libstdc++
rc_string_base.h
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1 // Reference-counted versatile string base -*- C++ -*-
2 
3 // Copyright (C) 2005-2025 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 ext/rc_string_base.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{ext/vstring.h}
28  */
29 
30 #ifndef _RC_STRING_BASE_H
31 #define _RC_STRING_BASE_H 1
32 
33 #include <bits/requires_hosted.h> // GNU extensions are currently omitted
34 
35 #include <ext/atomicity.h>
36 #include <ext/alloc_traits.h>
38 
39 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
40 {
41 _GLIBCXX_BEGIN_NAMESPACE_VERSION
42 
43  /**
44  * Documentation? What's that?
45  * Nathan Myers <ncm@cantrip.org>.
46  *
47  * A string looks like this:
48  *
49  * @code
50  * [_Rep]
51  * _M_length
52  * [__rc_string_base<char_type>] _M_capacity
53  * _M_dataplus _M_refcount
54  * _M_p ----------------> unnamed array of char_type
55  * @endcode
56  *
57  * Where the _M_p points to the first character in the string, and
58  * you cast it to a pointer-to-_Rep and subtract 1 to get a
59  * pointer to the header.
60  *
61  * This approach has the enormous advantage that a string object
62  * requires only one allocation. All the ugliness is confined
63  * within a single pair of inline functions, which each compile to
64  * a single @a add instruction: _Rep::_M_refdata(), and
65  * __rc_string_base::_M_rep(); and the allocation function which gets a
66  * block of raw bytes and with room enough and constructs a _Rep
67  * object at the front.
68  *
69  * The reason you want _M_data pointing to the character array and
70  * not the _Rep is so that the debugger can see the string
71  * contents. (Probably we should add a non-inline member to get
72  * the _Rep for the debugger to use, so users can check the actual
73  * string length.)
74  *
75  * Note that the _Rep object is a POD so that you can have a
76  * static <em>empty string</em> _Rep object already @a constructed before
77  * static constructors have run. The reference-count encoding is
78  * chosen so that a 0 indicates one reference, so you never try to
79  * destroy the empty-string _Rep object.
80  *
81  * All but the last paragraph is considered pretty conventional
82  * for a C++ string implementation.
83  */
84  template<typename _CharT, typename _Traits, typename _Alloc>
86  : protected __vstring_utility<_CharT, _Traits, _Alloc>
87  {
88  public:
89  typedef _Traits traits_type;
90  typedef typename _Traits::char_type value_type;
91  typedef _Alloc allocator_type;
92 
93  typedef __vstring_utility<_CharT, _Traits, _Alloc> _Util_Base;
94  typedef typename _Util_Base::_CharT_alloc_type _CharT_alloc_type;
95  typedef typename _CharT_alloc_type::size_type size_type;
96 
97  private:
98  // _Rep: string representation
99  // Invariants:
100  // 1. String really contains _M_length + 1 characters: due to 21.3.4
101  // must be kept null-terminated.
102  // 2. _M_capacity >= _M_length
103  // Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
104  // 3. _M_refcount has three states:
105  // -1: leaked, one reference, no ref-copies allowed, non-const.
106  // 0: one reference, non-const.
107  // n>0: n + 1 references, operations require a lock, const.
108  // 4. All fields == 0 is an empty string, given the extra storage
109  // beyond-the-end for a null terminator; thus, the shared
110  // empty string representation needs no constructor.
111  struct _Rep
112  {
113  union
114  {
115  struct
116  {
117  size_type _M_length;
118  size_type _M_capacity;
119  _Atomic_word _M_refcount;
120  } _M_info;
121 
122  // Only for alignment purposes.
123  _CharT _M_align;
124  };
125 
126  typedef typename __alloc_traits<_Alloc>::template rebind<_Rep>::other
127  _Rep_alloc_type;
128 
129  _CharT*
130  _M_refdata() throw()
131  { return reinterpret_cast<_CharT*>(this + 1); }
132 
133  _CharT*
134  _M_refcopy() throw()
135  {
136  __atomic_add_dispatch(&_M_info._M_refcount, 1);
137  return _M_refdata();
138  } // XXX MT
139 
140  void
141  _M_set_length(size_type __n)
142  {
143  _M_info._M_refcount = 0; // One reference.
144  _M_info._M_length = __n;
145  // grrr. (per 21.3.4)
146  // You cannot leave those LWG people alone for a second.
147  traits_type::assign(_M_refdata()[__n], _CharT());
148  }
149 
150  // Create & Destroy
151  static _Rep*
152  _S_create(size_type, size_type, const _Alloc&);
153 
154  void
155  _M_destroy(const _Alloc&) throw();
156 
157  _CharT*
158  _M_clone(const _Alloc&, size_type __res = 0);
159  };
160 
161  struct _Rep_empty
162  : public _Rep
163  {
164  _CharT _M_terminal;
165  };
166 
167  static _Rep_empty _S_empty_rep;
168 
169  // The maximum number of individual char_type elements of an
170  // individual string is determined by _S_max_size. This is the
171  // value that will be returned by max_size(). (Whereas npos
172  // is the maximum number of bytes the allocator can allocate.)
173  // If one was to divvy up the theoretical largest size string,
174  // with a terminating character and m _CharT elements, it'd
175  // look like this:
176  // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
177  // + sizeof(_Rep) - 1
178  // (NB: last two terms for rounding reasons, see _M_create below)
179  // Solving for m:
180  // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
181  // In addition, this implementation halves this amount.
182  enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
183  + 1) / sizeof(_CharT)) - 1) / 2 };
184 
185  // Data Member (private):
186  mutable typename _Util_Base::template _Alloc_hider<_Alloc> _M_dataplus;
187 
188  void
189  _M_data(_CharT* __p)
190  { _M_dataplus._M_p = __p; }
191 
192  _Rep*
193  _M_rep() const
194  { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
195 
196  _CharT*
197  _M_grab(const _Alloc& __alloc) const
198  {
199  return (!_M_is_leaked() && _M_get_allocator() == __alloc)
200  ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
201  }
202 
203  void
204  _M_dispose()
205  {
206  // Be race-detector-friendly. For more info see bits/c++config.
207  _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
208  _M_refcount);
209  if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
210  -1) <= 0)
211  {
212  _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
213  _M_refcount);
214  _M_rep()->_M_destroy(_M_get_allocator());
215  }
216  } // XXX MT
217 
218  bool
219  _M_is_leaked() const
220  { return _M_rep()->_M_info._M_refcount < 0; }
221 
222  void
223  _M_set_sharable()
224  { _M_rep()->_M_info._M_refcount = 0; }
225 
226  void
227  _M_leak_hard();
228 
229  // _S_construct_aux is used to implement the 21.3.1 para 15 which
230  // requires special behaviour if _InIterator is an integral type
231  template<typename _InIterator>
232  static _CharT*
233  _S_construct_aux(_InIterator __beg, _InIterator __end,
234  const _Alloc& __a, std::__false_type)
235  {
237  _Tag;
238  return _S_construct(__beg, __end, __a, _Tag());
239  }
240 
241  // _GLIBCXX_RESOLVE_LIB_DEFECTS
242  // 438. Ambiguity in the "do the right thing" clause
243  template<typename _Integer>
244  static _CharT*
245  _S_construct_aux(_Integer __beg, _Integer __end,
246  const _Alloc& __a, std::__true_type)
247  { return _S_construct_aux_2(static_cast<size_type>(__beg),
248  __end, __a); }
249 
250  static _CharT*
251  _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
252  { return _S_construct(__req, __c, __a); }
253 
254  template<typename _InIterator>
255  static _CharT*
256  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
257  {
258  typedef typename std::__is_integer<_InIterator>::__type _Integral;
259  return _S_construct_aux(__beg, __end, __a, _Integral());
260  }
261 
262  // For Input Iterators, used in istreambuf_iterators, etc.
263  template<typename _InIterator>
264  static _CharT*
265  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
267 
268  // For forward_iterators up to random_access_iterators, used for
269  // string::iterator, _CharT*, etc.
270  template<typename _FwdIterator>
271  static _CharT*
272  _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
274 
275  static _CharT*
276  _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
277 
278  public:
279  size_type
280  _M_max_size() const
281  { return size_type(_S_max_size); }
282 
283  _CharT*
284  _M_data() const
285  { return _M_dataplus._M_p; }
286 
287  size_type
288  _M_length() const
289  { return _M_rep()->_M_info._M_length; }
290 
291  size_type
292  _M_capacity() const
293  { return _M_rep()->_M_info._M_capacity; }
294 
295  bool
296  _M_is_shared() const
297  { return _M_rep()->_M_info._M_refcount > 0; }
298 
299  void
300  _M_set_leaked()
301  { _M_rep()->_M_info._M_refcount = -1; }
302 
303  void
304  _M_leak() // for use in begin() & non-const op[]
305  {
306  if (!_M_is_leaked())
307  _M_leak_hard();
308  }
309 
310  void
311  _M_set_length(size_type __n)
312  { _M_rep()->_M_set_length(__n); }
313 
315  : _M_dataplus(_S_empty_rep._M_refcopy()) { }
316 
317  __rc_string_base(const _Alloc& __a);
318 
319  __rc_string_base(const __rc_string_base& __rcs);
320 
321 #if __cplusplus >= 201103L
323  : _M_dataplus(__rcs._M_dataplus)
324  { __rcs._M_data(_S_empty_rep._M_refcopy()); }
325 #endif
326 
327  __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
328 
329  template<typename _InputIterator>
330  __rc_string_base(_InputIterator __beg, _InputIterator __end,
331  const _Alloc& __a);
332 
334  { _M_dispose(); }
335 
336  allocator_type&
337  _M_get_allocator()
338  { return _M_dataplus; }
339 
340  const allocator_type&
341  _M_get_allocator() const
342  { return _M_dataplus; }
343 
344  void
345  _M_swap(__rc_string_base& __rcs);
346 
347  void
348  _M_assign(const __rc_string_base& __rcs);
349 
350  void
351  _M_reserve(size_type __res);
352 
353  void
354  _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
355  size_type __len2);
356 
357  void
358  _M_erase(size_type __pos, size_type __n);
359 
360  void
361  _M_clear()
362  {
363  _M_dispose();
364  _M_data(_S_empty_rep._M_refcopy());
365  }
366 
367  bool
368  _M_compare(const __rc_string_base&) const
369  { return false; }
370  };
371 
372  template<typename _CharT, typename _Traits, typename _Alloc>
375 
376  template<typename _CharT, typename _Traits, typename _Alloc>
379  _S_create(size_type __capacity, size_type __old_capacity,
380  const _Alloc& __alloc)
381  {
382  // _GLIBCXX_RESOLVE_LIB_DEFECTS
383  // 83. String::npos vs. string::max_size()
384  if (__capacity > size_type(_S_max_size))
385  std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
386 
387  // The standard places no restriction on allocating more memory
388  // than is strictly needed within this layer at the moment or as
389  // requested by an explicit application call to reserve().
390 
391  // Many malloc implementations perform quite poorly when an
392  // application attempts to allocate memory in a stepwise fashion
393  // growing each allocation size by only 1 char. Additionally,
394  // it makes little sense to allocate less linear memory than the
395  // natural blocking size of the malloc implementation.
396  // Unfortunately, we would need a somewhat low-level calculation
397  // with tuned parameters to get this perfect for any particular
398  // malloc implementation. Fortunately, generalizations about
399  // common features seen among implementations seems to suffice.
400 
401  // __pagesize need not match the actual VM page size for good
402  // results in practice, thus we pick a common value on the low
403  // side. __malloc_header_size is an estimate of the amount of
404  // overhead per memory allocation (in practice seen N * sizeof
405  // (void*) where N is 0, 2 or 4). According to folklore,
406  // picking this value on the high side is better than
407  // low-balling it (especially when this algorithm is used with
408  // malloc implementations that allocate memory blocks rounded up
409  // to a size which is a power of 2).
410  const size_type __pagesize = 4096;
411  const size_type __malloc_header_size = 4 * sizeof(void*);
412 
413  // The below implements an exponential growth policy, necessary to
414  // meet amortized linear time requirements of the library: see
415  // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
416  if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
417  {
418  __capacity = 2 * __old_capacity;
419  // Never allocate a string bigger than _S_max_size.
420  if (__capacity > size_type(_S_max_size))
421  __capacity = size_type(_S_max_size);
422  }
423 
424  // NB: Need an array of char_type[__capacity], plus a terminating
425  // null char_type() element, plus enough for the _Rep data structure,
426  // plus sizeof(_Rep) - 1 to upper round to a size multiple of
427  // sizeof(_Rep).
428  // Whew. Seemingly so needy, yet so elemental.
429  size_type __size = ((__capacity + 1) * sizeof(_CharT)
430  + 2 * sizeof(_Rep) - 1);
431 
432  const size_type __adj_size = __size + __malloc_header_size;
433  if (__adj_size > __pagesize && __capacity > __old_capacity)
434  {
435  const size_type __extra = __pagesize - __adj_size % __pagesize;
436  __capacity += __extra / sizeof(_CharT);
437  if (__capacity > size_type(_S_max_size))
438  __capacity = size_type(_S_max_size);
439  __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
440  }
441 
442  // NB: Might throw, but no worries about a leak, mate: _Rep()
443  // does not throw.
444  _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
445  _Rep* __p = new (__place) _Rep;
446  __p->_M_info._M_capacity = __capacity;
447  return __p;
448  }
449 
450  template<typename _CharT, typename _Traits, typename _Alloc>
451  void
452  __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
453  _M_destroy(const _Alloc& __a) throw ()
454  {
455  const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
456  + 2 * sizeof(_Rep) - 1);
457  _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
458  }
459 
460  template<typename _CharT, typename _Traits, typename _Alloc>
461  _CharT*
462  __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
463  _M_clone(const _Alloc& __alloc, size_type __res)
464  {
465  // Requested capacity of the clone.
466  const size_type __requested_cap = _M_info._M_length + __res;
467  _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
468  __alloc);
469 
470  if (_M_info._M_length)
471  __rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
472 
473  __r->_M_set_length(_M_info._M_length);
474  return __r->_M_refdata();
475  }
476 
477  template<typename _CharT, typename _Traits, typename _Alloc>
478  __rc_string_base<_CharT, _Traits, _Alloc>::
479  __rc_string_base(const _Alloc& __a)
480  : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
481 
482  template<typename _CharT, typename _Traits, typename _Alloc>
483  __rc_string_base<_CharT, _Traits, _Alloc>::
484  __rc_string_base(const __rc_string_base& __rcs)
485  : _M_dataplus(__rcs._M_get_allocator(),
486  __rcs._M_grab(__rcs._M_get_allocator())) { }
487 
488  template<typename _CharT, typename _Traits, typename _Alloc>
489  __rc_string_base<_CharT, _Traits, _Alloc>::
490  __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
491  : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
492 
493  template<typename _CharT, typename _Traits, typename _Alloc>
494  template<typename _InputIterator>
495  __rc_string_base<_CharT, _Traits, _Alloc>::
496  __rc_string_base(_InputIterator __beg, _InputIterator __end,
497  const _Alloc& __a)
498  : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
499 
500  template<typename _CharT, typename _Traits, typename _Alloc>
501  void
502  __rc_string_base<_CharT, _Traits, _Alloc>::
503  _M_leak_hard()
504  {
505  if (_M_is_shared())
506  _M_erase(0, 0);
507  _M_set_leaked();
508  }
509 
510  // NB: This is the special case for Input Iterators, used in
511  // istreambuf_iterators, etc.
512  // Input Iterators have a cost structure very different from
513  // pointers, calling for a different coding style.
514  template<typename _CharT, typename _Traits, typename _Alloc>
515  template<typename _InIterator>
516  _CharT*
517  __rc_string_base<_CharT, _Traits, _Alloc>::
518  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
520  {
521  if (__beg == __end && __a == _Alloc())
522  return _S_empty_rep._M_refcopy();
523 
524  // Avoid reallocation for common case.
525  _CharT __buf[128];
526  size_type __len = 0;
527  while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
528  {
529  __buf[__len++] = *__beg;
530  ++__beg;
531  }
532  _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
533  _S_copy(__r->_M_refdata(), __buf, __len);
534  __try
535  {
536  while (__beg != __end)
537  {
538  if (__len == __r->_M_info._M_capacity)
539  {
540  // Allocate more space.
541  _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
542  _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
543  __r->_M_destroy(__a);
544  __r = __another;
545  }
546  __r->_M_refdata()[__len++] = *__beg;
547  ++__beg;
548  }
549  }
550  __catch(...)
551  {
552  __r->_M_destroy(__a);
553  __throw_exception_again;
554  }
555  __r->_M_set_length(__len);
556  return __r->_M_refdata();
557  }
558 
559  template<typename _CharT, typename _Traits, typename _Alloc>
560  template<typename _InIterator>
561  _CharT*
562  __rc_string_base<_CharT, _Traits, _Alloc>::
563  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
565  {
566  if (__beg == __end && __a == _Alloc())
567  return _S_empty_rep._M_refcopy();
568 
569  // NB: Not required, but considered best practice.
570  if (__is_null_pointer(__beg) && __beg != __end)
571  std::__throw_logic_error(__N("__rc_string_base::"
572  "_S_construct null not valid"));
573 
574  const size_type __dnew = static_cast<size_type>(std::distance(__beg,
575  __end));
576  // Check for out_of_range and length_error exceptions.
577  _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
578  __try
579  { __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
580  __catch(...)
581  {
582  __r->_M_destroy(__a);
583  __throw_exception_again;
584  }
585  __r->_M_set_length(__dnew);
586  return __r->_M_refdata();
587  }
588 
589  template<typename _CharT, typename _Traits, typename _Alloc>
590  _CharT*
591  __rc_string_base<_CharT, _Traits, _Alloc>::
592  _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
593  {
594  if (__n == 0 && __a == _Alloc())
595  return _S_empty_rep._M_refcopy();
596 
597  // Check for out_of_range and length_error exceptions.
598  _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
599  if (__n)
600  __rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
601 
602  __r->_M_set_length(__n);
603  return __r->_M_refdata();
604  }
605 
606  template<typename _CharT, typename _Traits, typename _Alloc>
607  void
608  __rc_string_base<_CharT, _Traits, _Alloc>::
609  _M_swap(__rc_string_base& __rcs)
610  {
611  if (_M_is_leaked())
612  _M_set_sharable();
613  if (__rcs._M_is_leaked())
614  __rcs._M_set_sharable();
615 
616  _CharT* __tmp = _M_data();
617  _M_data(__rcs._M_data());
618  __rcs._M_data(__tmp);
619 
620  // _GLIBCXX_RESOLVE_LIB_DEFECTS
621  // 431. Swapping containers with unequal allocators.
622  std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
623  __rcs._M_get_allocator());
624  }
625 
626  template<typename _CharT, typename _Traits, typename _Alloc>
627  void
628  __rc_string_base<_CharT, _Traits, _Alloc>::
629  _M_assign(const __rc_string_base& __rcs)
630  {
631  if (_M_rep() != __rcs._M_rep())
632  {
633  _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
634  _M_dispose();
635  _M_data(__tmp);
636  }
637  }
638 
639  template<typename _CharT, typename _Traits, typename _Alloc>
640  void
641  __rc_string_base<_CharT, _Traits, _Alloc>::
642  _M_reserve(size_type __res)
643  {
644  // Make sure we don't shrink below the current size.
645  if (__res < _M_length())
646  __res = _M_length();
647 
648  if (__res != _M_capacity() || _M_is_shared())
649  {
650  _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
651  __res - _M_length());
652  _M_dispose();
653  _M_data(__tmp);
654  }
655  }
656 
657  template<typename _CharT, typename _Traits, typename _Alloc>
658  void
659  __rc_string_base<_CharT, _Traits, _Alloc>::
660  _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
661  size_type __len2)
662  {
663  const size_type __how_much = _M_length() - __pos - __len1;
664 
665  _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
666  _M_capacity(), _M_get_allocator());
667 
668  if (__pos)
669  this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
670  if (__s && __len2)
671  this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
672  if (__how_much)
673  this->_S_copy(__r->_M_refdata() + __pos + __len2,
674  _M_data() + __pos + __len1, __how_much);
675 
676  _M_dispose();
677  _M_data(__r->_M_refdata());
678  }
679 
680  template<typename _CharT, typename _Traits, typename _Alloc>
681  void
682  __rc_string_base<_CharT, _Traits, _Alloc>::
683  _M_erase(size_type __pos, size_type __n)
684  {
685  const size_type __new_size = _M_length() - __n;
686  const size_type __how_much = _M_length() - __pos - __n;
687 
688  if (_M_is_shared())
689  {
690  // Must reallocate.
691  _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
692  _M_get_allocator());
693 
694  if (__pos)
695  this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
696  if (__how_much)
697  this->_S_copy(__r->_M_refdata() + __pos,
698  _M_data() + __pos + __n, __how_much);
699 
700  _M_dispose();
701  _M_data(__r->_M_refdata());
702  }
703  else if (__how_much && __n)
704  {
705  // Work in-place.
706  this->_S_move(_M_data() + __pos,
707  _M_data() + __pos + __n, __how_much);
708  }
709 
710  _M_rep()->_M_set_length(__new_size);
711  }
712 
713  template<>
714  inline bool
715  __rc_string_base<char, std::char_traits<char>,
717  _M_compare(const __rc_string_base& __rcs) const
718  {
719  if (_M_rep() == __rcs._M_rep())
720  return true;
721  return false;
722  }
723 
724  template<>
725  inline bool
726  __rc_string_base<wchar_t, std::char_traits<wchar_t>,
728  _M_compare(const __rc_string_base& __rcs) const
729  {
730  if (_M_rep() == __rcs._M_rep())
731  return true;
732  return false;
733  }
734 
735 _GLIBCXX_END_NAMESPACE_VERSION
736 } // namespace
737 
738 #endif /* _RC_STRING_BASE_H */
constexpr iterator_traits< _InputIterator >::difference_type distance(_InputIterator __first, _InputIterator __last)
A generalization of pointer arithmetic.
GNU extensions for public use.
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:134
Marking input iterators.
Forward iterators support a superset of input iterator operations.
Traits class for iterators.
Uniform interface to C++98 and C++11 allocators.