libstdc++-v3/include/std/streambuf

   1 // Stream buffer classes -*- C++ -*-
   2
   3 // Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
   4 // 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
   5 //
   6 // This file is part of the GNU ISO C++ Library.  This library is free
   7 // software; you can redistribute it and/or modify it under the
   8 // terms of the GNU General Public License as published by the
   9 // Free Software Foundation; either version 3, or (at your option)
  10 // any later version.
  11
  12 // This library is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16
  17 // Under Section 7 of GPL version 3, you are granted additional
  18 // permissions described in the GCC Runtime Library Exception, version
  19 // 3.1, as published by the Free Software Foundation.
  20
  21 // You should have received a copy of the GNU General Public License and
  22 // a copy of the GCC Runtime Library Exception along with this program;
  23 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24 // <http://www.gnu.org/licenses/>.
  25
  26 /** @file streambuf
  27  *  This is a Standard C++ Library header.
  28  */
  29
  30 //
  31 // ISO C++ 14882: 27.5  Stream buffers
  32 //
  33
  34 #ifndef _GLIBXX_STREAMBUF
  35 #define _GLIBXX_STREAMBUF 1
  36
  37 #pragma GCC system_header
  38
  39 #include <bits/c++config.h>
  40 #include <iosfwd>
  41 #include <bits/localefwd.h>
  42 #include <bits/ios_base.h>
  43 #include <bits/cpp_type_traits.h>
  44 #include <ext/type_traits.h>
  45
  46 _GLIBCXX_BEGIN_NAMESPACE(std)
  47
  48   template<typename _CharT, typename _Traits>
  49     streamsize
  50     __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
  51                           basic_streambuf<_CharT, _Traits>*, bool&);
  52
  53   /**
  54    *  @brief  The actual work of input and output (interface).
  55    *
  56    *  This is a base class.  Derived stream buffers each control a
  57    *  pair of character sequences:  one for input, and one for output.
  58    *
  59    *  Section [27.5.1] of the standard describes the requirements and
  60    *  behavior of stream buffer classes.  That section (three paragraphs)
  61    *  is reproduced here, for simplicity and accuracy.
  62    *
  63    *  -# Stream buffers can impose various constraints on the sequences
  64    *     they control.  Some constraints are:
  65    *     - The controlled input sequence can be not readable.
  66    *     - The controlled output sequence can be not writable.
  67    *     - The controlled sequences can be associated with the contents of
  68    *       other representations for character sequences, such as external
  69    *       files.
  70    *     - The controlled sequences can support operations @e directly to or
  71    *       from associated sequences.
  72    *     - The controlled sequences can impose limitations on how the
  73    *       program can read characters from a sequence, write characters to
  74    *       a sequence, put characters back into an input sequence, or alter
  75    *       the stream position.
  76    *     .
  77    *  -# Each sequence is characterized by three pointers which, if non-null,
  78    *     all point into the same @c charT array object.  The array object
  79    *     represents, at any moment, a (sub)sequence of characters from the
  80    *     sequence.  Operations performed on a sequence alter the values
  81    *     stored in these pointers, perform reads and writes directly to or
  82    *     from associated sequences, and alter <em>the stream position</em> and
  83    *     conversion state as needed to maintain this subsequence relationship.
  84    *     The three pointers are:
  85    *     - the <em>beginning pointer</em>, or lowest element address in the
  86    *       array (called @e xbeg here);
  87    *     - the <em>next pointer</em>, or next element address that is a
  88    *       current candidate for reading or writing (called @e xnext here);
  89    *     - the <em>end pointer</em>, or first element address beyond the
  90    *       end of the array (called @e xend here).
  91    *     .
  92    *  -# The following semantic constraints shall always apply for any set
  93    *     of three pointers for a sequence, using the pointer names given
  94    *     immediately above:
  95    *     - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
  96    *       also be non-null pointers into the same @c charT array, as
  97    *       described above; otherwise, @e xbeg and @e xend shall also be null.
  98    *     - If @e xnext is not a null pointer and @e xnext < @e xend for an
  99    *       output sequence, then a <em>write position</em> is available.
 100    *       In this case, @e *xnext shall be assignable as the next element
 101    *       to write (to put, or to store a character value, into the sequence).
 102    *     - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
 103    *       input sequence, then a <em>putback position</em> is available.
 104    *       In this case, @e xnext[-1] shall have a defined value and is the
 105    *       next (preceding) element to store a character that is put back
 106    *       into the input sequence.
 107    *     - If @e xnext is not a null pointer and @e xnext< @e xend for an
 108    *       input sequence, then a <em>read position</em> is available.
 109    *       In this case, @e *xnext shall have a defined value and is the
 110    *       next element to read (to get, or to obtain a character value,
 111    *       from the sequence).
 112   */
 113   template<typename _CharT, typename _Traits>
 114     class basic_streambuf
 115     {
 116     public:
 117       //@{
 118       /**
 119        *  These are standard types.  They permit a standardized way of
 120        *  referring to names of (or names dependant on) the template
 121        *  parameters, which are specific to the implementation.
 122       */
 123       typedef _CharT                                    char_type;
 124       typedef _Traits                                   traits_type;
 125       typedef typename traits_type::int_type            int_type;
 126       typedef typename traits_type::pos_type            pos_type;
 127       typedef typename traits_type::off_type            off_type;
 128       //@}
 129
 130       //@{
 131       /// This is a non-standard type.
 132       typedef basic_streambuf<char_type, traits_type>   __streambuf_type;
 133       //@}
 134
 135       friend class basic_ios<char_type, traits_type>;
 136       friend class basic_istream<char_type, traits_type>;
 137       friend class basic_ostream<char_type, traits_type>;
 138       friend class istreambuf_iterator<char_type, traits_type>;
 139       friend class ostreambuf_iterator<char_type, traits_type>;
 140
 141       friend streamsize
 142       __copy_streambufs_eof<>(__streambuf_type*, __streambuf_type*, bool&);
 143
 144       template<bool _IsMove, typename _CharT2>
 145         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
 146                                                _CharT2*>::__type
 147         __copy_move_a2(istreambuf_iterator<_CharT2>,
 148                        istreambuf_iterator<_CharT2>, _CharT2*);
 149
 150       template<typename _CharT2>
 151         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
 152                                   istreambuf_iterator<_CharT2> >::__type
 153         find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
 154              const _CharT2&);
 155
 156       template<typename _CharT2, typename _Traits2>
 157         friend basic_istream<_CharT2, _Traits2>&
 158         operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
 159
 160       template<typename _CharT2, typename _Traits2, typename _Alloc>
 161         friend basic_istream<_CharT2, _Traits2>&
 162         operator>>(basic_istream<_CharT2, _Traits2>&,
 163                    basic_string<_CharT2, _Traits2, _Alloc>&);
 164
 165       template<typename _CharT2, typename _Traits2, typename _Alloc>
 166         friend basic_istream<_CharT2, _Traits2>&
 167         getline(basic_istream<_CharT2, _Traits2>&,
 168                 basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
 169
 170     protected:
 171       //@{
 172       /**
 173        *  This is based on _IO_FILE, just reordered to be more consistent,
 174        *  and is intended to be the most minimal abstraction for an
 175        *  internal buffer.
 176        *  -  get == input == read
 177        *  -  put == output == write
 178       */
 179       char_type*                _M_in_beg;     // Start of get area.
 180       char_type*                _M_in_cur;     // Current read area.
 181       char_type*                _M_in_end;     // End of get area.
 182       char_type*                _M_out_beg;    // Start of put area.
 183       char_type*                _M_out_cur;    // Current put area.
 184       char_type*                _M_out_end;    // End of put area.
 185
 186       /// Current locale setting.
 187       locale                    _M_buf_locale;
 188
 189   public:
 190       /// Destructor deallocates no buffer space.
 191       virtual
 192       ~basic_streambuf()
 193       { }
 194
 195       // [27.5.2.2.1] locales
 196       /**
 197        *  @brief  Entry point for imbue().
 198        *  @param  loc  The new locale.
 199        *  @return  The previous locale.
 200        *
 201        *  Calls the derived imbue(loc).
 202       */
 203       locale
 204       pubimbue(const locale &__loc)
 205       {
 206         locale __tmp(this->getloc());
 207         this->imbue(__loc);
 208         _M_buf_locale = __loc;
 209         return __tmp;
 210       }
 211
 212       /**
 213        *  @brief  Locale access.
 214        *  @return  The current locale in effect.
 215        *
 216        *  If pubimbue(loc) has been called, then the most recent @c loc
 217        *  is returned.  Otherwise the global locale in effect at the time
 218        *  of construction is returned.
 219       */
 220       locale
 221       getloc() const
 222       { return _M_buf_locale; }
 223
 224       // [27.5.2.2.2] buffer management and positioning
 225       //@{
 226       /**
 227        *  @brief  Entry points for derived buffer functions.
 228        *
 229        *  The public versions of @c pubfoo dispatch to the protected
 230        *  derived @c foo member functions, passing the arguments (if any)
 231        *  and returning the result unchanged.
 232       */
 233       __streambuf_type*
 234       pubsetbuf(char_type* __s, streamsize __n)
 235       { return this->setbuf(__s, __n); }
 236
 237       pos_type
 238       pubseekoff(off_type __off, ios_base::seekdir __way,
 239                  ios_base::openmode __mode = ios_base::in | ios_base::out)
 240       { return this->seekoff(__off, __way, __mode); }
 241
 242       pos_type
 243       pubseekpos(pos_type __sp,
 244                  ios_base::openmode __mode = ios_base::in | ios_base::out)
 245       { return this->seekpos(__sp, __mode); }
 246
 247       int
 248       pubsync() { return this->sync(); }
 249       //@}
 250
 251       // [27.5.2.2.3] get area
 252       /**
 253        *  @brief  Looking ahead into the stream.
 254        *  @return  The number of characters available.
 255        *
 256        *  If a read position is available, returns the number of characters
 257        *  available for reading before the buffer must be refilled.
 258        *  Otherwise returns the derived @c showmanyc().
 259       */
 260       streamsize
 261       in_avail()
 262       {
 263         const streamsize __ret = this->egptr() - this->gptr();
 264         return __ret ? __ret : this->showmanyc();
 265       }
 266
 267       /**
 268        *  @brief  Getting the next character.
 269        *  @return  The next character, or eof.
 270        *
 271        *  Calls @c sbumpc(), and if that function returns
 272        *  @c traits::eof(), so does this function.  Otherwise, @c sgetc().
 273       */
 274       int_type
 275       snextc()
 276       {
 277         int_type __ret = traits_type::eof();
 278         if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(),
 279                                                        __ret), true))
 280           __ret = this->sgetc();
 281         return __ret;
 282       }
 283
 284       /**
 285        *  @brief  Getting the next character.
 286        *  @return  The next character, or eof.
 287        *
 288        *  If the input read position is available, returns that character
 289        *  and increments the read pointer, otherwise calls and returns
 290        *  @c uflow().
 291       */
 292       int_type
 293       sbumpc()
 294       {
 295         int_type __ret;
 296         if (__builtin_expect(this->gptr() < this->egptr(), true))
 297           {
 298             __ret = traits_type::to_int_type(*this->gptr());
 299             this->gbump(1);
 300           }
 301         else
 302           __ret = this->uflow();
 303         return __ret;
 304       }
 305
 306       /**
 307        *  @brief  Getting the next character.
 308        *  @return  The next character, or eof.
 309        *
 310        *  If the input read position is available, returns that character,
 311        *  otherwise calls and returns @c underflow().  Does not move the
 312        *  read position after fetching the character.
 313       */
 314       int_type
 315       sgetc()
 316       {
 317         int_type __ret;
 318         if (__builtin_expect(this->gptr() < this->egptr(), true))
 319           __ret = traits_type::to_int_type(*this->gptr());
 320         else
 321           __ret = this->underflow();
 322         return __ret;
 323       }
 324
 325       /**
 326        *  @brief  Entry point for xsgetn.
 327        *  @param  s  A buffer area.
 328        *  @param  n  A count.
 329        *
 330        *  Returns xsgetn(s,n).  The effect is to fill @a s[0] through
 331        *  @a s[n-1] with characters from the input sequence, if possible.
 332       */
 333       streamsize
 334       sgetn(char_type* __s, streamsize __n)
 335       { return this->xsgetn(__s, __n); }
 336
 337       // [27.5.2.2.4] putback
 338       /**
 339        *  @brief  Pushing characters back into the input stream.
 340        *  @param  c  The character to push back.
 341        *  @return  The previous character, if possible.
 342        *
 343        *  Similar to sungetc(), but @a c is pushed onto the stream
 344        *  instead of <em>the previous character.</em> If successful,
 345        *  the next character fetched from the input stream will be @a
 346        *  c.
 347       */
 348       int_type
 349       sputbackc(char_type __c)
 350       {
 351         int_type __ret;
 352         const bool __testpos = this->eback() < this->gptr();
 353         if (__builtin_expect(!__testpos ||
 354                              !traits_type::eq(__c, this->gptr()[-1]), false))
 355           __ret = this->pbackfail(traits_type::to_int_type(__c));
 356         else
 357           {
 358             this->gbump(-1);
 359             __ret = traits_type::to_int_type(*this->gptr());
 360           }
 361         return __ret;
 362       }
 363
 364       /**
 365        *  @brief  Moving backwards in the input stream.
 366        *  @return  The previous character, if possible.
 367        *
 368        *  If a putback position is available, this function decrements
 369        *  the input pointer and returns that character.  Otherwise,
 370        *  calls and returns pbackfail().  The effect is to @a unget
 371        *  the last character @a gotten.
 372       */
 373       int_type
 374       sungetc()
 375       {
 376         int_type __ret;
 377         if (__builtin_expect(this->eback() < this->gptr(), true))
 378           {
 379             this->gbump(-1);
 380             __ret = traits_type::to_int_type(*this->gptr());
 381           }
 382         else
 383           __ret = this->pbackfail();
 384         return __ret;
 385       }
 386
 387       // [27.5.2.2.5] put area
 388       /**
 389        *  @brief  Entry point for all single-character output functions.
 390        *  @param  c  A character to output.
 391        *  @return  @a c, if possible.
 392        *
 393        *  One of two public output functions.
 394        *
 395        *  If a write position is available for the output sequence (i.e.,
 396        *  the buffer is not full), stores @a c in that position, increments
 397        *  the position, and returns @c traits::to_int_type(c).  If a write
 398        *  position is not available, returns @c overflow(c).
 399       */
 400       int_type
 401       sputc(char_type __c)
 402       {
 403         int_type __ret;
 404         if (__builtin_expect(this->pptr() < this->epptr(), true))
 405           {
 406             *this->pptr() = __c;
 407             this->pbump(1);
 408             __ret = traits_type::to_int_type(__c);
 409           }
 410         else
 411           __ret = this->overflow(traits_type::to_int_type(__c));
 412         return __ret;
 413       }
 414
 415       /**
 416        *  @brief  Entry point for all single-character output functions.
 417        *  @param  s  A buffer read area.
 418        *  @param  n  A count.
 419        *
 420        *  One of two public output functions.
 421        *
 422        *
 423        *  Returns xsputn(s,n).  The effect is to write @a s[0] through
 424        *  @a s[n-1] to the output sequence, if possible.
 425       */
 426       streamsize
 427       sputn(const char_type* __s, streamsize __n)
 428       { return this->xsputn(__s, __n); }
 429
 430     protected:
 431       /**
 432        *  @brief  Base constructor.
 433        *
 434        *  Only called from derived constructors, and sets up all the
 435        *  buffer data to zero, including the pointers described in the
 436        *  basic_streambuf class description.  Note that, as a result,
 437        *  - the class starts with no read nor write positions available,
 438        *  - this is not an error
 439       */
 440       basic_streambuf()
 441       : _M_in_beg(0), _M_in_cur(0), _M_in_end(0),
 442       _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
 443       _M_buf_locale(locale())
 444       { }
 445
 446       // [27.5.2.3.1] get area access
 447       //@{
 448       /**
 449        *  @brief  Access to the get area.
 450        *
 451        *  These functions are only available to other protected functions,
 452        *  including derived classes.
 453        *
 454        *  - eback() returns the beginning pointer for the input sequence
 455        *  - gptr() returns the next pointer for the input sequence
 456        *  - egptr() returns the end pointer for the input sequence
 457       */
 458       char_type*
 459       eback() const { return _M_in_beg; }
 460
 461       char_type*
 462       gptr()  const { return _M_in_cur;  }
 463
 464       char_type*
 465       egptr() const { return _M_in_end; }
 466       //@}
 467
 468       /**
 469        *  @brief  Moving the read position.
 470        *  @param  n  The delta by which to move.
 471        *
 472        *  This just advances the read position without returning any data.
 473       */
 474       void
 475       gbump(int __n) { _M_in_cur += __n; }
 476
 477       /**
 478        *  @brief  Setting the three read area pointers.
 479        *  @param  gbeg  A pointer.
 480        *  @param  gnext  A pointer.
 481        *  @param  gend  A pointer.
 482        *  @post  @a gbeg == @c eback(), @a gnext == @c gptr(), and
 483        *         @a gend == @c egptr()
 484       */
 485       void
 486       setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
 487       {
 488         _M_in_beg = __gbeg;
 489         _M_in_cur = __gnext;
 490         _M_in_end = __gend;
 491       }
 492
 493       // [27.5.2.3.2] put area access
 494       //@{
 495       /**
 496        *  @brief  Access to the put area.
 497        *
 498        *  These functions are only available to other protected functions,
 499        *  including derived classes.
 500        *
 501        *  - pbase() returns the beginning pointer for the output sequence
 502        *  - pptr() returns the next pointer for the output sequence
 503        *  - epptr() returns the end pointer for the output sequence
 504       */
 505       char_type*
 506       pbase() const { return _M_out_beg; }
 507
 508       char_type*
 509       pptr() const { return _M_out_cur; }
 510
 511       char_type*
 512       epptr() const { return _M_out_end; }
 513       //@}
 514
 515       /**
 516        *  @brief  Moving the write position.
 517        *  @param  n  The delta by which to move.
 518        *
 519        *  This just advances the write position without returning any data.
 520       */
 521       void
 522       pbump(int __n) { _M_out_cur += __n; }
 523
 524       /**
 525        *  @brief  Setting the three write area pointers.
 526        *  @param  pbeg  A pointer.
 527        *  @param  pend  A pointer.
 528        *  @post  @a pbeg == @c pbase(), @a pbeg == @c pptr(), and
 529        *         @a pend == @c epptr()
 530       */
 531       void
 532       setp(char_type* __pbeg, char_type* __pend)
 533       {
 534         _M_out_beg = _M_out_cur = __pbeg;
 535         _M_out_end = __pend;
 536       }
 537
 538       // [27.5.2.4] virtual functions
 539       // [27.5.2.4.1] locales
 540       /**
 541        *  @brief  Changes translations.
 542        *  @param  loc  A new locale.
 543        *
 544        *  Translations done during I/O which depend on the current
 545        *  locale are changed by this call.  The standard adds,
 546        *  <em>Between invocations of this function a class derived
 547        *  from streambuf can safely cache results of calls to locale
 548        *  functions and to members of facets so obtained.</em>
 549        *
 550        *  @note  Base class version does nothing.
 551       */
 552       virtual void
 553       imbue(const locale&)
 554       { }
 555
 556       // [27.5.2.4.2] buffer management and positioning
 557       /**
 558        *  @brief  Manipulates the buffer.
 559        *
 560        *  Each derived class provides its own appropriate behavior.  See
 561        *  the next-to-last paragraph of
 562        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25s02.html
 563        *  for more on this function.
 564        *
 565        *  @note  Base class version does nothing, returns @c this.
 566       */
 567       virtual basic_streambuf<char_type,_Traits>*
 568       setbuf(char_type*, streamsize)
 569       { return this; }
 570
 571       /**
 572        *  @brief  Alters the stream positions.
 573        *
 574        *  Each derived class provides its own appropriate behavior.
 575        *  @note  Base class version does nothing, returns a @c pos_type
 576        *         that represents an invalid stream position.
 577       */
 578       virtual pos_type
 579       seekoff(off_type, ios_base::seekdir,
 580               ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
 581       { return pos_type(off_type(-1)); }
 582
 583       /**
 584        *  @brief  Alters the stream positions.
 585        *
 586        *  Each derived class provides its own appropriate behavior.
 587        *  @note  Base class version does nothing, returns a @c pos_type
 588        *         that represents an invalid stream position.
 589       */
 590       virtual pos_type
 591       seekpos(pos_type,
 592               ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
 593       { return pos_type(off_type(-1)); }
 594
 595       /**
 596        *  @brief  Synchronizes the buffer arrays with the controlled sequences.
 597        *  @return  -1 on failure.
 598        *
 599        *  Each derived class provides its own appropriate behavior,
 600        *  including the definition of @a failure.
 601        *  @note  Base class version does nothing, returns zero.
 602       */
 603       virtual int
 604       sync() { return 0; }
 605
 606       // [27.5.2.4.3] get area
 607       /**
 608        *  @brief  Investigating the data available.
 609        *  @return  An estimate of the number of characters available in the
 610        *           input sequence, or -1.
 611        *
 612        *  <em>If it returns a positive value, then successive calls to
 613        *  @c underflow() will not return @c traits::eof() until at
 614        *  least that number of characters have been supplied.  If @c
 615        *  showmanyc() returns -1, then calls to @c underflow() or @c
 616        *  uflow() will fail.</em> [27.5.2.4.3]/1
 617        *
 618        *  @note  Base class version does nothing, returns zero.
 619        *  @note  The standard adds that <em>the intention is not only that the
 620        *         calls [to underflow or uflow] will not return @c eof() but
 621        *         that they will return immediately.</em>
 622        *  @note  The standard adds that <em>the morphemes of @c showmanyc are
 623        *         @b es-how-many-see, not @b show-manic.</em>
 624       */
 625       virtual streamsize
 626       showmanyc() { return 0; }
 627
 628       /**
 629        *  @brief  Multiple character extraction.
 630        *  @param  s  A buffer area.
 631        *  @param  n  Maximum number of characters to assign.
 632        *  @return  The number of characters assigned.
 633        *
 634        *  Fills @a s[0] through @a s[n-1] with characters from the input
 635        *  sequence, as if by @c sbumpc().  Stops when either @a n characters
 636        *  have been copied, or when @c traits::eof() would be copied.
 637        *
 638        *  It is expected that derived classes provide a more efficient
 639        *  implementation by overriding this definition.
 640       */
 641       virtual streamsize
 642       xsgetn(char_type* __s, streamsize __n);
 643
 644       /**
 645        *  @brief  Fetches more data from the controlled sequence.
 646        *  @return  The first character from the <em>pending sequence</em>.
 647        *
 648        *  Informally, this function is called when the input buffer is
 649        *  exhausted (or does not exist, as buffering need not actually be
 650        *  done).  If a buffer exists, it is @a refilled.  In either case, the
 651        *  next available character is returned, or @c traits::eof() to
 652        *  indicate a null pending sequence.
 653        *
 654        *  For a formal definition of the pending sequence, see a good text
 655        *  such as Langer & Kreft, or [27.5.2.4.3]/7-14.
 656        *
 657        *  A functioning input streambuf can be created by overriding only
 658        *  this function (no buffer area will be used).  For an example, see
 659        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25.html
 660        *
 661        *  @note  Base class version does nothing, returns eof().
 662       */
 663       virtual int_type
 664       underflow()
 665       { return traits_type::eof(); }
 666
 667       /**
 668        *  @brief  Fetches more data from the controlled sequence.
 669        *  @return  The first character from the <em>pending sequence</em>.
 670        *
 671        *  Informally, this function does the same thing as @c underflow(),
 672        *  and in fact is required to call that function.  It also returns
 673        *  the new character, like @c underflow() does.  However, this
 674        *  function also moves the read position forward by one.
 675       */
 676       virtual int_type
 677       uflow()
 678       {
 679         int_type __ret = traits_type::eof();
 680         const bool __testeof = traits_type::eq_int_type(this->underflow(),
 681                                                         __ret);
 682         if (!__testeof)
 683           {
 684             __ret = traits_type::to_int_type(*this->gptr());
 685             this->gbump(1);
 686           }
 687         return __ret;
 688       }
 689
 690       // [27.5.2.4.4] putback
 691       /**
 692        *  @brief  Tries to back up the input sequence.
 693        *  @param  c  The character to be inserted back into the sequence.
 694        *  @return  eof() on failure, <em>some other value</em> on success
 695        *  @post  The constraints of @c gptr(), @c eback(), and @c pptr()
 696        *         are the same as for @c underflow().
 697        *
 698        *  @note  Base class version does nothing, returns eof().
 699       */
 700       virtual int_type
 701       pbackfail(int_type /* __c */  = traits_type::eof())
 702       { return traits_type::eof(); }
 703
 704       // Put area:
 705       /**
 706        *  @brief  Multiple character insertion.
 707        *  @param  s  A buffer area.
 708        *  @param  n  Maximum number of characters to write.
 709        *  @return  The number of characters written.
 710        *
 711        *  Writes @a s[0] through @a s[n-1] to the output sequence, as if
 712        *  by @c sputc().  Stops when either @a n characters have been
 713        *  copied, or when @c sputc() would return @c traits::eof().
 714        *
 715        *  It is expected that derived classes provide a more efficient
 716        *  implementation by overriding this definition.
 717       */
 718       virtual streamsize
 719       xsputn(const char_type* __s, streamsize __n);
 720
 721       /**
 722        *  @brief  Consumes data from the buffer; writes to the
 723        *          controlled sequence.
 724        *  @param  c  An additional character to consume.
 725        *  @return  eof() to indicate failure, something else (usually
 726        *           @a c, or not_eof())
 727        *
 728        *  Informally, this function is called when the output buffer
 729        *  is full (or does not exist, as buffering need not actually
 730        *  be done).  If a buffer exists, it is @a consumed, with
 731        *  <em>some effect</em> on the controlled sequence.
 732        *  (Typically, the buffer is written out to the sequence
 733        *  verbatim.)  In either case, the character @a c is also
 734        *  written out, if @a c is not @c eof().
 735        *
 736        *  For a formal definition of this function, see a good text
 737        *  such as Langer & Kreft, or [27.5.2.4.5]/3-7.
 738        *
 739        *  A functioning output streambuf can be created by overriding only
 740        *  this function (no buffer area will be used).
 741        *
 742        *  @note  Base class version does nothing, returns eof().
 743       */
 744       virtual int_type
 745       overflow(int_type /* __c */ = traits_type::eof())
 746       { return traits_type::eof(); }
 747
 748 #if _GLIBCXX_DEPRECATED
 749     // Annex D.6
 750     public:
 751       /**
 752        *  @brief  Tosses a character.
 753        *
 754        *  Advances the read pointer, ignoring the character that would have
 755        *  been read.
 756        *
 757        *  See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
 758        */
 759       void
 760       stossc()
 761       {
 762         if (this->gptr() < this->egptr())
 763           this->gbump(1);
 764         else
 765           this->uflow();
 766       }
 767 #endif
 768
 769     private:
 770       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 771       // Side effect of DR 50.
 772       basic_streambuf(const __streambuf_type& __sb)
 773       : _M_in_beg(__sb._M_in_beg), _M_in_cur(__sb._M_in_cur),
 774       _M_in_end(__sb._M_in_end), _M_out_beg(__sb._M_out_beg),
 775       _M_out_cur(__sb._M_out_cur), _M_out_end(__sb._M_out_cur),
 776       _M_buf_locale(__sb._M_buf_locale)
 777       { }
 778
 779       __streambuf_type&
 780       operator=(const __streambuf_type&) { return *this; };
 781     };
 782
 783   // Explicit specialization declarations, defined in src/streambuf.cc.
 784   template<>
 785     streamsize
 786     __copy_streambufs_eof(basic_streambuf<char>* __sbin,
 787                           basic_streambuf<char>* __sbout, bool& __ineof);
 788 #ifdef _GLIBCXX_USE_WCHAR_T
 789   template<>
 790     streamsize
 791     __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
 792                           basic_streambuf<wchar_t>* __sbout, bool& __ineof);
 793 #endif
 794
 795 _GLIBCXX_END_NAMESPACE
 796
 797 #ifndef _GLIBCXX_EXPORT_TEMPLATE
 798 # include <bits/streambuf.tcc>
 799 #endif
 800
 801 #endif /* _GLIBCXX_STREAMBUF */