libstdc++
rc_string_base.h
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1 // Reference-counted versatile string base -*- C++ -*-
2 
3 // Copyright (C) 2005-2021 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>
34 #include <ext/alloc_traits.h>
36 
37 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
38 {
39 _GLIBCXX_BEGIN_NAMESPACE_VERSION
40 
41  /**
42  * Documentation? What's that?
43  * Nathan Myers <ncm@cantrip.org>.
44  *
45  * A string looks like this:
46  *
47  * @code
48  * [_Rep]
49  * _M_length
50  * [__rc_string_base<char_type>] _M_capacity
51  * _M_dataplus _M_refcount
52  * _M_p ----------------> unnamed array of char_type
53  * @endcode
54  *
55  * Where the _M_p points to the first character in the string, and
56  * you cast it to a pointer-to-_Rep and subtract 1 to get a
57  * pointer to the header.
58  *
59  * This approach has the enormous advantage that a string object
60  * requires only one allocation. All the ugliness is confined
61  * within a single pair of inline functions, which each compile to
62  * a single @a add instruction: _Rep::_M_refdata(), and
63  * __rc_string_base::_M_rep(); and the allocation function which gets a
64  * block of raw bytes and with room enough and constructs a _Rep
65  * object at the front.
66  *
67  * The reason you want _M_data pointing to the character array and
68  * not the _Rep is so that the debugger can see the string
69  * contents. (Probably we should add a non-inline member to get
70  * the _Rep for the debugger to use, so users can check the actual
71  * string length.)
72  *
73  * Note that the _Rep object is a POD so that you can have a
74  * static <em>empty string</em> _Rep object already @a constructed before
75  * static constructors have run. The reference-count encoding is
76  * chosen so that a 0 indicates one reference, so you never try to
77  * destroy the empty-string _Rep object.
78  *
79  * All but the last paragraph is considered pretty conventional
80  * for a C++ string implementation.
81  */
82  template<typename _CharT, typename _Traits, typename _Alloc>
84  : protected __vstring_utility<_CharT, _Traits, _Alloc>
85  {
86  public:
87  typedef _Traits traits_type;
88  typedef typename _Traits::char_type value_type;
89  typedef _Alloc allocator_type;
90 
91  typedef __vstring_utility<_CharT, _Traits, _Alloc> _Util_Base;
92  typedef typename _Util_Base::_CharT_alloc_type _CharT_alloc_type;
93  typedef typename _CharT_alloc_type::size_type size_type;
94 
95  private:
96  // _Rep: string representation
97  // Invariants:
98  // 1. String really contains _M_length + 1 characters: due to 21.3.4
99  // must be kept null-terminated.
100  // 2. _M_capacity >= _M_length
101  // Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
102  // 3. _M_refcount has three states:
103  // -1: leaked, one reference, no ref-copies allowed, non-const.
104  // 0: one reference, non-const.
105  // n>0: n + 1 references, operations require a lock, const.
106  // 4. All fields == 0 is an empty string, given the extra storage
107  // beyond-the-end for a null terminator; thus, the shared
108  // empty string representation needs no constructor.
109  struct _Rep
110  {
111  union
112  {
113  struct
114  {
115  size_type _M_length;
116  size_type _M_capacity;
117  _Atomic_word _M_refcount;
118  } _M_info;
119 
120  // Only for alignment purposes.
121  _CharT _M_align;
122  };
123 
124  typedef typename __alloc_traits<_Alloc>::template rebind<_Rep>::other
125  _Rep_alloc_type;
126 
127  _CharT*
128  _M_refdata() throw()
129  { return reinterpret_cast<_CharT*>(this + 1); }
130 
131  _CharT*
132  _M_refcopy() throw()
133  {
134  __atomic_add_dispatch(&_M_info._M_refcount, 1);
135  return _M_refdata();
136  } // XXX MT
137 
138  void
139  _M_set_length(size_type __n)
140  {
141  _M_info._M_refcount = 0; // One reference.
142  _M_info._M_length = __n;
143  // grrr. (per 21.3.4)
144  // You cannot leave those LWG people alone for a second.
145  traits_type::assign(_M_refdata()[__n], _CharT());
146  }
147 
148  // Create & Destroy
149  static _Rep*
150  _S_create(size_type, size_type, const _Alloc&);
151 
152  void
153  _M_destroy(const _Alloc&) throw();
154 
155  _CharT*
156  _M_clone(const _Alloc&, size_type __res = 0);
157  };
158 
159  struct _Rep_empty
160  : public _Rep
161  {
162  _CharT _M_terminal;
163  };
164 
165  static _Rep_empty _S_empty_rep;
166 
167  // The maximum number of individual char_type elements of an
168  // individual string is determined by _S_max_size. This is the
169  // value that will be returned by max_size(). (Whereas npos
170  // is the maximum number of bytes the allocator can allocate.)
171  // If one was to divvy up the theoretical largest size string,
172  // with a terminating character and m _CharT elements, it'd
173  // look like this:
174  // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
175  // + sizeof(_Rep) - 1
176  // (NB: last two terms for rounding reasons, see _M_create below)
177  // Solving for m:
178  // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
179  // In addition, this implementation halves this amount.
180  enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
181  + 1) / sizeof(_CharT)) - 1) / 2 };
182 
183  // Data Member (private):
184  mutable typename _Util_Base::template _Alloc_hider<_Alloc> _M_dataplus;
185 
186  void
187  _M_data(_CharT* __p)
188  { _M_dataplus._M_p = __p; }
189 
190  _Rep*
191  _M_rep() const
192  { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
193 
194  _CharT*
195  _M_grab(const _Alloc& __alloc) const
196  {
197  return (!_M_is_leaked() && _M_get_allocator() == __alloc)
198  ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
199  }
200 
201  void
202  _M_dispose()
203  {
204  // Be race-detector-friendly. For more info see bits/c++config.
205  _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
206  _M_refcount);
207  if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
208  -1) <= 0)
209  {
210  _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
211  _M_refcount);
212  _M_rep()->_M_destroy(_M_get_allocator());
213  }
214  } // XXX MT
215 
216  bool
217  _M_is_leaked() const
218  { return _M_rep()->_M_info._M_refcount < 0; }
219 
220  void
221  _M_set_sharable()
222  { _M_rep()->_M_info._M_refcount = 0; }
223 
224  void
225  _M_leak_hard();
226 
227  // _S_construct_aux is used to implement the 21.3.1 para 15 which
228  // requires special behaviour if _InIterator is an integral type
229  template<typename _InIterator>
230  static _CharT*
231  _S_construct_aux(_InIterator __beg, _InIterator __end,
232  const _Alloc& __a, std::__false_type)
233  {
235  _Tag;
236  return _S_construct(__beg, __end, __a, _Tag());
237  }
238 
239  // _GLIBCXX_RESOLVE_LIB_DEFECTS
240  // 438. Ambiguity in the "do the right thing" clause
241  template<typename _Integer>
242  static _CharT*
243  _S_construct_aux(_Integer __beg, _Integer __end,
244  const _Alloc& __a, std::__true_type)
245  { return _S_construct_aux_2(static_cast<size_type>(__beg),
246  __end, __a); }
247 
248  static _CharT*
249  _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
250  { return _S_construct(__req, __c, __a); }
251 
252  template<typename _InIterator>
253  static _CharT*
254  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
255  {
256  typedef typename std::__is_integer<_InIterator>::__type _Integral;
257  return _S_construct_aux(__beg, __end, __a, _Integral());
258  }
259 
260  // For Input Iterators, used in istreambuf_iterators, etc.
261  template<typename _InIterator>
262  static _CharT*
263  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
265 
266  // For forward_iterators up to random_access_iterators, used for
267  // string::iterator, _CharT*, etc.
268  template<typename _FwdIterator>
269  static _CharT*
270  _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
272 
273  static _CharT*
274  _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
275 
276  public:
277  size_type
278  _M_max_size() const
279  { return size_type(_S_max_size); }
280 
281  _CharT*
282  _M_data() const
283  { return _M_dataplus._M_p; }
284 
285  size_type
286  _M_length() const
287  { return _M_rep()->_M_info._M_length; }
288 
289  size_type
290  _M_capacity() const
291  { return _M_rep()->_M_info._M_capacity; }
292 
293  bool
294  _M_is_shared() const
295  { return _M_rep()->_M_info._M_refcount > 0; }
296 
297  void
298  _M_set_leaked()
299  { _M_rep()->_M_info._M_refcount = -1; }
300 
301  void
302  _M_leak() // for use in begin() & non-const op[]
303  {
304  if (!_M_is_leaked())
305  _M_leak_hard();
306  }
307 
308  void
309  _M_set_length(size_type __n)
310  { _M_rep()->_M_set_length(__n); }
311 
313  : _M_dataplus(_S_empty_rep._M_refcopy()) { }
314 
315  __rc_string_base(const _Alloc& __a);
316 
317  __rc_string_base(const __rc_string_base& __rcs);
318 
319 #if __cplusplus >= 201103L
321  : _M_dataplus(__rcs._M_dataplus)
322  { __rcs._M_data(_S_empty_rep._M_refcopy()); }
323 #endif
324 
325  __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
326 
327  template<typename _InputIterator>
328  __rc_string_base(_InputIterator __beg, _InputIterator __end,
329  const _Alloc& __a);
330 
332  { _M_dispose(); }
333 
334  allocator_type&
335  _M_get_allocator()
336  { return _M_dataplus; }
337 
338  const allocator_type&
339  _M_get_allocator() const
340  { return _M_dataplus; }
341 
342  void
343  _M_swap(__rc_string_base& __rcs);
344 
345  void
346  _M_assign(const __rc_string_base& __rcs);
347 
348  void
349  _M_reserve(size_type __res);
350 
351  void
352  _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
353  size_type __len2);
354 
355  void
356  _M_erase(size_type __pos, size_type __n);
357 
358  void
359  _M_clear()
360  {
361  _M_dispose();
362  _M_data(_S_empty_rep._M_refcopy());
363  }
364 
365  bool
366  _M_compare(const __rc_string_base&) const
367  { return false; }
368  };
369 
370  template<typename _CharT, typename _Traits, typename _Alloc>
373 
374  template<typename _CharT, typename _Traits, typename _Alloc>
377  _S_create(size_type __capacity, size_type __old_capacity,
378  const _Alloc& __alloc)
379  {
380  // _GLIBCXX_RESOLVE_LIB_DEFECTS
381  // 83. String::npos vs. string::max_size()
382  if (__capacity > size_type(_S_max_size))
383  std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
384 
385  // The standard places no restriction on allocating more memory
386  // than is strictly needed within this layer at the moment or as
387  // requested by an explicit application call to reserve().
388 
389  // Many malloc implementations perform quite poorly when an
390  // application attempts to allocate memory in a stepwise fashion
391  // growing each allocation size by only 1 char. Additionally,
392  // it makes little sense to allocate less linear memory than the
393  // natural blocking size of the malloc implementation.
394  // Unfortunately, we would need a somewhat low-level calculation
395  // with tuned parameters to get this perfect for any particular
396  // malloc implementation. Fortunately, generalizations about
397  // common features seen among implementations seems to suffice.
398 
399  // __pagesize need not match the actual VM page size for good
400  // results in practice, thus we pick a common value on the low
401  // side. __malloc_header_size is an estimate of the amount of
402  // overhead per memory allocation (in practice seen N * sizeof
403  // (void*) where N is 0, 2 or 4). According to folklore,
404  // picking this value on the high side is better than
405  // low-balling it (especially when this algorithm is used with
406  // malloc implementations that allocate memory blocks rounded up
407  // to a size which is a power of 2).
408  const size_type __pagesize = 4096;
409  const size_type __malloc_header_size = 4 * sizeof(void*);
410 
411  // The below implements an exponential growth policy, necessary to
412  // meet amortized linear time requirements of the library: see
413  // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
414  if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
415  {
416  __capacity = 2 * __old_capacity;
417  // Never allocate a string bigger than _S_max_size.
418  if (__capacity > size_type(_S_max_size))
419  __capacity = size_type(_S_max_size);
420  }
421 
422  // NB: Need an array of char_type[__capacity], plus a terminating
423  // null char_type() element, plus enough for the _Rep data structure,
424  // plus sizeof(_Rep) - 1 to upper round to a size multiple of
425  // sizeof(_Rep).
426  // Whew. Seemingly so needy, yet so elemental.
427  size_type __size = ((__capacity + 1) * sizeof(_CharT)
428  + 2 * sizeof(_Rep) - 1);
429 
430  const size_type __adj_size = __size + __malloc_header_size;
431  if (__adj_size > __pagesize && __capacity > __old_capacity)
432  {
433  const size_type __extra = __pagesize - __adj_size % __pagesize;
434  __capacity += __extra / sizeof(_CharT);
435  if (__capacity > size_type(_S_max_size))
436  __capacity = size_type(_S_max_size);
437  __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
438  }
439 
440  // NB: Might throw, but no worries about a leak, mate: _Rep()
441  // does not throw.
442  _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
443  _Rep* __p = new (__place) _Rep;
444  __p->_M_info._M_capacity = __capacity;
445  return __p;
446  }
447 
448  template<typename _CharT, typename _Traits, typename _Alloc>
449  void
450  __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
451  _M_destroy(const _Alloc& __a) throw ()
452  {
453  const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
454  + 2 * sizeof(_Rep) - 1);
455  _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
456  }
457 
458  template<typename _CharT, typename _Traits, typename _Alloc>
459  _CharT*
460  __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
461  _M_clone(const _Alloc& __alloc, size_type __res)
462  {
463  // Requested capacity of the clone.
464  const size_type __requested_cap = _M_info._M_length + __res;
465  _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
466  __alloc);
467 
468  if (_M_info._M_length)
469  __rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
470 
471  __r->_M_set_length(_M_info._M_length);
472  return __r->_M_refdata();
473  }
474 
475  template<typename _CharT, typename _Traits, typename _Alloc>
476  __rc_string_base<_CharT, _Traits, _Alloc>::
477  __rc_string_base(const _Alloc& __a)
478  : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
479 
480  template<typename _CharT, typename _Traits, typename _Alloc>
481  __rc_string_base<_CharT, _Traits, _Alloc>::
482  __rc_string_base(const __rc_string_base& __rcs)
483  : _M_dataplus(__rcs._M_get_allocator(),
484  __rcs._M_grab(__rcs._M_get_allocator())) { }
485 
486  template<typename _CharT, typename _Traits, typename _Alloc>
487  __rc_string_base<_CharT, _Traits, _Alloc>::
488  __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
489  : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
490 
491  template<typename _CharT, typename _Traits, typename _Alloc>
492  template<typename _InputIterator>
493  __rc_string_base<_CharT, _Traits, _Alloc>::
494  __rc_string_base(_InputIterator __beg, _InputIterator __end,
495  const _Alloc& __a)
496  : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
497 
498  template<typename _CharT, typename _Traits, typename _Alloc>
499  void
500  __rc_string_base<_CharT, _Traits, _Alloc>::
501  _M_leak_hard()
502  {
503  if (_M_is_shared())
504  _M_erase(0, 0);
505  _M_set_leaked();
506  }
507 
508  // NB: This is the special case for Input Iterators, used in
509  // istreambuf_iterators, etc.
510  // Input Iterators have a cost structure very different from
511  // pointers, calling for a different coding style.
512  template<typename _CharT, typename _Traits, typename _Alloc>
513  template<typename _InIterator>
514  _CharT*
515  __rc_string_base<_CharT, _Traits, _Alloc>::
516  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
518  {
519  if (__beg == __end && __a == _Alloc())
520  return _S_empty_rep._M_refcopy();
521 
522  // Avoid reallocation for common case.
523  _CharT __buf[128];
524  size_type __len = 0;
525  while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
526  {
527  __buf[__len++] = *__beg;
528  ++__beg;
529  }
530  _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
531  _S_copy(__r->_M_refdata(), __buf, __len);
532  __try
533  {
534  while (__beg != __end)
535  {
536  if (__len == __r->_M_info._M_capacity)
537  {
538  // Allocate more space.
539  _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
540  _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
541  __r->_M_destroy(__a);
542  __r = __another;
543  }
544  __r->_M_refdata()[__len++] = *__beg;
545  ++__beg;
546  }
547  }
548  __catch(...)
549  {
550  __r->_M_destroy(__a);
551  __throw_exception_again;
552  }
553  __r->_M_set_length(__len);
554  return __r->_M_refdata();
555  }
556 
557  template<typename _CharT, typename _Traits, typename _Alloc>
558  template<typename _InIterator>
559  _CharT*
560  __rc_string_base<_CharT, _Traits, _Alloc>::
561  _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
563  {
564  if (__beg == __end && __a == _Alloc())
565  return _S_empty_rep._M_refcopy();
566 
567  // NB: Not required, but considered best practice.
568  if (__is_null_pointer(__beg) && __beg != __end)
569  std::__throw_logic_error(__N("__rc_string_base::"
570  "_S_construct null not valid"));
571 
572  const size_type __dnew = static_cast<size_type>(std::distance(__beg,
573  __end));
574  // Check for out_of_range and length_error exceptions.
575  _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
576  __try
577  { __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
578  __catch(...)
579  {
580  __r->_M_destroy(__a);
581  __throw_exception_again;
582  }
583  __r->_M_set_length(__dnew);
584  return __r->_M_refdata();
585  }
586 
587  template<typename _CharT, typename _Traits, typename _Alloc>
588  _CharT*
589  __rc_string_base<_CharT, _Traits, _Alloc>::
590  _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
591  {
592  if (__n == 0 && __a == _Alloc())
593  return _S_empty_rep._M_refcopy();
594 
595  // Check for out_of_range and length_error exceptions.
596  _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
597  if (__n)
598  __rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
599 
600  __r->_M_set_length(__n);
601  return __r->_M_refdata();
602  }
603 
604  template<typename _CharT, typename _Traits, typename _Alloc>
605  void
606  __rc_string_base<_CharT, _Traits, _Alloc>::
607  _M_swap(__rc_string_base& __rcs)
608  {
609  if (_M_is_leaked())
610  _M_set_sharable();
611  if (__rcs._M_is_leaked())
612  __rcs._M_set_sharable();
613 
614  _CharT* __tmp = _M_data();
615  _M_data(__rcs._M_data());
616  __rcs._M_data(__tmp);
617 
618  // _GLIBCXX_RESOLVE_LIB_DEFECTS
619  // 431. Swapping containers with unequal allocators.
620  std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
621  __rcs._M_get_allocator());
622  }
623 
624  template<typename _CharT, typename _Traits, typename _Alloc>
625  void
626  __rc_string_base<_CharT, _Traits, _Alloc>::
627  _M_assign(const __rc_string_base& __rcs)
628  {
629  if (_M_rep() != __rcs._M_rep())
630  {
631  _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
632  _M_dispose();
633  _M_data(__tmp);
634  }
635  }
636 
637  template<typename _CharT, typename _Traits, typename _Alloc>
638  void
639  __rc_string_base<_CharT, _Traits, _Alloc>::
640  _M_reserve(size_type __res)
641  {
642  // Make sure we don't shrink below the current size.
643  if (__res < _M_length())
644  __res = _M_length();
645 
646  if (__res != _M_capacity() || _M_is_shared())
647  {
648  _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
649  __res - _M_length());
650  _M_dispose();
651  _M_data(__tmp);
652  }
653  }
654 
655  template<typename _CharT, typename _Traits, typename _Alloc>
656  void
657  __rc_string_base<_CharT, _Traits, _Alloc>::
658  _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
659  size_type __len2)
660  {
661  const size_type __how_much = _M_length() - __pos - __len1;
662 
663  _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
664  _M_capacity(), _M_get_allocator());
665 
666  if (__pos)
667  this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
668  if (__s && __len2)
669  this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
670  if (__how_much)
671  this->_S_copy(__r->_M_refdata() + __pos + __len2,
672  _M_data() + __pos + __len1, __how_much);
673 
674  _M_dispose();
675  _M_data(__r->_M_refdata());
676  }
677 
678  template<typename _CharT, typename _Traits, typename _Alloc>
679  void
680  __rc_string_base<_CharT, _Traits, _Alloc>::
681  _M_erase(size_type __pos, size_type __n)
682  {
683  const size_type __new_size = _M_length() - __n;
684  const size_type __how_much = _M_length() - __pos - __n;
685 
686  if (_M_is_shared())
687  {
688  // Must reallocate.
689  _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
690  _M_get_allocator());
691 
692  if (__pos)
693  this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
694  if (__how_much)
695  this->_S_copy(__r->_M_refdata() + __pos,
696  _M_data() + __pos + __n, __how_much);
697 
698  _M_dispose();
699  _M_data(__r->_M_refdata());
700  }
701  else if (__how_much && __n)
702  {
703  // Work in-place.
704  this->_S_move(_M_data() + __pos,
705  _M_data() + __pos + __n, __how_much);
706  }
707 
708  _M_rep()->_M_set_length(__new_size);
709  }
710 
711  template<>
712  inline bool
713  __rc_string_base<char, std::char_traits<char>,
715  _M_compare(const __rc_string_base& __rcs) const
716  {
717  if (_M_rep() == __rcs._M_rep())
718  return true;
719  return false;
720  }
721 
722 #ifdef _GLIBCXX_USE_WCHAR_T
723  template<>
724  inline bool
725  __rc_string_base<wchar_t, std::char_traits<wchar_t>,
727  _M_compare(const __rc_string_base& __rcs) const
728  {
729  if (_M_rep() == __rcs._M_rep())
730  return true;
731  return false;
732  }
733 #endif
734 
735 _GLIBCXX_END_NAMESPACE_VERSION
736 } // namespace
737 
738 #endif /* _RC_STRING_BASE_H */
GNU extensions for public use.
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:141
Traits class for iterators.
Marking input iterators.
Forward iterators support a superset of input iterator operations.
Uniform interface to C++98 and C++11 allocators.