rc_string_base.h

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00001 // Reference-counted versatile string base -*- C++ -*-
00002 
00003 // Copyright (C) 2005, 2006 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 
00041 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
00042 
00043   /**
00044    *  @if maint
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    *  @endif
00085   */
00086  template<typename _CharT, typename _Traits, typename _Alloc>
00087     class __rc_string_base
00088     : protected __vstring_utility<_CharT, _Traits, _Alloc>
00089     {
00090     public:
00091       typedef _Traits                       traits_type;
00092       typedef typename _Traits::char_type           value_type;
00093       typedef _Alloc                        allocator_type;
00094 
00095       typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;
00096       typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;
00097       typedef typename _CharT_alloc_type::size_type     size_type;
00098 
00099     private:
00100       // _Rep: string representation
00101       //   Invariants:
00102       //   1. String really contains _M_length + 1 characters: due to 21.3.4
00103       //      must be kept null-terminated.
00104       //   2. _M_capacity >= _M_length
00105       //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
00106       //   3. _M_refcount has three states:
00107       //      -1: leaked, one reference, no ref-copies allowed, non-const.
00108       //       0: one reference, non-const.
00109       //     n>0: n + 1 references, operations require a lock, const.
00110       //   4. All fields == 0 is an empty string, given the extra storage
00111       //      beyond-the-end for a null terminator; thus, the shared
00112       //      empty string representation needs no constructor.
00113       struct _Rep
00114       {
00115     union
00116     {
00117       struct
00118       {
00119         size_type       _M_length;
00120         size_type       _M_capacity;
00121         _Atomic_word    _M_refcount;
00122       }                 _M_info;
00123       
00124       // Only for alignment purposes.
00125       _CharT            _M_align;
00126     };
00127 
00128     typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
00129 
00130     _CharT*
00131     _M_refdata() throw()
00132     { return reinterpret_cast<_CharT*>(this + 1); }
00133 
00134     _CharT*
00135     _M_refcopy() throw()
00136     {
00137       __atomic_add_dispatch(&_M_info._M_refcount, 1);
00138       return _M_refdata();
00139     }  // XXX MT
00140     
00141     void
00142     _M_set_length(size_type __n)
00143     { 
00144       _M_info._M_refcount = 0;  // One reference.
00145       _M_info._M_length = __n;
00146       // grrr. (per 21.3.4)
00147       // You cannot leave those LWG people alone for a second.
00148       traits_type::assign(_M_refdata()[__n], _CharT());
00149     }
00150 
00151     // Create & Destroy
00152     static _Rep*
00153     _S_create(size_type, size_type, const _Alloc&);
00154 
00155     void
00156     _M_destroy(const _Alloc&) throw();
00157 
00158     _CharT*
00159     _M_clone(const _Alloc&, size_type __res = 0);
00160       };
00161 
00162       struct _Rep_empty
00163       : public _Rep
00164       {
00165     _CharT              _M_terminal;
00166       };
00167 
00168       static _Rep_empty     _S_empty_rep;
00169 
00170       // The maximum number of individual char_type elements of an
00171       // individual string is determined by _S_max_size. This is the
00172       // value that will be returned by max_size().  (Whereas npos
00173       // is the maximum number of bytes the allocator can allocate.)
00174       // If one was to divvy up the theoretical largest size string,
00175       // with a terminating character and m _CharT elements, it'd
00176       // look like this:
00177       // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
00178       //        + sizeof(_Rep) - 1
00179       // (NB: last two terms for rounding reasons, see _M_create below)
00180       // Solving for m:
00181       // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
00182       // In addition, this implementation halfs this amount.
00183       enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
00184                   + 1) / sizeof(_CharT)) - 1) / 2 };
00185 
00186       // Data Member (private):
00187       mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;
00188 
00189       void
00190       _M_data(_CharT* __p)
00191       { _M_dataplus._M_p = __p; }
00192 
00193       _Rep*
00194       _M_rep() const
00195       { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
00196 
00197       _CharT*
00198       _M_grab(const _Alloc& __alloc) const
00199       {
00200     return (!_M_is_leaked() && _M_get_allocator() == __alloc)
00201             ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
00202       }
00203 
00204       void
00205       _M_dispose()
00206       {
00207     if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
00208                     -1) <= 0)
00209       _M_rep()->_M_destroy(_M_get_allocator());
00210       }  // XXX MT
00211 
00212       bool
00213       _M_is_leaked() const
00214       { return _M_rep()->_M_info._M_refcount < 0; }
00215 
00216       void
00217       _M_set_sharable()
00218       { _M_rep()->_M_info._M_refcount = 0; }
00219 
00220       void
00221       _M_leak_hard();
00222 
00223       // _S_construct_aux is used to implement the 21.3.1 para 15 which
00224       // requires special behaviour if _InIterator is an integral type
00225       template<typename _InIterator>
00226         static _CharT*
00227         _S_construct_aux(_InIterator __beg, _InIterator __end,
00228              const _Alloc& __a, std::__false_type)
00229     {
00230           typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
00231           return _S_construct(__beg, __end, __a, _Tag());
00232     }
00233 
00234       template<typename _InIterator>
00235         static _CharT*
00236         _S_construct_aux(_InIterator __beg, _InIterator __end,
00237              const _Alloc& __a, std::__true_type)
00238     { return _S_construct(static_cast<size_type>(__beg),
00239                   static_cast<value_type>(__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(_Alloc(), _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       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
00309 
00310       template<typename _InputIterator>
00311         __rc_string_base(_InputIterator __beg, _InputIterator __end,
00312              const _Alloc& __a);
00313 
00314       ~__rc_string_base()
00315       { _M_dispose(); }      
00316 
00317       allocator_type&
00318       _M_get_allocator()
00319       { return _M_dataplus; }
00320 
00321       const allocator_type&
00322       _M_get_allocator() const
00323       { return _M_dataplus; }
00324 
00325       void
00326       _M_swap(__rc_string_base& __rcs);
00327 
00328       void
00329       _M_assign(const __rc_string_base& __rcs);
00330 
00331       void
00332       _M_reserve(size_type __res);
00333 
00334       void
00335       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00336         size_type __len2);
00337       
00338       void
00339       _M_erase(size_type __pos, size_type __n);
00340 
00341       void
00342       _M_clear()
00343       { _M_erase(size_type(0), _M_length()); }
00344 
00345       bool
00346       _M_compare(const __rc_string_base&) const
00347       { return false; }
00348     };
00349 
00350   template<typename _CharT, typename _Traits, typename _Alloc>
00351     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
00352     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
00353 
00354   template<typename _CharT, typename _Traits, typename _Alloc>
00355     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
00356     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00357     _S_create(size_type __capacity, size_type __old_capacity,
00358           const _Alloc& __alloc)
00359     {
00360       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00361       // 83.  String::npos vs. string::max_size()
00362       if (__capacity > size_type(_S_max_size))
00363     std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
00364 
00365       // The standard places no restriction on allocating more memory
00366       // than is strictly needed within this layer at the moment or as
00367       // requested by an explicit application call to reserve().
00368 
00369       // Many malloc implementations perform quite poorly when an
00370       // application attempts to allocate memory in a stepwise fashion
00371       // growing each allocation size by only 1 char.  Additionally,
00372       // it makes little sense to allocate less linear memory than the
00373       // natural blocking size of the malloc implementation.
00374       // Unfortunately, we would need a somewhat low-level calculation
00375       // with tuned parameters to get this perfect for any particular
00376       // malloc implementation.  Fortunately, generalizations about
00377       // common features seen among implementations seems to suffice.
00378 
00379       // __pagesize need not match the actual VM page size for good
00380       // results in practice, thus we pick a common value on the low
00381       // side.  __malloc_header_size is an estimate of the amount of
00382       // overhead per memory allocation (in practice seen N * sizeof
00383       // (void*) where N is 0, 2 or 4).  According to folklore,
00384       // picking this value on the high side is better than
00385       // low-balling it (especially when this algorithm is used with
00386       // malloc implementations that allocate memory blocks rounded up
00387       // to a size which is a power of 2).
00388       const size_type __pagesize = 4096;
00389       const size_type __malloc_header_size = 4 * sizeof(void*);
00390 
00391       // The below implements an exponential growth policy, necessary to
00392       // meet amortized linear time requirements of the library: see
00393       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
00394       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
00395     {
00396       __capacity = 2 * __old_capacity;
00397       // Never allocate a string bigger than _S_max_size.
00398       if (__capacity > size_type(_S_max_size))
00399         __capacity = size_type(_S_max_size);
00400     }
00401 
00402       // NB: Need an array of char_type[__capacity], plus a terminating
00403       // null char_type() element, plus enough for the _Rep data structure,
00404       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
00405       // sizeof(_Rep).
00406       // Whew. Seemingly so needy, yet so elemental.
00407       size_type __size = ((__capacity + 1) * sizeof(_CharT)
00408               + 2 * sizeof(_Rep) - 1);
00409 
00410       const size_type __adj_size = __size + __malloc_header_size;
00411       if (__adj_size > __pagesize && __capacity > __old_capacity)
00412     {
00413       const size_type __extra = __pagesize - __adj_size % __pagesize;
00414       __capacity += __extra / sizeof(_CharT);
00415       if (__capacity > size_type(_S_max_size))
00416         __capacity = size_type(_S_max_size);
00417       __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
00418     }
00419 
00420       // NB: Might throw, but no worries about a leak, mate: _Rep()
00421       // does not throw.
00422       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
00423       _Rep* __p = new (__place) _Rep;
00424       __p->_M_info._M_capacity = __capacity;
00425       return __p;
00426     }
00427 
00428   template<typename _CharT, typename _Traits, typename _Alloc>
00429     void
00430     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00431     _M_destroy(const _Alloc& __a) throw ()
00432     {
00433       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
00434                 + 2 * sizeof(_Rep) - 1);
00435       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
00436     }
00437 
00438   template<typename _CharT, typename _Traits, typename _Alloc>
00439     _CharT*
00440     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00441     _M_clone(const _Alloc& __alloc, size_type __res)
00442     {
00443       // Requested capacity of the clone.
00444       const size_type __requested_cap = _M_info._M_length + __res;
00445       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
00446                   __alloc);
00447 
00448       if (_M_info._M_length)
00449     _S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
00450 
00451       __r->_M_set_length(_M_info._M_length);
00452       return __r->_M_refdata();
00453     }
00454 
00455   template<typename _CharT, typename _Traits, typename _Alloc>
00456     __rc_string_base<_CharT, _Traits, _Alloc>::
00457     __rc_string_base(const _Alloc& __a)
00458     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
00459 
00460   template<typename _CharT, typename _Traits, typename _Alloc>
00461     __rc_string_base<_CharT, _Traits, _Alloc>::
00462     __rc_string_base(const __rc_string_base& __rcs)
00463     : _M_dataplus(__rcs._M_get_allocator(),
00464           __rcs._M_grab(__rcs._M_get_allocator())) { }
00465 
00466   template<typename _CharT, typename _Traits, typename _Alloc>
00467     __rc_string_base<_CharT, _Traits, _Alloc>::
00468     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
00469     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
00470 
00471   template<typename _CharT, typename _Traits, typename _Alloc>
00472     template<typename _InputIterator>
00473     __rc_string_base<_CharT, _Traits, _Alloc>::
00474     __rc_string_base(_InputIterator __beg, _InputIterator __end,
00475              const _Alloc& __a)
00476     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
00477 
00478   template<typename _CharT, typename _Traits, typename _Alloc>
00479     void
00480     __rc_string_base<_CharT, _Traits, _Alloc>::
00481     _M_leak_hard()
00482     {
00483       if (_M_is_shared())
00484     _M_erase(0, 0);
00485       _M_set_leaked();
00486     }
00487 
00488   // NB: This is the special case for Input Iterators, used in
00489   // istreambuf_iterators, etc.
00490   // Input Iterators have a cost structure very different from
00491   // pointers, calling for a different coding style.
00492   template<typename _CharT, typename _Traits, typename _Alloc>
00493     template<typename _InIterator>
00494       _CharT*
00495       __rc_string_base<_CharT, _Traits, _Alloc>::
00496       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00497            std::input_iterator_tag)
00498       {
00499     if (__beg == __end && __a == _Alloc())
00500       return _S_empty_rep._M_refcopy();
00501 
00502     // Avoid reallocation for common case.
00503     _CharT __buf[128];
00504     size_type __len = 0;
00505     while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
00506       {
00507         __buf[__len++] = *__beg;
00508         ++__beg;
00509       }
00510     _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
00511     _S_copy(__r->_M_refdata(), __buf, __len);
00512     try
00513       {
00514         while (__beg != __end)
00515           {
00516         if (__len == __r->_M_info._M_capacity)
00517           {
00518             // Allocate more space.
00519             _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
00520             _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
00521             __r->_M_destroy(__a);
00522             __r = __another;
00523           }
00524         __r->_M_refdata()[__len++] = *__beg;
00525         ++__beg;
00526           }
00527       }
00528     catch(...)
00529       {
00530         __r->_M_destroy(__a);
00531         __throw_exception_again;
00532       }
00533     __r->_M_set_length(__len);
00534     return __r->_M_refdata();
00535       }
00536 
00537   template<typename _CharT, typename _Traits, typename _Alloc>
00538     template<typename _InIterator>
00539       _CharT*
00540       __rc_string_base<_CharT, _Traits, _Alloc>::
00541       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00542            std::forward_iterator_tag)
00543       {
00544     if (__beg == __end && __a == _Alloc())
00545       return _S_empty_rep._M_refcopy();
00546 
00547     // NB: Not required, but considered best practice.
00548     if (__builtin_expect(_S_is_null_pointer(__beg) && __beg != __end, 0))
00549       std::__throw_logic_error(__N("__rc_string_base::"
00550                        "_S_construct NULL not valid"));
00551 
00552     const size_type __dnew = static_cast<size_type>(std::distance(__beg,
00553                                       __end));
00554     // Check for out_of_range and length_error exceptions.
00555     _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
00556     try
00557       { _S_copy_chars(__r->_M_refdata(), __beg, __end); }
00558     catch(...)
00559       {
00560         __r->_M_destroy(__a);
00561         __throw_exception_again;
00562       }
00563     __r->_M_set_length(__dnew);
00564     return __r->_M_refdata();
00565       }
00566 
00567   template<typename _CharT, typename _Traits, typename _Alloc>
00568     _CharT*
00569     __rc_string_base<_CharT, _Traits, _Alloc>::
00570     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
00571     {
00572       if (__n == 0 && __a == _Alloc())
00573     return _S_empty_rep._M_refcopy();
00574 
00575       // Check for out_of_range and length_error exceptions.
00576       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
00577       if (__n)
00578     _S_assign(__r->_M_refdata(), __n, __c);
00579 
00580       __r->_M_set_length(__n);
00581       return __r->_M_refdata();
00582     }
00583 
00584   template<typename _CharT, typename _Traits, typename _Alloc>
00585     void
00586     __rc_string_base<_CharT, _Traits, _Alloc>::
00587     _M_swap(__rc_string_base& __rcs)
00588     {
00589       if (_M_is_leaked())
00590     _M_set_sharable();
00591       if (__rcs._M_is_leaked())
00592     __rcs._M_set_sharable();
00593       
00594       _CharT* __tmp = _M_data();
00595       _M_data(__rcs._M_data());
00596       __rcs._M_data(__tmp);
00597 
00598       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00599       // 431. Swapping containers with unequal allocators.
00600       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
00601                           __rcs._M_get_allocator());
00602     } 
00603 
00604   template<typename _CharT, typename _Traits, typename _Alloc>
00605     void
00606     __rc_string_base<_CharT, _Traits, _Alloc>::
00607     _M_assign(const __rc_string_base& __rcs)
00608     {
00609       if (_M_rep() != __rcs._M_rep())
00610     {
00611       _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
00612       _M_dispose();
00613       _M_data(__tmp);
00614     }
00615     }
00616 
00617   template<typename _CharT, typename _Traits, typename _Alloc>
00618     void
00619     __rc_string_base<_CharT, _Traits, _Alloc>::
00620     _M_reserve(size_type __res)
00621     {
00622       // Make sure we don't shrink below the current size.
00623       if (__res < _M_length())
00624     __res = _M_length();
00625       
00626       if (__res != _M_capacity() || _M_is_shared())
00627     {
00628       _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
00629                          __res - _M_length());
00630       _M_dispose();
00631       _M_data(__tmp);
00632     }
00633     }
00634 
00635   template<typename _CharT, typename _Traits, typename _Alloc>
00636     void
00637     __rc_string_base<_CharT, _Traits, _Alloc>::
00638     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00639           size_type __len2)
00640     {
00641       const size_type __how_much = _M_length() - __pos - __len1;
00642       
00643       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
00644                   _M_capacity(), _M_get_allocator());
00645       
00646       if (__pos)
00647     _S_copy(__r->_M_refdata(), _M_data(), __pos);
00648       if (__s && __len2)
00649     _S_copy(__r->_M_refdata() + __pos, __s, __len2);
00650       if (__how_much)
00651     _S_copy(__r->_M_refdata() + __pos + __len2,
00652         _M_data() + __pos + __len1, __how_much);
00653       
00654       _M_dispose();
00655       _M_data(__r->_M_refdata());
00656     }
00657 
00658   template<typename _CharT, typename _Traits, typename _Alloc>
00659     void
00660     __rc_string_base<_CharT, _Traits, _Alloc>::
00661     _M_erase(size_type __pos, size_type __n)
00662     {
00663       const size_type __new_size = _M_length() - __n;
00664       const size_type __how_much = _M_length() - __pos - __n;
00665       
00666       if (_M_is_shared())
00667     {
00668       // Must reallocate.
00669       _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
00670                       _M_get_allocator());
00671 
00672       if (__pos)
00673         _S_copy(__r->_M_refdata(), _M_data(), __pos);
00674       if (__how_much)
00675         _S_copy(__r->_M_refdata() + __pos,
00676             _M_data() + __pos + __n, __how_much);
00677 
00678       _M_dispose();
00679       _M_data(__r->_M_refdata());
00680     }
00681       else if (__how_much && __n)
00682     {
00683       // Work in-place.
00684       _S_move(_M_data() + __pos,
00685           _M_data() + __pos + __n, __how_much);
00686     }
00687 
00688       _M_rep()->_M_set_length(__new_size);      
00689     }
00690 
00691   template<>
00692     inline bool
00693     __rc_string_base<char, std::char_traits<char>,
00694              std::allocator<char> >::
00695     _M_compare(const __rc_string_base& __rcs) const
00696     {
00697       if (_M_rep() == __rcs._M_rep())
00698     return true;
00699       return false;
00700     }
00701 
00702 #ifdef _GLIBCXX_USE_WCHAR_T
00703   template<>
00704     inline bool
00705     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
00706              std::allocator<wchar_t> >::
00707     _M_compare(const __rc_string_base& __rcs) const
00708     {
00709       if (_M_rep() == __rcs._M_rep())
00710     return true;
00711       return false;
00712     }
00713 #endif
00714 
00715 _GLIBCXX_END_NAMESPACE
00716 
00717 #endif /* _RC_STRING_BASE_H */

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