libstdc++
rc_string_base.h
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1 // Reference-counted versatile string base -*- C++ -*-
2 
3 // Copyright (C) 2005-2018 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 <ext/atomicity.h>
35 
36 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
37 {
38 _GLIBCXX_BEGIN_NAMESPACE_VERSION
39 
40  /**
41  * Documentation? What's that?
42  * Nathan Myers <[email protected]>.
43  *
44  * A string looks like this:
45  *
46  * @code
47  * [_Rep]
48  * _M_length
49  * [__rc_string_base<char_type>] _M_capacity
50  * _M_dataplus _M_refcount
51  * _M_p ----------------> unnamed array of char_type
52  * @endcode
53  *
54  * Where the _M_p points to the first character in the string, and
55  * you cast it to a pointer-to-_Rep and subtract 1 to get a
56  * pointer to the header.
57  *
58  * This approach has the enormous advantage that a string object
59  * requires only one allocation. All the ugliness is confined
60  * within a single pair of inline functions, which each compile to
61  * a single @a add instruction: _Rep::_M_refdata(), and
62  * __rc_string_base::_M_rep(); and the allocation function which gets a
63  * block of raw bytes and with room enough and constructs a _Rep
64  * object at the front.
65  *
66  * The reason you want _M_data pointing to the character array and
67  * not the _Rep is so that the debugger can see the string
68  * contents. (Probably we should add a non-inline member to get
69  * the _Rep for the debugger to use, so users can check the actual
70  * string length.)
71  *
72  * Note that the _Rep object is a POD so that you can have a
73  * static <em>empty string</em> _Rep object already @a constructed before
74  * static constructors have run. The reference-count encoding is
75  * chosen so that a 0 indicates one reference, so you never try to
76  * destroy the empty-string _Rep object.
77  *
78  * All but the last paragraph is considered pretty conventional
79  * for a C++ string implementation.
80  */
81  template<typename _CharT, typename _Traits, typename _Alloc>
83  : protected __vstring_utility<_CharT, _Traits, _Alloc>
84  {
85  public:
86  typedef _Traits traits_type;
87  typedef typename _Traits::char_type value_type;
88  typedef _Alloc allocator_type;
89 
90  typedef __vstring_utility<_CharT, _Traits, _Alloc> _Util_Base;
91  typedef typename _Util_Base::_CharT_alloc_type _CharT_alloc_type;
92  typedef typename _CharT_alloc_type::size_type size_type;
93 
94  private:
95  // _Rep: string representation
96  // Invariants:
97  // 1. String really contains _M_length + 1 characters: due to 21.3.4
98  // must be kept null-terminated.
99  // 2. _M_capacity >= _M_length
100  // Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
101  // 3. _M_refcount has three states:
102  // -1: leaked, one reference, no ref-copies allowed, non-const.
103  // 0: one reference, non-const.
104  // n>0: n + 1 references, operations require a lock, const.
105  // 4. All fields == 0 is an empty string, given the extra storage
106  // beyond-the-end for a null terminator; thus, the shared
107  // empty string representation needs no constructor.
108  struct _Rep
109  {
110  union
111  {
112  struct
113  {
114  size_type _M_length;
115  size_type _M_capacity;
116  _Atomic_word _M_refcount;
117  } _M_info;
118 
119  // Only for alignment purposes.
120  _CharT _M_align;
121  };
122 
123  typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
124 
125  _CharT*
126  _M_refdata() throw()
127  { return reinterpret_cast<_CharT*>(this + 1); }
128 
129  _CharT*
130  _M_refcopy() throw()
131  {
132  __atomic_add_dispatch(&_M_info._M_refcount, 1);
133  return _M_refdata();
134  } // XXX MT
135 
136  void
137  _M_set_length(size_type __n)
138  {
139  _M_info._M_refcount = 0; // One reference.
140  _M_info._M_length = __n;
141  // grrr. (per 21.3.4)
142  // You cannot leave those LWG people alone for a second.
143  traits_type::assign(_M_refdata()[__n], _CharT());
144  }
145 
146  // Create & Destroy
147  static _Rep*
148  _S_create(size_type, size_type, const _Alloc&);
149 
150  void
151  _M_destroy(const _Alloc&) throw();
152 
153  _CharT*
154  _M_clone(const _Alloc&, size_type __res = 0);
155  };
156 
157  struct _Rep_empty
158  : public _Rep
159  {
160  _CharT _M_terminal;
161  };
162 
163  static _Rep_empty _S_empty_rep;
164 
165  // The maximum number of individual char_type elements of an
166  // individual string is determined by _S_max_size. This is the
167  // value that will be returned by max_size(). (Whereas npos
168  // is the maximum number of bytes the allocator can allocate.)
169  // If one was to divvy up the theoretical largest size string,
170  // with a terminating character and m _CharT elements, it'd
171  // look like this:
172  // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
173  // + sizeof(_Rep) - 1
174  // (NB: last two terms for rounding reasons, see _M_create below)
175  // Solving for m:
176  // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
177  // In addition, this implementation halves this amount.
178  enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
179  + 1) / sizeof(_CharT)) - 1) / 2 };
180 
181  // Data Member (private):
182  mutable typename _Util_Base::template _Alloc_hider<_Alloc> _M_dataplus;
183 
184  void
185  _M_data(_CharT* __p)
186  { _M_dataplus._M_p = __p; }
187 
188  _Rep*
189  _M_rep() const
190  { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
191 
192  _CharT*
193  _M_grab(const _Alloc& __alloc) const
194  {
195  return (!_M_is_leaked() && _M_get_allocator() == __alloc)
196  ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
197  }
198 
199  void
200  _M_dispose()
201  {
202  // Be race-detector-friendly. For more info see bits/c++config.
203  _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
204  _M_refcount);
205  if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
206  -1) <= 0)
207  {
208  _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
209  _M_refcount);
210  _M_rep()->_M_destroy(_M_get_allocator());
211  }
212  } // XXX MT
213 
214  bool
215  _M_is_leaked() const
216  { return _M_rep()->_M_info._M_refcount < 0; }
217 
218  void
219  _M_set_sharable()
220  { _M_rep()->_M_info._M_refcount = 0; }
221 
222  void
223  _M_leak_hard();
224 
225  // _S_construct_aux is used to implement the 21.3.1 para 15 which
226  // requires special behaviour if _InIterator is an integral type
227  template<typename _InIterator>
228  static _CharT*
229  _S_construct_aux(_InIterator __beg, _InIterator __end,
230  const _Alloc& __a, std::__false_type)
231  {
232  typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
233  return _S_construct(__beg, __end, __a, _Tag());
234  }
235 
236  // _GLIBCXX_RESOLVE_LIB_DEFECTS
237  // 438. Ambiguity in the "do the right thing" clause
238  template<typename _Integer>
239  static _CharT*
240  _S_construct_aux(_Integer __beg, _Integer __end,
241  const _Alloc& __a, std::__true_type)
242  { return _S_construct_aux_2(static_cast<size_type>(__beg),
243  __end, __a); }
244 
245  static _CharT*
246  _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
247  { return _S_construct(__req, __c, __a); }
248 
249  template<typename _InIterator>
250  static _CharT*
251  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
252  {
253  typedef typename std::__is_integer<_InIterator>::__type _Integral;
254  return _S_construct_aux(__beg, __end, __a, _Integral());
255  }
256 
257  // For Input Iterators, used in istreambuf_iterators, etc.
258  template<typename _InIterator>
259  static _CharT*
260  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
262 
263  // For forward_iterators up to random_access_iterators, used for
264  // string::iterator, _CharT*, etc.
265  template<typename _FwdIterator>
266  static _CharT*
267  _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
269 
270  static _CharT*
271  _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
272 
273  public:
274  size_type
275  _M_max_size() const
276  { return size_type(_S_max_size); }
277 
278  _CharT*
279  _M_data() const
280  { return _M_dataplus._M_p; }
281 
282  size_type
283  _M_length() const
284  { return _M_rep()->_M_info._M_length; }
285 
286  size_type
287  _M_capacity() const
288  { return _M_rep()->_M_info._M_capacity; }
289 
290  bool
291  _M_is_shared() const
292  { return _M_rep()->_M_info._M_refcount > 0; }
293 
294  void
295  _M_set_leaked()
296  { _M_rep()->_M_info._M_refcount = -1; }
297 
298  void
299  _M_leak() // for use in begin() & non-const op[]
300  {
301  if (!_M_is_leaked())
302  _M_leak_hard();
303  }
304 
305  void
306  _M_set_length(size_type __n)
307  { _M_rep()->_M_set_length(__n); }
308 
310  : _M_dataplus(_S_empty_rep._M_refcopy()) { }
311 
312  __rc_string_base(const _Alloc& __a);
313 
314  __rc_string_base(const __rc_string_base& __rcs);
315 
316 #if __cplusplus >= 201103L
318  : _M_dataplus(__rcs._M_dataplus)
319  { __rcs._M_data(_S_empty_rep._M_refcopy()); }
320 #endif
321 
322  __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
323 
324  template<typename _InputIterator>
325  __rc_string_base(_InputIterator __beg, _InputIterator __end,
326  const _Alloc& __a);
327 
329  { _M_dispose(); }
330 
331  allocator_type&
332  _M_get_allocator()
333  { return _M_dataplus; }
334 
335  const allocator_type&
336  _M_get_allocator() const
337  { return _M_dataplus; }
338 
339  void
340  _M_swap(__rc_string_base& __rcs);
341 
342  void
343  _M_assign(const __rc_string_base& __rcs);
344 
345  void
346  _M_reserve(size_type __res);
347 
348  void
349  _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
350  size_type __len2);
351 
352  void
353  _M_erase(size_type __pos, size_type __n);
354 
355  void
356  _M_clear()
357  {
358  _M_dispose();
359  _M_data(_S_empty_rep._M_refcopy());
360  }
361 
362  bool
363  _M_compare(const __rc_string_base&) const
364  { return false; }
365  };
366 
367  template<typename _CharT, typename _Traits, typename _Alloc>
370 
371  template<typename _CharT, typename _Traits, typename _Alloc>
374  _S_create(size_type __capacity, size_type __old_capacity,
375  const _Alloc& __alloc)
376  {
377  // _GLIBCXX_RESOLVE_LIB_DEFECTS
378  // 83. String::npos vs. string::max_size()
379  if (__capacity > size_type(_S_max_size))
380  std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
381 
382  // The standard places no restriction on allocating more memory
383  // than is strictly needed within this layer at the moment or as
384  // requested by an explicit application call to reserve().
385 
386  // Many malloc implementations perform quite poorly when an
387  // application attempts to allocate memory in a stepwise fashion
388  // growing each allocation size by only 1 char. Additionally,
389  // it makes little sense to allocate less linear memory than the
390  // natural blocking size of the malloc implementation.
391  // Unfortunately, we would need a somewhat low-level calculation
392  // with tuned parameters to get this perfect for any particular
393  // malloc implementation. Fortunately, generalizations about
394  // common features seen among implementations seems to suffice.
395 
396  // __pagesize need not match the actual VM page size for good
397  // results in practice, thus we pick a common value on the low
398  // side. __malloc_header_size is an estimate of the amount of
399  // overhead per memory allocation (in practice seen N * sizeof
400  // (void*) where N is 0, 2 or 4). According to folklore,
401  // picking this value on the high side is better than
402  // low-balling it (especially when this algorithm is used with
403  // malloc implementations that allocate memory blocks rounded up
404  // to a size which is a power of 2).
405  const size_type __pagesize = 4096;
406  const size_type __malloc_header_size = 4 * sizeof(void*);
407 
408  // The below implements an exponential growth policy, necessary to
409  // meet amortized linear time requirements of the library: see
410  // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
411  if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
412  {
413  __capacity = 2 * __old_capacity;
414  // Never allocate a string bigger than _S_max_size.
415  if (__capacity > size_type(_S_max_size))
416  __capacity = size_type(_S_max_size);
417  }
418 
419  // NB: Need an array of char_type[__capacity], plus a terminating
420  // null char_type() element, plus enough for the _Rep data structure,
421  // plus sizeof(_Rep) - 1 to upper round to a size multiple of
422  // sizeof(_Rep).
423  // Whew. Seemingly so needy, yet so elemental.
424  size_type __size = ((__capacity + 1) * sizeof(_CharT)
425  + 2 * sizeof(_Rep) - 1);
426 
427  const size_type __adj_size = __size + __malloc_header_size;
428  if (__adj_size > __pagesize && __capacity > __old_capacity)
429  {
430  const size_type __extra = __pagesize - __adj_size % __pagesize;
431  __capacity += __extra / sizeof(_CharT);
432  if (__capacity > size_type(_S_max_size))
433  __capacity = size_type(_S_max_size);
434  __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
435  }
436 
437  // NB: Might throw, but no worries about a leak, mate: _Rep()
438  // does not throw.
439  _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
440  _Rep* __p = new (__place) _Rep;
441  __p->_M_info._M_capacity = __capacity;
442  return __p;
443  }
444 
445  template<typename _CharT, typename _Traits, typename _Alloc>
446  void
447  __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
448  _M_destroy(const _Alloc& __a) throw ()
449  {
450  const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
451  + 2 * sizeof(_Rep) - 1);
452  _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
453  }
454 
455  template<typename _CharT, typename _Traits, typename _Alloc>
456  _CharT*
457  __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
458  _M_clone(const _Alloc& __alloc, size_type __res)
459  {
460  // Requested capacity of the clone.
461  const size_type __requested_cap = _M_info._M_length + __res;
462  _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
463  __alloc);
464 
465  if (_M_info._M_length)
466  __rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
467 
468  __r->_M_set_length(_M_info._M_length);
469  return __r->_M_refdata();
470  }
471 
472  template<typename _CharT, typename _Traits, typename _Alloc>
473  __rc_string_base<_CharT, _Traits, _Alloc>::
474  __rc_string_base(const _Alloc& __a)
475  : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
476 
477  template<typename _CharT, typename _Traits, typename _Alloc>
478  __rc_string_base<_CharT, _Traits, _Alloc>::
479  __rc_string_base(const __rc_string_base& __rcs)
480  : _M_dataplus(__rcs._M_get_allocator(),
481  __rcs._M_grab(__rcs._M_get_allocator())) { }
482 
483  template<typename _CharT, typename _Traits, typename _Alloc>
484  __rc_string_base<_CharT, _Traits, _Alloc>::
485  __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
486  : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
487 
488  template<typename _CharT, typename _Traits, typename _Alloc>
489  template<typename _InputIterator>
490  __rc_string_base<_CharT, _Traits, _Alloc>::
491  __rc_string_base(_InputIterator __beg, _InputIterator __end,
492  const _Alloc& __a)
493  : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
494 
495  template<typename _CharT, typename _Traits, typename _Alloc>
496  void
497  __rc_string_base<_CharT, _Traits, _Alloc>::
498  _M_leak_hard()
499  {
500  if (_M_is_shared())
501  _M_erase(0, 0);
502  _M_set_leaked();
503  }
504 
505  // NB: This is the special case for Input Iterators, used in
506  // istreambuf_iterators, etc.
507  // Input Iterators have a cost structure very different from
508  // pointers, calling for a different coding style.
509  template<typename _CharT, typename _Traits, typename _Alloc>
510  template<typename _InIterator>
511  _CharT*
512  __rc_string_base<_CharT, _Traits, _Alloc>::
513  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
515  {
516  if (__beg == __end && __a == _Alloc())
517  return _S_empty_rep._M_refcopy();
518 
519  // Avoid reallocation for common case.
520  _CharT __buf[128];
521  size_type __len = 0;
522  while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
523  {
524  __buf[__len++] = *__beg;
525  ++__beg;
526  }
527  _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
528  _S_copy(__r->_M_refdata(), __buf, __len);
529  __try
530  {
531  while (__beg != __end)
532  {
533  if (__len == __r->_M_info._M_capacity)
534  {
535  // Allocate more space.
536  _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
537  _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
538  __r->_M_destroy(__a);
539  __r = __another;
540  }
541  __r->_M_refdata()[__len++] = *__beg;
542  ++__beg;
543  }
544  }
545  __catch(...)
546  {
547  __r->_M_destroy(__a);
548  __throw_exception_again;
549  }
550  __r->_M_set_length(__len);
551  return __r->_M_refdata();
552  }
553 
554  template<typename _CharT, typename _Traits, typename _Alloc>
555  template<typename _InIterator>
556  _CharT*
557  __rc_string_base<_CharT, _Traits, _Alloc>::
558  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
560  {
561  if (__beg == __end && __a == _Alloc())
562  return _S_empty_rep._M_refcopy();
563 
564  // NB: Not required, but considered best practice.
565  if (__is_null_pointer(__beg) && __beg != __end)
566  std::__throw_logic_error(__N("__rc_string_base::"
567  "_S_construct null not valid"));
568 
569  const size_type __dnew = static_cast<size_type>(std::distance(__beg,
570  __end));
571  // Check for out_of_range and length_error exceptions.
572  _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
573  __try
574  { __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
575  __catch(...)
576  {
577  __r->_M_destroy(__a);
578  __throw_exception_again;
579  }
580  __r->_M_set_length(__dnew);
581  return __r->_M_refdata();
582  }
583 
584  template<typename _CharT, typename _Traits, typename _Alloc>
585  _CharT*
586  __rc_string_base<_CharT, _Traits, _Alloc>::
587  _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
588  {
589  if (__n == 0 && __a == _Alloc())
590  return _S_empty_rep._M_refcopy();
591 
592  // Check for out_of_range and length_error exceptions.
593  _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
594  if (__n)
595  __rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
596 
597  __r->_M_set_length(__n);
598  return __r->_M_refdata();
599  }
600 
601  template<typename _CharT, typename _Traits, typename _Alloc>
602  void
603  __rc_string_base<_CharT, _Traits, _Alloc>::
604  _M_swap(__rc_string_base& __rcs)
605  {
606  if (_M_is_leaked())
607  _M_set_sharable();
608  if (__rcs._M_is_leaked())
609  __rcs._M_set_sharable();
610 
611  _CharT* __tmp = _M_data();
612  _M_data(__rcs._M_data());
613  __rcs._M_data(__tmp);
614 
615  // _GLIBCXX_RESOLVE_LIB_DEFECTS
616  // 431. Swapping containers with unequal allocators.
617  std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
618  __rcs._M_get_allocator());
619  }
620 
621  template<typename _CharT, typename _Traits, typename _Alloc>
622  void
623  __rc_string_base<_CharT, _Traits, _Alloc>::
624  _M_assign(const __rc_string_base& __rcs)
625  {
626  if (_M_rep() != __rcs._M_rep())
627  {
628  _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
629  _M_dispose();
630  _M_data(__tmp);
631  }
632  }
633 
634  template<typename _CharT, typename _Traits, typename _Alloc>
635  void
636  __rc_string_base<_CharT, _Traits, _Alloc>::
637  _M_reserve(size_type __res)
638  {
639  // Make sure we don't shrink below the current size.
640  if (__res < _M_length())
641  __res = _M_length();
642 
643  if (__res != _M_capacity() || _M_is_shared())
644  {
645  _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
646  __res - _M_length());
647  _M_dispose();
648  _M_data(__tmp);
649  }
650  }
651 
652  template<typename _CharT, typename _Traits, typename _Alloc>
653  void
654  __rc_string_base<_CharT, _Traits, _Alloc>::
655  _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
656  size_type __len2)
657  {
658  const size_type __how_much = _M_length() - __pos - __len1;
659 
660  _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
661  _M_capacity(), _M_get_allocator());
662 
663  if (__pos)
664  this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
665  if (__s && __len2)
666  this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
667  if (__how_much)
668  this->_S_copy(__r->_M_refdata() + __pos + __len2,
669  _M_data() + __pos + __len1, __how_much);
670 
671  _M_dispose();
672  _M_data(__r->_M_refdata());
673  }
674 
675  template<typename _CharT, typename _Traits, typename _Alloc>
676  void
677  __rc_string_base<_CharT, _Traits, _Alloc>::
678  _M_erase(size_type __pos, size_type __n)
679  {
680  const size_type __new_size = _M_length() - __n;
681  const size_type __how_much = _M_length() - __pos - __n;
682 
683  if (_M_is_shared())
684  {
685  // Must reallocate.
686  _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
687  _M_get_allocator());
688 
689  if (__pos)
690  this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
691  if (__how_much)
692  this->_S_copy(__r->_M_refdata() + __pos,
693  _M_data() + __pos + __n, __how_much);
694 
695  _M_dispose();
696  _M_data(__r->_M_refdata());
697  }
698  else if (__how_much && __n)
699  {
700  // Work in-place.
701  this->_S_move(_M_data() + __pos,
702  _M_data() + __pos + __n, __how_much);
703  }
704 
705  _M_rep()->_M_set_length(__new_size);
706  }
707 
708  template<>
709  inline bool
710  __rc_string_base<char, std::char_traits<char>,
712  _M_compare(const __rc_string_base& __rcs) const
713  {
714  if (_M_rep() == __rcs._M_rep())
715  return true;
716  return false;
717  }
718 
719 #ifdef _GLIBCXX_USE_WCHAR_T
720  template<>
721  inline bool
722  __rc_string_base<wchar_t, std::char_traits<wchar_t>,
724  _M_compare(const __rc_string_base& __rcs) const
725  {
726  if (_M_rep() == __rcs._M_rep())
727  return true;
728  return false;
729  }
730 #endif
731 
732 _GLIBCXX_END_NAMESPACE_VERSION
733 } // namespace
734 
735 #endif /* _RC_STRING_BASE_H */
_GLIBCXX17_CONSTEXPR iterator_traits< _InputIterator >::difference_type distance(_InputIterator __first, _InputIterator __last)
A generalization of pointer arithmetic.
Marking input iterators.
The standard allocator, as per [20.4].
Definition: allocator.h:108
Forward iterators support a superset of input iterator operations.
GNU extensions for public use.