# rc_string_base.h

Go to the documentation of this file.

    00001 // Reference-counted versatile string base -*- C++ -*-
    00002
    00003 // Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
    00004 // Free Software Foundation, Inc.
    00005 //
    00006 // This file is part of the GNU ISO C++ Library.  This library is free
    00007 // software; you can redistribute it and/or modify it under the
    00008 // terms of the GNU General Public License as published by the
    00009 // Free Software Foundation; either version 3, or (at your option)
    00010 // any later version.
    00011
    00012 // This library is distributed in the hope that it will be useful,
    00013 // but WITHOUT ANY WARRANTY; without even the implied warranty of
    00014 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    00015 // GNU General Public License for more details.
    00016
    00017 // Under Section 7 of GPL version 3, you are granted additional
    00018 // permissions described in the GCC Runtime Library Exception, version
    00019 // 3.1, as published by the Free Software Foundation.
    00020
    00021 // You should have received a copy of the GNU General Public License and
    00022 // a copy of the GCC Runtime Library Exception along with this program;
    00023 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    00024 // <http://www.gnu.org/licenses/>.
    00025
    00026 /** @file ext/rc_string_base.h
    00027  *  This file is a GNU extension to the Standard C++ Library.
    00028  *  This is an internal header file, included by other library headers.
    00029  *  You should not attempt to use it directly.
    00030  */
    00031
    00032 #ifndef _RC_STRING_BASE_H
    00033 #define _RC_STRING_BASE_H 1
    00034
    00035 #include <ext/atomicity.h>
    00036 #include <bits/stl_iterator_base_funcs.h>
    00037
    00038 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
    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     if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
    00203                     -1) <= 0)
    00204       _M_rep()->_M_destroy(_M_get_allocator());
    00205       }  // XXX MT
    00206
    00207       bool
    00208       _M_is_leaked() const
    00209       { return _M_rep()->_M_info._M_refcount < 0; }
    00210
    00211       void
    00212       _M_set_sharable()
    00213       { _M_rep()->_M_info._M_refcount = 0; }
    00214
    00215       void
    00216       _M_leak_hard();
    00217
    00218       // _S_construct_aux is used to implement the 21.3.1 para 15 which
    00219       // requires special behaviour if _InIterator is an integral type
    00220       template<typename _InIterator>
    00221         static _CharT*
    00222         _S_construct_aux(_InIterator __beg, _InIterator __end,
    00223              const _Alloc& __a, std::__false_type)
    00224     {
    00225           typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
    00226           return _S_construct(__beg, __end, __a, _Tag());
    00227     }
    00228
    00229       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00230       // 438. Ambiguity in the "do the right thing" clause
    00231       template<typename _Integer>
    00232         static _CharT*
    00233         _S_construct_aux(_Integer __beg, _Integer __end,
    00234              const _Alloc& __a, std::__true_type)
    00235     { return _S_construct_aux_2(static_cast<size_type>(__beg),
    00236                     __end, __a); }
    00237
    00238       static _CharT*
    00239       _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
    00240       { return _S_construct(__req, __c, __a); }
    00241
    00242       template<typename _InIterator>
    00243         static _CharT*
    00244         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
    00245     {
    00246       typedef typename std::__is_integer<_InIterator>::__type _Integral;
    00247       return _S_construct_aux(__beg, __end, __a, _Integral());
    00248         }
    00249
    00250       // For Input Iterators, used in istreambuf_iterators, etc.
    00251       template<typename _InIterator>
    00252         static _CharT*
    00253          _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
    00254               std::input_iterator_tag);
    00255
    00256       // For forward_iterators up to random_access_iterators, used for
    00257       // string::iterator, _CharT*, etc.
    00258       template<typename _FwdIterator>
    00259         static _CharT*
    00260         _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
    00261              std::forward_iterator_tag);
    00262
    00263       static _CharT*
    00264       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
    00265
    00266     public:
    00267       size_type
    00268       _M_max_size() const
    00269       { return size_type(_S_max_size); }
    00270
    00271       _CharT*
    00272       _M_data() const
    00273       { return _M_dataplus._M_p; }
    00274
    00275       size_type
    00276       _M_length() const
    00277       { return _M_rep()->_M_info._M_length; }
    00278
    00279       size_type
    00280       _M_capacity() const
    00281       { return _M_rep()->_M_info._M_capacity; }
    00282
    00283       bool
    00284       _M_is_shared() const
    00285       { return _M_rep()->_M_info._M_refcount > 0; }
    00286
    00287       void
    00288       _M_set_leaked()
    00289       { _M_rep()->_M_info._M_refcount = -1; }
    00290
    00291       void
    00292       _M_leak()    // for use in begin() & non-const op[]
    00293       {
    00294     if (!_M_is_leaked())
    00295       _M_leak_hard();
    00296       }
    00297
    00298       void
    00299       _M_set_length(size_type __n)
    00300       { _M_rep()->_M_set_length(__n); }
    00301
    00302       __rc_string_base()
    00303       : _M_dataplus(_S_empty_rep._M_refcopy()) { }
    00304
    00305       __rc_string_base(const _Alloc& __a);
    00306
    00307       __rc_string_base(const __rc_string_base& __rcs);
    00308
    00309 #ifdef __GXX_EXPERIMENTAL_CXX0X__
    00310       __rc_string_base(__rc_string_base&& __rcs)
    00311       : _M_dataplus(__rcs._M_dataplus)
    00312       { __rcs._M_data(_S_empty_rep._M_refcopy()); }
    00313 #endif
    00314
    00315       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
    00316
    00317       template<typename _InputIterator>
    00318         __rc_string_base(_InputIterator __beg, _InputIterator __end,
    00319              const _Alloc& __a);
    00320
    00321       ~__rc_string_base()
    00322       { _M_dispose(); }
    00323
    00324       allocator_type&
    00325       _M_get_allocator()
    00326       { return _M_dataplus; }
    00327
    00328       const allocator_type&
    00329       _M_get_allocator() const
    00330       { return _M_dataplus; }
    00331
    00332       void
    00333       _M_swap(__rc_string_base& __rcs);
    00334
    00335       void
    00336       _M_assign(const __rc_string_base& __rcs);
    00337
    00338       void
    00339       _M_reserve(size_type __res);
    00340
    00341       void
    00342       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
    00343         size_type __len2);
    00344
    00345       void
    00346       _M_erase(size_type __pos, size_type __n);
    00347
    00348       void
    00349       _M_clear()
    00350       { _M_erase(size_type(0), _M_length()); }
    00351
    00352       bool
    00353       _M_compare(const __rc_string_base&) const
    00354       { return false; }
    00355     };
    00356
    00357   template<typename _CharT, typename _Traits, typename _Alloc>
    00358     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
    00359     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
    00360
    00361   template<typename _CharT, typename _Traits, typename _Alloc>
    00362     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
    00363     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    00364     _S_create(size_type __capacity, size_type __old_capacity,
    00365           const _Alloc& __alloc)
    00366     {
    00367       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00368       // 83.  String::npos vs. string::max_size()
    00369       if (__capacity > size_type(_S_max_size))
    00370     std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
    00371
    00372       // The standard places no restriction on allocating more memory
    00373       // than is strictly needed within this layer at the moment or as
    00374       // requested by an explicit application call to reserve().
    00375
    00376       // Many malloc implementations perform quite poorly when an
    00377       // application attempts to allocate memory in a stepwise fashion
    00378       // growing each allocation size by only 1 char.  Additionally,
    00379       // it makes little sense to allocate less linear memory than the
    00380       // natural blocking size of the malloc implementation.
    00381       // Unfortunately, we would need a somewhat low-level calculation
    00382       // with tuned parameters to get this perfect for any particular
    00383       // malloc implementation.  Fortunately, generalizations about
    00384       // common features seen among implementations seems to suffice.
    00385
    00386       // __pagesize need not match the actual VM page size for good
    00387       // results in practice, thus we pick a common value on the low
    00388       // side.  __malloc_header_size is an estimate of the amount of
    00389       // overhead per memory allocation (in practice seen N * sizeof
    00390       // (void*) where N is 0, 2 or 4).  According to folklore,
    00391       // picking this value on the high side is better than
    00392       // low-balling it (especially when this algorithm is used with
    00393       // malloc implementations that allocate memory blocks rounded up
    00394       // to a size which is a power of 2).
    00395       const size_type __pagesize = 4096;
    00396       const size_type __malloc_header_size = 4 * sizeof(void*);
    00397
    00398       // The below implements an exponential growth policy, necessary to
    00399       // meet amortized linear time requirements of the library: see
    00400       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
    00401       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
    00402     {
    00403       __capacity = 2 * __old_capacity;
    00404       // Never allocate a string bigger than _S_max_size.
    00405       if (__capacity > size_type(_S_max_size))
    00406         __capacity = size_type(_S_max_size);
    00407     }
    00408
    00409       // NB: Need an array of char_type[__capacity], plus a terminating
    00410       // null char_type() element, plus enough for the _Rep data structure,
    00411       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
    00412       // sizeof(_Rep).
    00413       // Whew. Seemingly so needy, yet so elemental.
    00414       size_type __size = ((__capacity + 1) * sizeof(_CharT)
    00415               + 2 * sizeof(_Rep) - 1);
    00416
    00417       const size_type __adj_size = __size + __malloc_header_size;
    00418       if (__adj_size > __pagesize && __capacity > __old_capacity)
    00419     {
    00420       const size_type __extra = __pagesize - __adj_size % __pagesize;
    00421       __capacity += __extra / sizeof(_CharT);
    00422       if (__capacity > size_type(_S_max_size))
    00423         __capacity = size_type(_S_max_size);
    00424       __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
    00425     }
    00426
    00427       // NB: Might throw, but no worries about a leak, mate: _Rep()
    00428       // does not throw.
    00429       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
    00430       _Rep* __p = new (__place) _Rep;
    00431       __p->_M_info._M_capacity = __capacity;
    00432       return __p;
    00433     }
    00434
    00435   template<typename _CharT, typename _Traits, typename _Alloc>
    00436     void
    00437     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    00438     _M_destroy(const _Alloc& __a) throw ()
    00439     {
    00440       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
    00441                 + 2 * sizeof(_Rep) - 1);
    00442       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
    00443     }
    00444
    00445   template<typename _CharT, typename _Traits, typename _Alloc>
    00446     _CharT*
    00447     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    00448     _M_clone(const _Alloc& __alloc, size_type __res)
    00449     {
    00450       // Requested capacity of the clone.
    00451       const size_type __requested_cap = _M_info._M_length + __res;
    00452       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
    00453                   __alloc);
    00454
    00455       if (_M_info._M_length)
    00456     _S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
    00457
    00458       __r->_M_set_length(_M_info._M_length);
    00459       return __r->_M_refdata();
    00460     }
    00461
    00462   template<typename _CharT, typename _Traits, typename _Alloc>
    00463     __rc_string_base<_CharT, _Traits, _Alloc>::
    00464     __rc_string_base(const _Alloc& __a)
    00465     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
    00466
    00467   template<typename _CharT, typename _Traits, typename _Alloc>
    00468     __rc_string_base<_CharT, _Traits, _Alloc>::
    00469     __rc_string_base(const __rc_string_base& __rcs)
    00470     : _M_dataplus(__rcs._M_get_allocator(),
    00471           __rcs._M_grab(__rcs._M_get_allocator())) { }
    00472
    00473   template<typename _CharT, typename _Traits, typename _Alloc>
    00474     __rc_string_base<_CharT, _Traits, _Alloc>::
    00475     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
    00476     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
    00477
    00478   template<typename _CharT, typename _Traits, typename _Alloc>
    00479     template<typename _InputIterator>
    00480     __rc_string_base<_CharT, _Traits, _Alloc>::
    00481     __rc_string_base(_InputIterator __beg, _InputIterator __end,
    00482              const _Alloc& __a)
    00483     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
    00484
    00485   template<typename _CharT, typename _Traits, typename _Alloc>
    00486     void
    00487     __rc_string_base<_CharT, _Traits, _Alloc>::
    00488     _M_leak_hard()
    00489     {
    00490       if (_M_is_shared())
    00491     _M_erase(0, 0);
    00492       _M_set_leaked();
    00493     }
    00494
    00495   // NB: This is the special case for Input Iterators, used in
    00496   // istreambuf_iterators, etc.
    00497   // Input Iterators have a cost structure very different from
    00498   // pointers, calling for a different coding style.
    00499   template<typename _CharT, typename _Traits, typename _Alloc>
    00500     template<typename _InIterator>
    00501       _CharT*
    00502       __rc_string_base<_CharT, _Traits, _Alloc>::
    00503       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
    00504            std::input_iterator_tag)
    00505       {
    00506     if (__beg == __end && __a == _Alloc())
    00507       return _S_empty_rep._M_refcopy();
    00508
    00509     // Avoid reallocation for common case.
    00510     _CharT __buf[128];
    00511     size_type __len = 0;
    00512     while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
    00513       {
    00514         __buf[__len++] = *__beg;
    00515         ++__beg;
    00516       }
    00517     _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
    00518     _S_copy(__r->_M_refdata(), __buf, __len);
    00519     __try
    00520       {
    00521         while (__beg != __end)
    00522           {
    00523         if (__len == __r->_M_info._M_capacity)
    00524           {
    00525             // Allocate more space.
    00526             _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
    00527             _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
    00528             __r->_M_destroy(__a);
    00529             __r = __another;
    00530           }
    00531         __r->_M_refdata()[__len++] = *__beg;
    00532         ++__beg;
    00533           }
    00534       }
    00535     __catch(...)
    00536       {
    00537         __r->_M_destroy(__a);
    00538         __throw_exception_again;
    00539       }
    00540     __r->_M_set_length(__len);
    00541     return __r->_M_refdata();
    00542       }
    00543
    00544   template<typename _CharT, typename _Traits, typename _Alloc>
    00545     template<typename _InIterator>
    00546       _CharT*
    00547       __rc_string_base<_CharT, _Traits, _Alloc>::
    00548       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
    00549            std::forward_iterator_tag)
    00550       {
    00551     if (__beg == __end && __a == _Alloc())
    00552       return _S_empty_rep._M_refcopy();
    00553
    00554     // NB: Not required, but considered best practice.
    00555     if (__is_null_pointer(__beg) && __beg != __end)
    00556       std::__throw_logic_error(__N("__rc_string_base::"
    00557                        "_S_construct NULL not valid"));
    00558
    00559     const size_type __dnew = static_cast<size_type>(std::distance(__beg,
    00560                                       __end));
    00561     // Check for out_of_range and length_error exceptions.
    00562     _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
    00563     __try
    00564       { _S_copy_chars(__r->_M_refdata(), __beg, __end); }
    00565     __catch(...)
    00566       {
    00567         __r->_M_destroy(__a);
    00568         __throw_exception_again;
    00569       }
    00570     __r->_M_set_length(__dnew);
    00571     return __r->_M_refdata();
    00572       }
    00573
    00574   template<typename _CharT, typename _Traits, typename _Alloc>
    00575     _CharT*
    00576     __rc_string_base<_CharT, _Traits, _Alloc>::
    00577     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
    00578     {
    00579       if (__n == 0 && __a == _Alloc())
    00580     return _S_empty_rep._M_refcopy();
    00581
    00582       // Check for out_of_range and length_error exceptions.
    00583       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
    00584       if (__n)
    00585     _S_assign(__r->_M_refdata(), __n, __c);
    00586
    00587       __r->_M_set_length(__n);
    00588       return __r->_M_refdata();
    00589     }
    00590
    00591   template<typename _CharT, typename _Traits, typename _Alloc>
    00592     void
    00593     __rc_string_base<_CharT, _Traits, _Alloc>::
    00594     _M_swap(__rc_string_base& __rcs)
    00595     {
    00596       if (_M_is_leaked())
    00597     _M_set_sharable();
    00598       if (__rcs._M_is_leaked())
    00599     __rcs._M_set_sharable();
    00600
    00601       _CharT* __tmp = _M_data();
    00602       _M_data(__rcs._M_data());
    00603       __rcs._M_data(__tmp);
    00604
    00605       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00606       // 431. Swapping containers with unequal allocators.
    00607       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
    00608                           __rcs._M_get_allocator());
    00609     }
    00610
    00611   template<typename _CharT, typename _Traits, typename _Alloc>
    00612     void
    00613     __rc_string_base<_CharT, _Traits, _Alloc>::
    00614     _M_assign(const __rc_string_base& __rcs)
    00615     {
    00616       if (_M_rep() != __rcs._M_rep())
    00617     {
    00618       _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
    00619       _M_dispose();
    00620       _M_data(__tmp);
    00621     }
    00622     }
    00623
    00624   template<typename _CharT, typename _Traits, typename _Alloc>
    00625     void
    00626     __rc_string_base<_CharT, _Traits, _Alloc>::
    00627     _M_reserve(size_type __res)
    00628     {
    00629       // Make sure we don't shrink below the current size.
    00630       if (__res < _M_length())
    00631     __res = _M_length();
    00632
    00633       if (__res != _M_capacity() || _M_is_shared())
    00634     {
    00635       _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
    00636                          __res - _M_length());
    00637       _M_dispose();
    00638       _M_data(__tmp);
    00639     }
    00640     }
    00641
    00642   template<typename _CharT, typename _Traits, typename _Alloc>
    00643     void
    00644     __rc_string_base<_CharT, _Traits, _Alloc>::
    00645     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
    00646           size_type __len2)
    00647     {
    00648       const size_type __how_much = _M_length() - __pos - __len1;
    00649
    00650       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
    00651                   _M_capacity(), _M_get_allocator());
    00652
    00653       if (__pos)
    00654     _S_copy(__r->_M_refdata(), _M_data(), __pos);
    00655       if (__s && __len2)
    00656     _S_copy(__r->_M_refdata() + __pos, __s, __len2);
    00657       if (__how_much)
    00658     _S_copy(__r->_M_refdata() + __pos + __len2,
    00659         _M_data() + __pos + __len1, __how_much);
    00660
    00661       _M_dispose();
    00662       _M_data(__r->_M_refdata());
    00663     }
    00664
    00665   template<typename _CharT, typename _Traits, typename _Alloc>
    00666     void
    00667     __rc_string_base<_CharT, _Traits, _Alloc>::
    00668     _M_erase(size_type __pos, size_type __n)
    00669     {
    00670       const size_type __new_size = _M_length() - __n;
    00671       const size_type __how_much = _M_length() - __pos - __n;
    00672
    00673       if (_M_is_shared())
    00674     {
    00675       // Must reallocate.
    00676       _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
    00677                       _M_get_allocator());
    00678
    00679       if (__pos)
    00680         _S_copy(__r->_M_refdata(), _M_data(), __pos);
    00681       if (__how_much)
    00682         _S_copy(__r->_M_refdata() + __pos,
    00683             _M_data() + __pos + __n, __how_much);
    00684
    00685       _M_dispose();
    00686       _M_data(__r->_M_refdata());
    00687     }
    00688       else if (__how_much && __n)
    00689     {
    00690       // Work in-place.
    00691       _S_move(_M_data() + __pos,
    00692           _M_data() + __pos + __n, __how_much);
    00693     }
    00694
    00695       _M_rep()->_M_set_length(__new_size);
    00696     }
    00697
    00698   template<>
    00699     inline bool
    00700     __rc_string_base<char, std::char_traits<char>,
    00701              std::allocator<char> >::
    00702     _M_compare(const __rc_string_base& __rcs) const
    00703     {
    00704       if (_M_rep() == __rcs._M_rep())
    00705     return true;
    00706       return false;
    00707     }
    00708
    00709 #ifdef _GLIBCXX_USE_WCHAR_T
    00710   template<>
    00711     inline bool
    00712     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
    00713              std::allocator<wchar_t> >::
    00714     _M_compare(const __rc_string_base& __rcs) const
    00715     {
    00716       if (_M_rep() == __rcs._M_rep())
    00717     return true;
    00718       return false;
    00719     }
    00720 #endif
    00721
    00722 _GLIBCXX_END_NAMESPACE
    00723
    00724 #endif /* _RC_STRING_BASE_H */