libstdc++
rc_string_base.h
Go to the documentation of this file.
00001 // Reference-counted versatile string base -*- C++ -*-
00002 
00003 // Copyright (C) 2005-2019 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file ext/rc_string_base.h
00026  *  This is an internal header file, included by other library headers.
00027  *  Do not attempt to use it directly. @headername{ext/vstring.h}
00028  */
00029 
00030 #ifndef _RC_STRING_BASE_H
00031 #define _RC_STRING_BASE_H 1
00032 
00033 #include <ext/atomicity.h>
00034 #include <bits/stl_iterator_base_funcs.h>
00035 
00036 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
00037 {
00038 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00039 
00040   /**
00041    *  Documentation?  What's that?
00042    *  Nathan Myers <ncm@cantrip.org>.
00043    *
00044    *  A string looks like this:
00045    *
00046    *  @code
00047    *                                        [_Rep]
00048    *                                        _M_length
00049    *   [__rc_string_base<char_type>]        _M_capacity
00050    *   _M_dataplus                          _M_refcount
00051    *   _M_p ---------------->               unnamed array of char_type
00052    *  @endcode
00053    *
00054    *  Where the _M_p points to the first character in the string, and
00055    *  you cast it to a pointer-to-_Rep and subtract 1 to get a
00056    *  pointer to the header.
00057    *
00058    *  This approach has the enormous advantage that a string object
00059    *  requires only one allocation.  All the ugliness is confined
00060    *  within a single pair of inline functions, which each compile to
00061    *  a single @a add instruction: _Rep::_M_refdata(), and
00062    *  __rc_string_base::_M_rep(); and the allocation function which gets a
00063    *  block of raw bytes and with room enough and constructs a _Rep
00064    *  object at the front.
00065    *
00066    *  The reason you want _M_data pointing to the character array and
00067    *  not the _Rep is so that the debugger can see the string
00068    *  contents. (Probably we should add a non-inline member to get
00069    *  the _Rep for the debugger to use, so users can check the actual
00070    *  string length.)
00071    *
00072    *  Note that the _Rep object is a POD so that you can have a
00073    *  static <em>empty string</em> _Rep object already @a constructed before
00074    *  static constructors have run.  The reference-count encoding is
00075    *  chosen so that a 0 indicates one reference, so you never try to
00076    *  destroy the empty-string _Rep object.
00077    *
00078    *  All but the last paragraph is considered pretty conventional
00079    *  for a C++ string implementation.
00080   */
00081  template<typename _CharT, typename _Traits, typename _Alloc>
00082     class __rc_string_base
00083     : protected __vstring_utility<_CharT, _Traits, _Alloc>
00084     {
00085     public:
00086       typedef _Traits                                       traits_type;
00087       typedef typename _Traits::char_type                   value_type;
00088       typedef _Alloc                                        allocator_type;
00089 
00090       typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;
00091       typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;
00092       typedef typename _CharT_alloc_type::size_type         size_type;
00093 
00094     private:
00095       // _Rep: string representation
00096       //   Invariants:
00097       //   1. String really contains _M_length + 1 characters: due to 21.3.4
00098       //      must be kept null-terminated.
00099       //   2. _M_capacity >= _M_length
00100       //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
00101       //   3. _M_refcount has three states:
00102       //      -1: leaked, one reference, no ref-copies allowed, non-const.
00103       //       0: one reference, non-const.
00104       //     n>0: n + 1 references, operations require a lock, const.
00105       //   4. All fields == 0 is an empty string, given the extra storage
00106       //      beyond-the-end for a null terminator; thus, the shared
00107       //      empty string representation needs no constructor.
00108       struct _Rep
00109       {
00110         union
00111         {
00112           struct
00113           {
00114             size_type       _M_length;
00115             size_type       _M_capacity;
00116             _Atomic_word    _M_refcount;
00117           }                 _M_info;
00118 
00119           // Only for alignment purposes.
00120           _CharT            _M_align;
00121         };
00122 
00123         typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
00124 
00125         _CharT*
00126         _M_refdata() throw()
00127         { return reinterpret_cast<_CharT*>(this + 1); }
00128 
00129         _CharT*
00130         _M_refcopy() throw()
00131         {
00132           __atomic_add_dispatch(&_M_info._M_refcount, 1);
00133           return _M_refdata();
00134         }  // XXX MT
00135 
00136         void
00137         _M_set_length(size_type __n)
00138         {
00139           _M_info._M_refcount = 0;  // One reference.
00140           _M_info._M_length = __n;
00141           // grrr. (per 21.3.4)
00142           // You cannot leave those LWG people alone for a second.
00143           traits_type::assign(_M_refdata()[__n], _CharT());
00144         }
00145 
00146         // Create & Destroy
00147         static _Rep*
00148         _S_create(size_type, size_type, const _Alloc&);
00149 
00150         void
00151         _M_destroy(const _Alloc&) throw();
00152 
00153         _CharT*
00154         _M_clone(const _Alloc&, size_type __res = 0);
00155       };
00156 
00157       struct _Rep_empty
00158       : public _Rep
00159       {
00160         _CharT              _M_terminal;
00161       };
00162 
00163       static _Rep_empty     _S_empty_rep;
00164 
00165       // The maximum number of individual char_type elements of an
00166       // individual string is determined by _S_max_size. This is the
00167       // value that will be returned by max_size().  (Whereas npos
00168       // is the maximum number of bytes the allocator can allocate.)
00169       // If one was to divvy up the theoretical largest size string,
00170       // with a terminating character and m _CharT elements, it'd
00171       // look like this:
00172       // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
00173       //        + sizeof(_Rep) - 1
00174       // (NB: last two terms for rounding reasons, see _M_create below)
00175       // Solving for m:
00176       // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
00177       // In addition, this implementation halves this amount.
00178       enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
00179                               + 1) / sizeof(_CharT)) - 1) / 2 };
00180 
00181       // Data Member (private):
00182       mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;
00183 
00184       void
00185       _M_data(_CharT* __p)
00186       { _M_dataplus._M_p = __p; }
00187 
00188       _Rep*
00189       _M_rep() const
00190       { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
00191 
00192       _CharT*
00193       _M_grab(const _Alloc& __alloc) const
00194       {
00195         return (!_M_is_leaked() && _M_get_allocator() == __alloc)
00196                 ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
00197       }
00198 
00199       void
00200       _M_dispose()
00201       {
00202         // Be race-detector-friendly.  For more info see bits/c++config.
00203         _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
00204                                                 _M_refcount);
00205         if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
00206                                         -1) <= 0)
00207           {
00208             _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
00209                                                    _M_refcount);
00210             _M_rep()->_M_destroy(_M_get_allocator());
00211           }
00212       }  // XXX MT
00213 
00214       bool
00215       _M_is_leaked() const
00216       { return _M_rep()->_M_info._M_refcount < 0; }
00217 
00218       void
00219       _M_set_sharable()
00220       { _M_rep()->_M_info._M_refcount = 0; }
00221 
00222       void
00223       _M_leak_hard();
00224 
00225       // _S_construct_aux is used to implement the 21.3.1 para 15 which
00226       // requires special behaviour if _InIterator is an integral type
00227       template<typename _InIterator>
00228         static _CharT*
00229         _S_construct_aux(_InIterator __beg, _InIterator __end,
00230                          const _Alloc& __a, std::__false_type)
00231         {
00232           typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
00233           return _S_construct(__beg, __end, __a, _Tag());
00234         }
00235 
00236       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00237       // 438. Ambiguity in the "do the right thing" clause
00238       template<typename _Integer>
00239         static _CharT*
00240         _S_construct_aux(_Integer __beg, _Integer __end,
00241                          const _Alloc& __a, std::__true_type)
00242         { return _S_construct_aux_2(static_cast<size_type>(__beg),
00243                                     __end, __a); }
00244 
00245       static _CharT*
00246       _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
00247       { return _S_construct(__req, __c, __a); }
00248 
00249       template<typename _InIterator>
00250         static _CharT*
00251         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
00252         {
00253           typedef typename std::__is_integer<_InIterator>::__type _Integral;
00254           return _S_construct_aux(__beg, __end, __a, _Integral());
00255         }
00256 
00257       // For Input Iterators, used in istreambuf_iterators, etc.
00258       template<typename _InIterator>
00259         static _CharT*
00260          _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00261                       std::input_iterator_tag);
00262 
00263       // For forward_iterators up to random_access_iterators, used for
00264       // string::iterator, _CharT*, etc.
00265       template<typename _FwdIterator>
00266         static _CharT*
00267         _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
00268                      std::forward_iterator_tag);
00269 
00270       static _CharT*
00271       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
00272 
00273     public:
00274       size_type
00275       _M_max_size() const
00276       { return size_type(_S_max_size); }
00277 
00278       _CharT*
00279       _M_data() const
00280       { return _M_dataplus._M_p; }
00281 
00282       size_type
00283       _M_length() const
00284       { return _M_rep()->_M_info._M_length; }
00285 
00286       size_type
00287       _M_capacity() const
00288       { return _M_rep()->_M_info._M_capacity; }
00289 
00290       bool
00291       _M_is_shared() const
00292       { return _M_rep()->_M_info._M_refcount > 0; }
00293 
00294       void
00295       _M_set_leaked()
00296       { _M_rep()->_M_info._M_refcount = -1; }
00297 
00298       void
00299       _M_leak()    // for use in begin() & non-const op[]
00300       {
00301         if (!_M_is_leaked())
00302           _M_leak_hard();
00303       }
00304 
00305       void
00306       _M_set_length(size_type __n)
00307       { _M_rep()->_M_set_length(__n); }
00308 
00309       __rc_string_base()
00310       : _M_dataplus(_S_empty_rep._M_refcopy()) { }
00311 
00312       __rc_string_base(const _Alloc& __a);
00313 
00314       __rc_string_base(const __rc_string_base& __rcs);
00315 
00316 #if __cplusplus >= 201103L
00317       __rc_string_base(__rc_string_base&& __rcs)
00318       : _M_dataplus(__rcs._M_dataplus)
00319       { __rcs._M_data(_S_empty_rep._M_refcopy()); }
00320 #endif
00321 
00322       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
00323 
00324       template<typename _InputIterator>
00325         __rc_string_base(_InputIterator __beg, _InputIterator __end,
00326                          const _Alloc& __a);
00327 
00328       ~__rc_string_base()
00329       { _M_dispose(); }
00330 
00331       allocator_type&
00332       _M_get_allocator()
00333       { return _M_dataplus; }
00334 
00335       const allocator_type&
00336       _M_get_allocator() const
00337       { return _M_dataplus; }
00338 
00339       void
00340       _M_swap(__rc_string_base& __rcs);
00341 
00342       void
00343       _M_assign(const __rc_string_base& __rcs);
00344 
00345       void
00346       _M_reserve(size_type __res);
00347 
00348       void
00349       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00350                 size_type __len2);
00351 
00352       void
00353       _M_erase(size_type __pos, size_type __n);
00354 
00355       void
00356       _M_clear()
00357       {
00358         _M_dispose();
00359         _M_data(_S_empty_rep._M_refcopy());
00360       }
00361 
00362       bool
00363       _M_compare(const __rc_string_base&) const
00364       { return false; }
00365     };
00366 
00367   template<typename _CharT, typename _Traits, typename _Alloc>
00368     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
00369     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
00370 
00371   template<typename _CharT, typename _Traits, typename _Alloc>
00372     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
00373     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00374     _S_create(size_type __capacity, size_type __old_capacity,
00375               const _Alloc& __alloc)
00376     {
00377       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00378       // 83.  String::npos vs. string::max_size()
00379       if (__capacity > size_type(_S_max_size))
00380         std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
00381 
00382       // The standard places no restriction on allocating more memory
00383       // than is strictly needed within this layer at the moment or as
00384       // requested by an explicit application call to reserve().
00385 
00386       // Many malloc implementations perform quite poorly when an
00387       // application attempts to allocate memory in a stepwise fashion
00388       // growing each allocation size by only 1 char.  Additionally,
00389       // it makes little sense to allocate less linear memory than the
00390       // natural blocking size of the malloc implementation.
00391       // Unfortunately, we would need a somewhat low-level calculation
00392       // with tuned parameters to get this perfect for any particular
00393       // malloc implementation.  Fortunately, generalizations about
00394       // common features seen among implementations seems to suffice.
00395 
00396       // __pagesize need not match the actual VM page size for good
00397       // results in practice, thus we pick a common value on the low
00398       // side.  __malloc_header_size is an estimate of the amount of
00399       // overhead per memory allocation (in practice seen N * sizeof
00400       // (void*) where N is 0, 2 or 4).  According to folklore,
00401       // picking this value on the high side is better than
00402       // low-balling it (especially when this algorithm is used with
00403       // malloc implementations that allocate memory blocks rounded up
00404       // to a size which is a power of 2).
00405       const size_type __pagesize = 4096;
00406       const size_type __malloc_header_size = 4 * sizeof(void*);
00407 
00408       // The below implements an exponential growth policy, necessary to
00409       // meet amortized linear time requirements of the library: see
00410       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
00411       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
00412         {
00413           __capacity = 2 * __old_capacity;
00414           // Never allocate a string bigger than _S_max_size.
00415           if (__capacity > size_type(_S_max_size))
00416             __capacity = size_type(_S_max_size);
00417         }
00418 
00419       // NB: Need an array of char_type[__capacity], plus a terminating
00420       // null char_type() element, plus enough for the _Rep data structure,
00421       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
00422       // sizeof(_Rep).
00423       // Whew. Seemingly so needy, yet so elemental.
00424       size_type __size = ((__capacity + 1) * sizeof(_CharT)
00425                           + 2 * sizeof(_Rep) - 1);
00426 
00427       const size_type __adj_size = __size + __malloc_header_size;
00428       if (__adj_size > __pagesize && __capacity > __old_capacity)
00429         {
00430           const size_type __extra = __pagesize - __adj_size % __pagesize;
00431           __capacity += __extra / sizeof(_CharT);
00432           if (__capacity > size_type(_S_max_size))
00433             __capacity = size_type(_S_max_size);
00434           __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
00435         }
00436 
00437       // NB: Might throw, but no worries about a leak, mate: _Rep()
00438       // does not throw.
00439       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
00440       _Rep* __p = new (__place) _Rep;
00441       __p->_M_info._M_capacity = __capacity;
00442       return __p;
00443     }
00444 
00445   template<typename _CharT, typename _Traits, typename _Alloc>
00446     void
00447     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00448     _M_destroy(const _Alloc& __a) throw ()
00449     {
00450       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
00451                                 + 2 * sizeof(_Rep) - 1);
00452       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
00453     }
00454 
00455   template<typename _CharT, typename _Traits, typename _Alloc>
00456     _CharT*
00457     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00458     _M_clone(const _Alloc& __alloc, size_type __res)
00459     {
00460       // Requested capacity of the clone.
00461       const size_type __requested_cap = _M_info._M_length + __res;
00462       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
00463                                   __alloc);
00464 
00465       if (_M_info._M_length)
00466         __rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
00467 
00468       __r->_M_set_length(_M_info._M_length);
00469       return __r->_M_refdata();
00470     }
00471 
00472   template<typename _CharT, typename _Traits, typename _Alloc>
00473     __rc_string_base<_CharT, _Traits, _Alloc>::
00474     __rc_string_base(const _Alloc& __a)
00475     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
00476 
00477   template<typename _CharT, typename _Traits, typename _Alloc>
00478     __rc_string_base<_CharT, _Traits, _Alloc>::
00479     __rc_string_base(const __rc_string_base& __rcs)
00480     : _M_dataplus(__rcs._M_get_allocator(),
00481                   __rcs._M_grab(__rcs._M_get_allocator())) { }
00482 
00483   template<typename _CharT, typename _Traits, typename _Alloc>
00484     __rc_string_base<_CharT, _Traits, _Alloc>::
00485     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
00486     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
00487 
00488   template<typename _CharT, typename _Traits, typename _Alloc>
00489     template<typename _InputIterator>
00490     __rc_string_base<_CharT, _Traits, _Alloc>::
00491     __rc_string_base(_InputIterator __beg, _InputIterator __end,
00492                      const _Alloc& __a)
00493     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
00494 
00495   template<typename _CharT, typename _Traits, typename _Alloc>
00496     void
00497     __rc_string_base<_CharT, _Traits, _Alloc>::
00498     _M_leak_hard()
00499     {
00500       if (_M_is_shared())
00501         _M_erase(0, 0);
00502       _M_set_leaked();
00503     }
00504 
00505   // NB: This is the special case for Input Iterators, used in
00506   // istreambuf_iterators, etc.
00507   // Input Iterators have a cost structure very different from
00508   // pointers, calling for a different coding style.
00509   template<typename _CharT, typename _Traits, typename _Alloc>
00510     template<typename _InIterator>
00511       _CharT*
00512       __rc_string_base<_CharT, _Traits, _Alloc>::
00513       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00514                    std::input_iterator_tag)
00515       {
00516         if (__beg == __end && __a == _Alloc())
00517           return _S_empty_rep._M_refcopy();
00518 
00519         // Avoid reallocation for common case.
00520         _CharT __buf[128];
00521         size_type __len = 0;
00522         while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
00523           {
00524             __buf[__len++] = *__beg;
00525             ++__beg;
00526           }
00527         _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
00528         _S_copy(__r->_M_refdata(), __buf, __len);
00529         __try
00530           {
00531             while (__beg != __end)
00532               {
00533                 if (__len == __r->_M_info._M_capacity)
00534                   {
00535                     // Allocate more space.
00536                     _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
00537                     _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
00538                     __r->_M_destroy(__a);
00539                     __r = __another;
00540                   }
00541                 __r->_M_refdata()[__len++] = *__beg;
00542                 ++__beg;
00543               }
00544           }
00545         __catch(...)
00546           {
00547             __r->_M_destroy(__a);
00548             __throw_exception_again;
00549           }
00550         __r->_M_set_length(__len);
00551         return __r->_M_refdata();
00552       }
00553 
00554   template<typename _CharT, typename _Traits, typename _Alloc>
00555     template<typename _InIterator>
00556       _CharT*
00557       __rc_string_base<_CharT, _Traits, _Alloc>::
00558       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00559                    std::forward_iterator_tag)
00560       {
00561         if (__beg == __end && __a == _Alloc())
00562           return _S_empty_rep._M_refcopy();
00563 
00564         // NB: Not required, but considered best practice.
00565         if (__is_null_pointer(__beg) && __beg != __end)
00566           std::__throw_logic_error(__N("__rc_string_base::"
00567                                        "_S_construct null not valid"));
00568 
00569         const size_type __dnew = static_cast<size_type>(std::distance(__beg,
00570                                                                       __end));
00571         // Check for out_of_range and length_error exceptions.
00572         _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
00573         __try
00574           { __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
00575         __catch(...)
00576           {
00577             __r->_M_destroy(__a);
00578             __throw_exception_again;
00579           }
00580         __r->_M_set_length(__dnew);
00581         return __r->_M_refdata();
00582       }
00583 
00584   template<typename _CharT, typename _Traits, typename _Alloc>
00585     _CharT*
00586     __rc_string_base<_CharT, _Traits, _Alloc>::
00587     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
00588     {
00589       if (__n == 0 && __a == _Alloc())
00590         return _S_empty_rep._M_refcopy();
00591 
00592       // Check for out_of_range and length_error exceptions.
00593       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
00594       if (__n)
00595         __rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
00596 
00597       __r->_M_set_length(__n);
00598       return __r->_M_refdata();
00599     }
00600 
00601   template<typename _CharT, typename _Traits, typename _Alloc>
00602     void
00603     __rc_string_base<_CharT, _Traits, _Alloc>::
00604     _M_swap(__rc_string_base& __rcs)
00605     {
00606       if (_M_is_leaked())
00607         _M_set_sharable();
00608       if (__rcs._M_is_leaked())
00609         __rcs._M_set_sharable();
00610 
00611       _CharT* __tmp = _M_data();
00612       _M_data(__rcs._M_data());
00613       __rcs._M_data(__tmp);
00614 
00615       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00616       // 431. Swapping containers with unequal allocators.
00617       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
00618                                                   __rcs._M_get_allocator());
00619     }
00620 
00621   template<typename _CharT, typename _Traits, typename _Alloc>
00622     void
00623     __rc_string_base<_CharT, _Traits, _Alloc>::
00624     _M_assign(const __rc_string_base& __rcs)
00625     {
00626       if (_M_rep() != __rcs._M_rep())
00627         {
00628           _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
00629           _M_dispose();
00630           _M_data(__tmp);
00631         }
00632     }
00633 
00634   template<typename _CharT, typename _Traits, typename _Alloc>
00635     void
00636     __rc_string_base<_CharT, _Traits, _Alloc>::
00637     _M_reserve(size_type __res)
00638     {
00639       // Make sure we don't shrink below the current size.
00640       if (__res < _M_length())
00641         __res = _M_length();
00642 
00643       if (__res != _M_capacity() || _M_is_shared())
00644         {
00645           _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
00646                                              __res - _M_length());
00647           _M_dispose();
00648           _M_data(__tmp);
00649         }
00650     }
00651 
00652   template<typename _CharT, typename _Traits, typename _Alloc>
00653     void
00654     __rc_string_base<_CharT, _Traits, _Alloc>::
00655     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00656               size_type __len2)
00657     {
00658       const size_type __how_much = _M_length() - __pos - __len1;
00659 
00660       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
00661                                   _M_capacity(), _M_get_allocator());
00662 
00663       if (__pos)
00664         this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
00665       if (__s && __len2)
00666         this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
00667       if (__how_much)
00668         this->_S_copy(__r->_M_refdata() + __pos + __len2,
00669                 _M_data() + __pos + __len1, __how_much);
00670 
00671       _M_dispose();
00672       _M_data(__r->_M_refdata());
00673     }
00674 
00675   template<typename _CharT, typename _Traits, typename _Alloc>
00676     void
00677     __rc_string_base<_CharT, _Traits, _Alloc>::
00678     _M_erase(size_type __pos, size_type __n)
00679     {
00680       const size_type __new_size = _M_length() - __n;
00681       const size_type __how_much = _M_length() - __pos - __n;
00682 
00683       if (_M_is_shared())
00684         {
00685           // Must reallocate.
00686           _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
00687                                       _M_get_allocator());
00688 
00689           if (__pos)
00690             this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
00691           if (__how_much)
00692             this->_S_copy(__r->_M_refdata() + __pos,
00693                     _M_data() + __pos + __n, __how_much);
00694 
00695           _M_dispose();
00696           _M_data(__r->_M_refdata());
00697         }
00698       else if (__how_much && __n)
00699         {
00700           // Work in-place.
00701           this->_S_move(_M_data() + __pos,
00702                   _M_data() + __pos + __n, __how_much);
00703         }
00704 
00705       _M_rep()->_M_set_length(__new_size);
00706     }
00707 
00708   template<>
00709     inline bool
00710     __rc_string_base<char, std::char_traits<char>,
00711                      std::allocator<char> >::
00712     _M_compare(const __rc_string_base& __rcs) const
00713     {
00714       if (_M_rep() == __rcs._M_rep())
00715         return true;
00716       return false;
00717     }
00718 
00719 #ifdef _GLIBCXX_USE_WCHAR_T
00720   template<>
00721     inline bool
00722     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
00723                      std::allocator<wchar_t> >::
00724     _M_compare(const __rc_string_base& __rcs) const
00725     {
00726       if (_M_rep() == __rcs._M_rep())
00727         return true;
00728       return false;
00729     }
00730 #endif
00731 
00732 _GLIBCXX_END_NAMESPACE_VERSION
00733 } // namespace
00734 
00735 #endif /* _RC_STRING_BASE_H */