______________________________________________________________________

  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 Additional definitions:

  --character In this clause, the term ``character'' means any unit ele­
    ment which, treated sequentially, can represent text.  The term does
    not only mean char and wchar_t type objects, but any value which can
    be represented by a type which provides the definitions specified in
    (_lib.string.char.traits_).

  --character  container  type  Character container type is a class or a
    type used to represent a character.  It is used for one of the  tem­
    plate parameter of the iostream class templates.

  --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  Type requirements                  [lib.iostreams.type.reqmts]

1 There are several types and  functions  needed  for  implementing  the
  iostream class templates.  Some of these types and functions depend on
  the definition of the character container  type.   The  collection  of
  these functions describes the behavior which the implementation of the
  iostream class templates expects to the character container class.

  27.1.2.1  Type CHAR_T                           [lib.iostreams.char.t]

1 Those C++ programs that provide a character container type as the tem­
  plate  parameter have to provide all of these functions as well as the
  container class itself.  The collection  of  these  functions  can  be
  regarded as the collection of the common definitions for the implemen­
  tation of the character container class.

2 No special definition/declaration is provided here.   The  base  class
  (or   struct),  string_char_traits  provides  the  definitions  common
  between the string class templates and the iostream class templates.

3 Convertible to type INT_T.

  27.1.2.2  Type INT_T                             [lib.iostreams.int.t]

1 Another character container type which can also  hold  an  end-of-file
  value.   It  is  used as the return type of some of the iostream class
  member functions.  If CHAR_T is either char or wchar_t, INT_T shall be
  int or wint_t, respectively.

  27.1.2.3  Type OFF_T                             [lib.iostreams.off.t]

1 A type that can represent offsets to positional information.1)  It  is
  used to represent:

  --a  signed  displacement,  measured  in  characters, from a specified
    position within a sequence.

  --an absolute position within a sequence.

2 The value OFF_T(-1) can be used as an error indicator.

3 The effect of passing to any function defined in this clause an  OFF_T
  value  not  obtained from a function defined in this clause (for exam­
  ple, assigned an arbitrary integer), is undefined, except where other­
  wise noted.

4 Convertible  to  type  POS_T.2) But no validity of the resulting POS_T
  value is ensured, whether or not the OFF_T value is valid.

  27.1.2.4  Type POS_T                             [lib.iostreams.pos.t]

1 An implementation-defined type for seek operations which describes  an
  object  that  can store all the information necessary to reposition to
  the position.

2 The type POS_T describes an object that can store all the  information
  necessary  to restore an arbitrary sequence to a previous stream posi­
  tion and conversion state.3)

3 With a stream buffer for a repositional stream (but not an  arbitrary-
  positional  stream), a C++ program can either obtain the current posi­
  tion of the stream buffer or specify the previous position  previously
  _________________________
  1)  It is usually a synonym for one if the signed basic integral types
  whose representation at least as many bits as type long.
  2) An implementation may use the same type for both OFF_T and POS_T.
  3) The conversion state is used for sequences that  translate  between
  wide-character  and  generalized  multibyte  encoding, as described in
  Amendment 1 to the C Standard.

  obtained

4 A  class  or  built-in type P satisfies the requirements of a position
  type, and a class or built-in type O satisfies the requirements of  an
  offset  type if the following expressions are valid, as shown in Table
  2.

5 In the following table,

  --P refers to type POS_T,

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

  --O refers to type OFF_T,

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

  --i refers to a value of type int.

                    Table 2--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                       |
  +-----------------------------------------------------------------------------------------+

6 The behavior of the stream after restoring the position with  a  POS_T
  value modified using any other arithmetic operations is undefined.

7 The   stream   operations  whose  return  type  is  POS_T  may  return
  POS_T(OFF_T(-1)) as an invalid POS_T value to signal an error.

8 The conversion POS_T(OFF_T(-1)) constructs the  invalid  POS_T  value,
  which is available only for comparing to the return value of such mem­
  ber functions.

  27.2  Forward declarations                      [lib.iostream.forward]

  Header <iosfwd> synopsis

  namespace std {
    template<class charT> class basic_ios;
    template<class charT> class basic_istream;
    template<class charT> class basic_ostream;

    typedef basic_ios<char>     ios;
    typedef basic_ios<wchar_t> wios;

    typedef basic_istream<char>     istream;
    typedef basic_istream<wchar_t> wistream;

    typedef basic_ostream<char>     ostream;
    typedef basic_ostream<wchar_t> wostream;
  }

1 The template class basic_ios<charT,traits> serves as a base class  for
  the          classes          basic_istream<charT,traits>          and
  basic_ostream<charT,traits>.

2 The class ios is an instance of the template class basic_ios, special­
  ized by the type char.

3 The  class  wios is a version of the template class basic_ios special­
  ized by the type wchar_t.

  27.3  Standard iostream objects                 [lib.iostream.objects]

  Header <iostream> synopsis

  #include <fstream>

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

    extern wistream win;
    extern wostream wout;
    extern wostream werr;
    extern wostream wlog;
  }

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

2 Mixing operations on corresponding wide- and narrow-character  streams
  follows  the  same  semantics  as  mixing such operations on FILEs, as
  specified in Amendment 1 of the ISO C standard.  The objects are  con­
  structed,  and  the  associations  are  established, the first time an
  object of class  basic_ios<charT,traits>::Init  is  constructed.   The
  objects are not destroyed during program execution.4)

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

  istream cin;

1 The object cin controls input from an unbuffered stream buffer associ­
  ated 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 an unbuffered stream buffer associ­
  ated with the object stdout, declared in <cstdio> (_lib.c.files_).

  ostream cerr;

4 The object cerr controls output to an unbuffered stream buffer associ­
  ated 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_).

  _________________________
  4)  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 win;

1 The object win controls input from an unbuffered stream buffer associ­
  ated with the object stdin, declared in <cstdio>.

2 After the object win is initialized, win.tie() returns wout.

  wostream wout;

3 The object wout controls output to an unbuffered stream buffer associ­
  ated with the object stdout, declared in <cstdio> (_lib.c.files_).

  wostream werr;

4 The object werr controls output to an unbuffered stream buffer associ­
  ated with the object stderr, declared in <cstdio> (_lib.c.files_).

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

  wostream wlog;

6 The object wlog 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 <stdexcept>    // for exception

  namespace std {
    typedef OFF_T  streamoff;
    typedef OFF_T wstreamoff;
    typedef INT_T streamsize;

    template <class charT> struct ios_traits<charT>;
    struct ios_traits<char>;
    struct ios_traits<wchar_t>;

    class ios_base;
    template<class charT, class traits = ios_traits<charT> >
      class basic_ios;
    typedef basic_ios<char>     ios;
    typedef basic_ios<wchar_t> wios;
  // _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 type OFF_T (_lib.iostreams.off.t_).

  typedef OFF_T wstreamoff;

2 The type wstreamoff is an implementation-defined type  that  satisfies
  the requirements of type OFF_T (_lib.iostreams.off.t_).

  typedef POS_T streampos;

3 The  type  streampos  is an implementation-defined type that satisfies
  the requirements of type POS_T (_lib.iostreams.pos.t_).

  typedef POS_T wstreampos;

4 The type wstreampos is an implementation-defined type  that  satisfies
  the requirements of type POS_T (_lib.iostreams.pos.t_).

  typedef INT_T streamsize;

5 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.5)

  27.4.2  Template struct ios_traits                    [lib.ios.traits]
  namespace std {
    template <class charT> struct ios_traits<charT> {
    // _lib.ios.traits.types_ Types:
      typedef charT char_type;
      typedef INT_T int_type;
      typedef POS_T pos_type;
      typedef OFF_T off_type;
      typedef To be specified state_type;
    // _lib.ios.traits.values_ values:
      static char_type  eos();
      static int_type   eof();
      static int_type   not_eof(char_type c);
      static char_type  newline();
      static size_t     length(const char_type* s);
    // _lib.ios.traits.tests_ tests:
      static bool       eq_char_type(char_type, char_type);
      static bool       eq_int_type (int_type, int_type);
      static bool       is_eof(int_type);
      static bool       is_whitespace(const ctype<char_type> ctype&, char_type c);

  _________________________
  5)  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).

    // _lib.ios.traits.convert_ conversions:
      static char_type  to_char_type(int_type);
      static int_type   to_int_type (char_type);
      static char_type* copy(char_type* dst, const char_type* src, size_t n) ;
      static state_type get_state(pos_type pos);
      static pos_type   get_pos  (streampos fpos, state_type state);
    };
  }

1 The  template  struct  ios_traits<charT> is a traits class which main­
  tains the definitions of the types and functions necessary  to  imple­
  ment  the iostream class templates.  The template parameter charT rep­
  resents the character container type and each specialized version pro­
  vides the default definitions corresponding to the specialized charac­
  ter container type.

2 An implementation shall provide the following  two  instantiations  of
  ios_traits:
  struct ios_traits<char>;
  struct ios_traits<wchar_t>;

  27.4.2.1  ios_traits types                      [lib.ios.traits.types]
  state_type is an implementation-defined value-oriented type.  It holds
  the  conversion  state,  and   is   compatible   with   the   function
  locale::codecvt().

  27.4.2.2  ios_traits value functions           [lib.ios.traits.values]

  char_type eos();

  Returns:
    The  null  character which is used for the terminator of null termi­
    nated character strings.  The default constructor for the  character
    container type provides the value.

  int_type eof();

  Returns:
    an  int_type value which represents the end-of-file.  It is returned
    by several functions to indicate end-of-file state  (no  more  input
    from  an  input  sequence  or  no more output permitted to an output
    sequence), or to indicate an invalid return value.

  int_type not_eof(char_type c);

  Returns:
    a value other than the end-of-file, even if c==eof().
  Notes:
    It is used in basic_streambuf<charT,traits>::overflow().

  Returns:
    int_type(c) if c!=eof().

  char_type newline();

  Returns:
    a character value which represent the newline character of the basic
    character set.
  Notes:
    It      appears      as      the      default      parameter      of
    basic_istream<charT,traits>::getline().

  size_t length(const char_type* s);

  Effects:
    Determines the length of a null terminated character string  pointed
    to by s.

  27.4.2.3  ios_traits test functions             [lib.ios.traits.tests]

  bool eq_char_type(char_type c1, char_type c2);

  Returns:
    true if c1 and c2 represent the same character.

  bool eq_int_type(int_type c1, int_type c2);

  Returns:
    true if c1 and c2 represent the same character.

  bool is_eof(int_type c);

  Returns:
    true if c represents the end-of-file.

  bool is_whitespace(char_type c, const ctype<char_type>& ctype);

  Returns:
    true if c represents a whitespace character.  The default definition
    is   as    if    it    returns    ctype.isspace(c).     (See    also
    _lib.istream.prefix_)

1 An  implementation  of the iostream class templates may use all of the
  above static member functions in addition to the following three func­
  tions provided from the base struct string_char_traits<CHAR_T>.

  27.4.2.4  ios_traits conversion               [lib.ios.traits.convert]
       functions

  char_type to_char_type(int_type c);

  Effects:
    Converts a valid character value represented in the int_type to  the
    corresponding  char_type  value.  If c is the end-of-file value, the
    return value is unspecified.

  int_type to_int_type(char_type c);

  Effects:
    Converts a valid character value represented in the char_type to the
    corresponding int_type value.

  char_type* copy(char_type* dest, const char_type* src, size_t n);

  Effects:
    Copies  n  characters  from  the  object  pointed to by src into the
    object pointed to by dest.  If copying takes place  between  objects
    that overlap, the behavior is undefined.

  state_type get_state(pos_type pos);

  Returns:
    0.

  pos_type get_pos(streampos fpos, state_type state);

  Returns:
    pos_type(pos).

  27.4.3  Class ios_base                                  [lib.ios.base]
  namespace std {
    class ios_base {
    public:
      class failure;

      typedef T1 fmtflags;
      static const fmtflags boolalpha;
      static const fmtflags dec;
      static const fmtflags fixed;
      static const fmtflags hex;
      static const fmtflags internal;
      static const fmtflags left;
      static const fmtflags oct;
      static const fmtflags right;
      static const fmtflags scientific;
      static const fmtflags showbase;
      static const fmtflags showpoint;
      static const fmtflags showpos;
      static const fmtflags skipws;
      static const fmtflags unitbuf;
      static const fmtflags uppercase;
      static const fmtflags adjustfield;
      static const fmtflags basefield;
      static const fmtflags floatfield;
      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.iostate.flags_ iostate flags:
      iostate exceptions() const;
      void exceptions(iostate except);
    // _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);
      int_type fill() const;
      int_type fill(int_type ch);
      int precision() const;
      int precision(int prec);
      int width() const;
      int width(int 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);
    protected:
      ios_base();
    private:
  //  static int index;  exposition only
  //  int* 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;

  --int* iarray, points to the  first  element  of  an  arbitrary-length
    integer 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]

  27.4.3.1  Types                                        [lib.ios.types]

  27.4.3.1.1  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.

  27.4.3.1.2  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 3:

                        Table 3--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;            |
       |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 4:

                       Table 4--fmtflags constants

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

  27.4.3.1.3  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 5:

                         Table 5--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.

  27.4.3.1.4  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 6:

                        Table 6--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 |
           +---------------------------------------------------+

  27.4.3.1.5  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 7:

                         Table 7--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                                    |
       +----------------------------------------------------------+

  27.4.3.1.6  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_).

  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.narrow.stream.objects_),    win,    wout,   werr,   and   wlog
    (_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(), and clog.flush().

  27.4.3.2  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().

  int_type fill() const;

  Returns:
    The character to use to pad (fill) an output conversion to the spec­
    ified field width (_lib.ostream.formatted_).

  int_type fill(int_type fillch);

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

  int precision() const;

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

  int precision(int prec);

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

  int width() const;

  Returns:
    The field width (number of characters) to generate on certain output
    conversions.

  int width(int wide);

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

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

  locale imbue(const locale loc);

  Postcondition:
    loc == getloc().
  Returns:
    The previous value of getloc().

  locale getloc() const;

  Returns:
    The classic "C" locale if no locale  has  been  imbued.   Otherwise,
    returns  the  locale  in which to perform locale-dependent input and
    output operations.

  27.4.3.4  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 int  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.
  Returns:
    iarray[idx].
  Notes:
    After a subsequent call to iword(int) for the same object, the  ear­
    lier return value may no longer be valid.6)
  _________________________
  6)  An  implementation  is  free  to  implement both the integer array

  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.
  Returns:
    parray[idx].
  Notes:
    After  a subsequent call to pword(int) for the same object, the ear­
    lier return value may no longer be valid.

  27.4.3.5  ios_base constructors                    [lib.ios.base.cons]

  ios_base();

  Effects:
    Constructs an object of class ios_base, assigning initial values  to
    its  member  objects.  The postconditions of this function are indi­
    cated in Table 8:

                        Table 8--ios_base() effects

             +------------------------------------------------+
             |  Element                   Value               |
             +------------------------------------------------+
             |rdstate()      goodbit if  sb  is  not  a  null |
             |               pointer, otherwise badbit.       |
             |exceptions()   goodbit                          |
             |flags()        skipws | dec                     |
             |width()        zero                             |
             |precision()    6                                |
             |fill()         the space character              |
             |getloc()       locale::classic()                |
             |index          ???                              |
             |iarray         a null pointer                   |
             |parray         a null pointer                   |
             +------------------------------------------------+

  _________________________
  pointed at by iarray and the pointer array pointed  at  by  parray  as
  sparse data structures, possibly with a one-element cache for each.

  27.4.4  Template class basic_ios                             [lib.ios]
  namespace std {
    template<class charT, class traits = ios_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;
      operator bool() 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;
    // _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);
    // _lib.ios.base.locales_ locales:
      locale imbue(const locale& loc);
    protected:
      basic_ios();
      void init(basic_streambuf<charT,traits>* sb);
    };
  }

  27.4.4.1  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_),

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

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

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

  Returns:
    An output sequence that is tied  to  (synchronized  with)  an  input
    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
    rdbuf()->pubimbue(loc) (_lib.streambuf.locales_).

  basic_ios& copyfmt(const basic_ios& rhs);

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

  --rdstate() is left unchanged;

  --exceptions() is altered last by calling exception(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.
  Returns:
    *this.

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

  operator bool() const

  Returns:
    !fail().

  bool operator!() const

  Returns:
    fail().

  iostate rdstate() const;

  Returns:
    The control state of the stream buffer.

  void clear(iostate state = goodbit) throw(failure);

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

  void setstate(iostate state) throw(failure);

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

  bool good() const;

  Returns:
    rdstate() == 0
  _________________________
  can  keep track of the maximum element of the arrays that is non-zero.

  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()).

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

  27.4.5.1  fmtflags manipulators                   [lib.fmtflags.manip]

  ios_base& boolalpha(ios_base& str);

  Effects:
    Calls str.setf(ios_base::boolalpha).
  Returns:
    str.9)

  ios_base& noboolalpha(ios_base& str);

  Effects:
    Calls str.unsetf(ios_base::boolalpha).
  _________________________
  8) Checking badbit also for fail() is historical practice.

  Returns:
    str.

  ios_base& showbase(ios_base& str);

  Effects:
    Calls str.setf(ios_base::showbase).
  Returns:
    str.
  Notes:
    Does not affect any extractors.

  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.

  27.4.5.2  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.

  27.4.5.3  basefield manipulators                 [lib.basefield.manip]

  ios_base& dec(ios_base& str);

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

  ios_base& hex(ios_base& str);

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

  ios_base& oct(ios_base& str);

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

  27.4.5.4  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).

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

  Returns:
    str.

  27.5  Stream buffers                              [lib.stream.buffers]

  Header <streambuf> synopsis

  #include <ios>   // for ios_traits

  namespace std {
    template<class charT, class traits = ios_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

    candidate 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.

  --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 = ios_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;
      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:
      int      in_avail();
      int_type snextc();
      int_type sbumpc();
      int_type sgetc();
      int      sgetn(char_type* s, streamsize n);
    // _lib.streambuf.pub.pback_ Putback:
      int_type sputbackc(char_type c);
      int      sungetc();
    // _lib.streambuf.pub.put_ Put area:
      int      sputc(char_type c);
      int_type 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

  control 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 the return value of locale::classic().
  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;

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

  Returns:
    If  pubimbue() has ever been called, then the last value of loc sup­
    plied, otherwise classic "C" locale  locale::classic().   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]

  int in_avail();

  Returns:
    If a read position is available, returns gend() -  gnext().   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().

  Notes:
    Uses traits::eof().

  int_type sbumpc();

  Returns:
    If the input  sequence  read  position  is  not  available,  returns
    uflow().   Otherwise,  returns char_type(*gptr()) and increments 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 char_type(*gptr()).

  int 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 c !=
    gptr()[-1], returns pbackfail(c).  Otherwise,  decrements  the  next
    pointer for the input sequence and returns *gptr().

  int sungetc();

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

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

  int sputc(char_type c);

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

  int_type 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 output 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.
  Note:
    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.virtuals_, _lib.filebuf.virtuals_).
  Default behavior:
    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::seekpos_,
    _lib.filebuf::seekpos_).
  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, and if gptr() is non-null, the
    characters between gptr() and egptr()  are  restored  to  the  input
    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:
    a  guaranteed  lower  bound  on the number of characters that can be
    read from the input sequence before a call to uflow() or underflow()
    returns  traits::eof().   A  positive return value of indicates that
    the next such call will not return traits::eof().12)
  Default behavior:
    Returns zero.
  Notes:
    Uses traits::eof().
  _________________________
  11) The morphemes of showmany are "es-how-many-see", not "show-manic".
  12) The next such call might fail by throwing an exception.   The  in­
  tention is that the next call will return ``immediately.''

  streamsize xsgetn(char_type* s, streamsize n);

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

  int_type underflow();

  Notes:
    The  public  members  of  basic_streambuf call this virtual function
    only if gptr() is null or gptr() >= egptr()
  Returns:
    the first character of the pending sequence,  if  possible,  without
    moving the input sequence position past it.  If the pending sequence
    is null then the function fails.

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:

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

  a)If  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)
  Returns:
    traits::eof() to indicate failure.
  Default behavior:
    Returns traits::eof().

  int_type uflow();

  Requires:
    The  constraints  are  the  same as for underflow(), except that the
    result character is transfered from  the  pending  sequence  to  the
    backup  sequence,  and  the pending sequence may not be empty before
    the transfer.
  Default behavior:
    Calls    underflow(traits::eof()).     If    underflow()     returns
    traits::eof(), returns traits::eof().  Otherwise, does gbump(-1) and
    returns *gptr().
  Returns:
    traits::not_eof(c).
  Notes:
    Uses traits::eof().

  27.5.2.4.4  Putback                         [lib.streambuf.virt.pback]

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

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

  --If c == traits::eof() then the input sequence is backed up one char­
    acter before the pending sequence is determined.

  --If c != traits::eof()  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  successive elements of the array whose first element is desig­
    nated by s.  Writing stops when either n characters have been  writ­
    ten 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  c  ==  traits::eof()  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)
  _________________________
  14)  That  is,  for  each  class  derived  from  an  instance  of  ba­
  sic_streambuf in this clause (_lib.stringbuf_, _lib.filebuf_), a spec­
  ification of how consuming a character effects the  associated  output

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

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

  27.6  Formatting and manipulators                [lib.iostream.format]

  Header <istream> synopsis

  #include <ios>  // for ios_traits

  namespace std {
    template <class charT, class traits = ios_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

  _________________________
  sequence  is  given.   There  is  no  requirement on a program-defined
  class.
  15) Typically, overflow returns c to indicate success.

  #include <ios>  // for ios_traits

  namespace std {
    template <class charT, class traits = ioc_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

  #include <istream>
  #include <ostream>

  namespace std {
      typedef ? smanip;

      smanip resetiosflags(ios_base::fmtflags mask);
      smanip setiosflags  (ios_base::fmtflags mask);
      smanip setbase(int base);
      smanip setfill(int c);
      smanip setprecision(int n);
      smanip setw(int n);
  }

  27.6.1  Input streams                              [lib.input.streams]

1 The header <istream> defines a type and a function signature that con­
  trol input from a stream buffer.

  27.6.1.1  Template class basic_istream                   [lib.istream]
  namespace std {
    template <class charT, class traits = ios_traits<charT> >
    class basic_istream : virtual public basic_ios<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.istream.cons_ Constructor/destructor:
      explicit basic_istream(basic_streambuf<charT,traits>* sb);
      virtual ~basic_istream();
    // _lib.istream.prefix_ Prefix/suffix:
      bool ipfx(bool noskipws = false);
      void isfx();

    // _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>>(char_type* s);
      basic_istream<charT,traits>& operator>>(char_type& c);
      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,
                        char_type delim = traits::newline());
      basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb,
                        char_type delim = traits::newline());
      basic_istream<charT,traits>& getline(char_type* s, streamsize n,
                            char_type delim = traits::newline());
      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);
    };
  }

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 except

  that they do not invoke any virtual members of rdbuf() except uflow().

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::failure (_lib.iostate.flags_), before returning.

4 If  one  of  these  called  functions throws an exception, then unless
  explicitly noted otherwise the input function  calls  setstate(badbit)
  and if badbit is on in exception() rethrows the exception without com­
  pleting its actions.

  27.6.1.1.1  basic_istream constructors        [lib.basic.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  basic_istream prefix and suffix       [lib.istream.prefix]

  bool ipfx(bool noskipws = false);

  Effects:
    If good() is true, prepares  for  formatted  or  unformatted  input.
    First,   if  tie()  is  not  a  null  pointer,  the  function  calls
    tie()->flush() to synchronize the output sequence with  any  associ­
    ated external C stream.16) If noskipws is zero and flags() &  skipws
    is  nonzero,  the  function  extracts and discards each character as
    long as the next available input character c is a whitespace charac­
    ter.
  Notes:
    The  function  basic_istream<charT,traits>::ipfx() uses the function
    bool  traits::is_whitespace(charT,  const  locale*)  in  the  traits
    structure   to   determine  whether  the  next  input  character  is
  _________________________
  16) The call tie()->flush() does not necessarily occur if the function
  can determine that no synchronization is necessary.

    whitespace or not.

1 To decide if the character c is a whitespace character,  the  function
  performs ``as if'' it executes the following code fragment:
    ctype<charT> ctype = getloc().use<ctype<charT> >();
    if (traits::is_whitespace (c, ctype)!=0)
    // c is a whitespace character.
  Returns:
    If,  after  any  preparation  is  completed, good() is true, returns
    true.   Otherwise,  it  calls  setstate(failbit)  (which  may  throw
    ios_base::failure (_lib.iostate.flags_)) and returns false.17)

2 [Example: A typical implementation of the ipfx() function  may  be  as
  follows:
  template <class charT, class traits = ios_traits<charT> >
  int basic_istream<charT,traits>::ipfx() {
      ...
  // skipping whitespace according to a constraint function,
  // is_whitespace
      intT c;
      typedef ctype<charT> ctype_type;
      ctype_type& ctype = getloc().use<ctype_type>();
      while ((c = rdbuf()->snextc()) != traits::eof()) {
        if (!traits::is_whitespace (c,ctype)==0) {
          rdbuf()->sputbackc (c);
          break;
        }
      }
      ...
   }
   --end example]

3 When  using  ios_traits<char>  or ios_traits<wchar_t>, the behavior of
  the function traits::is_whitespace() is ``as if'' it invokes:
     ctype = getloc().use<ctype<charT> >().is(ctype<charT>::space, c);
  (see _lib.ios.traits.tests_); otherwise, the behavior of the  function
  traits::is_whitespace() is unspecified.

4 [Example:  Those  C++  programs  that  want  to use locale-independent
  whitespace predicate can specify their definition of is_whitespace  in
  their new ios_traits as follows:
  struct my_traits : public ios_traits<char> {
      typedef my_char_traits char_traits;
  };
  struct my_char_traits : public ios_traits<char> {
      static bool is_whitespace (char c, const ctype<charT>& ctype) {
      ....(my own implementation)...
      }
  };
  _________________________
  17) The functions ipfx(int) and isfx() can also perform additional im­
  plementation-dependent operations.

   --end example]

  void isfx();

  Effects:
    None.

  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 calling ipfx().  If
  that function returns true,  the  function  endeavors  to  obtain  the
  requested  input.   In  any case, the formatted input function ends by
  calling isfx(), then returns *this

2 Some formatted input functions endeavor to obtain the requested  input
  by  parsing  characters  extracted from the input sequence, converting
  the result to a value of some scalar data type, and storing  the  con­
  verted value in an object of that scalar data type.

3 The  numeric  conversion  behaviors  of  the  following extractors are
  locale-dependent.

  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);

  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''  it  performed
  the following code fragment:
    HOLDTYPE tmp;
    num_get<charT>& fmt = loc.use< num_get<charT> >();
    fmt.get (*this, 0, *this, loc, tmp);
    if ((TYPE)tmp != tmp) { // set fail bit...
    } else val = (TYPE)tmp;
  In  the  above  fragment,  loc  stands  for  the private member of the
  basic_ios class, TYPE stands for the  type  of  the  argument  of  the
  extractor, and HOLDTYPE is as follows;

  --for short, int and long, HOLDTYPE is long;

  --for  unsigned  short,  unsigned  int  and unsigned long, HOLDTYPE is
    unsigned long.

  --for float, double, HOLDTYPE is double.

  --for long double, HOLDTYPE is long double.

4 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.  Class locale relies on this type as its
  interface  to  istream,  since  the flexibility it has been abstracted
  away from direct dependence on istream.

5 In case the converting result is a value of either an integral type  (
  short,  unsigned  short,  int, unsigned int, long, unsigned long) or a
  float type ( float, double, long double), performing to parse and con­
  vert  the  result depend on the imbued locale object.  So the behavior
  of the above type extractors are locale-dependent.  The imbued  locale
  object  uses  an  istreambuf_iterator  to  access  the input character
  sequence.

6 The behavior of such functions is described in terms of the conversion
  specification  ``as  if''  for  an  equivalent  call  to  the function
  ::fscanf()18)  operating  with the global locale set to getloc(), with
  the following alterations:

  --The formatted input  function  extracts  characters  from  a  stream
    buffer, rather than reading them from an input file.19)

  --If (flags() & skipws) == 0, the function does not skip  any  leading
    white  space.   In  that  case, if the next input character is white
    space, the scan fails.

  --If the converted data value cannot be represented as a value of  the
    specified scalar data type, a scan failure occurs.

7 [Note: For conversion to an integral type other than a character type,
  the function determines the integral conversion specifier as indicated
  in Table 9:

  _________________________
  18) The signature fscanf(FILE*, const  char*,  ...)   is  declared  in
  <cstdio> (_lib.c.files_)
  19)  The  stream  buffer  can,  of course, be associated with an input
  file, but it need not be.

                       Table 9--Integer conversions

            +------------------------------------------------+
            |           State               stdio equivalent |
            +------------------------------------------------+
            |(flags() & basefield) == oct          %o        |
            +------------------------------------------------+
            |(flags() & basefield) == hex          %x        |
            |(flags() & uppercase) != 0            %X        |
            +------------------------------------------------+
            |(flags() & basefield) == 0            %i        |
            +------------------------------------------------+
            |Otherwise,                                      |
            +------------------------------------------------+
            |signed integral type                  %d        |
            +------------------------------------------------+
            |unsigned integral type                %u        |
            +------------------------------------------------+
   --end note]

8 If  the  scan fails for any reason, the formatted input function calls
  setstate(failbit),     which     may      throw      ios_base::failure
  (_lib.iostate.flags_).

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

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

  Returns:
    pf(*this).20)

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

  Effects:
    Calls pf(*this), then returns *this.21)

  basic_istream<charT,traits>& operator>>(char_type* s);

  _________________________
  20)  See,  for  example,  the  function  signature  ws(basic_istream&)
  (_lib.istream.manip_).
  21)     See,     for     example,     the      function      signature
  dec(basic_ios<charT,traits>&) (_lib.basefield.manip_).

  Effects:
    Extracts  characters and stores them into successive locations of an
    array  whose  first  element  is  designated  by s.22) If width() is
    greater than zero, the maximum number  of  characters  stored  n  is
    width();  otherwise it is numeric_limits<int>::max() (_lib.limits_).

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;

  --traits::is_whitespace(c,ctype)  is true for the next available input
    character c.  In the above code  fragment,  the  argument  ctype  is
    acquired by getloc().use<ctype<charT> >().

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 location of
  the array and calls width(0).
  Returns:
    *this.
  Notes:
    Uses traits::eos().

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

  Effects:
    Extracts a character, if one is available, and stores it in c.  Oth­
    erwise, the function calls setstate(failbit).
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(bool& n);

  Effects:
    Converts a boolean value, if one is available, and stores it in x.
  Returns:
    *this.
  Notes:
    Behaves as if:
        getloc().use<num_get<charT,istreambuf_iterator<charT,traits> >().
          get(*this, 0, *this, getloc(), n);
    [Note:  num_get<>::get() just sets the iostate flags, without check­
    ing whether failure() should be thrown;  so  operator>>()  needs  to
    check that.   --end note]

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

3 If  flags.flag()  &  ios_base::boolalpha  is  false,  num_get<>::get()
  (_lib.category.numeric_) tries to read  an  integer  value,  which  if
  found  must be 0 or 1; if the boolalpha flag is true, it reads charac­
  ters until it determines whether the numpunct<>::truename() or  false­
  name() sequence23) is present.  In either case if an  exact  match  is
  not found calls setstate(failbit).

  basic_istream<charT,traits>& operator>>(short& n);

  Effects:
    Converts  a signed short integer, if one is available, and stores it
    in n.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(unsigned short& n);

  Effects:
    Converts an unsigned short integer, if one is available, and  stores
    it in n.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(int& n);

  Effects:
    Converts  a signed integer, if one is available, and stores it in n.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(unsigned int& n);

  Effects:
    Converts an unsigned integer, if one is available, and stores it  in
    n.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(long& n);

  Effects:
    Converts  a  signed long integer, if one is available, and stores it
    in n.

  _________________________
  23)  The  boolean  value  names  for the default classic C" locale are
  false" and true".

  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(unsigned long& n);

  Effects:
    Converts an unsigned long integer, if one is available,  and  stores
    it in n.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(float& f);

  Effects:
    Converts a float, if one is available, and stores it in f.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(double& f);

  Effects:
    Converts a double, if one is available, and stores it in f.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(long double& f);

  Effects:
    Converts a long double, if one is available, and stores it in f.
  Returns:
    *this.

  basic_istream<charT,traits>& operator>>(void*& p);

  Effects:
    Converts a pointer to void, if one is available, and stores it in p.
  Returns:
    *this.

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

  Requires:
    sb shall be non-null.
  Effects:
    If  sb  is   null,   calls   setstate(badbit),   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).   set­
    state(badbit) is not called

4 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 calling ipfx(1).
  If that function returns nonzero, the function  endeavors  to  extract
  the  requested  input.   It  also  counts  the  number  of  characters
  extracted.  In any case, the unformatted input function ends by  stor­
  ing  the  count  in a member object and calling isfx(), then returning
  the value specified for 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.24)
  _________________________
  24)  Note that this function is not overloaded on types signed charand

    Otherwise,  the  function  calls  setstate(failbit) (which may throw
    ios_base::failure (_lib.iostate.flags_)).
  Returns:
    *this.

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

  Effects:
    Extracts characters and stores them into successive locations of  an
    array whose first element is  designated  by  s.25)  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(basic_streambuf<char_type,traits>& sb,
                    char_type delim = traits::newline());

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

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

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

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

  --an exception occurs (in which case, the exception is caught but  not
    rethrown).
  _________________________
  unsigned char.
  25) Note that this function is not overloaded on types signed char and
  unsigned char.

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>& getline(char_type* s, streamsize n,
                        char_type delim = traits::newline());

  Effects:
    Extracts characters and stores them into successive locations of  an
    array whose first element is  designated  by  s.26)  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);27)

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

4 These conditions are tested in the order shown.28)

5 If  the  function  extracts  no characters, it calls setstate(failbit)
  (which may throw ios_base::failure (_lib.iostate.flags_)).29)

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

7 [Example:

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

    #include <iostream>

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

      char buffer[line_buffer_size];
      int line_number = 0;
      while (cin.getline(buffer, line_buffer_size) || 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>&
      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.30)  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:
    Extracts  characters and stores them into successive locations of an
    array whose first element is designated by s.
  Returns:
    A value based on in_avail():

  --If  in_avail()  <  0,  calls  setstate(eofbit)  (which   may   throw
    ios_base::failure (_lib.iostate.flags_)), and returns zero;

  --If in_avail() == 0, returns zero;

  --If in_avail() > 0, returns read(s, min(in_avail(),n)).

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

  Effects:
    Calls  rdbuf->sputbackc(c).  If that function returns traits::eof(),
    calls   setstate(badbit)   (which   may   throw    ios_base::failure
    (_lib.iostate.flags_)).
  Returns:
    *this.

  basic_istream<charT,traits>& unget();

  Effects:
    Calls  rdbuf->sungetc().   If  that  function returns traits::eof(),
    calls   setstate(badbit)   (which   may   throw    ios_base::failure
    (_lib.iostate.flags_)).
  _________________________
  30) Note that this function is not overloaded on types signed char and
  unsigned char.

  Returns:
    *this.

  int sync();

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

  pos_type tellg();

  Returns:
    if  fail() == true, returns streampos(-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:
    Skips  any  whitespace  in  the  input  sequence:  saves  a  copy of
    is.fmtflags,  then  clears  is.skipws  in  is.flags().   Then  calls
    is.ipfx(),  then  is.isfx(),  then  restores is.flags() to its saved
    value.
  Returns:
    is.

  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 = ioc_traits<charT> >
    class basic_ostream : virtual public basic_ios<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.ostream.cons_ Constructor/destructor:
      explicit basic_ostream(basic_streambuf<char_type,traits>* sb);
      virtual ~basic_ostream();
    // _lib.ostream.prefix_ Prefix/suffix:
      bool opfx();
      void osfx();
    // _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<<(const char_type* s);
      basic_ostream<charT,traits>& operator<<(char_type c);
      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();
      pos_type tellp();
      basic_ostream<charT,traits>& seekp(pos_type&);
      basic_ostream<charT,traits>& seekp(off_type&, ios_base::seekdir);
    };
  }

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).
  They may use other public members of basic_ostream except that they do
  not invoke any virtual members of rdbuf() except overflow().   If  the
  called  function  throws  an exception, the output function calls set­
  state(badbit),      which      may       throw       ios_base::failure
  (_lib.iostate.flags_),  and  if  badbit is on in exceptions() rethrows
  the exception.

  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  basic_ostream prefix and suffix         [lib.ostream.prefix]
       functions

  bool opfx();

1 If  good()  is  nonzero, prepares for formatted or unformatted output.
  If tie() is not a null pointer, calls tie()->flush().31)
  Returns:
    good().32)

  void osfx();

  _________________________
  31) The call tie()->flush() does not necessarily occur if the function
  can determine that no synchronization is necessary.
  32)  The  function signatures opfx() and osfx() can also perform addi­
  tional implementation-dependent operations.

2 If (flags() & unitbuf) != 0, calls flush().

  pos_type tellp();

  Returns:
    if fail() == true, returns streampos(-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.

  27.6.2.4  Formatted output functions           [lib.ostream.formatted]

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

1 Each formatted output function begins execution by calling opfx().  If
  that function returns nonzero, the function endeavors to generate  the
  requested  output.  In any case, the formatted output function ends by
  calling osfx(), then returning the value specified for  the  formatted
  output function.

2 The  numeric  conversion  behaviors  of  the  following  inserters are
  locale-dependent (_lib.category.numeric_):
    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);

3 The classes num_get<> and num_put<>  handle  locale-dependent  numeric
  formatting  and  parsing.   The  above  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:
    num_put<charT>& fmt = loc.use< num_put<charT> >();
    fmt.put (ostreambuf_iterator(*this), *this, loc, val);

  In the above fragment, loc  stands  for  the  private  member  of  the
  basic_ios  class  which  maintains the imbued localeobject.  The first
  argument provides an object of the ostreambuf_iterator class which  is
  an  iterator for ostream class.  It bypasses ostreams and uses stream­
  bufs 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.

4 Some formatted output functions endeavor  to  generate  the  requested
  output  by  converting  a  value from some scalar or NTBS type to text
  form and inserting the converted text in  the  output  sequence.   The
  behavior  of  such  functions  is described in terms of the conversion
  specification ``as  if''  for  an  equivalent  call  to  the  function
  ::fprintf(),33) operating with the global locale set to getloc(), with
  the following alterations:

  --The formatted output function inserts characters in a stream buffer,
    rather than writing them to an output file.34)

  --The  formatted  output  function uses the fill character returned by
    fill() as the padding character (rather than the space character for
    left or right padding, or 0 for internal padding).

5 If  the  operation fails for any reason, the formatted output function
  calls   setstate(badbit),   which    may    throw    ios_base::failure
  (_lib.iostate.flags_).

6 [Note:  For  conversion  from  an integral type other than a character
  type, the function determines the  integral  conversion  specifier  as
  indicated in Table 10:

  _________________________
  33)  The  signature fprintf(FILE*, const char_type*, ...)  is declared
  in <cstdio> (_lib.c.files_).
  34) The stream buffer can, of course, be  associated  with  an  output
  file, but it need not be.

                      Table 10--Integer conversions

            +------------------------------------------------+
            |           State               stdio equivalent |
            +------------------------------------------------+
            |(flags() & basefield) == oct          %o        |
            +------------------------------------------------+
            |(flags() & basefield) == hex          %x        |
            |(flags() & uppercase) != 0            %X        |
            +------------------------------------------------+
            |Otherwise,                                      |
            +------------------------------------------------+
            |signed integral type                  %d        |
            +------------------------------------------------+
            |unsigned integral type                %u        |
            +------------------------------------------------+
   --end note]

7 [Note:  For conversion from a floating-point type, the function deter­
  mines the floating-point conversion specifier as  indicated  in  Table
  11:

                   Table 11--Floating-point conversions

        +--------------------------------------------------------+
        |               State                   stdio equivalent |
        +--------------------------------------------------------+
        |(flags() & floatfield) == fixed               %f        |
        +--------------------------------------------------------+
        |(flags() & floatfield) == scientific          %e        |
        |(flags() & uppercase) != 0                    %E        |
        +--------------------------------------------------------+
        |Otherwise,                                              |
        +--------------------------------------------------------+
        |                                              %g        |
        |(flags() & uppercase) != 0                    %G        |
        +--------------------------------------------------------+
   --end note]

8 [Note:  The  conversion  specifier has the following additional quali­
  fiers prepended as indicated in Table 12:

                   Table 12--Floating-point conversions

  +----------------------------------------------------------------------+
  |       Type(s)                    State              stdio equivalent |
  +----------------------------------------------------------------------+
  |an integral type oth­   (flags() & showpos)   != 0          +         |
  |er than a character     (flags() & showbase)  != 0          #         |
  |type                                                                  |
  +----------------------------------------------------------------------+
  |a floating-point type   (flags() & showpos)   != 0          +         |
  |                        (flags() & showpoint) != 0          #         |
  +----------------------------------------------------------------------+
   --end note]

9 [Note: For any conversion, if width() is nonzero, then a  field  width
  is specified in the conversion specification.  The value is width().
  --end note]

10For conversion from a floating-point type, if (flags() & fixed)  !=  0
  or if precision() > 0, then precision() is specified in the conversion
  specification.

11[Note: Moreover, for any conversion, padding with the  fill  character
  returned by fill() behaves as indicated in Table 13:

                          Table 13--Fill padding

  +------------------------------------------------------------------------------------+
  |              State                      Justification        fprintf flag,padding  |
  +------------------------------------------------------------------------------------+
  |(flags() & adjustfield)==left       left (pad after text)     (none), space padding |
  +------------------------------------------------------------------------------------+
  |(flags() & adjustfield)==internal   internal                  0, zero padding35)    |
  +------------------------------------------------------------------------------------+
  |Otherwise                           right (pad before text)   -, space padding      |
  +------------------------------------------------------------------------------------+
   --end note]

12Unless explicitly stated otherwise for  a  particular  inserter,  each
  formatted  output  function calls width(0) after determining the field
  width.

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

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

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

  Returns:
    pf(*this).36)

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

  Effects:
    Calls pf(*this).
  Returns:
    *this.37)

  basic_ostream<charT,traits>& operator<<(const char_type* s);

  Requires:
    s shall be a null-terminated byte string.
  Effects:
    Converts the NTBS s with the conversion specifier s.
  Returns:
    *this.

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

  Effects:
    Converts the char_type c with the conversion specifier c and a field
    width of zero.38)
  Notes:
    The stored field width (  basic_ios<charT,traits>::width())  is  not
    set to zero.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(bool n);

  _________________________
  36) See, for  example,  the  function  signature  endl(basic_ostream&)
  (_lib.ostream.manip_) .
  37)   See,   for   example,   the  function  signature  dec(ios_base&)
  (_lib.basefield.manip_).
  38) Note that this function is not overloaded on types signed char and
  unsigned char.

1 Behaves as if:
      getloc().use<num_put<charT,istreambuf_iterator<charT,traits> >()
        .put(*this, *this, getloc(), n);
  which   writes   out   a   0   or   1,   or   the   results   of  get­
  loc().use<numpunct<charT>      >().truename()      or      falsename()
  (_lib.category.numeric_),  according  as whether the boolalpha flag is
  set.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(short n);

  Effects:
    Converts the signed short integer n  with  the  integral  conversion
    specifier preceded by h.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(unsigned short n);

  Effects:
    Converts  the  unsigned short integer n with the integral conversion
    specifier preceded by h.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(int n);

  Effects:
    Converts the signed integer n with the  integral  conversion  speci­
    fier.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(unsigned int n);

  Effects:
    Converts  the unsigned integer n with the integral conversion speci­
    fier.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(long n);

  Effects:
    Converts the signed long integer  n  with  the  integral  conversion
    specifier preceded by l.

  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(unsigned long n);

  Effects:
    Converts  the  unsigned  long integer n with the integral conversion
    specifier preceded by l.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(float f);

  Effects:
    Converts the float f with the floating-point conversion specifier.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(double f);

  Effects:
    Converts the double f with the floating-point conversion  specifier.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(long double f);

  Effects:
    Converts the long double f with the floating-point conversion speci­
    fier preceded by L.
  Returns:
    *this.

  basic_ostream<charT,traits>& operator<<(void* p);

  Effects:
    Converts the pointer to void p with the conversion specifier p.
  Returns:
    *this.

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

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

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

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

  --an exception occurs while getting a  character  from  sb  (in  which
    case, the exception is rethrown).

2 If  the  function  inserts  no  characters or if it stopped because an
  exception was thrown while  extracting  a  character,  it  calls  set­
  state(failbit)       (which      may      throw      ios_base::failure
  (_lib.iostate.flags_)).  If an exception was thrown while extracting a
  character  and  failbit  is on in exceptions() the caught exception is
  rethrown.
  Returns:
    *this.

  27.6.2.5  Unformatted output functions       [lib.ostream.unformatted]

1 Each unformatted output function begins execution by  calling  opfx().
  If  that  function returns nonzero, the function endeavors to generate
  the requested output.  In any case, the  unformatted  output  function
  ends  by  calling  osfx(),  then returning the value specified for the
  unformatted output function.

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

  Effects:
    Inserts the character c, if possible.39)

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

  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.40) Characters  are  inserted
    until either of the following occurs:

  --n characters are inserted;

  --inserting  in  the output sequence fails (in which case the function
  _________________________
  39) Note that this function is not overloaded on types signed char and
  unsigned char.
  40) Note that this function is not overloaded on types signed char and
  unsigned char.

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

  27.6.2.6  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(traits::newline()), then os.flush().
  Returns:
    os.41)

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

  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().
  _________________________
  41) 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.

  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 smanip is an implementation-defined function type (_dcl.fct_)
  returned by the standard manipulators.

  smanip resetiosflags(ios_base::fmtflags mask);

  Returns:
    smanip(f, mask), where f can be defined as:42)
        template<class charT, class traits>
          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:
    smanip(f,mask), 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:
    smanip(f, base), where f can be defined as:

  _________________________
  42)  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).

          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(int c);

  Returns:
    smanip(f, c), where f can be defined as:
          ios_base& f(ios_base& str, int c)
          { // set fill character
            str.fill(c);
            return str;
          }

  smanip setprecision(int n);

  Returns:
    smanip(f, n), 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:
    smanip(f, n), 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 three 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

  #include <streambuf>
  #include <istream>
  #include <ostream>

  namespace std {
    template <class charT, class traits = int_charT_traits<charT> >
      class basic_stringbuf;
    typedef basic_stringbuf<char>     stringbuf;
    typedef basic_stringbuf<wchar_t> wstringbuf;

    template <class charT, class traits = ios_traits<charT> >
      class basic_istringstream;
    typedef basic_istringstream<char>     istringstream;
    typedef basic_istringstream<wchar_t> wistringstream;

    template <class charT, class traits = ios_traits<charT> >
      class basic_ostringstream;
    typedef basic_ostringstream<char>     ostringstream;
    typedef basic_ostringstream<wchar_t> wostringstream;
  }

                   Table 13--Header <cstdlib> synopsis

                          +---------------------+
                          |Type      Name(s)    |
                          +---------------------+
                          |Functions:           |
                          |       atof   stroul |
                          |       atoi   strtod |
                          |       atol   strtol |
                          +---------------------+

2
  SEE ALSO: ISO C subclause 7.10.1.

  27.7.1  Template class basic_stringbuf                 [lib.stringbuf]
  namespace std {
    template <class charT, class traits = int_charT_traits<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<char_type>& str,
                               ios_base::openmode which
                                = ios_base::in | ios_base::out);

    // _lib.stringbuf.members_ Get and set:
      basic_string<char_type> str() const;
      void                    str(const basic_string<char_type>& 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 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.

  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<char_type>& 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(),  initializing  the  base  class with
    basic_streambuf() (_lib.streambuf.cons_), and initializing mode with
    which.
  Postconditions:
    str()  ==  str.  If str.size() > 0, sets the get and/or put pointers
    as indicated in Table 14:

                        Table 14--str get/set areas

    +------------------------------------------------------------------+
    |         Condition                          Setting               |
    +------------------------------------------------------------------+
    |(which & ios_base::in)  != 0   setg(str(),str(),str()+str.size()) |
    +------------------------------------------------------------------+
    |(which & ios_base::out) != 0   setp(str(),str(),str()+str.size()) |
    +------------------------------------------------------------------+

  27.7.1.2  Member functions                     [lib.stringbuf.members]

  basic_string<char_type> str() const;

  Returns:
    The return value of this function are indicated in Table 15:

                        Table 15--str return values

  +---------------------------------------------------------------------------+
  |       Condition                            Return Value                   |
  +---------------------------------------------------------------------------+
  |(mode & basic_ios::in)    basic_string<char_type>(eback(),egptr()-eback()) |
  |!= 0 and (gptr() != 0)                                                     |
  +---------------------------------------------------------------------------+
  |(mode & basic_ios::out)   basic_string<char_type>(pbase(),pptr()-pbase())  |
  |!= 0 and (pptr() != 0)                                                     |
  +---------------------------------------------------------------------------+
  |Otherwise                 basic_string<char_type>()                        |
  +---------------------------------------------------------------------------+

  void str(const basic_string<char_type>& s);

  Effects:
    If s.length() is zero, executes:
        setg(0, 0, 0);
        setp(0, 0);
  Postcondition:
    str() == s.  If str.size() > 0, sets the get and/or put pointers  as
    indicated in Table 16:

                        Table 16--str get/set areas

    +------------------------------------------------------------------+
    |         Condition                          Setting               |
    +------------------------------------------------------------------+
    |(which & ios_base::in)  != 0   setg(str(),str(),str()+str.size()) |
    +------------------------------------------------------------------+
    |(which & ios_base::out) != 0   setp(str(),str(),str()+str.size()) |
    +------------------------------------------------------------------+

  27.7.1.3  Overridden virtual functions        [lib.stringbuf.virtuals]

  int_type underflow();

  Returns:
    If  the  input  sequence  has  a  read  position  available, returns
    char_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  c != traits::eof(), if the input sequence has a putback position
    available, and if  char_type(c)  ==  char_type(gptr()[-1]),  assigns
    gptr() - 1 to gptr().
    Returns: c.

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

  --If  c == traits::eof() and if the input sequence has a putback posi­
    tion available, assigns gptr() - 1 to gptr().
    Returns: char_type(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 c != traits::eof() 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 c == traits::eof(), 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 [Note:  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 suf­
  ficient 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()).
  --end note]

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

  Effects:
    Alters the stream position within one of the  controlled  sequences,
    if possible, as indicated in Table 17:

                       Table 17--seekoff positioning

  +----------------------------------------------------------------------------------+
  |         Conditions                                  Result                       |
  +----------------------------------------------------------------------------------+
  |(which & basic_ios::in)  != 0   positions the input sequence                      |
  +----------------------------------------------------------------------------------+
  |(which & basic_ios::out) != 0   positions the output sequence                     |
  +----------------------------------------------------------------------------------+
  |Otherwise,                                                                        |
  |(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 18:

                         Table 18--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

    possible.  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 one of the controlled sequences,
    if possible, 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  the  function positions neither sequence, the positioning opera­
    tion fails.

4 For a sequence to be positionedif its next pointer (either  gptr()  or
  pptr())  is  a  null pointer, the positioning operation fails.  Other­
  wise, the function determines newoff from sp.offset():

  --If newoff is an invalid stream position, has a  negative  value,  or
    has  a  value  greater than (xend - xbeg), the positioning operation
    fails.

  --Otherwise, the function adds newoff to the  beginning  pointer  xbeg
    and stores the result in 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.

  27.7.2  Template class basic_istringstream         [lib.istringstream]
  namespace std {
    template <class charT, class traits = ios_traits<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>& str,
                                   ios_base::openmode which = ios_base::in);
    // _lib.istringstream.members_ Members:
      basic_stringbuf<charT,traits>* rdbuf() const;

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

1 The  class  basic_istringstream<charT,traits> supports reading objects
  of class basic_string<charT,traits>.  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.

  27.7.2.1  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>(which))
    (_lib.stringbuf.cons_).

  explicit basic_istringstream(const basic_string<charT>& 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>(str,       which))
    (_lib.stringbuf.cons_).

  27.7.2.2  Member functions                 [lib.istringstream.members]

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

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

  basic_string<charT> str() const;

  Returns:
    rdbuf()->str().

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

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

  27.7.2.3  Class basic_ostringstream                [lib.ostringstream]
  namespace std {
    template <class charT, class traits = ios_traits<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>& str,
                                   ios_base::openmode which = ios_base::out);
      virtual ~basic_ostringstream();
    // _lib.ostringstream.members_ Members:
      basic_stringbuf<charT,traits>* rdbuf() const;
      basic_string<charT> str() const;
      void                str(const basic_string<charT>& s);
    private:
  //  basic_stringbuf<charT,traits> sb;   exposition only
    };
  }

1 The  class  basic_ostringstream<charT,traits> supports writing objects
  of class basic_string<charT,traits>.  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.

  27.7.2.4  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>(which)) (_lib.stringbuf.cons_).

  explicit basic_ostringstream(const basic_string<charT>& 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>(str,       which))

    (_lib.stringbuf.cons_).

  27.7.2.5  Member functions                 [lib.ostringstream.members]

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

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

  basic_string<charT> str() const;

  Returns:
    rdbuf()->str().

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

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

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

  27.8.1  File streams                                    [lib.fstreams]

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

  Header <fstream> synopsis

  #include <streambuf>
  #include <istream>
  #include <ostream>

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

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

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

2 In this subclause, the type name  FILE  is  a  synonym  for  the  type
  FILE.43)

  --File  A File provides an external source/sink stream whose underlaid
    character type is char (byte).44)

  --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-
    oriented  filebuf,  namely  wfilebuf  should  convert wide character
    sequences.  Because of  necessity  of  the  conversion  between  the
    external source/sink streams and wide character sequences.

  27.8.1.1  Template class basic_filebuf                   [lib.filebuf]
  namespace std {
    template <class charT, class traits = ios_traits<charT> >
    class basic_filebuf : 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.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 pbackfail(int_type c = traits::eof());
      virtual int_type overflow (int_type c = traits::eof());

  _________________________
  43) FILE is defined in <cstdio> (_lib.c.files_).
  44) 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.

      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  or  for  update,  the  input
    sequence cannot be read.

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

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

4 In  order to support file I/O and multibyte/wide character conversion,
  conversions are performed using getloc().  Specifically:

  --when input is performed, bytes are read from the file and  converted
    to charT ``as if'' by using
    getloc().use<codecvt<char,charT,ios_traits::state_type> >()

  --when output is performed, charT's are converted to char ``as if'' by
    using
    getloc().use<codecvt<charT,char,ios_traits::state_type> >().

  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 the associated file is available and open.

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

  Effects:
    If  is_open()  ==  false,  returns a null pointer.  Otherwise, calls
    basic_streambuf<charT,traits>::basic_streambuf()
    (_lib.streambuf.cons_).
    It  then  opens  a file, if possible, whose name is the NTBS s (``as
    if'' by calling ::fopen(s,modstr)).
    [Note: The NTBS modstr is determined from mode &  ~ios_base::ate  as
    indicated in Table 19:

                         Table 19--File open modes

               +---------------------------------------------+
               |        ios_base            stdio equivalent |
               |        Value(s)                             |
               +---------------------------------------------+
               |in                          "r"              |
               |out | trunc                 "w"              |
               |out | app                   "a"              |
               |in | out                    "r+"             |
               |in | binary                 "rb"             |
               |out | trunc | binary        "wb"             |
               |out | app | binary          "ab"             |
               |in | out                    "r+              |
               |in | out | trunc            "w+"             |
               |in | out | app              "a+"             |
               |in | out | binary           "r+b"            |
               |in | out | trunc | binary   "w+b"            |
               |in | out | app | binary     "a+b"            |
               +---------------------------------------------+
     --end note]

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)).45)

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();

  Effects:
    If is_open() == false, returns a null  pointer.   Otherwise,  closes
    the file (``as if'' by calling ::fclose(file)).46)
  Returns:
    this on success, a null pointer otherwise.
  Postcondition:
    is_open() == false.

  27.8.1.4  Overridden virtual functions          [lib.filebuf.virtuals]

  int showmanyc();

  Requires:
    is_open() == true.
  Effects:
    Behaves      the      same      as      basic_streambuf::showmanyc()
    (_lib.streambuf.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();

  Requires:
    is_open() == true.
  Effects:
    Behaves       according       to       the       description      of
    basic_streambuf<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  (
    from_buf) and then ``as if'' doing

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

          char   from_buf[FSIZE];
          char*  from_end;
          charT  to_buf[TSIZE];
          charT* to_end;
          codecvt_base::result r
              = getloc().use<codecvt<char,charT,typename ios_traits::state_type> >().
                  convert(st,from_buf,from_buf+FSIZE,from_end,
                          to_buf, to_buf+to_size, to_end);
    This must be done in such a way that the class can recover the posi­
    tion ( fpos_t) corresponding to each character  between  to_buf  and
    to_end.  If the value of r indicates that convert() ran out of space
    in to_buf, retry with a larger to_buf.

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

  Requires:
    is_open() == true.
  Effects:
    Puts back the character designated by c to the  input  sequence,  if
    possible, in one of four ways:

  --If  c  != traits::eof() and if the function makes a putback position
    available and if char_type(c) ==  char_type(gptr()[-1]),  decrements
    the next pointer for the input sequence, gptr().

  --If  c  != traits::eof() 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.

  --If c == traits::eof() and if either the input sequence has a putback
    position  available  or the function makes a putback position avail­
    able, decrements the next pointer for the input sequence, gptr().
  Returns:
    traits::eof() to indicate failure, otherwise c.
  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.
  Default behavior:
    Returns traits::eof().

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

  Requires:
    is_open() == true.
  Effects:
    Behaves       according       to       the       description      of

    basic_streambuf<charT,traits>::overflow(c), except that the behavior
    of  ``consuming  characters''  is  performed by first coverting ``as
    if'' by:
          charT* b = pbase();
          charT* p = pptr();
          charT* end;
          char   buf[BSIZE];
          char*  ebuf;
          codecvt_base::result r
              = getloc().use<codecvt<charT, char, ios_traits::state_type> >().
                  convert(st,b(),p(),end,buf,buf+BSIZE,ebuf);
    and then

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

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

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

  --Otherwise  output  from  buf  to ebuf, 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::eof() to indicate failure.  If is_open() == false, the func­
    tion always fails.

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

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

  Requires:
    is_open() == true.
  Effects:
    The current state is determined as follows: If the the  last  opera­
    tion  was overflow(), the current state is obtained by combining the
    shiftstate contained in st with the current position  (  fpos_t)  of
    the file.  If the last operation was underflow(), the shiftstate and
    file position are determined (according to whatever means they  were
    saved by underflow()) as corresponding to pptr().
    Then, alters the stream position within the controlled sequences, if
    possible, as described below.
    If is_open() == false, the positioning operation fails.   Otherwise,
    repositions  within  the  associated  file  (``as  if''  by  calling
    ::fseek(file,off,whence).47)
  _________________________

    [Note: The function determines one of three values for the  argument
    whence, of type int, as indicated in Table 20:

                         Table 20--seekoff effects

                    +----------------------------------+
                    |  way Value      stdio Equivalent |
                    +----------------------------------+
                    |basic_ios::beg   SEEK_SET         |
                    |basic_ios::cur   SEEK_CUR         |
                    |basic_ios::end   SEEK_END         |
                    +----------------------------------+
     --end note]
    The  function  extracts  the  conversion  state from off by means of
    get_offstate() to reset the rdstate() member.
  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);

  Requires:
    is_open() == true.

  int sync();

  void imbue(const locale& loc);

  Effects:
    Calls  sync()  and if sync() fails, sets a flag and the next call to
    any virtual will fail.

  27.8.1.5  Template class basic_ifstream                 [lib.ifstream]

  _________________________
  47) 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_).

  namespace std {
    template <class charT, class traits = file_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, openmode mode = 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.filebuf.cons_).

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

  Effects:
    Constructs an object of class basic_ifstream, initializing the  base
    class    with    basic_istream(&sb)   and   initializing   sb   with
    basic_filebuf<charT,traits>())                  (_lib.istream.cons_,
    _lib.filebuf.cons_), then calls rdbuf()->open(s,mode).

  27.8.1.7  Member functions                      [lib.ifstream.members]

  explicit 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 = in);

  Effects:
    Calls rdbuf()->open(s,mode).  If is_open() returns false, calls set­
    state(failbit)     (which      may      throw      ios_base::failure
    (_lib.iostate.flags_)).

  void close();

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

  27.8.1.8  Template class basic_ofstream                 [lib.ofstream]
  namespace std {
    template <class charT, class traits = file_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, openmode mode = out);
    // _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.filebuf.cons_).

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

  Effects:
    Constructs an object of class basic_ofstream<charT,traits>, initial­
    izing the base class with  basic_ostream(&sb)  and  initializing  sb
    with       basic_filebuf<charT,traits>())       (_lib.ostream.cons_,
    _lib.filebuf.cons_), then calls rdbuf()->open(s, mode).

  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).  If is_open() is then false, calls set­
    state(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_)).

  27.8.2  C Library files                                  [lib.c.files]

1 Headers <cstdio>, and <cwchar>.

                    Table 20--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    tmpfile  |
  |fclose         fopen           fseek      perror            scanf     tmpnam   |
  |feof           fprintf         fsetpos    printf            setbuf    ungetc   |
  |ferror         fputc           ftell      putc              setvbuf   vprintf  |
  |fflush         fputs           fwrite     puts              sprintf   vprintf  |
  |fgetc          fread           getc       remove            sscanf    vsprintf |
  |fgetpos        freopen         getchar    rename            tmpfile            |
  +-------------------------------------------------------------------------------+

                    Table 20--Header <cwchar> synopsis

  +------------------------------------------------------------------------+
  |  Type                               Name(s)                            |
  +------------------------------------------------------------------------+
  |Macros:    NULL <cwchar>   WCHAR_MAX   WCHAR_MIN   WEOF <cwchar>        |
  +------------------------------------------------------------------------+
  |Types:     mbstate_t       wint_t <cwchar>                              |
  +------------------------------------------------------------------------+
  |Struct:    tm <cwchar>                                                  |
  +------------------------------------------------------------------------+
  |Functions:                                                              |
  |btowc      getwchar        ungetwc     wcscpy      wcsrtombs   wmemchr  |
  |fgetwc     mbrlen          vfwprintf   wcscspn     wcsspn      wmemcmp  |
  |fgetws     mbrtowc         vswprintf   wcsftime    wcsstr      wmemcpy  |
  |fputwc     mbsinit         vwprintf    wcslen      wcstod      wmemmove |
  |fputws     mbsrtowcs       wcrtomb     wcsncat     wcstok      wmemset  |
  |fwide      putwc           wcscat      wcsncmp     wcstol      wprintf  |
  |fwprintf   putwchar        wcschr      wcsncpy     wcstoul     wscanf   |
  |fwscanf    swprintf        wcscmp      wcspbrk     wcsxfrm              |
  |getwc      swscanf         wcscoll     wcsrchr     wctob                |
  +------------------------------------------------------------------------+

2 The contents are the same as the Standard C library, except that  none
  of the headers defines wchar_t.

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