libstdc++
streambuf
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1 // Stream buffer classes -*- C++ -*-
2 
3 // Copyright (C) 1997-2020 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
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22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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24 
25 /** @file include/streambuf
26  * This is a Standard C++ Library header.
27  */
28 
29 //
30 // ISO C++ 14882: 27.5 Stream buffers
31 //
32 
33 #ifndef _GLIBXX_STREAMBUF
34 #define _GLIBXX_STREAMBUF 1
35 
36 #pragma GCC system_header
37 
38 #include <bits/c++config.h>
39 #include <iosfwd>
40 #include <bits/localefwd.h>
41 #include <bits/ios_base.h>
42 #include <bits/cpp_type_traits.h>
43 #include <ext/type_traits.h>
44 
45 namespace std _GLIBCXX_VISIBILITY(default)
46 {
47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
48 
49 #define _IsUnused __attribute__ ((__unused__))
50 
51  template<typename _CharT, typename _Traits>
52  streamsize
53  __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
54  basic_streambuf<_CharT, _Traits>*, bool&);
55 
56  /**
57  * @brief The actual work of input and output (interface).
58  * @ingroup io
59  *
60  * @tparam _CharT Type of character stream.
61  * @tparam _Traits Traits for character type, defaults to
62  * char_traits<_CharT>.
63  *
64  * This is a base class. Derived stream buffers each control a
65  * pair of character sequences: one for input, and one for output.
66  *
67  * Section [27.5.1] of the standard describes the requirements and
68  * behavior of stream buffer classes. That section (three paragraphs)
69  * is reproduced here, for simplicity and accuracy.
70  *
71  * -# Stream buffers can impose various constraints on the sequences
72  * they control. Some constraints are:
73  * - The controlled input sequence can be not readable.
74  * - The controlled output sequence can be not writable.
75  * - The controlled sequences can be associated with the contents of
76  * other representations for character sequences, such as external
77  * files.
78  * - The controlled sequences can support operations @e directly to or
79  * from associated sequences.
80  * - The controlled sequences can impose limitations on how the
81  * program can read characters from a sequence, write characters to
82  * a sequence, put characters back into an input sequence, or alter
83  * the stream position.
84  * .
85  * -# Each sequence is characterized by three pointers which, if non-null,
86  * all point into the same @c charT array object. The array object
87  * represents, at any moment, a (sub)sequence of characters from the
88  * sequence. Operations performed on a sequence alter the values
89  * stored in these pointers, perform reads and writes directly to or
90  * from associated sequences, and alter <em>the stream position</em> and
91  * conversion state as needed to maintain this subsequence relationship.
92  * The three pointers are:
93  * - the <em>beginning pointer</em>, or lowest element address in the
94  * array (called @e xbeg here);
95  * - the <em>next pointer</em>, or next element address that is a
96  * current candidate for reading or writing (called @e xnext here);
97  * - the <em>end pointer</em>, or first element address beyond the
98  * end of the array (called @e xend here).
99  * .
100  * -# The following semantic constraints shall always apply for any set
101  * of three pointers for a sequence, using the pointer names given
102  * immediately above:
103  * - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
104  * also be non-null pointers into the same @c charT array, as
105  * described above; otherwise, @e xbeg and @e xend shall also be null.
106  * - If @e xnext is not a null pointer and @e xnext < @e xend for an
107  * output sequence, then a <em>write position</em> is available.
108  * In this case, @e *xnext shall be assignable as the next element
109  * to write (to put, or to store a character value, into the sequence).
110  * - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
111  * input sequence, then a <em>putback position</em> is available.
112  * In this case, @e xnext[-1] shall have a defined value and is the
113  * next (preceding) element to store a character that is put back
114  * into the input sequence.
115  * - If @e xnext is not a null pointer and @e xnext< @e xend for an
116  * input sequence, then a <em>read position</em> is available.
117  * In this case, @e *xnext shall have a defined value and is the
118  * next element to read (to get, or to obtain a character value,
119  * from the sequence).
120  */
121  template<typename _CharT, typename _Traits>
122  class basic_streambuf
123  {
124  public:
125  ///@{
126  /**
127  * These are standard types. They permit a standardized way of
128  * referring to names of (or names dependent on) the template
129  * parameters, which are specific to the implementation.
130  */
131  typedef _CharT char_type;
132  typedef _Traits traits_type;
133  typedef typename traits_type::int_type int_type;
134  typedef typename traits_type::pos_type pos_type;
135  typedef typename traits_type::off_type off_type;
136  ///@}
137 
138  ///@{
139  /// This is a non-standard type.
140  typedef basic_streambuf<char_type, traits_type> __streambuf_type;
141  ///@}
142 
143  friend class basic_ios<char_type, traits_type>;
144  friend class basic_istream<char_type, traits_type>;
145  friend class basic_ostream<char_type, traits_type>;
146  friend class istreambuf_iterator<char_type, traits_type>;
147  friend class ostreambuf_iterator<char_type, traits_type>;
148 
149  friend streamsize
150  __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&);
151 
152  template<bool _IsMove, typename _CharT2>
153  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
154  _CharT2*>::__type
155  __copy_move_a2(istreambuf_iterator<_CharT2>,
156  istreambuf_iterator<_CharT2>, _CharT2*);
157 
158  template<typename _CharT2>
159  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
160  istreambuf_iterator<_CharT2> >::__type
161  find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
162  const _CharT2&);
163 
164  template<typename _CharT2, typename _Distance>
165  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
166  void>::__type
167  advance(istreambuf_iterator<_CharT2>&, _Distance);
168 
169  template<typename _CharT2, typename _Traits2>
170  friend basic_istream<_CharT2, _Traits2>&
171  operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
172 
173  template<typename _CharT2, typename _Traits2, typename _Alloc>
174  friend basic_istream<_CharT2, _Traits2>&
175  operator>>(basic_istream<_CharT2, _Traits2>&,
176  basic_string<_CharT2, _Traits2, _Alloc>&);
177 
178  template<typename _CharT2, typename _Traits2, typename _Alloc>
179  friend basic_istream<_CharT2, _Traits2>&
180  getline(basic_istream<_CharT2, _Traits2>&,
181  basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
182 
183  protected:
184  /*
185  * This is based on _IO_FILE, just reordered to be more consistent,
186  * and is intended to be the most minimal abstraction for an
187  * internal buffer.
188  * - get == input == read
189  * - put == output == write
190  */
191  char_type* _M_in_beg; ///< Start of get area.
192  char_type* _M_in_cur; ///< Current read area.
193  char_type* _M_in_end; ///< End of get area.
194  char_type* _M_out_beg; ///< Start of put area.
195  char_type* _M_out_cur; ///< Current put area.
196  char_type* _M_out_end; ///< End of put area.
197 
198  /// Current locale setting.
199  locale _M_buf_locale;
200 
201  public:
202  /// Destructor deallocates no buffer space.
203  virtual
204  ~basic_streambuf()
205  { }
206 
207  // [27.5.2.2.1] locales
208  /**
209  * @brief Entry point for imbue().
210  * @param __loc The new locale.
211  * @return The previous locale.
212  *
213  * Calls the derived imbue(__loc).
214  */
215  locale
216  pubimbue(const locale& __loc)
217  {
218  locale __tmp(this->getloc());
219  this->imbue(__loc);
220  _M_buf_locale = __loc;
221  return __tmp;
222  }
223 
224  /**
225  * @brief Locale access.
226  * @return The current locale in effect.
227  *
228  * If pubimbue(loc) has been called, then the most recent @c loc
229  * is returned. Otherwise the global locale in effect at the time
230  * of construction is returned.
231  */
232  locale
233  getloc() const
234  { return _M_buf_locale; }
235 
236  // [27.5.2.2.2] buffer management and positioning
237  ///@{
238  /**
239  * @brief Entry points for derived buffer functions.
240  *
241  * The public versions of @c pubfoo dispatch to the protected
242  * derived @c foo member functions, passing the arguments (if any)
243  * and returning the result unchanged.
244  */
245  basic_streambuf*
246  pubsetbuf(char_type* __s, streamsize __n)
247  { return this->setbuf(__s, __n); }
248 
249  /**
250  * @brief Alters the stream position.
251  * @param __off Offset.
252  * @param __way Value for ios_base::seekdir.
253  * @param __mode Value for ios_base::openmode.
254  *
255  * Calls virtual seekoff function.
256  */
257  pos_type
258  pubseekoff(off_type __off, ios_base::seekdir __way,
259  ios_base::openmode __mode = ios_base::in | ios_base::out)
260  { return this->seekoff(__off, __way, __mode); }
261 
262  /**
263  * @brief Alters the stream position.
264  * @param __sp Position
265  * @param __mode Value for ios_base::openmode.
266  *
267  * Calls virtual seekpos function.
268  */
269  pos_type
270  pubseekpos(pos_type __sp,
271  ios_base::openmode __mode = ios_base::in | ios_base::out)
272  { return this->seekpos(__sp, __mode); }
273 
274  /**
275  * @brief Calls virtual sync function.
276  */
277  int
278  pubsync() { return this->sync(); }
279  ///@}
280 
281  // [27.5.2.2.3] get area
282  /**
283  * @brief Looking ahead into the stream.
284  * @return The number of characters available.
285  *
286  * If a read position is available, returns the number of characters
287  * available for reading before the buffer must be refilled.
288  * Otherwise returns the derived @c showmanyc().
289  */
290  streamsize
291  in_avail()
292  {
293  const streamsize __ret = this->egptr() - this->gptr();
294  return __ret ? __ret : this->showmanyc();
295  }
296 
297  /**
298  * @brief Getting the next character.
299  * @return The next character, or eof.
300  *
301  * Calls @c sbumpc(), and if that function returns
302  * @c traits::eof(), so does this function. Otherwise, @c sgetc().
303  */
304  int_type
305  snextc()
306  {
307  int_type __ret = traits_type::eof();
308  if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(),
309  __ret), true))
310  __ret = this->sgetc();
311  return __ret;
312  }
313 
314  /**
315  * @brief Getting the next character.
316  * @return The next character, or eof.
317  *
318  * If the input read position is available, returns that character
319  * and increments the read pointer, otherwise calls and returns
320  * @c uflow().
321  */
322  int_type
323  sbumpc()
324  {
325  int_type __ret;
326  if (__builtin_expect(this->gptr() < this->egptr(), true))
327  {
328  __ret = traits_type::to_int_type(*this->gptr());
329  this->gbump(1);
330  }
331  else
332  __ret = this->uflow();
333  return __ret;
334  }
335 
336  /**
337  * @brief Getting the next character.
338  * @return The next character, or eof.
339  *
340  * If the input read position is available, returns that character,
341  * otherwise calls and returns @c underflow(). Does not move the
342  * read position after fetching the character.
343  */
344  int_type
345  sgetc()
346  {
347  int_type __ret;
348  if (__builtin_expect(this->gptr() < this->egptr(), true))
349  __ret = traits_type::to_int_type(*this->gptr());
350  else
351  __ret = this->underflow();
352  return __ret;
353  }
354 
355  /**
356  * @brief Entry point for xsgetn.
357  * @param __s A buffer area.
358  * @param __n A count.
359  *
360  * Returns xsgetn(__s,__n). The effect is to fill @a __s[0] through
361  * @a __s[__n-1] with characters from the input sequence, if possible.
362  */
363  streamsize
364  sgetn(char_type* __s, streamsize __n)
365  { return this->xsgetn(__s, __n); }
366 
367  // [27.5.2.2.4] putback
368  /**
369  * @brief Pushing characters back into the input stream.
370  * @param __c The character to push back.
371  * @return The previous character, if possible.
372  *
373  * Similar to sungetc(), but @a __c is pushed onto the stream
374  * instead of <em>the previous character.</em> If successful,
375  * the next character fetched from the input stream will be @a
376  * __c.
377  */
378  int_type
379  sputbackc(char_type __c)
380  {
381  int_type __ret;
382  const bool __testpos = this->eback() < this->gptr();
383  if (__builtin_expect(!__testpos ||
384  !traits_type::eq(__c, this->gptr()[-1]), false))
385  __ret = this->pbackfail(traits_type::to_int_type(__c));
386  else
387  {
388  this->gbump(-1);
389  __ret = traits_type::to_int_type(*this->gptr());
390  }
391  return __ret;
392  }
393 
394  /**
395  * @brief Moving backwards in the input stream.
396  * @return The previous character, if possible.
397  *
398  * If a putback position is available, this function decrements
399  * the input pointer and returns that character. Otherwise,
400  * calls and returns pbackfail(). The effect is to @a unget
401  * the last character @a gotten.
402  */
403  int_type
404  sungetc()
405  {
406  int_type __ret;
407  if (__builtin_expect(this->eback() < this->gptr(), true))
408  {
409  this->gbump(-1);
410  __ret = traits_type::to_int_type(*this->gptr());
411  }
412  else
413  __ret = this->pbackfail();
414  return __ret;
415  }
416 
417  // [27.5.2.2.5] put area
418  /**
419  * @brief Entry point for all single-character output functions.
420  * @param __c A character to output.
421  * @return @a __c, if possible.
422  *
423  * One of two public output functions.
424  *
425  * If a write position is available for the output sequence (i.e.,
426  * the buffer is not full), stores @a __c in that position, increments
427  * the position, and returns @c traits::to_int_type(__c). If a write
428  * position is not available, returns @c overflow(__c).
429  */
430  int_type
431  sputc(char_type __c)
432  {
433  int_type __ret;
434  if (__builtin_expect(this->pptr() < this->epptr(), true))
435  {
436  *this->pptr() = __c;
437  this->pbump(1);
438  __ret = traits_type::to_int_type(__c);
439  }
440  else
441  __ret = this->overflow(traits_type::to_int_type(__c));
442  return __ret;
443  }
444 
445  /**
446  * @brief Entry point for all single-character output functions.
447  * @param __s A buffer read area.
448  * @param __n A count.
449  *
450  * One of two public output functions.
451  *
452  *
453  * Returns xsputn(__s,__n). The effect is to write @a __s[0] through
454  * @a __s[__n-1] to the output sequence, if possible.
455  */
456  streamsize
457  sputn(const char_type* __s, streamsize __n)
458  { return this->xsputn(__s, __n); }
459 
460  protected:
461  /**
462  * @brief Base constructor.
463  *
464  * Only called from derived constructors, and sets up all the
465  * buffer data to zero, including the pointers described in the
466  * basic_streambuf class description. Note that, as a result,
467  * - the class starts with no read nor write positions available,
468  * - this is not an error
469  */
470  basic_streambuf()
471  : _M_in_beg(0), _M_in_cur(0), _M_in_end(0),
472  _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
473  _M_buf_locale(locale())
474  { }
475 
476  // [27.5.2.3.1] get area access
477  ///@{
478  /**
479  * @brief Access to the get area.
480  *
481  * These functions are only available to other protected functions,
482  * including derived classes.
483  *
484  * - eback() returns the beginning pointer for the input sequence
485  * - gptr() returns the next pointer for the input sequence
486  * - egptr() returns the end pointer for the input sequence
487  */
488  char_type*
489  eback() const { return _M_in_beg; }
490 
491  char_type*
492  gptr() const { return _M_in_cur; }
493 
494  char_type*
495  egptr() const { return _M_in_end; }
496  ///@}
497 
498  /**
499  * @brief Moving the read position.
500  * @param __n The delta by which to move.
501  *
502  * This just advances the read position without returning any data.
503  */
504  void
505  gbump(int __n) { _M_in_cur += __n; }
506 
507  /**
508  * @brief Setting the three read area pointers.
509  * @param __gbeg A pointer.
510  * @param __gnext A pointer.
511  * @param __gend A pointer.
512  * @post @a __gbeg == @c eback(), @a __gnext == @c gptr(), and
513  * @a __gend == @c egptr()
514  */
515  void
516  setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
517  {
518  _M_in_beg = __gbeg;
519  _M_in_cur = __gnext;
520  _M_in_end = __gend;
521  }
522 
523  // [27.5.2.3.2] put area access
524  ///@{
525  /**
526  * @brief Access to the put area.
527  *
528  * These functions are only available to other protected functions,
529  * including derived classes.
530  *
531  * - pbase() returns the beginning pointer for the output sequence
532  * - pptr() returns the next pointer for the output sequence
533  * - epptr() returns the end pointer for the output sequence
534  */
535  char_type*
536  pbase() const { return _M_out_beg; }
537 
538  char_type*
539  pptr() const { return _M_out_cur; }
540 
541  char_type*
542  epptr() const { return _M_out_end; }
543  ///@}
544 
545  /**
546  * @brief Moving the write position.
547  * @param __n The delta by which to move.
548  *
549  * This just advances the write position without returning any data.
550  */
551  void
552  pbump(int __n) { _M_out_cur += __n; }
553 
554  /**
555  * @brief Setting the three write area pointers.
556  * @param __pbeg A pointer.
557  * @param __pend A pointer.
558  * @post @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and
559  * @a __pend == @c epptr()
560  */
561  void
562  setp(char_type* __pbeg, char_type* __pend)
563  {
564  _M_out_beg = _M_out_cur = __pbeg;
565  _M_out_end = __pend;
566  }
567 
568  // [27.5.2.4] virtual functions
569  // [27.5.2.4.1] locales
570  /**
571  * @brief Changes translations.
572  * @param __loc A new locale.
573  *
574  * Translations done during I/O which depend on the current
575  * locale are changed by this call. The standard adds,
576  * <em>Between invocations of this function a class derived
577  * from streambuf can safely cache results of calls to locale
578  * functions and to members of facets so obtained.</em>
579  *
580  * @note Base class version does nothing.
581  */
582  virtual void
583  imbue(const locale& __loc _IsUnused)
584  { }
585 
586  // [27.5.2.4.2] buffer management and positioning
587  /**
588  * @brief Manipulates the buffer.
589  *
590  * Each derived class provides its own appropriate behavior. See
591  * the next-to-last paragraph of
592  * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
593  * for more on this function.
594  *
595  * @note Base class version does nothing, returns @c this.
596  */
597  virtual basic_streambuf<char_type,_Traits>*
598  setbuf(char_type*, streamsize)
599  { return this; }
600 
601  /**
602  * @brief Alters the stream positions.
603  *
604  * Each derived class provides its own appropriate behavior.
605  * @note Base class version does nothing, returns a @c pos_type
606  * that represents an invalid stream position.
607  */
608  virtual pos_type
609  seekoff(off_type, ios_base::seekdir,
610  ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
611  { return pos_type(off_type(-1)); }
612 
613  /**
614  * @brief Alters the stream positions.
615  *
616  * Each derived class provides its own appropriate behavior.
617  * @note Base class version does nothing, returns a @c pos_type
618  * that represents an invalid stream position.
619  */
620  virtual pos_type
621  seekpos(pos_type,
622  ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
623  { return pos_type(off_type(-1)); }
624 
625  /**
626  * @brief Synchronizes the buffer arrays with the controlled sequences.
627  * @return -1 on failure.
628  *
629  * Each derived class provides its own appropriate behavior,
630  * including the definition of @a failure.
631  * @note Base class version does nothing, returns zero.
632  */
633  virtual int
634  sync() { return 0; }
635 
636  // [27.5.2.4.3] get area
637  /**
638  * @brief Investigating the data available.
639  * @return An estimate of the number of characters available in the
640  * input sequence, or -1.
641  *
642  * <em>If it returns a positive value, then successive calls to
643  * @c underflow() will not return @c traits::eof() until at
644  * least that number of characters have been supplied. If @c
645  * showmanyc() returns -1, then calls to @c underflow() or @c
646  * uflow() will fail.</em> [27.5.2.4.3]/1
647  *
648  * @note Base class version does nothing, returns zero.
649  * @note The standard adds that <em>the intention is not only that the
650  * calls [to underflow or uflow] will not return @c eof() but
651  * that they will return immediately.</em>
652  * @note The standard adds that <em>the morphemes of @c showmanyc are
653  * @b es-how-many-see, not @b show-manic.</em>
654  */
655  virtual streamsize
656  showmanyc() { return 0; }
657 
658  /**
659  * @brief Multiple character extraction.
660  * @param __s A buffer area.
661  * @param __n Maximum number of characters to assign.
662  * @return The number of characters assigned.
663  *
664  * Fills @a __s[0] through @a __s[__n-1] with characters from the input
665  * sequence, as if by @c sbumpc(). Stops when either @a __n characters
666  * have been copied, or when @c traits::eof() would be copied.
667  *
668  * It is expected that derived classes provide a more efficient
669  * implementation by overriding this definition.
670  */
671  virtual streamsize
672  xsgetn(char_type* __s, streamsize __n);
673 
674  /**
675  * @brief Fetches more data from the controlled sequence.
676  * @return The first character from the <em>pending sequence</em>.
677  *
678  * Informally, this function is called when the input buffer is
679  * exhausted (or does not exist, as buffering need not actually be
680  * done). If a buffer exists, it is @a refilled. In either case, the
681  * next available character is returned, or @c traits::eof() to
682  * indicate a null pending sequence.
683  *
684  * For a formal definition of the pending sequence, see a good text
685  * such as Langer & Kreft, or [27.5.2.4.3]/7-14.
686  *
687  * A functioning input streambuf can be created by overriding only
688  * this function (no buffer area will be used). For an example, see
689  * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html
690  *
691  * @note Base class version does nothing, returns eof().
692  */
693  virtual int_type
694  underflow()
695  { return traits_type::eof(); }
696 
697  /**
698  * @brief Fetches more data from the controlled sequence.
699  * @return The first character from the <em>pending sequence</em>.
700  *
701  * Informally, this function does the same thing as @c underflow(),
702  * and in fact is required to call that function. It also returns
703  * the new character, like @c underflow() does. However, this
704  * function also moves the read position forward by one.
705  */
706  virtual int_type
707  uflow()
708  {
709  int_type __ret = traits_type::eof();
710  const bool __testeof = traits_type::eq_int_type(this->underflow(),
711  __ret);
712  if (!__testeof)
713  {
714  __ret = traits_type::to_int_type(*this->gptr());
715  this->gbump(1);
716  }
717  return __ret;
718  }
719 
720  // [27.5.2.4.4] putback
721  /**
722  * @brief Tries to back up the input sequence.
723  * @param __c The character to be inserted back into the sequence.
724  * @return eof() on failure, <em>some other value</em> on success
725  * @post The constraints of @c gptr(), @c eback(), and @c pptr()
726  * are the same as for @c underflow().
727  *
728  * @note Base class version does nothing, returns eof().
729  */
730  virtual int_type
731  pbackfail(int_type __c _IsUnused = traits_type::eof())
732  { return traits_type::eof(); }
733 
734  // Put area:
735  /**
736  * @brief Multiple character insertion.
737  * @param __s A buffer area.
738  * @param __n Maximum number of characters to write.
739  * @return The number of characters written.
740  *
741  * Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if
742  * by @c sputc(). Stops when either @a n characters have been
743  * copied, or when @c sputc() would return @c traits::eof().
744  *
745  * It is expected that derived classes provide a more efficient
746  * implementation by overriding this definition.
747  */
748  virtual streamsize
749  xsputn(const char_type* __s, streamsize __n);
750 
751  /**
752  * @brief Consumes data from the buffer; writes to the
753  * controlled sequence.
754  * @param __c An additional character to consume.
755  * @return eof() to indicate failure, something else (usually
756  * @a __c, or not_eof())
757  *
758  * Informally, this function is called when the output buffer
759  * is full (or does not exist, as buffering need not actually
760  * be done). If a buffer exists, it is @a consumed, with
761  * <em>some effect</em> on the controlled sequence.
762  * (Typically, the buffer is written out to the sequence
763  * verbatim.) In either case, the character @a c is also
764  * written out, if @a __c is not @c eof().
765  *
766  * For a formal definition of this function, see a good text
767  * such as Langer & Kreft, or [27.5.2.4.5]/3-7.
768  *
769  * A functioning output streambuf can be created by overriding only
770  * this function (no buffer area will be used).
771  *
772  * @note Base class version does nothing, returns eof().
773  */
774  virtual int_type
775  overflow(int_type __c _IsUnused = traits_type::eof())
776  { return traits_type::eof(); }
777 
778 #if _GLIBCXX_USE_DEPRECATED && __cplusplus <= 201402L
779  // Annex D.6 (removed in C++17)
780  public:
781  /**
782  * @brief Tosses a character.
783  *
784  * Advances the read pointer, ignoring the character that would have
785  * been read.
786  *
787  * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
788  */
789  _GLIBCXX_DEPRECATED_SUGGEST("std::basic_streambuf::sbumpc")
790  void
791  stossc()
792  {
793  if (this->gptr() < this->egptr())
794  this->gbump(1);
795  else
796  this->uflow();
797  }
798 #endif
799 
800  // Also used by specializations for char and wchar_t in src.
801  void
802  __safe_gbump(streamsize __n) { _M_in_cur += __n; }
803 
804  void
805  __safe_pbump(streamsize __n) { _M_out_cur += __n; }
806 
807 #if __cplusplus < 201103L
808  private:
809 #else
810  protected:
811 #endif
812  basic_streambuf(const basic_streambuf&);
813 
814  basic_streambuf&
815  operator=(const basic_streambuf&);
816 
817 #if __cplusplus >= 201103L
818  void
819  swap(basic_streambuf& __sb)
820  {
821  std::swap(_M_in_beg, __sb._M_in_beg);
822  std::swap(_M_in_cur, __sb._M_in_cur);
823  std::swap(_M_in_end, __sb._M_in_end);
824  std::swap(_M_out_beg, __sb._M_out_beg);
825  std::swap(_M_out_cur, __sb._M_out_cur);
826  std::swap(_M_out_end, __sb._M_out_end);
827  std::swap(_M_buf_locale, __sb._M_buf_locale);
828  }
829 #endif
830  };
831 
832 #if __cplusplus >= 201103L
833  template<typename _CharT, typename _Traits>
834  std::basic_streambuf<_CharT, _Traits>::
835  basic_streambuf(const basic_streambuf&) = default;
836 
837  template<typename _CharT, typename _Traits>
838  std::basic_streambuf<_CharT, _Traits>&
839  std::basic_streambuf<_CharT, _Traits>::
840  operator=(const basic_streambuf&) = default;
841 #endif
842 
843  // Explicit specialization declarations, defined in src/streambuf.cc.
844  template<>
845  streamsize
846  __copy_streambufs_eof(basic_streambuf<char>* __sbin,
847  basic_streambuf<char>* __sbout, bool& __ineof);
848 #ifdef _GLIBCXX_USE_WCHAR_T
849  template<>
850  streamsize
851  __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
852  basic_streambuf<wchar_t>* __sbout, bool& __ineof);
853 #endif
854 
855 #undef _IsUnused
856 
857 _GLIBCXX_END_NAMESPACE_VERSION
858 } // namespace
859 
860 #include <bits/streambuf.tcc>
861 
862 #endif /* _GLIBCXX_STREAMBUF */