

          iostate exceptions() const;
          void exceptions(iostate except);
        // _lib.basic.ios.cons_ Constructor/destructor:
          explicit basic_ios(basic_streambuf<charT,traits>* sb);
          virtual ~basic_ios();
        // _lib.basic.ios.members_ Members:
          basic_ostream<charT,traits>* tie() const;
          basic_ostream<charT,traits>* tie(basic_ostream<charT,traits>* tiestr);
          basic_streambuf<charT,traits>* rdbuf() const;
          basic_streambuf<charT,traits>* rdbuf(basic_streambuf<charT,traits>* sb);
          basic_ios& copyfmt(const basic_ios& rhs);
          char_type fill() const;
          char_type fill(char_type ch);
        // _lib.ios.base.locales_ locales:
          locale imbue(const locale& loc);
          char     narrow(char_type c, char dfault) const;
          char_type widen(char c) const;
        protected:
          basic_ios();
          void init(basic_streambuf<charT,traits>* sb);
        };
      }

      27.4.5.1  basic_ios constructors                  [lib.basic.ios.cons]

      explicit basic_ios(basic_streambuf<charT,traits>* sb);

      Effects:
        Constructs an object of class basic_ios, assigning initial values to
        its member objects by calling init(sb).

      basic_ios();

      Effects:
        Constructs  an object of class basic_ios (_lib.ios.base.cons_) leav-
        ing its member objects uninitialized. The object must be initialized
        by  calling  its  init member function. If it is destroyed before it
        has been initialized the behavior is undefined.

      void init(basic_streambuf<charT,traits>* sb);

      Postconditions:
        The postconditions of this function are indicated in Table 8:

                            Table 8--ios_base() effects

             +--------------------------------------------------------+
             |  Element                       Value                   |
             +--------------------------------------------------------+
             |rdbuf()        sb                                       |
             |tie()          0                                        |
             |rdstate()      goodbit if sb is  not  a  null  pointer, |
             |               otherwise badbit.                        |
             |exceptions()   goodbit                                  |
             |flags()        skipws | dec                             |
             |width()        0                                        |
             |precision()    6                                        |
             |fill()         widen(' ');                              |
             |getloc()       a copy of the value returned by locale() |
             |iarray         a null pointer                           |
             |parray         a null pointer                           |
             +--------------------------------------------------------+

      27.4.5.2  Member functions                     [lib.basic.ios.members]

      basic_ostream<charT,traits>* tie() const;

      Returns:
        An  output sequence that is tied to (synchronized with) the sequence
        controlled by the stream buffer.

      basic_ostream<charT,traits>* tie(basic_ostream<charT,traits>* tiestr);

      Postcondition:
        tiestr == tie().
      Returns:
        The previous value of tie().

      basic_streambuf<charT,traits>* rdbuf() const;

      Returns:
        A pointer to the streambuf associated with the stream.

      basic_streambuf<charT,traits>* rdbuf(basic_streambuf<charT,traits>* sb);

      Postcondition:
        sb == rdbuf().
      Effects:
        Calls clear().
      Returns:
        The previous value of rdbuf().

        // _lib.ios.base.locales_ locales:
      locale imbue(const locale& loc);

      Effects:
        Calls   ios_base::imbue(loc)   (_lib.ios.base.locales_)    and    if
        rdbuf()!=0 then rdbuf()->pubimbue(loc) (_lib.streambuf.locales_).
      Returns:
        The prior value of ios_base::imbue().

      char narrow(char_type c, char dfault) const;

      Returns:
        use_facet< ctype<char_type> >(getloc()).narrow(c,dfault)

      char_type widen(char c) const;

      Returns:
        use_facet< ctype<char_type> >(getloc()).widen(c)

      char_type fill() const

      Returns:
        The  character used to pad (fill) an output conversion to the speci-
        fied field width.

      char_type fill(char_type fillch);

      Postcondition:
        fillch == fill()
      Returns:
        The previous value of fill().

      basic_ios& copyfmt(const basic_ios& rhs);

      Effects:
        Assigns to the member objects  of  *this  the  corresponding  member
        objects of rhs, except that:

      --rdstate() and rdbuf() are left unchanged;

      --exceptions() is altered last by calling exceptions(rhs.except).

      --The  contents of arrays pointed at by pword and iword are copied not
        the pointers themselves.7)

    1 If any newly stored pointer values in *this point  at  objects  stored
      outside  the  object  rhs, and those objects are destroyed when rhs is
      destroyed, the newly stored pointer values are  altered  to  point  at
      newly constructed copies of the objects.

    2 Before  copying any parts of rhs, calls each registered callback  pair
      (fn,index) as (*fn)(erase_event,*this,index).   After  all  parts  but
      exceptions()  have  been  replaced,  calls each callback pair that was
      copied from rhs as (*fn)(copy_event,*this,index).
      Notes:
        The second pass permits a copied pword value to be  zeroed,  or  its
        referent  deep  copied  or  reference  counted or have other special
        action taken.
      Returns:
        *this.

      27.4.5.3  basic_ios iostate flags functions        [lib.iostate.flags]

      operator void*() const

      Returns:
        If fail() then a null pointer; otherwise some  non-null  pointer  to
        indicate success.

      bool operator!() const
      _________________________
      7) This suggests an infinite amount of copying, but the implementation
      can  keep track of the maximum element of the arrays that is non-zero.

      Returns:
        fail().

      iostate rdstate() const;

      Returns:
        The control state of the stream buffer.

      void clear(iostate state = goodbit);

      Postcondition:
        If     rdbuf()!=0     then    state    ==    rdstate();    otherwise
        rdstate()==state|ios_base::badbit.
      Effects:
        If (rdstate() & exceptions()) == 0, returns.  Otherwise,  the  func-
        tion   throws   an   object   fail   of   class   basic_ios::failure
        (_lib.ios::failure_), constructed with implementation-defined  argu-
        ment values.

      void setstate(iostate state);

      Effects:
        Calls  clear(rdstate()  | state) (which may throw basic_ios::failure
        (_lib.ios::failure_)).

      bool good() const;

      Returns:
        rdstate() == 0

      bool eof() const;

      Returns:
        true if eofbit is set in rdstate().

      bool fail() const;

      Returns:
        true if failbit or badbit is set in rdstate().8)

      bool bad() const;

      Returns:
        true if badbit is set in rdstate().
      _________________________
      8) Checking badbit also for fail() is historical practice.

      iostate exceptions() const;

      Returns:
        A mask that determines what elements set in rdstate()  cause  excep-
        tions to be thrown.

      void exceptions(iostate except);

      Postcondition:
        except == exceptions().
      Effects:
        Calls clear(rdstate()).

      27.4.6  ios_base manipulators                      [lib.std.ios.manip]

      27.4.6.1  fmtflags manipulators                   [lib.fmtflags.manip]

      ios_base& boolalpha(ios_base& str);

      Effects:
        Calls str.setf(ios_base::boolalpha).
      Returns:
        str.

      ios_base& noboolalpha(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::boolalpha).
      Returns:
        str.

      ios_base& showbase(ios_base& str);

      Effects:
        Calls str.setf(ios_base::showbase).
      Returns:
        str.

      ios_base& noshowbase(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::showbase).
      Returns:
        str.

      ios_base& showpoint(ios_base& str);

      Effects:
        Calls str.setf(ios_base::showpoint).
      Returns:
        str.

      ios_base& noshowpoint(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::showpoint).
      Returns:
        str.

      ios_base& showpos(ios_base& str);

      Effects:
        Calls str.setf(ios_base::showpos).
      Returns:
        str.

      ios_base& noshowpos(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::showpos).
      Returns:
        str.

      ios_base& skipws(ios_base& str);

      Effects:
        Calls str.setf(ios_base::skipws).
      Returns:
        str.

      ios_base& noskipws(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::skipws).
      Returns:
        str.

      ios_base& uppercase(ios_base& str);

      Effects:
        Calls str.setf(ios_base::uppercase).
      Returns:
        str.

      ios_base& nouppercase(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::uppercase).
      Returns:
        str.

      ios_base& unitbuf(ios_base& str);

      Effects:
        Calls str.setf(ios_base::unitbuf).
      Returns:
        str.

      ios_base& nounitbuf(ios_base& str);

      Effects:
        Calls str.unsetf(ios_base::unitbuf).
      Returns:
        str.

      27.4.6.2  adjustfield manipulators             [lib.adjustfield.manip]

      ios_base& internal(ios_base& str);

      Effects:
        Calls str.setf(ios_base::internal, ios_base::adjustfield).
      Returns:
        str.

      ios_base& left(ios_base& str);

      Effects:
        Calls str.setf(ios_base::left, ios_base::adjustfield).
      Returns:
        str.

      ios_base& right(ios_base& str);

      Effects:
        Calls str.setf(ios_base::right, ios_base::adjustfield).
      Returns:
        str.

      27.4.6.3  basefield manipulators                 [lib.basefield.manip]

      ios_base& dec(ios_base& str);

      Effects:
        Calls str.setf(ios_base::dec, ios_base::basefield).
      Returns:
        str.

      ios_base& hex(ios_base& str);

      Effects:
        Calls str.setf(ios_base::hex, ios_base::basefield).
      Returns:
        str.

      ios_base& oct(ios_base& str);

      Effects:
        Calls str.setf(ios_base::oct, ios_base::basefield).
      Returns:
        str.

      27.4.6.4  floatfield manipulators               [lib.floatfield.manip]

      ios_base& fixed(ios_base& str);

      Effects:
        Calls str.setf(ios_base::fixed, ios_base::floatfield).
      Returns:
        str.

      ios_base& scientific(ios_base& str);

      Effects:
        Calls str.setf(ios_base::scientific, ios_base::floatfield).
      Returns:
        str.

      _________________________
      9) The function signature dec(ios_base&) can be called by the function
      signature basic_ostream& stream::operator<<(ios_base&  (*)(ios_base&))
      to  permit  expressions  of  the form cout << dec to change the format
      flags stored in cout.

      27.5  Stream buffers                              [lib.stream.buffers]

      Header <streambuf> synopsis

      namespace std {
        template <class charT, class traits = char_traits<charT> >
          class basic_streambuf;
        typedef basic_streambuf<char>     streambuf;
        typedef basic_streambuf<wchar_t> wstreambuf;
      }

    1 The header <streambuf> defines types that control input from and  out-
      put to character sequences.

      27.5.1  Stream buffer requirements               [lib.streambuf.reqts]

    1 Stream  buffers  can  impose various constraints on the sequences they
      control.  Some constraints are:

      --The controlled input sequence can be not readable.

      --The controlled output sequence can be not writable.

      --The controlled sequences can be  associated  with  the  contents  of
        other  representations  for  character  sequences,  such as external
        files.

      --The controlled sequences can support operations directly to or  from
        associated sequences.

      --The  controlled  sequences can impose limitations on how the program
        can read characters from a sequence, write characters to a sequence,
        put  characters  back  into  an  input sequence, or alter the stream
        position.

    2 Each sequence is characterized by three pointers which,  if  non-null,
      all  point  into the same charT array object.  The array object repre-
      sents, at any moment, a (sub)sequence of characters from the sequence.
      Operations  performed  on  a sequence alter the values stored in these
      pointers, perform reads and writes  directly  to  or  from  associated
      sequences,  and  alter ``the stream position'' and conversion state as
      needed to maintain this subsequence relationship.  The three  pointers
      are:

      --the  beginning  pointer,  or  lowest  element  address  in the array
        (called xbeg here);

      --the next pointer, or next element address that is a  current  candi-
        date for reading or writing (called xnext here);

      --the  end  pointer,  or  first  element address beyond the end of the
        array (called xend here).

    3 The following semantic constraints shall always apply for any  set  of
      three  pointers  for a sequence, using the pointer names given immedi-
      ately above:

      --If xnext is not a null pointer, then xbeg and  xend  shall  also  be
        non-null  pointers  into  the  same charT array, as described above;
        otherwise, xbeg and xend shall also be null.

      --If xnext is not a null pointer  and  xnext  <  xend  for  an  output
        sequence,  then a write position is available.  In this case, *xnext
        shall be assignable as the next element to  write  (to  put,  or  to
        store a character value, into the sequence).

      --If  xnext  is  not  a  null  pointer  and  xbeg < xnext for an input
        sequence, then a putback  position  is  available.   In  this  case,
        xnext[-1]  shall  have  a  defined value and is the next (preceding)
        element to store a  character  that  is  put  back  into  the  input
        sequence.

      --If  xnext  is  not  a  null  pointer  and  xnext < xend for an input
        sequence, then a read position is available.  In this  case,  *xnext
        shall  have a defined value and is the next element to read (to get,
        or to obtain a character value, from the sequence).

      27.5.2  Template class                                 [lib.streambuf]
           basic_streambuf<charT,traits>
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_streambuf {
        public:
        // Types:
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
          typedef traits                    traits_type;
          virtual ~basic_streambuf();
        // _lib.streambuf.locales_ locales:
          locale   pubimbue(const locale &loc);
          locale   getloc() const;
        // _lib.streambuf.buffer_ buffer and positioning:
          basic_streambuf<char_type,traits>*
                   pubsetbuf(char_type* s, streamsize n);
          pos_type pubseekoff(off_type off, ios_base::seekdir way,
                              ios_base::openmode which = ios_base::in | ios_base::out);
          pos_type pubseekpos(pos_type sp,
                              ios_base::openmode which = ios_base::in | ios_base::out);
          int      pubsync();

        // Get and put areas:
        // _lib.streambuf.pub.get_ Get area:
          streamsize in_avail();
          int_type snextc();
          int_type sbumpc();
          int_type sgetc();
          streamsize sgetn(char_type* s, streamsize n);
        // _lib.streambuf.pub.pback_ Putback:
          int_type sputbackc(char_type c);
          int_type sungetc();
        // _lib.streambuf.pub.put_ Put area:
          int_type   sputc(char_type c);
          streamsize sputn(const char_type* s, streamsize n);
        protected:
          basic_streambuf();
        // _lib.streambuf.get.area_ Get area:
          char_type* eback() const;
          char_type* gptr()  const;
          char_type* egptr() const;
          void       gbump(int n);
          void       setg(char_type* gbeg, char_type* gnext, char_type* gend);
        // _lib.streambuf.put.area_ Put area:
          char_type* pbase() const;
          char_type* pptr() const;
          char_type* epptr() const;
          void       pbump(int n);
          void       setp(char_type* pbeg, char_type* pend);
        // _lib.streambuf.virtuals_ virtual functions:
        // _lib.streambuf.virt.locales_ Locales:
          virtual void imbue(const locale &loc);
        // _lib.streambuf.virt.buffer_ Buffer management and positioning:
          virtual basic_streambuf<char_type,traits>*
                           setbuf(char_type* s, streamsize n);
          virtual pos_type seekoff(off_type off, ios_base::seekdir way,
                    ios_base::openmode which = ios_base::in | ios_base::out);
          virtual pos_type seekpos(pos_type sp,
                    ios_base::openmode which = ios_base::in | ios_base::out);
          virtual int      sync();
        // _lib.streambuf.virt.get_ Get area:
          virtual int        showmanyc();
          virtual streamsize xsgetn(char_type* s, streamsize n);
          virtual int_type   underflow();
          virtual int_type   uflow();
        // _lib.streambuf.virt.pback_ Putback:
          virtual int_type   pbackfail(int_type c = traits::eof());
        // _lib.streambuf.virt.put_ Put area:
          virtual streamsize xsputn(const char_type* s, streamsize n);
          virtual int_type   overflow (int_type c = traits::eof());
        };
      }

    1 The class template basic_streambuf<charT,traits> serves as an abstract
      base class for deriving various stream buffers whose objects each con-
      trol two character sequences:

      --a character input sequence;

      --a character output sequence.

    2 The  class  streambuf  is  an  instantiation  of  the  template  class
      basic_streambuf specialized by the type char.

    3 The class  wstreambuf  is  an  instantiation  of  the  template  class
      basic_streambuf specialized by the type wchar_t.

      27.5.2.1  basic_streambuf constructors            [lib.streambuf.cons]

      basic_streambuf();

      Effects:
        Constructs  an  object  of  class  basic_streambuf<charT,traits> and
        initializes:10)

      --all its pointer member objects to null pointers,

      --the getloc() member to to a copy the global locale, locale(), at the
        time of construction.
      Notes:
        Once  the  getloc() member is initialized, results of calling locale
        member functions, and of members of facets so obtained,  can  safely
        be cached until the next time the member imbue is called.

      27.5.2.2  basic_streambuf public member        [lib.streambuf.members]
           functions

      27.5.2.2.1  Locales                            [lib.streambuf.locales]

      locale pubimbue(const locale& loc);

      Postcondition:
        loc == getloc().
      Effects:
        Calls imbue(loc).
      Returns:
        Previous value of getloc().

      locale getloc() const;

      Returns:
        If pubimbue() has ever been called,  then  the  last  value  of  loc
      _________________________
      10) The default constructor is protected for class basic_streambuf  to
      assure  that  only  objects for classes derived from this class may be
      constructed.

        supplied,  otherwise  the current global locale, locale(), in effect
        at the time of contruction.  If called  after  pubimbue()  has  been
        called  but  before pubimbue has returned (i.e. from within the call
        of imbue()) then it returns the previous value.

      27.5.2.2.2  Buffer management and               [lib.streambuf.buffer]
           positioning

      basic_streambuf<char_type,traits>* pubsetbuf(char_type* s, streamsize n);

      Returns:
        setbuf(s,n).

      pos_type pubseekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which = ios_base::in | ios_base::out);

      Returns:
        seekoff(off,way,which).

      pos_type pubseekpos(pos_type sp,
                     ios_base::openmode which = ios_base::in | ios_base::out);

      Returns:
        seekpos(sp,which).

      int pubsync();

      Returns:
        sync().

      27.5.2.2.3  Get area                           [lib.streambuf.pub.get]

      streamsize in_avail();

      Returns:
        If  a  read position is available, returns egptr() - gptr().  Other-
        wise returns showmanyc() (_lib.streambuf.virt.get_).

      int_type snextc();

      Effects:
        Calls sbumpc().
      Returns:
        if that function returns traits::eof(), returns traits::eof().  Oth-
        erwise, returns sgetc().

      int_type sbumpc();

      Returns:
        If  the  input  sequence  read  position  is  not available, returns
        uflow().  Otherwise, returns traits::to_int_type(*gptr()) and incre-
        ments the next pointer for the input sequence.

      int_type sgetc();

      Returns:
        If the input sequence read position is not available, returns under-
        flow().  Otherwise, returns traits::to_int_type(*gptr()).

      streamsize sgetn(char_type* s, streamsize n);

      Returns:
        xsgetn(s,n).

      27.5.2.2.4  Putback                          [lib.streambuf.pub.pback]

      int_type sputbackc(char_type c);

      Returns:
        If the input sequence putback  position  is  not  available,  or  if
        traits::eq(c,gptr()[-1])      is      false,      returns     pback-
        fail(traits::to_int_type(c)).   Otherwise,   decrements   the   next
        pointer      for      the     input     sequence     and     returns
        traits::to_int_type(*gptr()).

      int_type sungetc();

      Returns:
        If the input sequence putback position  is  not  available,  returns
        pbackfail().   Otherwise,  decrements the next pointer for the input
        sequence and returns traits::to_int_type(*gptr()).

      27.5.2.2.5  Put area                           [lib.streambuf.pub.put]

      int_type sputc(char_type c);

      Returns:
        If the output sequence write  position  is  not  available,  returns
        overflow(traits::to_int_type(c)).   Otherwise,  stores c at the next
        pointer for the output sequence, increments the pointer, and returns
        traits::to_int_type(c).

      streamsize sputn(const char_type* s, streamsize n);

      Returns:
        xsputn(s,n).

      27.5.2.3  basic_streambuf protected          [lib.streambuf.protected]
           member functions

      27.5.2.3.1  Get area access                   [lib.streambuf.get.area]

      char_type* eback() const;

      Returns:
        The beginning pointer for the input sequence.

      char_type* gptr() const;

      Returns:
        The next pointer for the input sequence.

      char_type* egptr() const;

      Returns:
        The end pointer for the input sequence.

      void gbump(int n);

      Effects:
        Advances the next pointer for the input sequence by n.

      void setg(char_type* gbeg, char_type* gnext, char_type* gend);

      Postconditions:
        gbeg == eback(), gnext == gptr(), and gend == egptr().

      27.5.2.3.2  Put area access                   [lib.streambuf.put.area]

      char_type* pbase() const;

      Returns:
        The beginning pointer for the output sequence.

      char_type* pptr() const;

      Returns:
        The next pointer for the output sequence.

      char_type* epptr() const;

      Returns:
        The end pointer for the output sequence.

      void pbump(int n);

      Effects:
        Advances the next pointer for the output sequence by n.

      void setp(char_type* pbeg, char_type* pend);

      Postconditions:
        pbeg == pbase(), pbeg == pptr(), and pend == epptr().

      27.5.2.4  basic_streambuf virtual             [lib.streambuf.virtuals]
           functions

      27.5.2.4.1  Locales                       [lib.streambuf.virt.locales]

      void imbue(const locale&)

      Effects:
        Change any translations based on locale.
      Notes:
        Allows  the derived class to be informed of changes in locale at the
        time they occur.  Between  invocations  of  this  function  a  class
        derived  from  streambuf can safely cache results of calls to locale
        functions and to members of facets so obtained.
      Default behavior:
        Does nothing.

      27.5.2.4.2  Buffer management and          [lib.streambuf.virt.buffer]
           positioning

      basic_streambuf* setbuf(char_type* s, streamsize n);

      Effects:
        Performs  an  operation  that  is  defined separately for each class
        derived from basic_streambuf in this  clause  (_lib.stringbuf.virtu-
        als_, _lib.filebuf.virtuals_).
      Default behavior:
        If  gptr() is non-null and gptr()!=egptr() then do nothing.  Returns
        this.

      pos_type seekoff(off_type off, ios_base::seekdir way,
                       ios_base::openmode which
                        = ios_base::in | ios_base::out);

      Effects:
        Alters the stream positions within one or  more  of  the  controlled
        sequences in a way that is defined separately for each class derived
        from  basic_streambuf  in  this  clause   (_lib.stringbuf.virtuals_,
        _lib.filebuf.virtuals_).
      Default behavior:
        Returns  an  object  of class pos_type that stores an invalid stream
        position (_lib.iostreams.definitions_).

      pos_type seekpos(pos_type sp,
                               ios_base::openmode which = in | out);

      Effects:
        Alters the stream positions within one or  more  of  the  controlled
        sequences in a way that is defined separately for each class derived
        from basic_streambuf in  this  clause  (_lib.stringbuf_,  _lib.file-
        buf_).
      Default behavior:
        Returns  an  object  of class pos_type that stores an invalid stream
        position.

      int sync();

      Effects:
        Synchronizes the controlled sequences with the arrays.  That is,  if
        pbase()  is  non-null  the characters between pbase() and pptr() are
        written to the controlled sequence.  The pointers may then be  reset
        as appropriate.
      Returns:
        -1  on  failure.   What  constitutes  failure  is determined by each
        derived class (_lib.filebuf.virtuals_).
      Default behavior:
        Returns zero.

      27.5.2.4.3  Get area                          [lib.streambuf.virt.get]

      int showmanyc();11)

      Returns:
        an  estimate  of the number of characters available in the sequence,
        or -1.  If it returns a positive value,  then  successive  calls  to
        underflow() will not return traits::eof() until at least that number
        of characters have been supplied.  If showmanyc() returns  -1,  then
        calls to underflow() or uflow() will fail.12)
      _________________________
      11) The morphemes of showmanyc are "es-how-many-see",  not  "show-man-
      ic".
      12)  underflow or uflow might fail by throwing an exception premature-
      ly.  The intention is not only that the calls will  not  return  eof()
      but that they will return ``immediately.''

      Default behavior:
        Returns zero.
      Notes:
        Uses traits::eof().

      streamsize xsgetn(char_type* s, streamsize n);

      Effects:
        Assigns up to n characters to successive elements of the array whose
        first element is designated by s.  The characters assigned are  read
        from  the  input  sequence  as  if  by  repeated  calls to sbumpc().
        Assigning stops when either n characters have  been  assigned  or  a
        call to sbumpc() would return traits::eof().
      Returns:
        The number of characters assigned.13)
      Notes:
        Uses traits::eof().

      int_type underflow();

      Notes:
        The  public  members  of  basic_streambuf call this virtual function
        only if gptr() is null or gptr() >= egptr()
      Returns:
        traits::to_int_type(c), where c is the first character of the  pend-
        ing  sequence,  without  moving the input sequence position past it.
        If  the  pending  sequence  is  null  then  the   function   returns
        traits::eof() to indicate failure.

    1 The pending sequence of characters is defined as the concatenation of:

      a)If gptr() is non- NULL, then the egptr() - gptr() characters  start-
        ing at gptr(), otherwise the empty sequence.

      b)Some  sequence  (possibly  empty)  of characters read from the input
        sequence.

    2 The result character is

      a)If the pending sequence is non-empty, the  first  character  of  the
        sequence.

      b)If  the pending sequence empty then the next character that would be
        read from the input sequence.

    3 The backup sequence is defined as the concatenation of:

      _________________________
      13)  Classes  derived  from basic_streambuf can provide more efficient
      ways to implement xsgetn() and xsputn() by  overriding  these  defini-
      tions from the base class.

      a)If eback() is null then empty,

      b)Otherwise the gptr() - eback() characters beginning at eback().
      Effects:
        The function sets up the gptr() and egptr() satisfying one of:

      a)If the pending  sequence  is  non-empty,  egptr()  is  non-null  and
        egptr() - gptr() characters starting at gptr() are the characters in
        the pending sequence

      b)If the pending sequence is empty, either gptr() is  null  or  gptr()
        and egptr() are set to the same non-NULL pointer.

    4 If  eback()  and  gptr()  are  non-null  then the function is not con-
      strained as to their contents, but the ``usual backup  condition''  is
      that either:

      a)If  the  backup  sequence contains at least gptr() - eback() charac-
        ters, then the gptr() - eback() characters starting at eback() agree
        with the last gptr() - eback() characters of the backup sequence.

      b)Or  the  n  characters  starting at gptr() - n agree with the backup
        sequence (where n is the length of the backup sequence)
      Default behavior:
        Returns traits::eof().

      int_type uflow();

      Requires:
        The constraints are the same as for  underflow(),  except  that  the
        result  character  is  transferred  from the pending sequence to the
        backup sequence, and the pending sequence may not  be  empty  before
        the transfer.
      Default behavior:
        Calls  underflow().   If  underflow() returns traits::eof(), returns
        traits::eof().      Otherwise,     returns     the     value      of
        traits::to_int_type(*gptr())  and  increment  the  value of the next
        pointer for the input sequence.
      Returns:
        traits::eof() to indicate failure.

      27.5.2.4.4  Putback                         [lib.streambuf.virt.pback]

      int_type pbackfail(int_type c = traits::eof());

      Notes:
        The public functions of basic_streambuf call this  virtual  function
        only    when    gptr()    is    null,    gptr()   ==   eback(),   or
        traits::eq(*gptr(),traits::to_char_type(c))  returns  false.   Other
        calls shall also satisfy that constraint.
        The pending sequence is defined as for underflow(), with the modifi-
        cations that

      --If traits::eq_int_type(c,traits::eof()) returns true, then the input
        sequence  is  backed up one character before the pending sequence is
        determined.

      --If traits::eq_int_type(c,traits::eof())  return  false,  then  c  is
        prepended.   Whether  the input sequence is backed up or modified in
        any other way is unspecified.
      Postcondition:
        On return, the constraints of gptr(), eback(), and  pptr()  are  the
        same as for underflow().
      Returns:
        traits::eof()  to  indicate  failure.  Failure may occur because the
        input sequence could not be backed up, or if for some  other  reason
        the  pointers  could  not  be  set  consistent with the constraints.
        pbackfail() is called only when put back has really failed.
        Returns some value other than traits::eof() to indicate success.
      Default behavior:
        Returns traits::eof().

      27.5.2.4.5  Put area                          [lib.streambuf.virt.put]

      streamsize xsputn(const char_type* s, streamsize n);

      Effects:
        Writes up to n characters to the output sequence as if  by  repeated
        calls to sputc(c).  The characters written are obtained from succes-
        sive elements of the array whose first element is designated  by  s.
        Writing  stops  when either n characters have been written or a call
        to sputc(c) would return traits::eof().
      Returns:
        The number of characters written.

      int_type overflow(int_type c = traits::eof());

      Effects:
        Consumes some initial subsequence of the characters of  the  pending
        sequence.  The pending sequence is defined as the concatenation of

      a)if  pbase()  is  NULL  then  the  empty sequence otherwise, pptr() -
        pbase() characters beginning at pbase().

      b)if traits::eq_int_type(c,traits::eof()) returns true, then the empty
        sequence otherwise, the sequence consisting of c.
      Notes:
        The  member functions sputc() and sputn() call this function in case
        that no room can be found in the put buffer enough to accomodate the
        argument character sequence.
      Requires:
        Every  overriding definition of this virtual function shall obey the
        following constraints:

      1)The effect  of  consuming  a  character  on  the  associated  output

        sequence is specified14)

      2)Let r be the number of characters in the pending sequence  not  con-
        sumed.   If  r  is  non-zero  then pbase() and pptr() must be set so
        that: pptr() - pbase() == r and the r characters starting at pbase()
        are  the  associated output stream.  In case r  is zero (all charac-
        ters of the pending sequence have been consumed) then either pbase()
        is  set to NULL, or pbase() and pptr() are both set to the same non-
        NULL value.

      3)The function may fail if either  appending  some  character  to  the
        associated  output  stream  fails  or  if  it is unable to establish
        pbase() and pptr() according to the above rules.
      Returns:
        traits::eof() or throws an exception if the function fails.
        Otherwise, returns some value other than traits::eof()  to  indicate
        success.15)
      Default behavior:
        Returns traits::eof().

      27.6  Formatting and manipulators                [lib.iostream.format]

      Header <istream> synopsis

      namespace std {
        template <class charT, class traits = char_traits<charT> >
          class basic_istream;
        typedef basic_istream<char>     istream;
        typedef basic_istream<wchar_t> wistream;

        template <class charT, class traits>
          basic_istream<charT,traits>& ws(basic_istream<charT,traits>& is);
      }

      Header <ostream> synopsis

      _________________________
      14)  That is, for each class derived from an instance of basic_stream-
      buf in this clause (_lib.stringbuf_, _lib.filebuf_),  a  specification
      of how consuming a character effects the associated output sequence is
      given.  There is no requirement on a program-defined class.
      15)  Typically,  overflow  returns  c to indicate success, except when
      traits::eq_int_type(c,traits::eof()) returns true, in  which  case  it
      returns traits::not_eof(c).

      namespace std {
        template <class charT, class traits = char_traits<charT> >
          class basic_ostream;
        typedef basic_ostream<char>     ostream;
        typedef basic_ostream<wchar_t> wostream;

        template <class charT, class traits>
          basic_ostream<charT,traits>& endl(basic_ostream<charT,traits>& os);
        template <class charT, class traits>
          basic_ostream<charT,traits>& ends(basic_ostream<charT,traits>& os);
        template <class charT, class traits>
          basic_ostream<charT,traits>& flush(basic_ostream<charT,traits>& os);
      }

      Header <iomanip> synopsis

      namespace std {
          // Types T1, T2, ... are unspecified
          // implementation types
          T1 resetiosflags(ios_base::fmtflags mask);
          T2 setiosflags  (ios_base::fmtflags mask);
          T3 setbase(int base);
          template<charT> T4 setfill(charT c);
          T5 setprecision(int n);
          T6 setw(int n);
      }

      27.6.1  Input streams                              [lib.input.streams]

    1 The  header  <istream> defines two types and a function signature that
      control input from a stream buffer.

      27.6.1.1  Template class basic_istream                   [lib.istream]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_istream : virtual public basic_ios<charT,traits> {
        public:
        // Types (inherited from basic_ios (_lib.ios_)):
       // typedef charT                     char_type;
       // typedef typename traits::int_type int_type;
       // typedef typename traits::pos_type pos_type;
       // typedef typename traits::off_type off_type;
       // typedef traits                    traits_type;
        // _lib.istream.cons_ Constructor/destructor:
          explicit basic_istream(basic_streambuf<charT,traits>* sb);
          virtual ~basic_istream();
        // _lib.istream::sentry_ Prefix/suffix:
          class sentry;

        // _lib.istream.formatted_ Formatted input:
          basic_istream<charT,traits>& operator>>
              (basic_istream<charT,traits>& (*pf)(basic_istream<charT,traits>&))
          basic_istream<charT,traits>& operator>>
              (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&))
          basic_istream<charT,traits>& operator>>
              (ios_base& (*pf)(ios_base&))
          basic_istream<charT,traits>& operator>>(bool& n);
          basic_istream<charT,traits>& operator>>(short& n);
          basic_istream<charT,traits>& operator>>(unsigned short& n);
          basic_istream<charT,traits>& operator>>(int& n);
          basic_istream<charT,traits>& operator>>(unsigned int& n);
          basic_istream<charT,traits>& operator>>(long& n);
          basic_istream<charT,traits>& operator>>(unsigned long& n);
          basic_istream<charT,traits>& operator>>(float& f);
          basic_istream<charT,traits>& operator>>(double& f);
          basic_istream<charT,traits>& operator>>(long double& f);
          basic_istream<charT,traits>& operator>>(void*& p);
          basic_istream<charT,traits>& operator>>
              (basic_streambuf<char_type,traits>* sb);
        // _lib.istream.unformatted_ Unformatted input:
          streamsize gcount() const;
          int_type get();
          basic_istream<charT,traits>& get(char_type& c);
          basic_istream<charT,traits>& get(char_type* s, streamsize n);
          basic_istream<charT,traits>& get(char_type* s, streamsize n,
                            char_type delim);
          basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb);
          basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb,
                            char_type delim);
          basic_istream<charT,traits>& getline(char_type* s, streamsize n);
          basic_istream<charT,traits>& getline(char_type* s, streamsize n,
                            char_type delim);
          basic_istream<charT,traits>& ignore
              (streamsize n = 1, int_type delim = traits::eof());
          int_type                     peek();
          basic_istream<charT,traits>& read    (char_type* s, streamsize n);
          streamsize                   readsome(char_type* s, streamsize n);
          basic_istream<charT,traits>& putback(char_type c);
          basic_istream<charT,traits>& unget();
          int sync();

          pos_type tellg();
          basic_istream<charT,traits>& seekg(pos_type);
          basic_istream<charT,traits>& seekg(off_type, ios_base::seekdir);
        };

        // _lib.istream::extractors_ character extraction templates:
        template<class charT, class traits>
          basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>&,
                                                  charT&);
        template<class traits>
          basic_istream<char,traits>& operator>>(basic_istream<char,traits>&,
                                                 unsigned char&);
        template<class traits>
          basic_istream<char,traits>& operator>>(basic_istream<char,traits>&,
                                                 signed char&);

        template<class charT, class traits>
          basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>&,
                                                  charT*);
        template<class traits>
          basic_istream<char,traits>& operator>>(basic_istream<charT,traits>&,
                                                 unsigned char*);
        template<class traits>
          basic_istream<char,traits>& operator>>(basic_istream<charT,traits>&,
                                                 signed char*);
      }

    1 The class basic_istream defines a number of member function signatures
      that  assist  in  reading  and  interpreting input from sequences con-
      trolled by a stream buffer.

    2 Two groups of member function signatures share common properties:  the
      formatted  input  functions  (or extractors) and the unformatted input
      functions.  Both groups of input functions are described  as  if  they
      obtain  (or  extract) input characters by calling rdbuf()->sbumpc() or
      rdbuf()->sgetc().  They may use other public members of istream.

    3 If rdbuf()->sbumpc() or rdbuf()->sgetc() returns  traits::eof(),  then
      the  input  function,  except as explicitly noted otherwise, completes
      its actions and does setstate(eofbit), which may throw ios_base::fail-
      ure (_lib.iostate.flags_), before returning.

    4 If  one  of  these  called  functions throws an exception, then unless
      explicitly noted otherwise, the input function sets  badbit  in  error
      state.   If  badbit  is on in exception(), the input function rethrows
      the exception without completing its actions, otherwise  it  does  not
      throw  anything  and proceeds as if the called function had returned a
      failure indication.

      27.6.1.1.1  basic_istream constructors              [lib.istream.cons]

      explicit basic_istream(basic_streambuf<charT,traits>* sb);

      Effects:
        Constructs an object of class basic_istream, assigning initial  val-
        ues    to    the   base   class   by   calling   basic_ios::init(sb)
        (_lib.basic.ios.cons_).
      Postcondition:
        gcount() == 0

      virtual ~basic_istream();

      Effects:
        Destroys an object of class basic_istream.
      Notes:
        Does not perform any operations of rdbuf().

      27.6.1.1.2  Class basic_istream::sentry          [lib.istream::sentry]

      namespace std {
        template <class charT,class traits = char_traits<charT> >
        class basic_istream<charT,traits>::sentry {
          typedef traits traits_type;
          bool ok_; // exposition only
         public:
          explicit sentry(basic_istream<charT,traits>& is, bool noskipws = false);
          ~sentry();
          operator bool() { return ok_; }
        };
      }

    1 The class sentry defines a class that is responsible for doing  excep-
      tion safe prefix and suffix operations.

      explicit sentry(basic_istream<charT,traits>& is, bool noskipws = false);

      Effects:
        If  is.good()  is true, prepares for formatted or unformatted input.
        First, if is.tie()  is  not  a  null  pointer,  the  function  calls
        is.tie()->flush()  to synchronize the output sequence with any asso-
        ciated  external  C  stream.16) If noskipws is zero and is.flags() &
        ios_base::skipws is nonzero, the function extracts and discards each
        character  as  long  as  the  next  available input character c is a
        whitespace character.
      Notes:
        The  constructor  explicit  sentry(basic_istream<charT,traits>&  is,
        bool  noskipws  = false) uses the currently imbued locale in is , to
        determine whether the next input character is whitespace or not.

      _________________________
      16) The call is.tie()->flush() does not necessarily occur if the func-
      tion can determine that no synchronization is necessary.

        To decide if the character c is a  whitespace  character,  the  con-
        structor performs ``as if'' it executes the following code fragment:
            const ctype<charT>& ctype = use_facet<ctype<charT> >(is.getloc());
            if (ctype.is(ctype.space,c)!=0)
            // c is a whitespace character.
        If, after any preparation is completed, is.good() is  true,  ok_  !=
        false  otherwise, ok_ == false.  During preparation, the constructor
        may  call  setstate(failbit)  (which  may  throw   ios_base::failure
        (_lib.iostate.flags_))17)

    2 [Example: A typical implementation of  the  sentry  constructor  might
      include code such as:
      template <class charT, class traits = char_traits<charT> >
      basic_istream<charT,traits>::sentry(
               basic_istream<charT,traits>& is, bool noskipws = false) {
          ...
          int_type c;
          typedef ctype<charT> ctype_type;
          const ctype_type& ctype = use_facet<ctype_type>(is.getloc());
          while ((c = is.rdbuf()->snextc()) != traits::eof()) {
            if (ctype.is(ctype.space,c)==0) {
              is.rdbuf()->sputbackc (c);
              break;
            }
          }
          ...
       }
       --end example]

      ~sentry();

      Effects:
        None.

      operator bool();

      Effects:
        Returns ok_.

      27.6.1.2  Formatted input functions            [lib.istream.formatted]

      27.6.1.2.1  Common requirements         [lib.istream.formatted.reqmts]

    1 Each  formatted  input  function  begins  execution by constructing an
      object of class sentry with the noskipws (second) argument false.   If
      the  sentry  object  returns  true,  when converted to a value of type
      bool, the function endeavors to obtain the  requested  input.   If  an
      _________________________
      17)  The sentry constructor and destructor can also perform additional
      implementation-dependent operations.

      exception  is  thrown during input then ios::badbit is turned on18) in
      *this's error state.  If (exception()&badbit)!= 0 then  the  exception
      is  rethrown  In  any case, the formatted input function destructs the
      sentry object.  If no exception has been thrown it  returns *this

      27.6.1.2.2  Arithmetic              [lib.istream.formatted.arithmetic]
           Extractors

      operator>>(short& val);
      operator>>(unsigned short& val);
      operator>>(int& val);
      operator>>(unsigned int& val);
      operator>>(long& val);
      operator>>(unsigned long& val);
      operator>>(float& val);
      operator>>(double& val);
      operator>>(long double& val);
      operator>>(bool& val);
      operator>>(void*& val);

      As  in  the  case  of  the  inserters,  these extractors depend on the
      locale's num_get<> (_lib.locale.num.get_) object  to  perform  parsing
      the  input  stream data.  The conversion occurs as if performed by the
      following code fragment:
        typedef num_get< charT,istreambuf_iterator<charT,traits> > numget;
        iostate err = 0;
        use_facet< numget >(loc).get(*this, 0, *this, err, val);
        setstate(err);
      In the above fragment, loc  stands  for  the  private  member  of  the
      basic_ios  class,  [Note: The first argument provides an object of the
      istream_iterator class which  is  an  iterator  pointed  to  an  input
      stream.   It  bypasses  istreams and uses streambufs directly.   --end
      note] Class locale relies on this type as its  interface  to  istream,
      since  the  flexibility it has been abstracted away from direct depen-
      dence on istream.

      27.6.1.2.3  basic_istream::operator>>        [lib.istream::extractors]

      basic_istream<charT,traits>& operator>>
          (basic_istream<charT,traits>& (*pf)(basic_istream<charT,traits>&))

      Returns:
        pf(*this).19)

      _________________________
      18) This is done without causing an ios::failure to be thrown.
      19)  See,  for  example,  the  function  signature  ws(basic_istream&)
      (_lib.istream.manip_).

      basic_istream<charT,traits>& operator>>
          (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&));

      Effects:
        Calls pf(*this).
      Returns:
        *this.

      basic_istream<charT,traits>& operator>>
          (ios_base& (*pf)(ios_base&));

      Effects:
        Calls pf(*this).20)
      Returns:
        *this.

      template<class charT, class traits>
        basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>& in,
                                                charT* s);
      template<class traits>
        basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in,
                                               unsigned char* s);
      template<class traits>
        basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in,
                                               signed char* s);

      Effects:
        Behaves  like  a   formatted   input   member   (as   described   in
        _lib.istream.formatted.reqmts_)  of  in.   After  a sentry object is
        constructed, operator>> extracts characters  and  stores  them  into
        successive  locations  of an array whose first element is designated
        by s.  If width() is greater than zero, n is width().   Otherwise  n
        is the the number of elements of the largest array of char_type that
        can store a terminating eos.  n is the maximum number of  characters
        stored.

    1 Characters are extracted and stored until any of the following occurs:

      --n-1 characters are stored;

      --end of file occurs on the input sequence;

      --ct.is(ct.space,c) is true for the next available input character  c,
        where ct is use_facet<ctype<charT> >(in.getloc()).

      --A  null byte ( traits::eos()) in the next position, which may be the
        first position if no characters were extracted.
      _________________________
      20)   See,   for   example,   the  function  signature  dec(ios_base&)
      (_lib.basefield.manip_).

      operator>> then calls width(0).

    2 If the function extracted no characters, it  calls  setstate(failbit),
      which may throw ios_base::failure (_lib.iostate.flags_).
      Returns:
        in.

      template<class charT, class traits>
        basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>& in,
                                                charT& c);
      template<class traits>
        basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in,
                                               unsigned char& c);
      template<class traits>
        basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in,
                                               signed char& c);

      Effects:
        Behaves   like   a   formatted   input   member   (as  described  in
        _lib.istream.formatted.reqmts_) of in.  After  a  sentry  object  is
        constructed  a  character is extracted from in, if one is available,
        and stored in c.  Otherwise, the  function  calls  in.setstate(fail-
        bit).
      Returns:
        in.

      basic_istream<charT,traits>& operator>>
          (basic_streambuf<charT,traits>* sb);

      Effects:
        If   sb   is   null,   calls   setstate(failbit),  which  may  throw
        ios_base::failure (_lib.iostate.flags_).
        Extracts characters from  *this  and  inserts  them  in  the  output
        sequence  controlled  by  sb.  Characters are extracted and inserted
        until any of the following occurs:

      --end-of-file occurs on the input sequence;

      --inserting in the output sequence fails (in which case the  character
        to be inserted is not extracted);

      --an exception occurs (in which case the exception is caught).
         If  the function inserts no characters, it calls setstate(failbit),
        which may throw ios_base::failure (_lib.iostate.flags_).  If failure
        was  due to catching an exception thrown while extracting characters
        from sb and failbit is  on  in  exceptions()  (_lib.iostate.flags_),
        then the caught exception is rethrown.
      Returns:
        *this.

      27.6.1.3  Unformatted input functions        [lib.istream.unformatted]

    1 Each  unformatted  input  function begins execution by constructing an
      object of class sentry with the  default  argument  noskipws  (second)
      argument true.  If the sentry object returns true, when converted to a
      value of type bool, the function endeavors  to  obtain  the  requested
      input.   If  an  exception  is thrown during input then ios::badbit is
      turned on21) in *this's error state.  If (exception()&badbit)!= 0 then
      the  exception  is  rethrown  It  also counts the number of characters
      extracted.  If no exception has been thrown it  ends  by  storing  the
      count  in  a  member object and returning the value specified.  In any
      event the sentry object is destroyed before  leaving  the  unformatted
      input function.

      streamsize gcount() const;

      Returns:
        The  number  of  characters  extracted by the last unformatted input
        member function called for the object.

      int_type get();

      Effects:
        Extracts a character c, if one is available.  Otherwise,  the  func-
        tion  calls  setstate(failbit),  which  may  throw ios_base::failure
        (_lib.iostate.flags_),
      Returns:
        c if available, otherwise traits::eof().

      basic_istream<charT,traits>& get(char_type& c);

      Effects:
        Extracts  a  character, if one is available, and assigns it to c.22)
        Otherwise, the function calls  setstate(failbit)  (which  may  throw
        ios_base::failure (_lib.iostate.flags_)).
      Returns:
        *this.

      basic_istream<charT,traits>& get(char_type*  s, streamsize n,
                        char_type delim );

      Effects:
        Extracts  characters and stores them into successive locations of an
        array  whose  first  element  is  designated by s.23) Characters are
      _________________________
      21) This is done without causing an ios::failure to be thrown.
      22) Note that this function is not overloaded on types signed  charand
      unsigned char.
      23) Note that this function is not overloaded on types signed char and

        extracted and stored until any of the following occurs:

      --n - 1 characters are stored;

      --end-of-file occurs on the input sequence (in which case the function
        calls setstate(eofbit));

      --c == delim for the next available input character c (in which case c
        is not extracted).

    2 If the function  stores  no  characters,  it  calls  setstate(failbit)
      (which  may  throw  ios_base::failure  (_lib.iostate.flags_)).  In any
      case, it then stores a null character into the next  successive  loca-
      tion of the array.
      Returns:
        *this.

      basic_istream<charT,traits>& get(char_type*  s, streamsize n)

      Effects:
        Calls getline(s,n,widen('\n'))
      Returns:
        Value returned by the call.

      basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb,
                        char_type delim );

      Effects:
        Extracts  characters  and  inserts  them in the output sequence con-
        trolled by sb.  Characters are extracted and inserted until  any  of
        the following occurs:

      --end-of-file occurs on the input sequence;

      --inserting  in the output sequence fails (in which case the character
        to be inserted is not extracted);

      --c == delim for the next available input character c (in which case c
        is not extracted);

      --an  exception occurs (in which case, the exception is caught but not
        rethrown).

    3 If the function inserts no  characters,  it  calls  setstate(failbit),
      which may throw ios_base::failure (_lib.iostate.flags_).
      Returns:
        *this.

      _________________________
      unsigned char.

      basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb);

      Effects:
        Calls getline(s,n,widen('\n'))
      Returns:
        Value returned by the call.

      basic_istream<charT,traits>& getline(char_type* s, streamsize n,
                            char_type delim);

      Effects:
        Extracts  characters and stores them into successive locations of an
        array  whose  first  element  is  designated by s.24) Characters are
        extracted and stored until one of the following occurs:

      1)end-of-file occurs on the input sequence (in which case the function
        calls setstate(eofbit));

      2)c  ==  delim for the next available input character c (in which case
        the input character is extracted but not stored);25)

      3)n  -  1 characters are stored (in which case the function calls set-
        state(failbit)).

    4 These conditions are tested in the order shown.26)

    5 If the function extracts no  characters,  it  calls  setstate(failbit)
      (which may throw ios_base::failure (_lib.iostate.flags_)).27)

    6 In any case, it then stores a  null  character  (using  traits::eos())
      into the next successive location of the array.
      Returns:
        *this.

    7 [Example:

      _________________________
      24) Note that this function is not overloaded on types signed char and
      unsigned char.
      25) Since the final input character is ``extracted,'' it is counted in
      the gcount(), even though it is not stored.
      26) This allows an input line which exactly fills the buffer,  without
      setting  failbit.  This is different behavior than the historical AT&T
      implementation.
      27) This implies an empty input line will not cause failbit to be set.

        #include <iostream>

        int main()
        {
          using namespace std;
          const int line_buffer_size = 100;

          char buffer[line_buffer_size];
          int line_number = 0;
          while (cin.getline(buffer, line_buffer_size, '\n') || cin.gcount()) {
            int count = cin.gcount();
            if (cin.eof())
              cout << "Partial final line";   // cin.fail() is false
            else if (cin.fail()) {
              cout << "Partial long line";
              cin.clear(cin.rdstate() & ~ios::failbit);
            } else {
              count--;        // Don't include '\n' in count
              cout << "Line " << ++line_number;
            }
            cout << " (" << count << " chars): " << buffer << endl;
          }
        }
       --end example]

      basic_istream<charT,traits>& getline(char_type* s, streamsize n);

      Returns:
        getline(s,n,widen('\n'))

      basic_istream<charT,traits>&
          ignore(int n = 1, int_type delim = traits::eof());

      Effects:
        Extracts  characters  and  discards  them.  Characters are extracted
        until any of the following occurs:

      --if n  != numeric_limits<int>::max() (_lib.limits_), n characters are
        extracted

      --end-of-file occurs on the input sequence (in which case the function
        calls   setstate(eofbit),   which   may   throw    ios_base::failure
        (_lib.iostate.flags_));

      --c == delim for the next available input character c (in which case c
        is extracted).
      Notes:
        The last condition will never occur if delim == traits::eof().
      Returns:
        *this.

      int_type peek();

      Returns:
        traits::eof()   if   good()   is    false.     Otherwise,    returns
        rdbuf()->sgetc().

      basic_istream<charT,traits>& read(char_type* s, streamsize n);

      Effects:
        Extracts  characters and stores them into successive locations of an
        array  whose  first  element  is  designated by s.28) Characters are
        extracted and stored until either of the following occurs:

      --n characters are stored;

      --end-of-file occurs on the input sequence (in which case the function
        calls   setstate(failbit),   which   may   throw   ios_base::failure
        (_lib.iostate.flags_)).
      Returns:
        *this.

      streamsize readsome(char_type* s, streamsize n);

      Effects:
        If !good() calls setstate(failbit) which may throw an exception, and
        return.   Otherwise extracts characters and stores them into succes-
        sive locations of an array whose first element is designated  by  s.
        If  rdbuf()->in_avail()  ==  -1,  calls  setstate(eofbit) (which may
        throw  ios_base::failure  (_lib.iostate.flags_)),  and  extracts  no
        characters;

      --If rdbuf()->in_avail() == 0, extracts no characters

      --If rdbuf()->in_avail() > 0, extracts min(rdbuf()->in_avail(),n)).
      Returns:
        The number of characters extracted.

      basic_istream<charT,traits>& putback(char_type c);

      Effects:
        If !good() calls setstate(failbit) which may throw an exception, and
        return.  If rdbuf() is not  null,  calls  rdbuf->sputbackc()  .   If
        rdbuf()  is null, or if sputback() returns traits::eof(), calls set-
        state(badbit)      (which      may      throw      ios_base::failure
        (_lib.iostate.flags_)).
      _________________________
      28) Note that this function is not overloaded on types signed char and
      unsigned char.

      Returns:
        *this.

      basic_istream<charT,traits>& unget();

      Effects:
        If !good() calls setstate(failbit) which may throw an exception, and
        return.  If rdbuf()  is  not  null,  calls  rdbuf()->sungetc().   If
        rdbuf()  is  null, or if sungetc() returns traits::eof(), calls set-
        state(badbit)      (which      may      throw      ios_base::failure
        (_lib.iostate.flags_)).
      Returns:
        *this.

      int sync();

      Effects:
        If  rdbuf()  is  a  null  pointer,  returns  -1  .  Otherwise, calls
        rdbuf()->pubsync() and, if  that  function  returns  -1  calls  set-
        state(badbit)      (which      may      throw      ios_base::failure
        (_lib.iostate.flags_),  and   returns   traits::eof().    Otherwise,
        returns zero.

      pos_type tellg();

      Returns:
        if  fail() != false, returns pos_type(-1) to indicate failure.  Oth-
        erwise, returns rdbuf()->pubseekoff(0, cur, in).

      basic_istream<charT,traits>& seekg(pos_type pos);

      Effects:
        If fail() != true, executes rdbuf()->pubseekpos(pos).
      Returns:
        *this.

      basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);

      Effects:
        If fail() != true, executes rdbuf()->pubseekoff(off, dir).
      Returns:
        *this.

      27.6.1.4  Standard basic_istream manipulators      [lib.istream.manip]

      namespace std {
        template <class charT, class traits>
          basic_istream<charT,traits>& ws(basic_istream<charT,traits>& is);
      }

      Effects:
        Extracts  characters  as  long  as the next available character c is
        whitespace or until there are no more characters  in  the  sequence.
        Whitespace  characters  are distinguished with the same criterion as
        used  by  sentry::sentry  (_lib.istream::sentry_).   If   ws   stops
        extracting  characters  because  there are no more available it sets
        eofbit, but not failbit.
      Returns:
        is.

      27.6.1.5  Template class basic_iostream            [lib.iostreamclass]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_iostream :
          public basic_istream<charT,traits>,
          public basic_ostream<charT,traits> {
        public:
        // constructor/destructor
          explicit basic_iostream(basic_streambuf<charT,traits>* sb);
          virtual ~basic_iostream();
        };
      }

    1 The class basic_iostream inherits a number  of  functions  that  allow
      reading  input  and writing output to sequences controlled by a stream
      buffer.

      27.6.1.5.1  basic_iostream constructors            [lib.iostream.cons]

      explicit basic_iostream(basic_streambuf<charT,traits>* sb);

      Effects
        Constructs an object of class basic_iostream, assigning initial val-
        ues  to  the base classes by calling basic_istream<charT,traits>(sb)
        (_lib.istream_) and basic_ostream<charT,traits>(sb) (_lib.ostream_)
      Postcondition:
        rdbuf()==sb and gcount()==0.

      27.6.1.5.2  basic_iostream destructor              [lib.iostream.dest]

      virtual ~basic_iostream();

      Effects:
        Destroys an object of class basic_iostream.
      Notes:
        Does not perform any operations on rdbuf().

      27.6.2  Output streams                            [lib.output.streams]

    1 The header <ostream> defines a type and  several  function  signatures
      that control output to a stream buffer.

      27.6.2.1  Template class basic_ostream                   [lib.ostream]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_ostream : virtual public basic_ios<charT,traits> {
        public:
        // Types (inherited from basic_ios (_lib.ios_)):
       // typedef charT                     char_type;
       // typedef typename traits::int_type int_type;
       // typedef typename traits::pos_type pos_type;
       // typedef typename traits::off_type off_type;
       // typedef traits                    traits_type;
        // _lib.ostream.cons_ Constructor/destructor:
          explicit basic_ostream(basic_streambuf<char_type,traits>* sb);
          virtual ~basic_ostream();
        // _lib.ostream::sentry_ Prefix/suffix:
          class sentry;
        // _lib.ostream.formatted_ Formatted output:
          basic_ostream<charT,traits>& operator<<
              (basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&));
          basic_ostream<charT,traits>& operator<<
              (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&));
          basic_ostream<charT,traits>& operator<<
              (ios_base& (*pf)(ios_base&));
          basic_ostream<charT,traits>& operator<<(bool n);
          basic_ostream<charT,traits>& operator<<(short n);
          basic_ostream<charT,traits>& operator<<(unsigned short n);
          basic_ostream<charT,traits>& operator<<(int n);
          basic_ostream<charT,traits>& operator<<(unsigned int n);
          basic_ostream<charT,traits>& operator<<(long n);
          basic_ostream<charT,traits>& operator<<(unsigned long n);
          basic_ostream<charT,traits>& operator<<(float f);
          basic_ostream<charT,traits>& operator<<(double f);
          basic_ostream<charT,traits>& operator<<(long double f);
          basic_ostream<charT,traits>& operator<<(void* p);
          basic_ostream<charT,traits>& operator<<
              (basic_streambuf<char_type,traits>* sb);
        // _lib.ostream.unformatted_ Unformatted output:
          basic_ostream<charT,traits>& put(char_type c);
          basic_ostream<charT,traits>& write(const char_type* s, streamsize n);
          basic_ostream<charT,traits>& flush();
        // _lib.ostream.seeks_ seeks:
          pos_type tellp();
          basic_ostream<charT,traits>& seekp(pos_type);
          basic_ostream<charT,traits>& seekp(off_type, ios_base::seekdir);
        };

        // _lib.ostream.inserters.character_ character inserters
        template<class charT, class traits>
        basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
                                                charT);
        template<class charT, class traits>
        basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
                                                char);
        // specialization
        template<class traits>
          basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
                                                 char);
        // signed and unsigned
        template<class traits>
          basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
                                                 signed char);
        template<class traits>
          basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
                                                 unsigned char);

        template<class charT, class traits>
          basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
                                                  const charT*);
        template<class charT, class traits>
          basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
                                                  const char*);
        // partial specializationss
        template<class traits>
          basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
                                                 const char*);
        //  signed and unsigned
        template<class traits>
          basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
                                                 const signed char*);
        template<class traits>
          basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
                                                 const unsigned char*);
      }

    1 The class basic_ostream defines a number of member function signatures
      that assist in formatting and writing output to output sequences  con-
      trolled by a stream buffer.

    2 Two  groups of member function signatures share common properties: the
      formatted output functions (or inserters) and the  unformatted  output
      functions.   Both groups of output functions generate (or insert) out-
      put    characters     by     actions     equivalent     to     calling
      rdbuf().sputc(int_type).    They  may  use  other  public  members  of
      basic_ostream except that they do not invoke any  virtual  members  of
      rdbuf() except overflow().

    3 If  one  of  these  called  functions throws an exception, then unless
      explicitly noted otherwise the output function  set  badbit  in  error
      state.   If  badbit is on in exception(), the output function rethrows

      the exception without completing its actions, otherwise  it  does  not
      throw anything and treat as an error.

      27.6.2.2  basic_ostream constructors                [lib.ostream.cons]

      explicit basic_ostream(basic_streambuf<charT,traits>* sb);

      Effects:
        Constructs  an object of class basic_ostream, assigning initial val-
        ues to the base class by  calling  basic_ios<charT,traits>::init(sb)
        (_lib.basic.ios.cons_).
      Postcondition:
        rdbuf() == sb.

      virtual ~basic_ostream();

      Effects:
        Destroys an object of class basic_ostream.
      Notes:
        Does not perform any operations on rdbuf().

      27.6.2.3  Class basic_ostream::sentry            [lib.ostream::sentry]

      namespace std {
        template <class charT,class traits = char_traits<charT> >
        class basic_ostream<charT,traits>::sentry {
          bool ok_; // exposition only
         public:
          explicit sentry(basic_ostream<charT,traits>& os);
          ~sentry();
          operator bool() { return ok_; }
        };
      }

    1 The  class sentry defines a class that is responsible for doing excep-
      tion safe prefix and suffix operations.

      explicit sentry(basic_ostream<charT,traits>& os);

    2 If os.good() is nonzero, prepares for formatted or unformatted output.
      If os.tie() is not a null pointer, calls os.tie()->flush().29)

      _________________________
      29) The call os.tie()->flush() does not necessarily occur if the func-
      tion can determine that no synchronization is necessary.

    3 If, after any preparation is completed, os.good() is true, ok_ == true
      otherwise, ok_ == false.  During preparation, the constructor may call
      setstate(failbit)     (which     may      throw      ios_base::failure
      (_lib.iostate.flags_))30)

      ~sentry();

    4 If ((os.flags()  &  ios_base::unitbuf)  &&  !uncaught_exception())  is
      true, calls os.flush().

      operator bool();

      Effects:
        Returns ok_.

      27.6.2.4  basic_ostream seek members               [lib.ostream.seeks]

      pos_type tellp();

      Returns:
        if  fail() != false, returns pos_type(-1) to indicate failure.  Oth-
        erwise, returns rdbuf()->pubseekoff(0, cur, out).

      basic_ostream<charT,traits>& seekp(pos_type& pos);

      Effects:
        If fail() != true, executes rdbuf()->pubseekpos(pos).
      Returns:
        *this.

      basic_ostream<charT,traits>& seekp(off_type& off, ios_base::seekdir dir);

      If fail() != true, executes rdbuf()->pubseekoff(off, dir).
      Returns:
        *this.

      27.6.2.5  Formatted output functions           [lib.ostream.formatted]

      27.6.2.5.1  Common requirements         [lib.ostream.formatted.reqmts]

    1 Each formatted output function begins  execution  by  constructing  an
      object of class sentry.  If this object returns true when converted to
      a value of type bool, the function endeavors to generate the requested
      _________________________
      30)  The sentry constructor and destructor can also perform additional
      implementation-dependent operations.

      output.   If  the generation fails, then the formatted output function
      does setstate(ios::failbit) which might throw and  exception.   If  an
      exception  is thrown during output then ios::badbit is turned on31) in
      *this's error state If (exception()&badbit)!= 0 then the exception  is
      rethrown.  Whether or not an exception is thrown, the sentry object is
      destroyed before leaving the formatted output function.  If no  excep-
      tion is thrown, the result of the formattted output function is *this.

    2 The  descriptions  of  the  individual  formatted  output   operations
      describes  how  they  perform  output  and does not mention the sentry
      object.

      27.6.2.5.2  Arithmetic              [lib.ostream.inserters.arithmetic]
           Inserters

      operator<<(bool val);
      operator<<(short val);
      operator<<(unsigned short val);
      operator<<(int val);
      operator<<(unsigned int val);
      operator<<(long val);
      operator<<(unsigned long val);
      operator<<(float val);
      operator<<(double val);
      operator<<(long double val);
      operator<<(void* val);

      Effects:

    1 The  classes  num_get<>  and num_put<> handle locale-dependent numeric
      formatting and parsing.  These inserter functions  refers  the  imbued
      locale  value  to utilize these numeric formatting functionality.  The
      formatting conversion occurs as if it  performed  the  following  code
      fragment:
        bool failed =
          use_facet< num_put<charT,ostreambuf_iterator<charT,traits> > >(getloc()).
            put(*this, *this, fill(), val). failed();
      The  first  argument  provides  an object of the ostreambuf_iterator<>
      class which is an iterator for  class  basic_ostream<>.   It  bypasses
      ostreams  and  uses streambufs directly.  Class locale relies on these
      types as its interface to iostreams, since for flexibility it has been
      abstracted away from direct dependence on ostream.  The second parame-
      ter is a reference to the base subobject of type  ios_base.   It  pro-
      vides formatting specifications such as field width, and a locale from
      which to obtain other facets.
      Returns:
        *this.

      _________________________
      31) withhout causing an ios::failure to be thrown.

      27.6.2.5.3  basic_ostream::operator<<          [lib.ostream.inserters]

      basic_ostream<charT,traits>& operator<<
          (basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&))

      Returns:
        pf(*this).32)

      basic_ostream<charT,traits>& operator<<
          (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&))

      Effects:
        Calls pf(*this).
      Returns:
        *this.33)

      basic_ostream<charT,traits>& operator<<
          (ios_base& (*pf)(ios_base&))

      Effects:
        Calls pf(*this).
      Returns:
        *this.

      basic_ostream<charT,traits>& operator<<
          (basic_streambuf<charT,traits>* sb);

      Effects:
        If  sb   is   null   calls   setstate(badbit)   (which   may   throw
        ios_base::failure).

    1 Gets  characters  from  sb  and inserts them in *this.  Characters are
      read from sb and inserted until any of the following occurs:

      --end-of-file occurs on the input sequence;

      --inserting in the output sequence fails (in which case the  character
        to be inserted is not extracted);

      --an exception occurs while getting a character from sb.

    2 If  the  function  inserts  no  characters, it calls setstate(failbit)
      (which may  throw  ios_base::failure  (_lib.iostate.flags_)).   If  an
      _________________________
      32) See, for  example,  the  function  signature  endl(basic_ostream&)
      (_lib.ostream.manip_) .
      33)   See,   for   example,   the  function  signature  dec(ios_base&)
      (_lib.basefield.manip_).

      exception  was  thrown  while extracting a character, the function set
      failbit in error state, and if  failbit  is  on  in  exceptions()  the
      caught exception is rethrown.
      Returns:
        *this.

      27.6.2.5.4  Character inserter       [lib.ostream.inserters.character]
           template functions

      template<class charT, class traits>
        basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
                                                charT c);
      template<class charT, class traits>
        basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
                                                char c);
        // specialization
      template<class traits>
        basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
                                               char c);
        // signed and unsigned
      template<class traits>
        basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
                                               signed char c);
      template<class traits>
        basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
                                               unsigned char c);

      Effects:
        Behaves   like   an   formatted   inserter    (as    described    in
        _lib.ostream.formatted.reqmts_)  of  out.   After a sentry object is
        constructed  insert  characters.   In  case  c's  type  is  (signed,
        unsigned  or  plain)  char the character to be inserted is widen(c);
        otherwise  the  character is c34) Padding is determined as described
        in _lib.facet.num.put.virtuals_.  width(0) is called.  The insertion
        character and any required padding are inserted into out.
      Returns:
        out

      _________________________
      34) In case the insertion is into a char stream, widen(c) will usually
      be c.

      template<class charT, class traits>
        basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
                                                const charT* s);
      template<class charT, class traits>
        basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
                                                const char* s);
      template<class traits>
        basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
                                               const char* s);
      template<class traits>
        basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
                                               const signed char* s);
      template<class traits>
        basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
                                               const unsigned char* s);

      Requires:
        s is non-null.
      Effects:
        Behaves    like    an    formatted   inserter   (as   described   in
        _lib.ostream.formatted.reqmts_) of out.  After a  sentry  object  is
        constructed insert characters.  The number of characters starting at
        s to be inserted is traits::length(s).   Padding  is  determined  as
        described  in  _lib.facet.num.put.virtuals_.   The traits::length(s)
        characters starting at s and any required padding is  inserted  into
        out.  Calls width(0).
      Returns:
        out

      27.6.2.6  Unformatted output functions       [lib.ostream.unformatted]

    1 Each  formatted  output  function  begins execution by constructing an
      object of class sentry.  If this object returns true, while converting
      to  a  value  of  type  bool,  the  function endeavors to generate the
      requested output.  In any case, the unformatted output  function  ends
      by  destroying  the  sentry object, then returning the value specified
      for the formatted output function.

      basic_ostream<charT,traits>& put(char_type c);

      Effects:
        Inserts the character c, if possible.35)

    2 Otherwise,  calls  setstate(badbit) (which may throw ios_base::failure
      (_lib.iostate.flags_)).
      Returns:
        *this.

      _________________________
      35) Note that this function is not overloaded on types signed char and
      unsigned char.

      basic_ostream& write(const char_type* s, streamsize n);

      Effects:
        Obtains characters to insert from successive locations of  an  array
        whose first element is designated by s.36) Characters  are  inserted
        until either of the following occurs:

      --n characters are inserted;

      --inserting  in  the output sequence fails (in which case the function
        calls   setstate(badbit),   which   may   throw    ios_base::failure
        (_lib.iostate.flags_)).
      Returns:
        *this.

      basic_ostream& flush();

    3 If  rdbuf()  is not a null pointer, calls rdbuf()->pubsync().  If that
      function  returns  -1  calls   setstate(badbit)   (which   may   throw
      ios_base::failure (_lib.iostate.flags_)).
      Returns:
        *this.

      27.6.2.7  Standard basic_ostream manipulators      [lib.ostream.manip]

      namespace std {
        template <class charT, class traits>
          basic_ostream<charT,traits>& endl(basic_ostream<charT,traits>& os);
      }

      Effects:
        Calls os.put(os.widen('\n')) then os.flush().
      Returns:
        os.37)

      namespace std {
        template <class charT, class traits>
          basic_ostream<charT,traits>& ends(basic_ostream<charT,traits>& os);
      }

      _________________________
      36) Note that this function is not overloaded on types signed char and
      unsigned char.
      37) The effect of executing cout << endl is to insert a newline  char-
      acter  in  the output sequence controlled by cout, then synchronize it
      with any external file with which it might be associated.

      Effects:
        Inserts  a  null  character  into   the   output   sequence:   calls
        os.put(traits::eos()).
      Returns:
        os.

      namespace std {
        template <class charT, class traits>
          basic_ostream<charT,traits>& flush(basic_ostream<charT,traits>& os);
      }

      Effects:
        Calls os.flush().
      Returns:
        os.

      27.6.3  Standard manipulators                          [lib.std.manip]

    1 The header <iomanip> defines a type and several related functions that
      use this type to provide extractors and inserters that alter  informa-
      tion maintained by class ios_base and its derived classes.

    2 The  type designated smanip in each of the following function descrip-
      tions is implementation-specified and may be different for each  func-
      tion.

      smanip resetiosflags(ios_base::fmtflags mask);

      Returns:
        An  object s of implementation specified type such that if out is an
        (instance of) basic_ostream then the expression out<<s behaves as if
        f(s) were called, where f can be defined as:38)
              ios_base& f(ios_base& str, ios_base::fmtflags mask)
              { // reset specified flags
                str.setf(ios_base::fmtflags(0), mask);
                return str;
              }

      smanip setiosflags(ios_base::fmtflags mask);

      Returns:
        An object s of implementation specified type such that if out is  an
      _________________________
      38)  The  expression  cin  >>  resetiosflags(ios_base::skipws)  clears
      ios_base::skipws in the format flags stored in the istream object  cin
      (the  same  as  cin >> noskipws), and the expression cout << resetios-
      flags(ios_base::showbase)  clears  ios_base::showbase  in  the  format
      flags  stored  in the ostream object cout (the same as cout << noshow-
      base).

        (instance of) basic_ostream then the expression out<<s behaves as if
        f(s) were called, where f can be defined as:
              ios_base& f(ios_base& str, ios_base::fmtflags mask)
              { // set specified flags
                str.setf(mask);
                return str;
              }

      smanip setbase(int base);

      Returns:
        An object s of implementation specified type such that if out is  an
        (instance of) basic_ostream then the expression out<<s behaves as if
        f(s) were called, where f can be defined as:
              ios_base& f(ios_base& str, int base)
              { // set basefield
                str.setf(n ==  8 ? ios_base::oct :
                               n == 10 ? ios_base::dec :
                               n == 16 ? ios_base::hex :
                                         ios_base::fmtflags(0), ios_base::basefield);
                return str;
              }

      smanip setfill(char_type c);

      Returns:
        An object s of implementation specified type such that if out is (or
        is  derived  from)  basic_ostream<charT,traits> and c has type charT
        then the expression out<<s behaves as if f(s) were called,  where  f
        can be defined as:
              template<class charT, class traits>
              basic_ios<charT,traits>& f(basic_ios<charT,traits>& str, charT c)
              { // set fill character
                str.fill(c);
                return str;
              }

      smanip setprecision(int n);

      Returns:
        An  object s of implementation specified type such that if out is an
        (instance of) basic_ostream then the expression out<<s behaves as if
        f(s) were called, where f can be defined as:
              ios_base& f(ios_base& str, int n)
              { // set precision
                str.precision(n);
                return str;
              }

      smanip setw(int n);

      Returns:
        An  object s of implementation specified type such that if out is an
        (instance of) basic_ostream then the expression out<<s behaves as if
        f(s) were called, where f can be defined as:
              ios_base& f(ios_base& str, int n)
              { // set width
                str.width(n);
                return str;
              }

      27.7  String-based streams                        [lib.string.streams]

    1 The  header  <sstream>  defines  four template classes, and six types,
      that associate stream buffers with objects of class  basic_string,  as
      described in subclause _lib.string.classes_.

      Header <sstream> synopsis

      namespace std {
        template <class charT, class traits = char_traits<charT>,
                          class Allocator = allocator<charT> >
          class basic_stringbuf;

        typedef basic_stringbuf<char>     stringbuf;
        typedef basic_stringbuf<wchar_t> wstringbuf;

        template <class charT, class traits = char_traits<charT>,
                          class Allocator = allocator<charT> >
          class basic_istringstream;

        typedef basic_istringstream<char>     istringstream;
        typedef basic_istringstream<wchar_t> wistringstream;

        template <class charT, class traits = char_traits<charT>,
                          class Allocator = allocator<charT> >
          class basic_ostringstream;
        typedef basic_ostringstream<char>     ostringstream;
        typedef basic_ostringstream<wchar_t> wostringstream;

        template <class charT, class traits = char_traits<charT>,
                          class Allocator = allocator<charT> >
          class basic_stringstream;
        typedef basic_stringstream<char>     stringstream;
        typedef basic_stringstream<wchar_t> wstringstream;
      }

      27.7.1  Template class basic_stringbuf                 [lib.stringbuf]

      namespace std {
        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
        class basic_stringbuf : public basic_streambuf<charT,traits> {
        public:
        // Types:
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
        // _lib.stringbuf.cons_ Constructors:
          explicit basic_stringbuf(ios_base::openmode which
                                    = ios_base::in | ios_base::out);
          explicit basic_stringbuf(
                                      const basic_string<charT,traits,Allocator>& str,
                                    ios_base::openmode which
                                    = ios_base::in | ios_base::out);
        // _lib.stringbuf.members_ Get and set:
          basic_string<charT,traits,Allocator> str() const;
          void               str(const basic_string<charT,traits,Allocator>&
                                                      s);
        protected:
        // _lib.stringbuf.virtuals_ Overridden virtual functions:
          virtual int_type   underflow();
          virtual int_type   pbackfail(int_type c = traits::eof());
          virtual int_type   overflow (int_type c = traits::eof());
          virtual  basic_streambuf<charT,traits>* setbuf(charT*, streamsize);

          virtual pos_type   seekoff(off_type off, ios_base::seekdir way,
                                     ios_base::openmode which
                                      = ios_base::in | ios_base::out);
          virtual pos_type   seekpos(pos_type sp,
                                     ios_base::openmode which
                                      = ios_base::in | ios_base::out);
        private:
      //  ios_base::openmode mode;      exposition only
        };
      }

    1 The class basic_stringbuf is derived from basic_streambuf to associate
      possibly the input sequence and possibly the output  sequence  with  a
      sequence  of  arbitrary  characters.   The sequence can be initialized
      from, or made available as, an object of class basic_string.

    2 For the sake of exposition, the maintained data is presented here as:

      --ios_base::openmode mode, has in set if the  input  sequence  can  be
        read, and out set if the output sequence can be written.

      27.7.1.1  basic_stringbuf  constructors           [lib.stringbuf.cons]

      explicit basic_stringbuf(ios_base::openmode which =
                                 ios_base::in | ios_base::out);

      Effects:
        Constructs an object of class basic_stringbuf, initializing the base
        class with basic_streambuf() (_lib.streambuf.cons_), and  initializ-
        ing mode with which.
      Notes:
        The function allocates no array object.

      explicit basic_stringbuf(const basic_string<charT,traits,Allocator>& str,
                     ios_base::openmode which = ios_base::in | ios_base::out);

      Effects:
        Constructs an object of class basic_stringbuf, initializing the base
        class with basic_streambuf() (_lib.streambuf.cons_), and  initializ-
        ing  mode  with  which.   Then  copies  the  content of str into the
        basic_stringbuf underlying character sequence  and  initializes  the
        input   and  output  sequences  according  to  which.   If  which  &
        ios_base::out is true, initializes  the  output  sequence  with  the
        underlying  sequence.   If which & ios_base::in is true, initializes
        the input sequence with the underlying sequence.
      Postconditions:
        str() == str.

      27.7.1.2  Member functions                     [lib.stringbuf.members]

      basic_string<charT,traits,Allocator> str() const;

      Returns:
        A basic_string object whose content is equal to the  basic_stringbuf
        underlying  character  sequence.   If  the buffer is only created in
        input mode, the underlying character sequence is equal to the  input
        sequence; otherwise, it is equal to the output sequence.  In case of
        an  empty  underlying  character  sequence,  the  function   returns
        basic_string<charT,traits,Allocator>().

      void str(const basic_string<charT,traits,Allocator>& s);

      Effects:
        If the basic_stringbuf's underlying character sequence is not empty,
        deallocates it.  Then copies the content of s into the basic_string-
        buf underlying character sequence and initializes the input and out-
        put sequences  according  to  the  mode  stored  when  creating  the
        basic_stringbuf  object.  If (mode&ios_base::out) is true, then ini-
        tializes the output  sequence  with  the  underlying  sequence.   If
        (mode&ios_base::in)  is  true,  then  initializes the input sequence
        with the underlying sequence.
      Postcondition:
        str() == s.

      27.7.1.3  Overridden virtual functions        [lib.stringbuf.virtuals]

      int_type underflow();

      Returns:
        If the  input  sequence  has  a  read  position  available,  returns
        traits::to_int_type(*gptr()).
        Otherwise, returns traits::eof().

      int_type pbackfail(int_type c = traits::eof());

      Effects:
        Puts  back  the  character designated by c to the input sequence, if
        possible, in one of three ways:

      --If traits::eq_int_type(c,traits::eof()) returns  false  and  if  the
        input   sequence   has   a   putback   position  available,  and  if
        traits::eq(to_char_type(c),gptr()[-1]) returns true, assigns  gptr()
        - 1 to gptr().
        Returns: c.

      --If  traits::eq_int_type(c,traits::eof())  returns  false  and if the
        input sequence has a putback  position  available,  and  if  mode  &
        ios_base::out is nonzero, assigns c to *--gptr().
        Returns: c.

      --If  traits::eq_int_type(c,traits::eof())  returns  true  and  if the
        input sequence has a putback position available, assigns gptr() -  1
        to gptr().
        Returns: traits::not_eof(c).
      Returns:
        traits::eof() to indicate failure.
      Notes:
        If  the  function  can succeed in more than one of these ways, it is
        unspecified which way is chosen.

      int_type overflow(int_type c = traits::eof());

      Effects:
        Appends the character designated by c to  the  output  sequence,  if
        possible, in one of two ways:

      --If  traits::eq_int_type(c,traits::eof()) returns false and if either
        the output sequence has a write position available or  the  function
        makes  a write position available (as described below), the function
        calls sputc(c).
        Signals success by returning c.

      --If traits::eq_int_type(c,traits::eof()) returns true,  there  is  no
        character to append.

        Signals success by returning a value other than traits::eof().
      Notes:
        The  function can alter the number of write positions available as a
        result of any call.
      Returns:
        traits::eof() to indicate failure.

    1 Notes:
        The function can make a write position available  only  if  (mode  &
        ios_base::out)  != 0.  To make a write position available, the func-
        tion reallocates (or initially allocates) an  array  object  with  a
        sufficient  number  of elements to hold the current array object (if
        any), plus one additional write position.  If (mode &  ios_base::in)
        != 0, the function alters the read end pointer egptr() to point just
        past the new write position (as does the write end pointer epptr()).

      pos_type seekoff(off_type off, ios_base::seekdir way,
                       ios_base::openmode which
                        = ios_base::in | ios_base::out);

      Effects:
        Alters  the  stream position within one of the controlled sequences,
        if possible, as indicated in Table 9:

                            Table 9--seekoff positioning

      +----------------------------------------------------------------------------------+
      |         Conditions                                  Result                       |
      +----------------------------------------------------------------------------------+
      |(which & basic_ios::in)  != 0   positions the input sequence                      |
      +----------------------------------------------------------------------------------+
      |(which & basic_ios::out) != 0   positions the output sequence                     |
      +----------------------------------------------------------------------------------+
      |(which & (basic_ios::in | ba-   positions both the input and the output sequences |
      |sic_ios::out)) == (ba-                                                            |
      |sic_ios::in | ba-                                                                 |
      |sic_ios::out))                                                                    |
      |and way == either ba-                                                             |
      |sic_ios::beg or ba-                                                               |
      |sic_ios::end                                                                      |
      +----------------------------------------------------------------------------------+
      |Otherwise                       the positioning operation fails.                  |
      +----------------------------------------------------------------------------------+

    2 For a sequence to be positioned, if its next pointer (either gptr() or
      pptr()) is a null pointer, the positioning  operation  fails.   Other-
      wise, the function determines newoff as indicated in Table 10:

                             Table 10--newoff values

            +---------------------------------------------------------+
            |      Condition                   newoff Value           |
            +---------------------------------------------------------+
            |way == basic_ios::beg    0                               |
            +---------------------------------------------------------+
            |way == basic_ios::cur    the next pointer minus the be-  |
            |                         ginning pointer (xnext - xbeg). |
            +---------------------------------------------------------+
            |way == basic_ios::end    the end pointer minus the be-   |
            |                         ginning pointer (xend - xbeg)   |
            +---------------------------------------------------------+
            |If (newoff + off) < 0,   the positioning operation fails |
            |or (xend - xbeg) <                                       |
            |(newoff + off)                                           |
            +---------------------------------------------------------+

    3 Otherwise,  the  function  assigns  xbeg  +  newoff  + off to the next
      pointer xnext.
      Returns:
        pos_type(newoff), constructed from the resultant offset  newoff  (of
        type off_type), that stores the resultant stream position, if possi-
        ble.  If the positioning operation  fails,  or  if  the  constructed
        object  cannot  represent  the resultant stream position, the object
        stores an invalid stream position.

      pos_type seekpos(pos_type sp, ios_base::openmode which
                        = ios_base::in | ios_base::out);

      Effects:
        Alters the stream position within the controlled sequences, if  pos-
        sible,  to  correspond  to  the  stream  position  stored  in sp (as
        described below).

      --If (which & basic_ios::in)  != 0, positions the input sequence.

      --If (which & basic_ios::out) != 0, positions the output sequence.

      --If sp is an invalid stream position, of if  the  function  positions
        neither  sequence,  the  positioning operation fails.  If sp has not
        been obtained by a previous successful call to one of the  position-
        ing  functions( seekoff, seekpos, tellg, tellp ) the effect is unde-
        fined.
      Returns:
        sp to indicate success, or pos_type(off_type(-1)) to indicate  fail-
        ure.

      basic_streambuf<charT,traits>* setbuf(charT* s, streamsize n);

      setbuf(0,0) has no effect.
      Returns:
        this.

      27.7.2  Template class basic_istringstream         [lib.istringstream]
      namespace std {
        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
        class basic_istringstream : public basic_istream<charT,traits> {
        public:
        // Types:
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
        // _lib.istringstream.cons_ Constructors:
          explicit basic_istringstream(ios_base::openmode which = ios_base::in);
          explicit basic_istringstream(
                             const basic_string<charT,traits,Allocator>& str,
                             ios_base::openmode which = ios_base::in);
        // _lib.istringstream.members_ Members:
          basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
          basic_string<charT,traits,Allocator> str() const;
          void str(const basic_string<charT,traits,Allocator>& s);
      private:
      //  basic_stringbuf<charT,traits,Allocator> sb; exposition only
        };
      }

    1 The class basic_istringstream<charT,traits,Allocator> supports reading
      objects of  class  basic_string<charT,traits,Allocator>.   It  uses  a
      basic_stringbuf<charT,traits,Allocator>  object to control the associ-
      ated storage.  For the sake of exposition, the maintained data is pre-
      sented here as:

      --sb, the stringbuf object.

      27.7.2.1  basic_istringstream                 [lib.istringstream.cons]
           constructors

      explicit basic_istringstream(ios_base::openmode which = ios_base::in);

      Effects:
        Constructs an  object  of  class  basic_istringstream<charT,traits>,
        initializing the base class with basic_istream(&sb) and initializing
        sb with basic_stringbuf<charT,traits,Allocator>(which|ios_base::in))
        (_lib.stringbuf.cons_).

      explicit basic_istringstream(
                      const basic_string<charT,traits,allocator>& str,
                      ios_base::openmode which = ios_base::in);

      Effects:
        Constructs  an  object  of  class basic_istringstream<charT,traits>,
        initializing the base class with basic_istream(&sb) and initializing
        sb   with   basic_stringbuf<charT,traits,Allocator>(str,   which   |
        ios_base::in)) (_lib.stringbuf.cons_).

      27.7.2.2  Member functions                 [lib.istringstream.members]

      basic_stringbuf<charT,traits,Allocator>* rdbuf() const;

      Returns:
        (basic_stringbuf<charT,traits,Allocator>*)&sb.

      basic_string<charT,traits,Allocator> str() const;

      Returns:
        rdbuf()->str().39)

      void str(const basic_string<charT,traits,Allocator>& s);

      Effects:
        Calls rdbuf()->str(s).

      27.7.3  Class basic_ostringstream                  [lib.ostringstream]
      namespace std {
        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
        class basic_ostringstream : public basic_ostream<charT,traits> {
        public:
        // Types:
          typedef charT            char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
        // _lib.ostringstream.cons_ Constructors/destructor:
          explicit basic_ostringstream(ios_base::openmode which = ios_base::out);
          explicit basic_ostringstream(
                               const basic_string<charT,traits,Allocator>& str,
                               ios_base::openmode which = ios_base::out);
          virtual ~basic_ostringstream();
        // _lib.ostringstream.members_ Members:
          basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
      _________________________
      39) rdbuf() is never NULL because it always returns  the  private  ob-
      ject.

          basic_string<charT,traits,Allocator> str() const;
          void    str(const basic_string<charT,traits,Allocator>& s);
       private:
      //  basic_stringbuf<charT,traits,Allocator> sb; exposition only
        };
      }

    1 The class basic_ostringstream<charT,traits,Allocator> supports writing
      objects of  class  basic_string<charT,traits,Allocator>.   It  uses  a
      basic_stringbuf  object  to  control  the associated storage.  For the
      sake of exposition, the maintained data is presented here as:

      --sb, the stringbuf object.

      27.7.3.1  basic_ostringstream                 [lib.ostringstream.cons]
           constructors

      explicit basic_ostringstream(ios_base::openmode which = ios_base::out);

      Effects:
        Constructs  an object of class basic_ostringstream, initializing the
        base  class  with  basic_ostream(&sb)  and  initializing   sb   with
        basic_stringbuf<charT,traits,Allocator>(which    |   ios_base::out))
        (_lib.stringbuf.cons_).

      explicit basic_ostringstream(
                         const basic_string<charT,traits,Allocator>& str,
                         ios_base::openmode which = ios_base::out);

      Effects:
        Constructs an  object  of  class  basic_ostringstream<charT,traits>,
        initializing the base class with basic_ostream(&sb) and initializing
        sb   with   basic_stringbuf<charT,traits,Allocator>(str,   which   |
        ios_base::out)) (_lib.stringbuf.cons_).

      27.7.3.2  Member functions                 [lib.ostringstream.members]

      basic_stringbuf<charT,traits,Allocator>* rdbuf() const;

      Returns:
        (basic_stringbuf<charT,traits,Allocator>*)&sb.

      basic_string<charT,traits,Allocator> str() const;

      Returns:
        rdbuf()->str().40)
      _________________________
      40)  rdbuf()  is  never NULL because it always returns the private ob-
      ject.

      void str(const basic_string<charT,traits,Allocator>& s);

      Effects:
        Calls rdbuf()->str(s).

      27.7.4  Template class basic_stringstream           [lib.stringstream]
      namespace std {
        template <class charT, class traits = char_traits<charT>,
                  class Allocator = allocator<charT> >
        class basic_stringstream
          : public basic_iostream<charT,traits> {
        public:
          // Types
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
          // constructors/destructors
          explicit basic_stringstream(
              ios_base::openmode which = ios_base::out|ios_base::in);
          explicit basic_stringstream(
              const basic_string<charT,traits,Allocator>& str,
              ios_base::openmode which = ios_base::out|ios_base::in);
          // Members:
          basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
          basic_string<charT,traits,Allocator> str() const;
          void str(const basic_string<charT,traits,Allocator>& str);
        private:
           // basic_stringbuf<charT, traits> sb;  exposition only
      };

    1 The template class basic_stringstream<charT,traits>  supports  reading
      and  writing  from  objects of class basic_string<charT,traits,Alloca-
      tor>.  It uses  a  basic_stringbuf<charT,traits,Allocator>  object  to
      control  the  associated  sequence.   For  the sake of exposition, the
      maintained data is presented here as

      --sb, the stringbuf object.

      27.7.5  basic_stringstream constructors        [lib.stringstream.cons]

      explicit basic_stringstream(
          ios_base::openmode which = ios_base::out|iosbase::in);

      Effects:
        Constructs an object of class basic_stringstream<charT,traits>, ini-
        tializing  the  base class with basic_iostream(&sb) and initializing
        sb with basic_stringbuf<charT,traits,Allocator>(which).

      explicit basic_stringstream(
          const basic_string<charT,traits,Allocator>& str,
          ios_base::openmode which = ios_base::out|iosbase::in);

      Effects:
        Constructs an object of class basic_stringstream<charT,traits>, ini-
        tializing  the  base class with basic_iostream(&sb) and initializing
        sb with basic_stringbuf<charT,traits,Allocator>(str,which).

      27.7.6  Member functions                    [lib.stringstream.members]

      basic_stringbuf<charT,traits,Allocator>* rdbuf() const;

      Returns:
        &sb

      basic_string<charT,traits,Allocator> str() const;

      Returns:
        rdbuf()->str().41)

      void str(const basic_string<charT,traits,Allocator>& str);

      Effects:
        Calls rdbuf()->str(str).

      27.8  File-based streams                            [lib.file.streams]

      27.8.1  File streams                                    [lib.fstreams]

    1 The header <fstream> defines four class templates, and six types, that
      associate stream buffers with files and  assist  reading  and  writing
      files.

      Header <fstream> synopsis

      _________________________
      41) rdbuf() is never NULL because it always returns  the  private  ob-
      ject.

      namespace std {
        template <class charT, class traits = char_traits<charT> >
          class basic_filebuf;
        typedef basic_filebuf<char>    filebuf;
        typedef basic_filebuf<wchar_t> wfilebuf;

        template <class charT, class traits = char_traits<charT> >
          class basic_ifstream;
        typedef basic_ifstream<char>    ifstream;
        typedef basic_ifstream<wchar_t> wifstream;

        template <class charT, class traits = char_traits<charT> >
          class basic_ofstream;
        typedef basic_ofstream<char>    ofstream;
        typedef basic_ofstream<wchar_t> wofstream;

        template <class charT, class traits = char_traits<charT> >
          class basic_fstream;
        typedef basic_fstream<char>     fstream;
        typedef basic_fstream<wchar_t> wfstream;
      }

    2 In  this subclause, the type name FILE refers to the type FILE defined
      in <cstdio> (_lib.c.files_).42)

      --File  A File provides an external source/sink stream whose underlaid
        character type is char (byte).43)

      --Multibyte character and Files A File provides  byte  sequences.   So
        the streambuf (or its derived classes) treats a file as the external
        source/sink byte sequence.  In a large  character  set  environment,
        multibyte  character  sequences are held in files.  In order to pro-
        vide the contents of a file as wide character  sequences,  wide-ori-
        ented   filebuf,  namely  wfilebuf  should  convert  wide  character
        sequences.

      27.8.1.1  Template class basic_filebuf                   [lib.filebuf]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_filebuf : public basic_streambuf<charT,traits> {
        public:
        // Types (inherited from basic_streambuf (_lib.streambuf_)):
       // typedef charT                     char_type;
       // typedef typename traits::int_type int_type;
       // typedef typename traits::pos_type pos_type;
       // typedef typename traits::off_type off_type;
       // typedef traits                    traits_type;
      _________________________
      42) In C FILE must be a typedef.  In C++ it may be a typedef or  other
      type name.
      43) A File is a sequence of multibyte characters.  In order to provide
      the  contents as a wide character sequence, filebuf should convert be-
      tween wide character sequences and multibyte character sequences.

        // _lib.filebuf.cons_ Constructors/destructor:
          basic_filebuf();
          virtual ~basic_filebuf();
        // _lib.filebuf.members_ Members:
          bool is_open() const;
          basic_filebuf<charT,traits>* open(const char* s, ios_base::openmode mode);
          basic_filebuf<charT,traits>* close();
        protected:
        // _lib.filebuf.virtuals_ Overridden virtual functions:
          virtual int      showmanyc();
          virtual int_type underflow();
          virtual int_type uflow();
          virtual int_type pbackfail(int_type c = traits::eof());
          virtual int_type overflow (int_type c = traits::eof());
          virtual basic_streambuf<charT,traits>*
                           setbuf(char_type* s, streamsize n);
          virtual pos_type seekoff(off_type off, ios_base::seekdir way,
                                   ios_base::openmode which
                                     = ios_base::in | ios_base::out);
          virtual pos_type seekpos(pos_type sp, ios_base::openmode which
                                     = ios_base::in | ios_base::out);
          virtual int      sync();
          virtual void     imbue(const locale& loc);
        };
      }

    1 The  class  basic_filebuf<charT,traits>  associates  both  the   input
      sequence and the output sequence with a file.

    2 The  restrictions  on  reading and writing a sequence controlled by an
      object of class basic_filebuf<charT,traits> are the same as for  read-
      ing and writing with the Standard C library FILEs.

    3 In particular:

      --If  the  file  is  not open for reading the input sequence cannot be
        read.

      --If the file is not open for writing the output  sequence  cannot  be
        written.

      --A  joint file position is maintained for both the input sequence and
        the output sequence.

    4 An instance of basic_filebuf behaves  as  described  in  _lib.filebuf_
      provided  traits::pos_type is fpos<traits::state_type>.  Otherwise the
      behavior is undefined.

    5 In order to support file I/O and multibyte/wide character  conversion,
      conversions  are  performed  using  members of a facet, referred to as
      a_codecvt in following sections, obtained ``as if'' by

        codecvt<charT,char,typename traits::state_type> a_codecvt =
          use_facet<codecvt<charT,char,typename traits::state_type> >(getloc());

      27.8.1.2  basic_filebuf constructors                [lib.filebuf.cons]

      basic_filebuf();

      Effects:
        Constructs an object of class basic_filebuf<charT,traits>,  initial-
        izing    the   base   class   with   basic_streambuf<charT,traits>()
        (_lib.streambuf.cons_).
      Postcondition:
        is_open() == false.

      virtual ~basic_filebuf();

      Effects:
        Destroys an  object  of  class  basic_filebuf<charT,traits>.   Calls
        close().

      27.8.1.3  Member functions                       [lib.filebuf.members]

      bool is_open() const;

      Returns:
        true  if  a  previous  call  to  open succeeded (returned a non-null
        value) and there has been no intervening call to close.

      basic_filebuf<charT,traits>* open(
          const char* s,
          ios_base::openmode mode );

      Effects:
        If is_open() != false, returns a null pointer.  Otherwise,  initial-
        izes the filebuf as required.
        It  then  opens  a file, if possible, whose name is the NTBS s (``as
        if'' by calling ::fopen(s,modstr)).
        The NTBS modstr is determined from mode &  ~ios_base::ate  as  indi-
        cated in Table 11:

                             Table 11--File open modes

                +---------------------------------------------------+
                |   ios_base Flag combination      stdio equivalent |
                |binary   in   out   trunc   app                    |
                +---------------------------------------------------+
                |               +                  "w"              |
                +---------------------------------------------------+
                |               +             +    "a"              |
                +---------------------------------------------------+
                |               +      +           "w"              |
                +---------------------------------------------------+
                |         +                        "r"              |
                +---------------------------------------------------+
                |         +     +                  "r+"             |
                +---------------------------------------------------+
                |         +     +      +           "w+"             |
                +---------------------------------------------------+
                |  +            +                  "wb"             |
                +---------------------------------------------------+
                |  +            +             +    "ab"             |
                +---------------------------------------------------+
                |  +            +      +           "wb"             |
                +---------------------------------------------------+
                |  +      +                        "rb"             |
                +---------------------------------------------------+
                |  +      +     +                  "r+b"            |
                +---------------------------------------------------+
                |  +      +     +      +           "w+b"            |
                +---------------------------------------------------+
        If mode is not some combination of flags shown in the table then the
        open fails.

    1 If the open operation succeeds and (mode & ios_base::ate) != 0,  posi-
      tions    the    file    to    the    end   (``as   if''   by   calling
      ::fseek(file,0,SEEK_END)).44)

    2 If the repositioning operation fails, calls close() and returns a null
      pointer to indicate failure.
      Returns:
        this if successful, a null pointer otherwise.

      basic_filebuf<charT,traits>* close();

      _________________________
      44) The  macro  SEEK_END  is  defined,  and  the  function  signatures
      fopen(const  char_type*, const char_type*) and fseek(FILE*, long, int)
      are declared, in <cstdio> (_lib.c.files_).

      Effects:
        If  is_open()  ==  false,  returns  a  null  pointer.  If a put area
        exists, calls overflow(EOF) to flush characters.  If the  last  vir-
        tual  member  function called on *this (between underflow, overflow,
        seekoff, and seekpos)  was  overflow  then  calls  a_codecvt.unshift
        (possibly  several  times)  to  determine  a  termination  sequence,
        inserts those characters and calls overflow(EOF) again.  Finally  it
        closes the file (``as if'' by calling ::fclose(file)).45) If any  of
        the calls to overflow or ::fclose fails then close fails
      Returns:
        this on success, a null pointer otherwise.
      Postcondition:
        is_open() == false.

      27.8.1.4  Overridden virtual functions          [lib.filebuf.virtuals]

      int showmanyc();

      Effects:
        Behaves   the  same  as  basic_streambuf::showmanyc()  (_lib.stream-
        buf.virtuals_).
      Notes:
        An implementation might well provide an  overriding  definition  for
        this function signature if it can determine that more characters can
        be read from the input sequence.

      int_type underflow();

      Effects:
        Behaves   according   to   the    description    of    basic_stream-
        buf<charT,traits>::  underflow(),  with  the  specialization  that a
        sequence of characters is read from the input sequence ``as if''  by
        reading   from  the  associated  file  into  an  internal  buffer  (
        extern_buf) and then ``as if'' doing
              char   extern_buf[XSIZE];
              char*  extern_end;
              charT  intern_buf[ISIZE];
              charT* intern_end;
              codecvt_base::result r =
                  a_codecvt.in(st,extern_buf,extern_buf+XSIZE,extern_end,
                               intern_buf, intern_buf+ISIZE, intern_end);
        This must be done in such a way that the class can recover the posi-
        tion  fpos_t) corresponding to each character between intern_buf and
        intern_end.  If the value of r indicates that a_codecvt.in() ran out
        of space in intern_buf, retry with a larger intern_buf.

      _________________________
      45)  The  function  signature  fclose(FILE*)  is declared, in <cstdio>
      (_lib.c.files_).

      int_type uflow();

      Effects:
        Behaves    according    to    the   description   of   basic_stream-
        buf<charT,traits>:: uflow(), with the specialization that a sequence
        of characters is read from the input with the same method as used by
        underflow.

      int_type pbackfail(int_type c = traits::eof());

      Effects:
        Puts back the character designated by c to the  input  sequence,  if
        possible, in one of three ways:

      --If  traits::eq_int_type(c,traits::eof())  returns  false  and if the
        function   makes   a   putback    position    available    and    if
        traits::eq(to_char_type(c),gptr()[-1])  returns true, decrements the
        next pointer for the input sequence, gptr().
        Returns: c.

      --If traits::eq_int_type(c,traits::eof()) returns  false  and  if  the
        function  makes a putback position available, and if the function is
        permitted to assign to the putback  position,  decrements  the  next
        pointer for the input sequence, and stores c there.
        Returns: c.

      --If  traits::eq_int_type(c,traits::eof())  returns true and if either
        the input sequence has a putback position available or the  function
        makes  a putback position available, decrements the next pointer for
        the input sequence, gptr().
        Returns: traits::not_eof(c).
      Returns:
        traits::eof() to indicate failure.
      Notes:
        If is_open() == false, the function always fails.
        The function does not put back a character  directly  to  the  input
        sequence.
        If  the  function  can succeed in more than one of these ways, it is
        unspecified which way is chosen.  The function can alter the  number
        of putback positions available as a result of any call.

      int_type overflow(int_type c = traits::eof());

      Effects:
        Behaves    according    to    the   description   of   basic_stream-
        buf<charT,traits>::overflow(c), except that the behavior  of  ``con-
        suming characters'' is performed by first coverting ``as if'' by:

              charT* b = pbase();
              charT* p = pptr();
              charT* end;
              char   xbuf[XSIZE];
              char*  xbuf_end;
              codecvt_base::result r = a_codecvt.out(st,b,p,end,xbuf,xbuf+XSIZE,xbuf_end);
        and then

      --If r == codecvt_base::error then fail.

      --If r == codecvt_base::noconv then output characters from b upto (and
        not including) p.

      --If r == codecvt_base::partial then output  to  the  file  characters
        from  xbuf upto xbuf_end, and repeat using characters from end to p.
        If output fails, fail (without repeating).

      --Otherwise output from xbuf to xbuf_end, and fail  if  output  fails.
        At  this point if b != p and b == end ( buf isn't large enough) then
        increase BSIZE and repeat from the beginning.
      Returns:
        traits::not_eof(c) to indicate success, and traits::eof()  to  indi-
        cate failure.  If is_open() == false, the function always fails.

      basic_streambuf* setbuf(char_type* s, int n);

      Effects:
        If  setbuf(0,0)  is called on a stream before any I/O has occured on
        that stream, the stream becomes unbuffered.  Otherwise  the  results
        are  implementation-defined.   "Unbuffered"  means  that pbase() and
        pptr() always return null and output to the file  should  appear  as
        soon as possible.

      pos_type seekoff(off_type off, ios_base::seekdir way,
                       ios_base::openmode which
                        = ios_base::in | ios_base::out);

      Effects:
        If  is_open() == false, the positioning operation fails.  Otherwise,
        if a_codecvt.encoding()>0 repositions the sequence  by  off*e  posi-
        tions in file.  This is done by some combination of manipulating the
        put or get area and repositioning of the file (``as if'' by  comput-
        ing distance, the number of characters to be moved in file and call-
        ing ::fseek(file,distance*off,whence).46) Otherwise if off==0  repo-
        sitions   within   the   associated   file  (``as  if''  by  calling
        ::fseek(file,0,whence).  Otherwise the positioning operation  fails.
      _________________________
      46) The macros SEEK_SET, SEEK_CUR, and SEEK_END are defined,  and  the
      function  signature  fseek(FILE*,  long, int) is declared, in <cstdio>
      (_lib.c.files_).

      Notes:
        The function determines one of three values for the argument whence,
        of type int, as indicated in Table 12:

                             Table 12--seekoff effects

                        +----------------------------------+
                        |  way Value      stdio Equivalent |
                        +----------------------------------+
                        |basic_ios::beg   SEEK_SET         |
                        |basic_ios::cur   SEEK_CUR         |
                        |basic_ios::end   SEEK_END         |
                        +----------------------------------+
      Returns:
        a newly constructed pos_type object that stores the resultant stream
        position,  if  possible.   If the positioning operation fails, or if
        the object cannot represent the resultant stream  position,  returns
        an invalid stream position (_lib.iostreams.pos.t_).

      pos_type seekpos(pos_type sp, ios_base::openmode which
                                   = ios_base::in | ios_base::out);

      Otherwise  it  alters the file position, if possible, to correspond to
      the position stored in sp (as described below).

      --if (which&ios_base::in)!=0, set the file position to sp, then update
        the input sequence

      --if  (which&ios_base::out)!=0,  set  the  file  position  to sp, then
        update the output sequence

    1 If sp is an invalid stream position, or if the function positions nei-
      ther  sequence,  the  positioning operation fails.  If sp has not been
      obtained by a previous successful call to one of the positioning func-
      tions  (  seekoff  or  seekpos) on the same file the effects are unde-
      fined.
      Returns:
        sp  on  success.   Otherwise  returns   an   invaid   stream   posi-
        tion(_lib.iostreams.definitions_ .)

      int sync();

      Effects:
        If  a  put area exists, calls filebuf::overflow to write the charac-
        ters to the file.  If a get area exists the  effect  is  implementa-
        tion-defined.

      void imbue(const locale& loc);

      Precondition
        If  the file is not positioned at its  beginning and the encoding of
        the current locale as determined by a_codecvt.encoding()  is  state-
        dependent(_lib.locale.codecvt.virtuals_) then that facet is the same
        as the corresponding facet of loc.

      27.8.1.5  Template class basic_ifstream                 [lib.ifstream]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_ifstream : public basic_istream<charT,traits> {
        public:
        // Types:
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
        // _lib.ifstream.cons_ Constructors:
          basic_ifstream();
          explicit basic_ifstream(const char* s,
                                  ios_base::openmode mode = ios_base::in);
        // _lib.ifstream.members_ Members:
          basic_filebuf<charT,traits>* rdbuf() const;
          bool is_open();
          void open(const char* s, openmode mode = in);
          void close();
        private:
      //  basic_filebuf<charT,traits> sb;     exposition only
        };
      }

    1 The class basic_ifstream<charT,traits>  supports  reading  from  named
      files.   It  uses  a basic_filebuf<charT,traits> object to control the
      associated sequence.  For the sake of exposition, the maintained  data
      is presented here as:

      --sb, the filebuf object.

      27.8.1.6  basic_ifstream constructors              [lib.ifstream.cons]

      basic_ifstream();

      Effects:
        Constructs an object of class basic_ifstream<charT,traits>, initial-
        izing the base class with  basic_istream(&sb)  and  initializing  sb
        with  basic_filebuf<charT,traits>()) (_lib.istream.cons_, _lib.file-
        buf.cons_).

      explicit basic_ifstream(const char* s, openmode mode = in);

      Effects:
        Constructs an object of class basic_ifstream, initializing the  base
        class    with    basic_istream(&sb)   and   initializing   sb   with

        basic_filebuf<charT,traits>())    (_lib.istream.cons_,    _lib.file-
        buf.cons_), then calls rdbuf()->open(s,mode|in).47) If that function
        returns  a  null  pointer, calls setstate(failbit), (which may throw
        ios_base::failure).

      27.8.1.7  Member functions                      [lib.ifstream.members]

      basic_filebuf<charT,traits>* rdbuf() const;

      Returns:
        (basic_filebuf<charT,traits>*)&sb.

      bool is_open();

      Returns:
        rdbuf()->is_open().48)

      void open(const char* s, openmode mode = in);

      Effects:
        Calls  rdbuf()->open(s,mode|in).   If  that  function returns a null
        pointer , calls setstate(failbit) (which may throw ios_base::failure
        (_lib.iostate.flags_)).

      void close();

      Effects:
        Calls  rdbuf()->close()  and,  if that function returns false, calls
        setstate(failbit)     (which     may     throw     ios_base::failure
        (_lib.iostate.flags_)).

      27.8.1.8  Template class basic_ofstream                 [lib.ofstream]
      namespace std {
        template <class charT, class traits = char_traits<charT> >
        class basic_ofstream : public basic_ostream<charT,traits> {
        public:
        // Types:
          typedef charT                     char_type;
          typedef typename traits::int_type int_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;

      _________________________
      47)  rdbuf()  is  never NULL because it always returns the private ob-
      ject.
      48) rdbuf() is never NULL because it always returns  the  private  ob-
      ject.

        // _lib.ofstream.cons_ Constructors:
          basic_ofstream();
          explicit basic_ofstream(const char* s,
                                  ios_base::openmode mode
                                    = ios_base::out | ios_base::trunc);
        // _lib.ofstream.members_ Members:
          basic_filebuf<charT,traits>* rdbuf() const;
          bool is_open();
          void open(const char* s, ios_base::openmode mode = out | trunc);
          void close();
        private:
      //  basic_filebuf<charT,traits> sb;     exposition only
        };
      }

    1 The  class  basic_ofstream<charT,traits>  supports  writing  to  named
      files.  It uses a basic_filebuf<charT,traits> object  to  control  the
      associated  sequence.  For the sake of exposition, the maintained data
      is presented here as:

      --sb, the filebuf object.

      27.8.1.9  basic_ofstream constructors              [lib.ofstream.cons]

      basic_ofstream();

      Effects:
        Constructs an object of class basic_ofstream<charT,traits>, initial-
        izing  the  base  class  with basic_ostream(&sb) and initializing sb
        with basic_filebuf<charT,traits>()) (_lib.ostream.cons_,  _lib.file-
        buf.cons_).

      explicit basic_ofstream(const char* s, openmode mode = out);

      Effects:
        Constructs an object of class basic_ofstream<charT,traits>, initial-
        izing the base class with  basic_ostream(&sb)  and  initializing  sb
        with  basic_filebuf<charT,traits>()) (_lib.ostream.cons_, _lib.file-
        buf.cons_),  then calls rdbuf()->open(s, mode|out).49) If that func-
        tion returns a null pointer,  calls  setstate(failbit),  (which  may
        throw ios_base::failure).

      27.8.1.10  Member functions                     [lib.ofstream.members]

      basic_filebuf<charT,traits>* rdbuf() const;

      _________________________
      49) rdbuf() is never NULL because it always returns the private  file-
      buf object.

      Returns:
        (basic_filebuf<charT,traits>*)&sb.

      bool is_open();

      Returns:
        rdbuf()->is_open().

      void open(const char* s, openmode mode = out);

      Effects:
        Calls  rdbuf()->open(s,mode|out).   If  that function returns a null
        pointer, calls setstate(failbit) (which may throw  ios_base::failure
        (_lib.iostate.flags_)).

      void close();

      Effects:
        Calls  rdbuf()->close()  and, if that function fails (returns a null
        pointer), calls setstate(failbit) (which may throw ios_base::failure
        (_lib.iostate.flags_)).

      27.8.1.11  Template class basic_fstream                  [lib.fstream]
      namespace std {
        template <class charT, class traits=char_traits<charT> >
        class basic_fstream
          : public basic_iostream<charT,traits> {
        public:
          // Types
          typedef charT                     char_type;
          typedef typename traits::int_type ins_type;
          typedef typename traits::pos_type pos_type;
          typedef typename traits::off_type off_type;
          // constructors/destructor
          basic_fstream();
          explicit basic_fstream(
              const char* s,
              ios_base::openmode mode = ios_base::in|ios_base::out);
          // Members:
          basic_filebuf<charT,traits>* rdbuf() const;
          bool is_open();
          void open(
              const char* s,
              ios_base::openmode mode = ios_base::in|ios_base::out);
          void close();
        private:
          // basic_filebuf<charT,traits> sb; exposition only
      };

    1 The  template  class  basic_fstream<charT,traits> supports reading and
      writing from named files.  It uses a basic_filebuf<charT,traits>object
      For the sake of exposition, the maintained data is presented here as:

      --sb, the basic_filebuf object.

      27.8.1.12  basic_fstream constructors               [lib.fstream.cons]

      basic_fstream();

      Effects:
        Constructs  an object of class basic_fstream<charT,traits>, initial-
        izing the base class with basic_iostream(&sb)  and  initializing  sb
        with basic_filebuf<charT,traits>().

      explicit basic_fstream(const char* s, ios_base::openmode mode);

      Effects:
        Construcs an object of class basic_fstream<charT,traits>, initializ-
        ing the base class with basic_iostream(&sb) and initializing sb with
        basic_filebuf<charT,traits>().   Then  calls  rdbuf()->open(s,mode).
        If that function returns a  null  pointer,  calls  setstate(failbit)
        (which may throw ios_base::failure).

      27.8.1.13  Member functions                      [lib.fstream.members]

      basic_filebuf<charT,traits>* rdbuf() const;

      Returns:
        &sb

      bool is_open();

      Returns:
        rdbuf()->is_open().

      void open(const char* s, ios_base::openmode mode);

      Effects:
        Calls   rdbuf()->open(s,mode),  If  that  function  returns  a  null
        pointer, calls setstate(failbit), (which may  throw  ios_base::fail-
        ure).  (_lib.iostate.flags_) )

      void close();

      Effects:
        Calls  rdbuf()->close()  and,  if that function returns false, calls

        setstate(failbit)(_lib.iostate.flags_)     (which     may      throw
        ios_base::failure).

      27.8.2  C Library files                                  [lib.c.files]

    1 Table 13 describes header <cstdio>.

                        Table 13--Header <cstdio> synopsis

      +-------------------------------------------------------------------------------+
      |    Type                                   Name(s)                             |
      +-------------------------------------------------------------------------------+
      |Macros:                                                                        |
      |BUFSIZ         L_tmpnam        SEEK_SET   TMP_MAX                              |
      |EOF            NULL <cstdio>   stderr     _IOFBF                               |
      |FILENAME_MAX   SEEK_CUR        stdin      _IOLBF                               |
      |FOPEN_MAX      SEEK_END        stdout     _IONBF                               |
      +-------------------------------------------------------------------------------+
      |Types:         FILE            fpos_t     size_t <cstdio>                      |
      +-------------------------------------------------------------------------------+
      |Functions:                                                                     |
      |clearerr       fgets           fscanf     gets              rewind             |
      |fclose         fopen           fseek      perror            scanf     tmpnam   |
      |feof           fprintf         fsetpos    printf            setbuf    ungetc   |
      |ferror         fputc           ftell      putc              setvbuf   vprintf  |
      |fflush         fputs           fwrite     puts              sprintf   vfprintf |
      |fgetc          fread           getc       remove            sscanf    vsprintf |
      |fgetpos        freopen         getchar    putchar           rename    tmpfile  |
      +-------------------------------------------------------------------------------+

      SEE ALSO: ISO C subclause 7.9, Amendment 1 subclause 4.6.2.