______________________________________________________________________

  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;
  }

  +-------                      BEGIN BOX 1                     -------+
  streamoff here?
  +-------                       END BOX 1                      -------+

  [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

  constructed,  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)

  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_).

  +-------                      BEGIN BOX 2                     -------+
  This  leaves  other  parts  of  the  state unspecified. I believe they
  should be initialized as if by init.
  +-------                       END BOX 2                      -------+

  _________________________
  1) If it is possible for them to do so, implementations are encouraged
  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.

  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;

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;

  _________________________
  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 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;
      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.

  +-------                      BEGIN BOX 3                     -------+
  "independent operation" may be need a more careful definition.
  +-------                       END BOX 3                      -------+

  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()
  _________________________
  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.

    (_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
    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.

  +-------                      BEGIN BOX 4                     -------+
  Should the fpos constructor be explicit?
  +-------                       END BOX 4                      -------+

  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)
  _________________________
  7) This suggests an infinite amount of copying, but the implementation

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

  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.

  _________________________
  can keep track of the maximum element of the arrays that is  non-zero.

  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().

  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]

  _________________________
  8) Checking badbit also for fail() is historical practice.

  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);

  _________________________
  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.

  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.

  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.
  _________________________
  10)  The default constructor is protected for class basic_streambuf to
  assure that only objects for classes derived from this  class  may  be
  constructed.

  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 sup-
    plied, 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

    pbackfail(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)
  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()

  _________________________
  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.''
  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.

  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:

  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().
  _________________________
  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).

  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

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

    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.
     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_.

  _________________________
  17) The sentry constructor and destructor can also perform  additional
  implementation-dependent operations.

  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
  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>&))
  _________________________
  18) This is done without causing an ios::failure to be thrown.

  Returns:
    pf(*this).19)

  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;

  _________________________
  19)  See,  for  example,  the  function  signature  ws(basic_istream&)
  (_lib.istream.manip_).
  20)  See,  for  example,   the   function   signature   dec(ios_base&)
  (_lib.basefield.manip_).

  --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.

  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.

  _________________________
  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.

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

    rethrown).

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

  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.

  _________________________
  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.

7 [Example:
    #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.

  +-------                      BEGIN BOX 5                     -------+
  This  doesn't say what happens on failure.  It needs to set one of the
  error bits.  It isn't clear which one is right.
  _________________________
  31) withhout causing an ios::failure to be thrown.

  +-------                       END BOX 5                      -------+

  Returns:
    *this.

  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);
  _________________________
  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_).

  --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
  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);

  +-------                      BEGIN BOX 6                     -------+
  Check vs. _lib.filebuf.virtuals_
  +-------                       END BOX 6                      -------+

  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

    failure.

  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();

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

    // _lib.ostringstream.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_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)
  _________________________

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

    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;
  }

  +-------                      BEGIN BOX 7                     -------+
  Issue:  basic_filebuf<charT,traits>  should  be  specified  so that it
  treats a file as a sequence of charT.  Except for filebuf and wfilebuf
  that implies it treats the file as binary.
  +-------                       END BOX 7                      -------+

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.

  _________________________
  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.

  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;
    // _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.

  +-------                      BEGIN BOX 8                     -------+
  The library WG believes the correct  description  of  the  effects  of
  imbue  is  as follows.  Incorporating this however would create a con-
  flict with the current description of  overflow  and  underflow.   The
  current descriptions defer conversion until a complete put or get area
  is processed.   To  properly  decscribe  imbue,  conversions  must  be
  described as if they occur a the time of insertion or extraction.
  Effects
    Causes  characters  inserted or extracted after this call to be con-
    verted according to loc until another call of imbue.
  +-------                       END BOX 8                      -------+

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

  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();

  _________________________
  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.

  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;
    // _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>,

    initializing the base class with basic_ostream(&sb) and initializing
    sb    with    basic_filebuf<charT,traits>())    (_lib.ostream.cons_,
    _lib.filebuf.cons_),  then  calls  rdbuf()->open(s, mode|out).49) If
    that function  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;

  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;

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

      // 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.