libstdc++
streambuf
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1 // Stream buffer classes -*- C++ -*-
2 
3 // Copyright (C) 1997-2015 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
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
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  template<typename _CharT, typename _Traits>
50  streamsize
51  __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
52  basic_streambuf<_CharT, _Traits>*, bool&);
53 
54  /**
55  * @brief The actual work of input and output (interface).
56  * @ingroup io
57  *
58  * @tparam _CharT Type of character stream.
59  * @tparam _Traits Traits for character type, defaults to
60  * char_traits<_CharT>.
61  *
62  * This is a base class. Derived stream buffers each control a
63  * pair of character sequences: one for input, and one for output.
64  *
65  * Section [27.5.1] of the standard describes the requirements and
66  * behavior of stream buffer classes. That section (three paragraphs)
67  * is reproduced here, for simplicity and accuracy.
68  *
69  * -# Stream buffers can impose various constraints on the sequences
70  * they control. Some constraints are:
71  * - The controlled input sequence can be not readable.
72  * - The controlled output sequence can be not writable.
73  * - The controlled sequences can be associated with the contents of
74  * other representations for character sequences, such as external
75  * files.
76  * - The controlled sequences can support operations @e directly to or
77  * from associated sequences.
78  * - The controlled sequences can impose limitations on how the
79  * program can read characters from a sequence, write characters to
80  * a sequence, put characters back into an input sequence, or alter
81  * the stream position.
82  * .
83  * -# Each sequence is characterized by three pointers which, if non-null,
84  * all point into the same @c charT array object. The array object
85  * represents, at any moment, a (sub)sequence of characters from the
86  * sequence. Operations performed on a sequence alter the values
87  * stored in these pointers, perform reads and writes directly to or
88  * from associated sequences, and alter <em>the stream position</em> and
89  * conversion state as needed to maintain this subsequence relationship.
90  * The three pointers are:
91  * - the <em>beginning pointer</em>, or lowest element address in the
92  * array (called @e xbeg here);
93  * - the <em>next pointer</em>, or next element address that is a
94  * current candidate for reading or writing (called @e xnext here);
95  * - the <em>end pointer</em>, or first element address beyond the
96  * end of the array (called @e xend here).
97  * .
98  * -# The following semantic constraints shall always apply for any set
99  * of three pointers for a sequence, using the pointer names given
100  * immediately above:
101  * - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
102  * also be non-null pointers into the same @c charT array, as
103  * described above; otherwise, @e xbeg and @e xend shall also be null.
104  * - If @e xnext is not a null pointer and @e xnext < @e xend for an
105  * output sequence, then a <em>write position</em> is available.
106  * In this case, @e *xnext shall be assignable as the next element
107  * to write (to put, or to store a character value, into the sequence).
108  * - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
109  * input sequence, then a <em>putback position</em> is available.
110  * In this case, @e xnext[-1] shall have a defined value and is the
111  * next (preceding) element to store a character that is put back
112  * into the input sequence.
113  * - If @e xnext is not a null pointer and @e xnext< @e xend for an
114  * input sequence, then a <em>read position</em> is available.
115  * In this case, @e *xnext shall have a defined value and is the
116  * next element to read (to get, or to obtain a character value,
117  * from the sequence).
118  */
119  template<typename _CharT, typename _Traits>
120  class basic_streambuf
121  {
122  public:
123  //@{
124  /**
125  * These are standard types. They permit a standardized way of
126  * referring to names of (or names dependent on) the template
127  * parameters, which are specific to the implementation.
128  */
129  typedef _CharT char_type;
130  typedef _Traits traits_type;
131  typedef typename traits_type::int_type int_type;
132  typedef typename traits_type::pos_type pos_type;
133  typedef typename traits_type::off_type off_type;
134  //@}
135 
136  //@{
137  /// This is a non-standard type.
138  typedef basic_streambuf<char_type, traits_type> __streambuf_type;
139  //@}
140 
141  friend class basic_ios<char_type, traits_type>;
142  friend class basic_istream<char_type, traits_type>;
143  friend class basic_ostream<char_type, traits_type>;
144  friend class istreambuf_iterator<char_type, traits_type>;
145  friend class ostreambuf_iterator<char_type, traits_type>;
146 
147  friend streamsize
148  __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&);
149 
150  template<bool _IsMove, typename _CharT2>
151  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
152  _CharT2*>::__type
153  __copy_move_a2(istreambuf_iterator<_CharT2>,
154  istreambuf_iterator<_CharT2>, _CharT2*);
155 
156  template<typename _CharT2>
157  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
158  istreambuf_iterator<_CharT2> >::__type
159  find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
160  const _CharT2&);
161 
162  template<typename _CharT2, typename _Traits2>
163  friend basic_istream<_CharT2, _Traits2>&
164  operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
165 
166  template<typename _CharT2, typename _Traits2, typename _Alloc>
167  friend basic_istream<_CharT2, _Traits2>&
168  operator>>(basic_istream<_CharT2, _Traits2>&,
169  basic_string<_CharT2, _Traits2, _Alloc>&);
170 
171  template<typename _CharT2, typename _Traits2, typename _Alloc>
172  friend basic_istream<_CharT2, _Traits2>&
173  getline(basic_istream<_CharT2, _Traits2>&,
174  basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
175 
176  protected:
177  /*
178  * This is based on _IO_FILE, just reordered to be more consistent,
179  * and is intended to be the most minimal abstraction for an
180  * internal buffer.
181  * - get == input == read
182  * - put == output == write
183  */
184  char_type* _M_in_beg; ///< Start of get area.
185  char_type* _M_in_cur; ///< Current read area.
186  char_type* _M_in_end; ///< End of get area.
187  char_type* _M_out_beg; ///< Start of put area.
188  char_type* _M_out_cur; ///< Current put area.
189  char_type* _M_out_end; ///< End of put area.
190 
191  /// Current locale setting.
192  locale _M_buf_locale;
193 
194  public:
195  /// Destructor deallocates no buffer space.
196  virtual
197  ~basic_streambuf()
198  { }
199 
200  // [27.5.2.2.1] locales
201  /**
202  * @brief Entry point for imbue().
203  * @param __loc The new locale.
204  * @return The previous locale.
205  *
206  * Calls the derived imbue(__loc).
207  */
208  locale
209  pubimbue(const locale& __loc)
210  {
211  locale __tmp(this->getloc());
212  this->imbue(__loc);
213  _M_buf_locale = __loc;
214  return __tmp;
215  }
216 
217  /**
218  * @brief Locale access.
219  * @return The current locale in effect.
220  *
221  * If pubimbue(loc) has been called, then the most recent @c loc
222  * is returned. Otherwise the global locale in effect at the time
223  * of construction is returned.
224  */
225  locale
226  getloc() const
227  { return _M_buf_locale; }
228 
229  // [27.5.2.2.2] buffer management and positioning
230  //@{
231  /**
232  * @brief Entry points for derived buffer functions.
233  *
234  * The public versions of @c pubfoo dispatch to the protected
235  * derived @c foo member functions, passing the arguments (if any)
236  * and returning the result unchanged.
237  */
238  basic_streambuf*
239  pubsetbuf(char_type* __s, streamsize __n)
240  { return this->setbuf(__s, __n); }
241 
242  /**
243  * @brief Alters the stream position.
244  * @param __off Offset.
245  * @param __way Value for ios_base::seekdir.
246  * @param __mode Value for ios_base::openmode.
247  *
248  * Calls virtual seekoff function.
249  */
250  pos_type
251  pubseekoff(off_type __off, ios_base::seekdir __way,
252  ios_base::openmode __mode = ios_base::in | ios_base::out)
253  { return this->seekoff(__off, __way, __mode); }
254 
255  /**
256  * @brief Alters the stream position.
257  * @param __sp Position
258  * @param __mode Value for ios_base::openmode.
259  *
260  * Calls virtual seekpos function.
261  */
262  pos_type
263  pubseekpos(pos_type __sp,
264  ios_base::openmode __mode = ios_base::in | ios_base::out)
265  { return this->seekpos(__sp, __mode); }
266 
267  /**
268  * @brief Calls virtual sync function.
269  */
270  int
271  pubsync() { return this->sync(); }
272  //@}
273 
274  // [27.5.2.2.3] get area
275  /**
276  * @brief Looking ahead into the stream.
277  * @return The number of characters available.
278  *
279  * If a read position is available, returns the number of characters
280  * available for reading before the buffer must be refilled.
281  * Otherwise returns the derived @c showmanyc().
282  */
283  streamsize
284  in_avail()
285  {
286  const streamsize __ret = this->egptr() - this->gptr();
287  return __ret ? __ret : this->showmanyc();
288  }
289 
290  /**
291  * @brief Getting the next character.
292  * @return The next character, or eof.
293  *
294  * Calls @c sbumpc(), and if that function returns
295  * @c traits::eof(), so does this function. Otherwise, @c sgetc().
296  */
297  int_type
298  snextc()
299  {
300  int_type __ret = traits_type::eof();
301  if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(),
302  __ret), true))
303  __ret = this->sgetc();
304  return __ret;
305  }
306 
307  /**
308  * @brief Getting the next character.
309  * @return The next character, or eof.
310  *
311  * If the input read position is available, returns that character
312  * and increments the read pointer, otherwise calls and returns
313  * @c uflow().
314  */
315  int_type
316  sbumpc()
317  {
318  int_type __ret;
319  if (__builtin_expect(this->gptr() < this->egptr(), true))
320  {
321  __ret = traits_type::to_int_type(*this->gptr());
322  this->gbump(1);
323  }
324  else
325  __ret = this->uflow();
326  return __ret;
327  }
328 
329  /**
330  * @brief Getting the next character.
331  * @return The next character, or eof.
332  *
333  * If the input read position is available, returns that character,
334  * otherwise calls and returns @c underflow(). Does not move the
335  * read position after fetching the character.
336  */
337  int_type
338  sgetc()
339  {
340  int_type __ret;
341  if (__builtin_expect(this->gptr() < this->egptr(), true))
342  __ret = traits_type::to_int_type(*this->gptr());
343  else
344  __ret = this->underflow();
345  return __ret;
346  }
347 
348  /**
349  * @brief Entry point for xsgetn.
350  * @param __s A buffer area.
351  * @param __n A count.
352  *
353  * Returns xsgetn(__s,__n). The effect is to fill @a __s[0] through
354  * @a __s[__n-1] with characters from the input sequence, if possible.
355  */
356  streamsize
357  sgetn(char_type* __s, streamsize __n)
358  { return this->xsgetn(__s, __n); }
359 
360  // [27.5.2.2.4] putback
361  /**
362  * @brief Pushing characters back into the input stream.
363  * @param __c The character to push back.
364  * @return The previous character, if possible.
365  *
366  * Similar to sungetc(), but @a __c is pushed onto the stream
367  * instead of <em>the previous character.</em> If successful,
368  * the next character fetched from the input stream will be @a
369  * __c.
370  */
371  int_type
372  sputbackc(char_type __c)
373  {
374  int_type __ret;
375  const bool __testpos = this->eback() < this->gptr();
376  if (__builtin_expect(!__testpos ||
377  !traits_type::eq(__c, this->gptr()[-1]), false))
378  __ret = this->pbackfail(traits_type::to_int_type(__c));
379  else
380  {
381  this->gbump(-1);
382  __ret = traits_type::to_int_type(*this->gptr());
383  }
384  return __ret;
385  }
386 
387  /**
388  * @brief Moving backwards in the input stream.
389  * @return The previous character, if possible.
390  *
391  * If a putback position is available, this function decrements
392  * the input pointer and returns that character. Otherwise,
393  * calls and returns pbackfail(). The effect is to @a unget
394  * the last character @a gotten.
395  */
396  int_type
397  sungetc()
398  {
399  int_type __ret;
400  if (__builtin_expect(this->eback() < this->gptr(), true))
401  {
402  this->gbump(-1);
403  __ret = traits_type::to_int_type(*this->gptr());
404  }
405  else
406  __ret = this->pbackfail();
407  return __ret;
408  }
409 
410  // [27.5.2.2.5] put area
411  /**
412  * @brief Entry point for all single-character output functions.
413  * @param __c A character to output.
414  * @return @a __c, if possible.
415  *
416  * One of two public output functions.
417  *
418  * If a write position is available for the output sequence (i.e.,
419  * the buffer is not full), stores @a __c in that position, increments
420  * the position, and returns @c traits::to_int_type(__c). If a write
421  * position is not available, returns @c overflow(__c).
422  */
423  int_type
424  sputc(char_type __c)
425  {
426  int_type __ret;
427  if (__builtin_expect(this->pptr() < this->epptr(), true))
428  {
429  *this->pptr() = __c;
430  this->pbump(1);
431  __ret = traits_type::to_int_type(__c);
432  }
433  else
434  __ret = this->overflow(traits_type::to_int_type(__c));
435  return __ret;
436  }
437 
438  /**
439  * @brief Entry point for all single-character output functions.
440  * @param __s A buffer read area.
441  * @param __n A count.
442  *
443  * One of two public output functions.
444  *
445  *
446  * Returns xsputn(__s,__n). The effect is to write @a __s[0] through
447  * @a __s[__n-1] to the output sequence, if possible.
448  */
449  streamsize
450  sputn(const char_type* __s, streamsize __n)
451  { return this->xsputn(__s, __n); }
452 
453  protected:
454  /**
455  * @brief Base constructor.
456  *
457  * Only called from derived constructors, and sets up all the
458  * buffer data to zero, including the pointers described in the
459  * basic_streambuf class description. Note that, as a result,
460  * - the class starts with no read nor write positions available,
461  * - this is not an error
462  */
463  basic_streambuf()
464  : _M_in_beg(0), _M_in_cur(0), _M_in_end(0),
465  _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
466  _M_buf_locale(locale())
467  { }
468 
469  // [27.5.2.3.1] get area access
470  //@{
471  /**
472  * @brief Access to the get area.
473  *
474  * These functions are only available to other protected functions,
475  * including derived classes.
476  *
477  * - eback() returns the beginning pointer for the input sequence
478  * - gptr() returns the next pointer for the input sequence
479  * - egptr() returns the end pointer for the input sequence
480  */
481  char_type*
482  eback() const { return _M_in_beg; }
483 
484  char_type*
485  gptr() const { return _M_in_cur; }
486 
487  char_type*
488  egptr() const { return _M_in_end; }
489  //@}
490 
491  /**
492  * @brief Moving the read position.
493  * @param __n The delta by which to move.
494  *
495  * This just advances the read position without returning any data.
496  */
497  void
498  gbump(int __n) { _M_in_cur += __n; }
499 
500  /**
501  * @brief Setting the three read area pointers.
502  * @param __gbeg A pointer.
503  * @param __gnext A pointer.
504  * @param __gend A pointer.
505  * @post @a __gbeg == @c eback(), @a __gnext == @c gptr(), and
506  * @a __gend == @c egptr()
507  */
508  void
509  setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
510  {
511  _M_in_beg = __gbeg;
512  _M_in_cur = __gnext;
513  _M_in_end = __gend;
514  }
515 
516  // [27.5.2.3.2] put area access
517  //@{
518  /**
519  * @brief Access to the put area.
520  *
521  * These functions are only available to other protected functions,
522  * including derived classes.
523  *
524  * - pbase() returns the beginning pointer for the output sequence
525  * - pptr() returns the next pointer for the output sequence
526  * - epptr() returns the end pointer for the output sequence
527  */
528  char_type*
529  pbase() const { return _M_out_beg; }
530 
531  char_type*
532  pptr() const { return _M_out_cur; }
533 
534  char_type*
535  epptr() const { return _M_out_end; }
536  //@}
537 
538  /**
539  * @brief Moving the write position.
540  * @param __n The delta by which to move.
541  *
542  * This just advances the write position without returning any data.
543  */
544  void
545  pbump(int __n) { _M_out_cur += __n; }
546 
547  /**
548  * @brief Setting the three write area pointers.
549  * @param __pbeg A pointer.
550  * @param __pend A pointer.
551  * @post @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and
552  * @a __pend == @c epptr()
553  */
554  void
555  setp(char_type* __pbeg, char_type* __pend)
556  {
557  _M_out_beg = _M_out_cur = __pbeg;
558  _M_out_end = __pend;
559  }
560 
561  // [27.5.2.4] virtual functions
562  // [27.5.2.4.1] locales
563  /**
564  * @brief Changes translations.
565  * @param __loc A new locale.
566  *
567  * Translations done during I/O which depend on the current
568  * locale are changed by this call. The standard adds,
569  * <em>Between invocations of this function a class derived
570  * from streambuf can safely cache results of calls to locale
571  * functions and to members of facets so obtained.</em>
572  *
573  * @note Base class version does nothing.
574  */
575  virtual void
576  imbue(const locale& __loc)
577  { }
578 
579  // [27.5.2.4.2] buffer management and positioning
580  /**
581  * @brief Manipulates the buffer.
582  *
583  * Each derived class provides its own appropriate behavior. See
584  * the next-to-last paragraph of
585  * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
586  * for more on this function.
587  *
588  * @note Base class version does nothing, returns @c this.
589  */
590  virtual basic_streambuf<char_type,_Traits>*
591  setbuf(char_type*, streamsize)
592  { return this; }
593 
594  /**
595  * @brief Alters the stream positions.
596  *
597  * Each derived class provides its own appropriate behavior.
598  * @note Base class version does nothing, returns a @c pos_type
599  * that represents an invalid stream position.
600  */
601  virtual pos_type
602  seekoff(off_type, ios_base::seekdir,
603  ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
604  { return pos_type(off_type(-1)); }
605 
606  /**
607  * @brief Alters the stream positions.
608  *
609  * Each derived class provides its own appropriate behavior.
610  * @note Base class version does nothing, returns a @c pos_type
611  * that represents an invalid stream position.
612  */
613  virtual pos_type
614  seekpos(pos_type,
615  ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
616  { return pos_type(off_type(-1)); }
617 
618  /**
619  * @brief Synchronizes the buffer arrays with the controlled sequences.
620  * @return -1 on failure.
621  *
622  * Each derived class provides its own appropriate behavior,
623  * including the definition of @a failure.
624  * @note Base class version does nothing, returns zero.
625  */
626  virtual int
627  sync() { return 0; }
628 
629  // [27.5.2.4.3] get area
630  /**
631  * @brief Investigating the data available.
632  * @return An estimate of the number of characters available in the
633  * input sequence, or -1.
634  *
635  * <em>If it returns a positive value, then successive calls to
636  * @c underflow() will not return @c traits::eof() until at
637  * least that number of characters have been supplied. If @c
638  * showmanyc() returns -1, then calls to @c underflow() or @c
639  * uflow() will fail.</em> [27.5.2.4.3]/1
640  *
641  * @note Base class version does nothing, returns zero.
642  * @note The standard adds that <em>the intention is not only that the
643  * calls [to underflow or uflow] will not return @c eof() but
644  * that they will return immediately.</em>
645  * @note The standard adds that <em>the morphemes of @c showmanyc are
646  * @b es-how-many-see, not @b show-manic.</em>
647  */
648  virtual streamsize
649  showmanyc() { return 0; }
650 
651  /**
652  * @brief Multiple character extraction.
653  * @param __s A buffer area.
654  * @param __n Maximum number of characters to assign.
655  * @return The number of characters assigned.
656  *
657  * Fills @a __s[0] through @a __s[__n-1] with characters from the input
658  * sequence, as if by @c sbumpc(). Stops when either @a __n characters
659  * have been copied, or when @c traits::eof() would be copied.
660  *
661  * It is expected that derived classes provide a more efficient
662  * implementation by overriding this definition.
663  */
664  virtual streamsize
665  xsgetn(char_type* __s, streamsize __n);
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 is called when the input buffer is
672  * exhausted (or does not exist, as buffering need not actually be
673  * done). If a buffer exists, it is @a refilled. In either case, the
674  * next available character is returned, or @c traits::eof() to
675  * indicate a null pending sequence.
676  *
677  * For a formal definition of the pending sequence, see a good text
678  * such as Langer & Kreft, or [27.5.2.4.3]/7-14.
679  *
680  * A functioning input streambuf can be created by overriding only
681  * this function (no buffer area will be used). For an example, see
682  * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html
683  *
684  * @note Base class version does nothing, returns eof().
685  */
686  virtual int_type
687  underflow()
688  { return traits_type::eof(); }
689 
690  /**
691  * @brief Fetches more data from the controlled sequence.
692  * @return The first character from the <em>pending sequence</em>.
693  *
694  * Informally, this function does the same thing as @c underflow(),
695  * and in fact is required to call that function. It also returns
696  * the new character, like @c underflow() does. However, this
697  * function also moves the read position forward by one.
698  */
699  virtual int_type
700  uflow()
701  {
702  int_type __ret = traits_type::eof();
703  const bool __testeof = traits_type::eq_int_type(this->underflow(),
704  __ret);
705  if (!__testeof)
706  {
707  __ret = traits_type::to_int_type(*this->gptr());
708  this->gbump(1);
709  }
710  return __ret;
711  }
712 
713  // [27.5.2.4.4] putback
714  /**
715  * @brief Tries to back up the input sequence.
716  * @param __c The character to be inserted back into the sequence.
717  * @return eof() on failure, <em>some other value</em> on success
718  * @post The constraints of @c gptr(), @c eback(), and @c pptr()
719  * are the same as for @c underflow().
720  *
721  * @note Base class version does nothing, returns eof().
722  */
723  virtual int_type
724  pbackfail(int_type __c = traits_type::eof())
725  { return traits_type::eof(); }
726 
727  // Put area:
728  /**
729  * @brief Multiple character insertion.
730  * @param __s A buffer area.
731  * @param __n Maximum number of characters to write.
732  * @return The number of characters written.
733  *
734  * Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if
735  * by @c sputc(). Stops when either @a n characters have been
736  * copied, or when @c sputc() would return @c traits::eof().
737  *
738  * It is expected that derived classes provide a more efficient
739  * implementation by overriding this definition.
740  */
741  virtual streamsize
742  xsputn(const char_type* __s, streamsize __n);
743 
744  /**
745  * @brief Consumes data from the buffer; writes to the
746  * controlled sequence.
747  * @param __c An additional character to consume.
748  * @return eof() to indicate failure, something else (usually
749  * @a __c, or not_eof())
750  *
751  * Informally, this function is called when the output buffer
752  * is full (or does not exist, as buffering need not actually
753  * be done). If a buffer exists, it is @a consumed, with
754  * <em>some effect</em> on the controlled sequence.
755  * (Typically, the buffer is written out to the sequence
756  * verbatim.) In either case, the character @a c is also
757  * written out, if @a __c is not @c eof().
758  *
759  * For a formal definition of this function, see a good text
760  * such as Langer & Kreft, or [27.5.2.4.5]/3-7.
761  *
762  * A functioning output streambuf can be created by overriding only
763  * this function (no buffer area will be used).
764  *
765  * @note Base class version does nothing, returns eof().
766  */
767  virtual int_type
768  overflow(int_type __c = traits_type::eof())
769  { return traits_type::eof(); }
770 
771 #if _GLIBCXX_USE_DEPRECATED
772  // Annex D.6
773  public:
774  /**
775  * @brief Tosses a character.
776  *
777  * Advances the read pointer, ignoring the character that would have
778  * been read.
779  *
780  * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
781  */
782  void
783  stossc()
784  {
785  if (this->gptr() < this->egptr())
786  this->gbump(1);
787  else
788  this->uflow();
789  }
790 #endif
791 
792  // Also used by specializations for char and wchar_t in src.
793  void
794  __safe_gbump(streamsize __n) { _M_in_cur += __n; }
795 
796  void
797  __safe_pbump(streamsize __n) { _M_out_cur += __n; }
798 
799 #if __cplusplus < 201103L
800  private:
801 #else
802  protected:
803 #endif
804  basic_streambuf(const basic_streambuf&);
805 
806  basic_streambuf&
807  operator=(const basic_streambuf&);
808 
809 #if __cplusplus >= 201103L
810  void
811  swap(basic_streambuf& __sb)
812  {
813  std::swap(_M_in_beg, __sb._M_in_beg);
814  std::swap(_M_in_cur, __sb._M_in_cur);
815  std::swap(_M_in_end, __sb._M_in_end);
816  std::swap(_M_out_beg, __sb._M_out_beg);
817  std::swap(_M_out_cur, __sb._M_out_cur);
818  std::swap(_M_out_end, __sb._M_out_end);
819  std::swap(_M_buf_locale, __sb._M_buf_locale);
820  }
821 #endif
822  };
823 
824 #if __cplusplus >= 201103L
825  template<typename _CharT, typename _Traits>
826  std::basic_streambuf<_CharT, _Traits>::
827  basic_streambuf(const basic_streambuf&) = default;
828 
829  template<typename _CharT, typename _Traits>
830  std::basic_streambuf<_CharT, _Traits>&
831  std::basic_streambuf<_CharT, _Traits>::
832  operator=(const basic_streambuf&) = default;
833 #endif
834 
835  // Explicit specialization declarations, defined in src/streambuf.cc.
836  template<>
837  streamsize
838  __copy_streambufs_eof(basic_streambuf<char>* __sbin,
839  basic_streambuf<char>* __sbout, bool& __ineof);
840 #ifdef _GLIBCXX_USE_WCHAR_T
841  template<>
842  streamsize
843  __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
844  basic_streambuf<wchar_t>* __sbout, bool& __ineof);
845 #endif
846 
847 _GLIBCXX_END_NAMESPACE_VERSION
848 } // namespace
849 
850 #include <bits/streambuf.tcc>
851 
852 #endif /* _GLIBCXX_STREAMBUF */