rc_string_base.h

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00001 // Reference-counted versatile string base -*- C++ -*-
00002 
00003 // Copyright (C) 2005, 2006, 2007, 2008 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 2, 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 // You should have received a copy of the GNU General Public License along
00017 // with this library; see the file COPYING.  If not, write to the Free
00018 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
00019 // USA.
00020 
00021 // As a special exception, you may use this file as part of a free software
00022 // library without restriction.  Specifically, if other files instantiate
00023 // templates or use macros or inline functions from this file, or you compile
00024 // this file and link it with other files to produce an executable, this
00025 // file does not by itself cause the resulting executable to be covered by
00026 // the GNU General Public License.  This exception does not however
00027 // invalidate any other reasons why the executable file might be covered by
00028 // the GNU General Public License.
00029 
00030 /** @file ext/rc_string_base.h
00031  *  This file is a GNU extension to the Standard C++ Library.
00032  *  This is an internal header file, included by other library headers.
00033  *  You should not attempt to use it directly.
00034  */
00035 
00036 #ifndef _RC_STRING_BASE_H
00037 #define _RC_STRING_BASE_H 1
00038 
00039 #include <ext/atomicity.h>
00040 #include <bits/stl_iterator_base_funcs.h>
00041 
00042 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
00043 
00044   /**
00045    *  Documentation?  What's that?
00046    *  Nathan Myers <ncm@cantrip.org>.
00047    *
00048    *  A string looks like this:
00049    *
00050    *  @code
00051    *                                        [_Rep]
00052    *                                        _M_length
00053    *   [__rc_string_base<char_type>]        _M_capacity
00054    *   _M_dataplus                          _M_refcount
00055    *   _M_p ---------------->               unnamed array of char_type
00056    *  @endcode
00057    *
00058    *  Where the _M_p points to the first character in the string, and
00059    *  you cast it to a pointer-to-_Rep and subtract 1 to get a
00060    *  pointer to the header.
00061    *
00062    *  This approach has the enormous advantage that a string object
00063    *  requires only one allocation.  All the ugliness is confined
00064    *  within a single pair of inline functions, which each compile to
00065    *  a single "add" instruction: _Rep::_M_refdata(), and
00066    *  __rc_string_base::_M_rep(); and the allocation function which gets a
00067    *  block of raw bytes and with room enough and constructs a _Rep
00068    *  object at the front.
00069    *
00070    *  The reason you want _M_data pointing to the character array and
00071    *  not the _Rep is so that the debugger can see the string
00072    *  contents. (Probably we should add a non-inline member to get
00073    *  the _Rep for the debugger to use, so users can check the actual
00074    *  string length.)
00075    *
00076    *  Note that the _Rep object is a POD so that you can have a
00077    *  static "empty string" _Rep object already "constructed" before
00078    *  static constructors have run.  The reference-count encoding is
00079    *  chosen so that a 0 indicates one reference, so you never try to
00080    *  destroy the empty-string _Rep object.
00081    *
00082    *  All but the last paragraph is considered pretty conventional
00083    *  for a C++ string implementation.
00084   */
00085  template<typename _CharT, typename _Traits, typename _Alloc>
00086     class __rc_string_base
00087     : protected __vstring_utility<_CharT, _Traits, _Alloc>
00088     {
00089     public:
00090       typedef _Traits                       traits_type;
00091       typedef typename _Traits::char_type           value_type;
00092       typedef _Alloc                        allocator_type;
00093 
00094       typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;
00095       typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;
00096       typedef typename _CharT_alloc_type::size_type     size_type;
00097 
00098     private:
00099       // _Rep: string representation
00100       //   Invariants:
00101       //   1. String really contains _M_length + 1 characters: due to 21.3.4
00102       //      must be kept null-terminated.
00103       //   2. _M_capacity >= _M_length
00104       //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
00105       //   3. _M_refcount has three states:
00106       //      -1: leaked, one reference, no ref-copies allowed, non-const.
00107       //       0: one reference, non-const.
00108       //     n>0: n + 1 references, operations require a lock, const.
00109       //   4. All fields == 0 is an empty string, given the extra storage
00110       //      beyond-the-end for a null terminator; thus, the shared
00111       //      empty string representation needs no constructor.
00112       struct _Rep
00113       {
00114     union
00115     {
00116       struct
00117       {
00118         size_type       _M_length;
00119         size_type       _M_capacity;
00120         _Atomic_word    _M_refcount;
00121       }                 _M_info;
00122       
00123       // Only for alignment purposes.
00124       _CharT            _M_align;
00125     };
00126 
00127     typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
00128 
00129     _CharT*
00130     _M_refdata() throw()
00131     { return reinterpret_cast<_CharT*>(this + 1); }
00132 
00133     _CharT*
00134     _M_refcopy() throw()
00135     {
00136       __atomic_add_dispatch(&_M_info._M_refcount, 1);
00137       return _M_refdata();
00138     }  // XXX MT
00139     
00140     void
00141     _M_set_length(size_type __n)
00142     { 
00143       _M_info._M_refcount = 0;  // One reference.
00144       _M_info._M_length = __n;
00145       // grrr. (per 21.3.4)
00146       // You cannot leave those LWG people alone for a second.
00147       traits_type::assign(_M_refdata()[__n], _CharT());
00148     }
00149 
00150     // Create & Destroy
00151     static _Rep*
00152     _S_create(size_type, size_type, const _Alloc&);
00153 
00154     void
00155     _M_destroy(const _Alloc&) throw();
00156 
00157     _CharT*
00158     _M_clone(const _Alloc&, size_type __res = 0);
00159       };
00160 
00161       struct _Rep_empty
00162       : public _Rep
00163       {
00164     _CharT              _M_terminal;
00165       };
00166 
00167       static _Rep_empty     _S_empty_rep;
00168 
00169       // The maximum number of individual char_type elements of an
00170       // individual string is determined by _S_max_size. This is the
00171       // value that will be returned by max_size().  (Whereas npos
00172       // is the maximum number of bytes the allocator can allocate.)
00173       // If one was to divvy up the theoretical largest size string,
00174       // with a terminating character and m _CharT elements, it'd
00175       // look like this:
00176       // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
00177       //        + sizeof(_Rep) - 1
00178       // (NB: last two terms for rounding reasons, see _M_create below)
00179       // Solving for m:
00180       // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
00181       // In addition, this implementation halves this amount.
00182       enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
00183                   + 1) / sizeof(_CharT)) - 1) / 2 };
00184 
00185       // Data Member (private):
00186       mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;
00187 
00188       void
00189       _M_data(_CharT* __p)
00190       { _M_dataplus._M_p = __p; }
00191 
00192       _Rep*
00193       _M_rep() const
00194       { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
00195 
00196       _CharT*
00197       _M_grab(const _Alloc& __alloc) const
00198       {
00199     return (!_M_is_leaked() && _M_get_allocator() == __alloc)
00200             ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
00201       }
00202 
00203       void
00204       _M_dispose()
00205       {
00206     if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
00207                     -1) <= 0)
00208       _M_rep()->_M_destroy(_M_get_allocator());
00209       }  // XXX MT
00210 
00211       bool
00212       _M_is_leaked() const
00213       { return _M_rep()->_M_info._M_refcount < 0; }
00214 
00215       void
00216       _M_set_sharable()
00217       { _M_rep()->_M_info._M_refcount = 0; }
00218 
00219       void
00220       _M_leak_hard();
00221 
00222       // _S_construct_aux is used to implement the 21.3.1 para 15 which
00223       // requires special behaviour if _InIterator is an integral type
00224       template<typename _InIterator>
00225         static _CharT*
00226         _S_construct_aux(_InIterator __beg, _InIterator __end,
00227              const _Alloc& __a, std::__false_type)
00228     {
00229           typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
00230           return _S_construct(__beg, __end, __a, _Tag());
00231     }
00232 
00233       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00234       // 438. Ambiguity in the "do the right thing" clause
00235       template<typename _Integer>
00236         static _CharT*
00237         _S_construct_aux(_Integer __beg, _Integer __end,
00238              const _Alloc& __a, std::__true_type)
00239     { return _S_construct(static_cast<size_type>(__beg), __end, __a); }
00240 
00241       template<typename _InIterator>
00242         static _CharT*
00243         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
00244     {
00245       typedef typename std::__is_integer<_InIterator>::__type _Integral;
00246       return _S_construct_aux(__beg, __end, __a, _Integral());
00247         }
00248 
00249       // For Input Iterators, used in istreambuf_iterators, etc.
00250       template<typename _InIterator>
00251         static _CharT*
00252          _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00253               std::input_iterator_tag);
00254       
00255       // For forward_iterators up to random_access_iterators, used for
00256       // string::iterator, _CharT*, etc.
00257       template<typename _FwdIterator>
00258         static _CharT*
00259         _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
00260              std::forward_iterator_tag);
00261 
00262       static _CharT*
00263       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
00264 
00265     public:
00266       size_type
00267       _M_max_size() const
00268       { return size_type(_S_max_size); }
00269 
00270       _CharT*
00271       _M_data() const
00272       { return _M_dataplus._M_p; }
00273 
00274       size_type
00275       _M_length() const
00276       { return _M_rep()->_M_info._M_length; }
00277 
00278       size_type
00279       _M_capacity() const
00280       { return _M_rep()->_M_info._M_capacity; }
00281 
00282       bool
00283       _M_is_shared() const
00284       { return _M_rep()->_M_info._M_refcount > 0; }
00285 
00286       void
00287       _M_set_leaked()
00288       { _M_rep()->_M_info._M_refcount = -1; }
00289 
00290       void
00291       _M_leak()    // for use in begin() & non-const op[]
00292       {
00293     if (!_M_is_leaked())
00294       _M_leak_hard();
00295       }
00296 
00297       void
00298       _M_set_length(size_type __n)
00299       { _M_rep()->_M_set_length(__n); }
00300 
00301       __rc_string_base()
00302       : _M_dataplus(_S_empty_rep._M_refcopy()) { }
00303 
00304       __rc_string_base(const _Alloc& __a);
00305 
00306       __rc_string_base(const __rc_string_base& __rcs);
00307 
00308 #ifdef __GXX_EXPERIMENTAL_CXX0X__
00309       __rc_string_base(__rc_string_base&& __rcs)
00310       : _M_dataplus(__rcs._M_get_allocator(), __rcs._M_data())
00311       { __rcs._M_data(_S_empty_rep._M_refcopy()); }      
00312 #endif
00313 
00314       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
00315 
00316       template<typename _InputIterator>
00317         __rc_string_base(_InputIterator __beg, _InputIterator __end,
00318              const _Alloc& __a);
00319 
00320       ~__rc_string_base()
00321       { _M_dispose(); }      
00322 
00323       allocator_type&
00324       _M_get_allocator()
00325       { return _M_dataplus; }
00326 
00327       const allocator_type&
00328       _M_get_allocator() const
00329       { return _M_dataplus; }
00330 
00331       void
00332       _M_swap(__rc_string_base& __rcs);
00333 
00334       void
00335       _M_assign(const __rc_string_base& __rcs);
00336 
00337       void
00338       _M_reserve(size_type __res);
00339 
00340       void
00341       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00342         size_type __len2);
00343       
00344       void
00345       _M_erase(size_type __pos, size_type __n);
00346 
00347       void
00348       _M_clear()
00349       { _M_erase(size_type(0), _M_length()); }
00350 
00351       bool
00352       _M_compare(const __rc_string_base&) const
00353       { return false; }
00354     };
00355 
00356   template<typename _CharT, typename _Traits, typename _Alloc>
00357     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
00358     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
00359 
00360   template<typename _CharT, typename _Traits, typename _Alloc>
00361     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
00362     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00363     _S_create(size_type __capacity, size_type __old_capacity,
00364           const _Alloc& __alloc)
00365     {
00366       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00367       // 83.  String::npos vs. string::max_size()
00368       if (__capacity > size_type(_S_max_size))
00369     std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
00370 
00371       // The standard places no restriction on allocating more memory
00372       // than is strictly needed within this layer at the moment or as
00373       // requested by an explicit application call to reserve().
00374 
00375       // Many malloc implementations perform quite poorly when an
00376       // application attempts to allocate memory in a stepwise fashion
00377       // growing each allocation size by only 1 char.  Additionally,
00378       // it makes little sense to allocate less linear memory than the
00379       // natural blocking size of the malloc implementation.
00380       // Unfortunately, we would need a somewhat low-level calculation
00381       // with tuned parameters to get this perfect for any particular
00382       // malloc implementation.  Fortunately, generalizations about
00383       // common features seen among implementations seems to suffice.
00384 
00385       // __pagesize need not match the actual VM page size for good
00386       // results in practice, thus we pick a common value on the low
00387       // side.  __malloc_header_size is an estimate of the amount of
00388       // overhead per memory allocation (in practice seen N * sizeof
00389       // (void*) where N is 0, 2 or 4).  According to folklore,
00390       // picking this value on the high side is better than
00391       // low-balling it (especially when this algorithm is used with
00392       // malloc implementations that allocate memory blocks rounded up
00393       // to a size which is a power of 2).
00394       const size_type __pagesize = 4096;
00395       const size_type __malloc_header_size = 4 * sizeof(void*);
00396 
00397       // The below implements an exponential growth policy, necessary to
00398       // meet amortized linear time requirements of the library: see
00399       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
00400       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
00401     {
00402       __capacity = 2 * __old_capacity;
00403       // Never allocate a string bigger than _S_max_size.
00404       if (__capacity > size_type(_S_max_size))
00405         __capacity = size_type(_S_max_size);
00406     }
00407 
00408       // NB: Need an array of char_type[__capacity], plus a terminating
00409       // null char_type() element, plus enough for the _Rep data structure,
00410       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
00411       // sizeof(_Rep).
00412       // Whew. Seemingly so needy, yet so elemental.
00413       size_type __size = ((__capacity + 1) * sizeof(_CharT)
00414               + 2 * sizeof(_Rep) - 1);
00415 
00416       const size_type __adj_size = __size + __malloc_header_size;
00417       if (__adj_size > __pagesize && __capacity > __old_capacity)
00418     {
00419       const size_type __extra = __pagesize - __adj_size % __pagesize;
00420       __capacity += __extra / sizeof(_CharT);
00421       if (__capacity > size_type(_S_max_size))
00422         __capacity = size_type(_S_max_size);
00423       __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
00424     }
00425 
00426       // NB: Might throw, but no worries about a leak, mate: _Rep()
00427       // does not throw.
00428       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
00429       _Rep* __p = new (__place) _Rep;
00430       __p->_M_info._M_capacity = __capacity;
00431       return __p;
00432     }
00433 
00434   template<typename _CharT, typename _Traits, typename _Alloc>
00435     void
00436     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00437     _M_destroy(const _Alloc& __a) throw ()
00438     {
00439       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
00440                 + 2 * sizeof(_Rep) - 1);
00441       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
00442     }
00443 
00444   template<typename _CharT, typename _Traits, typename _Alloc>
00445     _CharT*
00446     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00447     _M_clone(const _Alloc& __alloc, size_type __res)
00448     {
00449       // Requested capacity of the clone.
00450       const size_type __requested_cap = _M_info._M_length + __res;
00451       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
00452                   __alloc);
00453 
00454       if (_M_info._M_length)
00455     _S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
00456 
00457       __r->_M_set_length(_M_info._M_length);
00458       return __r->_M_refdata();
00459     }
00460 
00461   template<typename _CharT, typename _Traits, typename _Alloc>
00462     __rc_string_base<_CharT, _Traits, _Alloc>::
00463     __rc_string_base(const _Alloc& __a)
00464     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
00465 
00466   template<typename _CharT, typename _Traits, typename _Alloc>
00467     __rc_string_base<_CharT, _Traits, _Alloc>::
00468     __rc_string_base(const __rc_string_base& __rcs)
00469     : _M_dataplus(__rcs._M_get_allocator(),
00470           __rcs._M_grab(__rcs._M_get_allocator())) { }
00471 
00472   template<typename _CharT, typename _Traits, typename _Alloc>
00473     __rc_string_base<_CharT, _Traits, _Alloc>::
00474     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
00475     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
00476 
00477   template<typename _CharT, typename _Traits, typename _Alloc>
00478     template<typename _InputIterator>
00479     __rc_string_base<_CharT, _Traits, _Alloc>::
00480     __rc_string_base(_InputIterator __beg, _InputIterator __end,
00481              const _Alloc& __a)
00482     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
00483 
00484   template<typename _CharT, typename _Traits, typename _Alloc>
00485     void
00486     __rc_string_base<_CharT, _Traits, _Alloc>::
00487     _M_leak_hard()
00488     {
00489       if (_M_is_shared())
00490     _M_erase(0, 0);
00491       _M_set_leaked();
00492     }
00493 
00494   // NB: This is the special case for Input Iterators, used in
00495   // istreambuf_iterators, etc.
00496   // Input Iterators have a cost structure very different from
00497   // pointers, calling for a different coding style.
00498   template<typename _CharT, typename _Traits, typename _Alloc>
00499     template<typename _InIterator>
00500       _CharT*
00501       __rc_string_base<_CharT, _Traits, _Alloc>::
00502       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00503            std::input_iterator_tag)
00504       {
00505     if (__beg == __end && __a == _Alloc())
00506       return _S_empty_rep._M_refcopy();
00507 
00508     // Avoid reallocation for common case.
00509     _CharT __buf[128];
00510     size_type __len = 0;
00511     while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
00512       {
00513         __buf[__len++] = *__beg;
00514         ++__beg;
00515       }
00516     _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
00517     _S_copy(__r->_M_refdata(), __buf, __len);
00518     try
00519       {
00520         while (__beg != __end)
00521           {
00522         if (__len == __r->_M_info._M_capacity)
00523           {
00524             // Allocate more space.
00525             _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
00526             _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
00527             __r->_M_destroy(__a);
00528             __r = __another;
00529           }
00530         __r->_M_refdata()[__len++] = *__beg;
00531         ++__beg;
00532           }
00533       }
00534     catch(...)
00535       {
00536         __r->_M_destroy(__a);
00537         __throw_exception_again;
00538       }
00539     __r->_M_set_length(__len);
00540     return __r->_M_refdata();
00541       }
00542 
00543   template<typename _CharT, typename _Traits, typename _Alloc>
00544     template<typename _InIterator>
00545       _CharT*
00546       __rc_string_base<_CharT, _Traits, _Alloc>::
00547       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00548            std::forward_iterator_tag)
00549       {
00550     if (__beg == __end && __a == _Alloc())
00551       return _S_empty_rep._M_refcopy();
00552 
00553     // NB: Not required, but considered best practice.
00554     if (__builtin_expect(__is_null_pointer(__beg) && __beg != __end, 0))
00555       std::__throw_logic_error(__N("__rc_string_base::"
00556                        "_S_construct NULL not valid"));
00557 
00558     const size_type __dnew = static_cast<size_type>(std::distance(__beg,
00559                                       __end));
00560     // Check for out_of_range and length_error exceptions.
00561     _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
00562     try
00563       { _S_copy_chars(__r->_M_refdata(), __beg, __end); }
00564     catch(...)
00565       {
00566         __r->_M_destroy(__a);
00567         __throw_exception_again;
00568       }
00569     __r->_M_set_length(__dnew);
00570     return __r->_M_refdata();
00571       }
00572 
00573   template<typename _CharT, typename _Traits, typename _Alloc>
00574     _CharT*
00575     __rc_string_base<_CharT, _Traits, _Alloc>::
00576     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
00577     {
00578       if (__n == 0 && __a == _Alloc())
00579     return _S_empty_rep._M_refcopy();
00580 
00581       // Check for out_of_range and length_error exceptions.
00582       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
00583       if (__n)
00584     _S_assign(__r->_M_refdata(), __n, __c);
00585 
00586       __r->_M_set_length(__n);
00587       return __r->_M_refdata();
00588     }
00589 
00590   template<typename _CharT, typename _Traits, typename _Alloc>
00591     void
00592     __rc_string_base<_CharT, _Traits, _Alloc>::
00593     _M_swap(__rc_string_base& __rcs)
00594     {
00595       if (_M_is_leaked())
00596     _M_set_sharable();
00597       if (__rcs._M_is_leaked())
00598     __rcs._M_set_sharable();
00599       
00600       _CharT* __tmp = _M_data();
00601       _M_data(__rcs._M_data());
00602       __rcs._M_data(__tmp);
00603 
00604       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00605       // 431. Swapping containers with unequal allocators.
00606       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
00607                           __rcs._M_get_allocator());
00608     } 
00609 
00610   template<typename _CharT, typename _Traits, typename _Alloc>
00611     void
00612     __rc_string_base<_CharT, _Traits, _Alloc>::
00613     _M_assign(const __rc_string_base& __rcs)
00614     {
00615       if (_M_rep() != __rcs._M_rep())
00616     {
00617       _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
00618       _M_dispose();
00619       _M_data(__tmp);
00620     }
00621     }
00622 
00623   template<typename _CharT, typename _Traits, typename _Alloc>
00624     void
00625     __rc_string_base<_CharT, _Traits, _Alloc>::
00626     _M_reserve(size_type __res)
00627     {
00628       // Make sure we don't shrink below the current size.
00629       if (__res < _M_length())
00630     __res = _M_length();
00631       
00632       if (__res != _M_capacity() || _M_is_shared())
00633     {
00634       _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
00635                          __res - _M_length());
00636       _M_dispose();
00637       _M_data(__tmp);
00638     }
00639     }
00640 
00641   template<typename _CharT, typename _Traits, typename _Alloc>
00642     void
00643     __rc_string_base<_CharT, _Traits, _Alloc>::
00644     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00645           size_type __len2)
00646     {
00647       const size_type __how_much = _M_length() - __pos - __len1;
00648       
00649       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
00650                   _M_capacity(), _M_get_allocator());
00651       
00652       if (__pos)
00653     _S_copy(__r->_M_refdata(), _M_data(), __pos);
00654       if (__s && __len2)
00655     _S_copy(__r->_M_refdata() + __pos, __s, __len2);
00656       if (__how_much)
00657     _S_copy(__r->_M_refdata() + __pos + __len2,
00658         _M_data() + __pos + __len1, __how_much);
00659       
00660       _M_dispose();
00661       _M_data(__r->_M_refdata());
00662     }
00663 
00664   template<typename _CharT, typename _Traits, typename _Alloc>
00665     void
00666     __rc_string_base<_CharT, _Traits, _Alloc>::
00667     _M_erase(size_type __pos, size_type __n)
00668     {
00669       const size_type __new_size = _M_length() - __n;
00670       const size_type __how_much = _M_length() - __pos - __n;
00671       
00672       if (_M_is_shared())
00673     {
00674       // Must reallocate.
00675       _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
00676                       _M_get_allocator());
00677 
00678       if (__pos)
00679         _S_copy(__r->_M_refdata(), _M_data(), __pos);
00680       if (__how_much)
00681         _S_copy(__r->_M_refdata() + __pos,
00682             _M_data() + __pos + __n, __how_much);
00683 
00684       _M_dispose();
00685       _M_data(__r->_M_refdata());
00686     }
00687       else if (__how_much && __n)
00688     {
00689       // Work in-place.
00690       _S_move(_M_data() + __pos,
00691           _M_data() + __pos + __n, __how_much);
00692     }
00693 
00694       _M_rep()->_M_set_length(__new_size);      
00695     }
00696 
00697   template<>
00698     inline bool
00699     __rc_string_base<char, std::char_traits<char>,
00700              std::allocator<char> >::
00701     _M_compare(const __rc_string_base& __rcs) const
00702     {
00703       if (_M_rep() == __rcs._M_rep())
00704     return true;
00705       return false;
00706     }
00707 
00708 #ifdef _GLIBCXX_USE_WCHAR_T
00709   template<>
00710     inline bool
00711     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
00712              std::allocator<wchar_t> >::
00713     _M_compare(const __rc_string_base& __rcs) const
00714     {
00715       if (_M_rep() == __rcs._M_rep())
00716     return true;
00717       return false;
00718     }
00719 #endif
00720 
00721 _GLIBCXX_END_NAMESPACE
00722 
00723 #endif /* _RC_STRING_BASE_H */

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