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  ______________________________________________________________________

  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.