1 // Reference-counted versatile string base -*- C++ -*-
3 // Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
4 // Free Software Foundation, Inc.
6 // This file is part of the GNU ISO C++ Library. This library is free
7 // software; you can redistribute it and/or modify it under the
8 // terms of the GNU General Public License as published by the
9 // Free Software Foundation; either version 3, or (at your option)
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
17 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 // <http://www.gnu.org/licenses/>.
26 /** @file ext/rc_string_base.h
27 * This is an internal header file, included by other library headers.
28 * Do not attempt to use it directly. @headername{ext/vstring.h}
31 #ifndef _RC_STRING_BASE_H
32 #define _RC_STRING_BASE_H 1
34 #include <ext/atomicity.h>
35 #include <bits/stl_iterator_base_funcs.h>
37 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
39 _GLIBCXX_BEGIN_NAMESPACE_VERSION
42 * Documentation? What's that?
43 * Nathan Myers <ncm@cantrip.org>.
45 * A string looks like this:
50 * [__rc_string_base<char_type>] _M_capacity
51 * _M_dataplus _M_refcount
52 * _M_p ----------------> unnamed array of char_type
55 * Where the _M_p points to the first character in the string, and
56 * you cast it to a pointer-to-_Rep and subtract 1 to get a
57 * pointer to the header.
59 * This approach has the enormous advantage that a string object
60 * requires only one allocation. All the ugliness is confined
61 * within a single pair of inline functions, which each compile to
62 * a single @a add instruction: _Rep::_M_refdata(), and
63 * __rc_string_base::_M_rep(); and the allocation function which gets a
64 * block of raw bytes and with room enough and constructs a _Rep
65 * object at the front.
67 * The reason you want _M_data pointing to the character array and
68 * not the _Rep is so that the debugger can see the string
69 * contents. (Probably we should add a non-inline member to get
70 * the _Rep for the debugger to use, so users can check the actual
73 * Note that the _Rep object is a POD so that you can have a
74 * static <em>empty string</em> _Rep object already @a constructed before
75 * static constructors have run. The reference-count encoding is
76 * chosen so that a 0 indicates one reference, so you never try to
77 * destroy the empty-string _Rep object.
79 * All but the last paragraph is considered pretty conventional
80 * for a C++ string implementation.
82 template<typename _CharT, typename _Traits, typename _Alloc>
83 class __rc_string_base
84 : protected __vstring_utility<_CharT, _Traits, _Alloc>
87 typedef _Traits traits_type;
88 typedef typename _Traits::char_type value_type;
89 typedef _Alloc allocator_type;
91 typedef __vstring_utility<_CharT, _Traits, _Alloc> _Util_Base;
92 typedef typename _Util_Base::_CharT_alloc_type _CharT_alloc_type;
93 typedef typename _CharT_alloc_type::size_type size_type;
96 // _Rep: string representation
98 // 1. String really contains _M_length + 1 characters: due to 21.3.4
99 // must be kept null-terminated.
100 // 2. _M_capacity >= _M_length
101 // Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
102 // 3. _M_refcount has three states:
103 // -1: leaked, one reference, no ref-copies allowed, non-const.
104 // 0: one reference, non-const.
105 // n>0: n + 1 references, operations require a lock, const.
106 // 4. All fields == 0 is an empty string, given the extra storage
107 // beyond-the-end for a null terminator; thus, the shared
108 // empty string representation needs no constructor.
116 size_type _M_capacity;
117 _Atomic_word _M_refcount;
120 // Only for alignment purposes.
124 typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
128 { return reinterpret_cast<_CharT*>(this + 1); }
133 __atomic_add_dispatch(&_M_info._M_refcount, 1);
138 _M_set_length(size_type __n)
140 _M_info._M_refcount = 0; // One reference.
141 _M_info._M_length = __n;
142 // grrr. (per 21.3.4)
143 // You cannot leave those LWG people alone for a second.
144 traits_type::assign(_M_refdata()[__n], _CharT());
149 _S_create(size_type, size_type, const _Alloc&);
152 _M_destroy(const _Alloc&) throw();
155 _M_clone(const _Alloc&, size_type __res = 0);
164 static _Rep_empty _S_empty_rep;
166 // The maximum number of individual char_type elements of an
167 // individual string is determined by _S_max_size. This is the
168 // value that will be returned by max_size(). (Whereas npos
169 // is the maximum number of bytes the allocator can allocate.)
170 // If one was to divvy up the theoretical largest size string,
171 // with a terminating character and m _CharT elements, it'd
173 // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
174 // + sizeof(_Rep) - 1
175 // (NB: last two terms for rounding reasons, see _M_create below)
177 // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
178 // In addition, this implementation halves this amount.
179 enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
180 + 1) / sizeof(_CharT)) - 1) / 2 };
182 // Data Member (private):
183 mutable typename _Util_Base::template _Alloc_hider<_Alloc> _M_dataplus;
187 { _M_dataplus._M_p = __p; }
191 { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
194 _M_grab(const _Alloc& __alloc) const
196 return (!_M_is_leaked() && _M_get_allocator() == __alloc)
197 ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
203 // Be race-detector-friendly. For more info see bits/c++config.
204 _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
206 if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
209 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
211 _M_rep()->_M_destroy(_M_get_allocator());
217 { return _M_rep()->_M_info._M_refcount < 0; }
221 { _M_rep()->_M_info._M_refcount = 0; }
226 // _S_construct_aux is used to implement the 21.3.1 para 15 which
227 // requires special behaviour if _InIterator is an integral type
228 template<typename _InIterator>
230 _S_construct_aux(_InIterator __beg, _InIterator __end,
231 const _Alloc& __a, std::__false_type)
233 typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
234 return _S_construct(__beg, __end, __a, _Tag());
237 // _GLIBCXX_RESOLVE_LIB_DEFECTS
238 // 438. Ambiguity in the "do the right thing" clause
239 template<typename _Integer>
241 _S_construct_aux(_Integer __beg, _Integer __end,
242 const _Alloc& __a, std::__true_type)
243 { return _S_construct_aux_2(static_cast<size_type>(__beg),
247 _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
248 { return _S_construct(__req, __c, __a); }
250 template<typename _InIterator>
252 _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
254 typedef typename std::__is_integer<_InIterator>::__type _Integral;
255 return _S_construct_aux(__beg, __end, __a, _Integral());
258 // For Input Iterators, used in istreambuf_iterators, etc.
259 template<typename _InIterator>
261 _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
262 std::input_iterator_tag);
264 // For forward_iterators up to random_access_iterators, used for
265 // string::iterator, _CharT*, etc.
266 template<typename _FwdIterator>
268 _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
269 std::forward_iterator_tag);
272 _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
277 { return size_type(_S_max_size); }
281 { return _M_dataplus._M_p; }
285 { return _M_rep()->_M_info._M_length; }
289 { return _M_rep()->_M_info._M_capacity; }
293 { return _M_rep()->_M_info._M_refcount > 0; }
297 { _M_rep()->_M_info._M_refcount = -1; }
300 _M_leak() // for use in begin() & non-const op[]
307 _M_set_length(size_type __n)
308 { _M_rep()->_M_set_length(__n); }
311 : _M_dataplus(_S_empty_rep._M_refcopy()) { }
313 __rc_string_base(const _Alloc& __a);
315 __rc_string_base(const __rc_string_base& __rcs);
317 #ifdef __GXX_EXPERIMENTAL_CXX0X__
318 __rc_string_base(__rc_string_base&& __rcs)
319 : _M_dataplus(__rcs._M_dataplus)
320 { __rcs._M_data(_S_empty_rep._M_refcopy()); }
323 __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
325 template<typename _InputIterator>
326 __rc_string_base(_InputIterator __beg, _InputIterator __end,
334 { return _M_dataplus; }
336 const allocator_type&
337 _M_get_allocator() const
338 { return _M_dataplus; }
341 _M_swap(__rc_string_base& __rcs);
344 _M_assign(const __rc_string_base& __rcs);
347 _M_reserve(size_type __res);
350 _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
354 _M_erase(size_type __pos, size_type __n);
358 { _M_erase(size_type(0), _M_length()); }
361 _M_compare(const __rc_string_base&) const
365 template<typename _CharT, typename _Traits, typename _Alloc>
366 typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
367 __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
369 template<typename _CharT, typename _Traits, typename _Alloc>
370 typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
371 __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
372 _S_create(size_type __capacity, size_type __old_capacity,
373 const _Alloc& __alloc)
375 // _GLIBCXX_RESOLVE_LIB_DEFECTS
376 // 83. String::npos vs. string::max_size()
377 if (__capacity > size_type(_S_max_size))
378 std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
380 // The standard places no restriction on allocating more memory
381 // than is strictly needed within this layer at the moment or as
382 // requested by an explicit application call to reserve().
384 // Many malloc implementations perform quite poorly when an
385 // application attempts to allocate memory in a stepwise fashion
386 // growing each allocation size by only 1 char. Additionally,
387 // it makes little sense to allocate less linear memory than the
388 // natural blocking size of the malloc implementation.
389 // Unfortunately, we would need a somewhat low-level calculation
390 // with tuned parameters to get this perfect for any particular
391 // malloc implementation. Fortunately, generalizations about
392 // common features seen among implementations seems to suffice.
394 // __pagesize need not match the actual VM page size for good
395 // results in practice, thus we pick a common value on the low
396 // side. __malloc_header_size is an estimate of the amount of
397 // overhead per memory allocation (in practice seen N * sizeof
398 // (void*) where N is 0, 2 or 4). According to folklore,
399 // picking this value on the high side is better than
400 // low-balling it (especially when this algorithm is used with
401 // malloc implementations that allocate memory blocks rounded up
402 // to a size which is a power of 2).
403 const size_type __pagesize = 4096;
404 const size_type __malloc_header_size = 4 * sizeof(void*);
406 // The below implements an exponential growth policy, necessary to
407 // meet amortized linear time requirements of the library: see
408 // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
409 if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
411 __capacity = 2 * __old_capacity;
412 // Never allocate a string bigger than _S_max_size.
413 if (__capacity > size_type(_S_max_size))
414 __capacity = size_type(_S_max_size);
417 // NB: Need an array of char_type[__capacity], plus a terminating
418 // null char_type() element, plus enough for the _Rep data structure,
419 // plus sizeof(_Rep) - 1 to upper round to a size multiple of
421 // Whew. Seemingly so needy, yet so elemental.
422 size_type __size = ((__capacity + 1) * sizeof(_CharT)
423 + 2 * sizeof(_Rep) - 1);
425 const size_type __adj_size = __size + __malloc_header_size;
426 if (__adj_size > __pagesize && __capacity > __old_capacity)
428 const size_type __extra = __pagesize - __adj_size % __pagesize;
429 __capacity += __extra / sizeof(_CharT);
430 if (__capacity > size_type(_S_max_size))
431 __capacity = size_type(_S_max_size);
432 __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
435 // NB: Might throw, but no worries about a leak, mate: _Rep()
437 _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
438 _Rep* __p = new (__place) _Rep;
439 __p->_M_info._M_capacity = __capacity;
443 template<typename _CharT, typename _Traits, typename _Alloc>
445 __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
446 _M_destroy(const _Alloc& __a) throw ()
448 const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
449 + 2 * sizeof(_Rep) - 1);
450 _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
453 template<typename _CharT, typename _Traits, typename _Alloc>
455 __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
456 _M_clone(const _Alloc& __alloc, size_type __res)
458 // Requested capacity of the clone.
459 const size_type __requested_cap = _M_info._M_length + __res;
460 _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
463 if (_M_info._M_length)
464 __rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
466 __r->_M_set_length(_M_info._M_length);
467 return __r->_M_refdata();
470 template<typename _CharT, typename _Traits, typename _Alloc>
471 __rc_string_base<_CharT, _Traits, _Alloc>::
472 __rc_string_base(const _Alloc& __a)
473 : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
475 template<typename _CharT, typename _Traits, typename _Alloc>
476 __rc_string_base<_CharT, _Traits, _Alloc>::
477 __rc_string_base(const __rc_string_base& __rcs)
478 : _M_dataplus(__rcs._M_get_allocator(),
479 __rcs._M_grab(__rcs._M_get_allocator())) { }
481 template<typename _CharT, typename _Traits, typename _Alloc>
482 __rc_string_base<_CharT, _Traits, _Alloc>::
483 __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
484 : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
486 template<typename _CharT, typename _Traits, typename _Alloc>
487 template<typename _InputIterator>
488 __rc_string_base<_CharT, _Traits, _Alloc>::
489 __rc_string_base(_InputIterator __beg, _InputIterator __end,
491 : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
493 template<typename _CharT, typename _Traits, typename _Alloc>
495 __rc_string_base<_CharT, _Traits, _Alloc>::
503 // NB: This is the special case for Input Iterators, used in
504 // istreambuf_iterators, etc.
505 // Input Iterators have a cost structure very different from
506 // pointers, calling for a different coding style.
507 template<typename _CharT, typename _Traits, typename _Alloc>
508 template<typename _InIterator>
510 __rc_string_base<_CharT, _Traits, _Alloc>::
511 _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
512 std::input_iterator_tag)
514 if (__beg == __end && __a == _Alloc())
515 return _S_empty_rep._M_refcopy();
517 // Avoid reallocation for common case.
520 while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
522 __buf[__len++] = *__beg;
525 _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
526 _S_copy(__r->_M_refdata(), __buf, __len);
529 while (__beg != __end)
531 if (__len == __r->_M_info._M_capacity)
533 // Allocate more space.
534 _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
535 _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
536 __r->_M_destroy(__a);
539 __r->_M_refdata()[__len++] = *__beg;
545 __r->_M_destroy(__a);
546 __throw_exception_again;
548 __r->_M_set_length(__len);
549 return __r->_M_refdata();
552 template<typename _CharT, typename _Traits, typename _Alloc>
553 template<typename _InIterator>
555 __rc_string_base<_CharT, _Traits, _Alloc>::
556 _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
557 std::forward_iterator_tag)
559 if (__beg == __end && __a == _Alloc())
560 return _S_empty_rep._M_refcopy();
562 // NB: Not required, but considered best practice.
563 if (__is_null_pointer(__beg) && __beg != __end)
564 std::__throw_logic_error(__N("__rc_string_base::"
565 "_S_construct null not valid"));
567 const size_type __dnew = static_cast<size_type>(std::distance(__beg,
569 // Check for out_of_range and length_error exceptions.
570 _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
572 { __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
575 __r->_M_destroy(__a);
576 __throw_exception_again;
578 __r->_M_set_length(__dnew);
579 return __r->_M_refdata();
582 template<typename _CharT, typename _Traits, typename _Alloc>
584 __rc_string_base<_CharT, _Traits, _Alloc>::
585 _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
587 if (__n == 0 && __a == _Alloc())
588 return _S_empty_rep._M_refcopy();
590 // Check for out_of_range and length_error exceptions.
591 _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
593 __rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
595 __r->_M_set_length(__n);
596 return __r->_M_refdata();
599 template<typename _CharT, typename _Traits, typename _Alloc>
601 __rc_string_base<_CharT, _Traits, _Alloc>::
602 _M_swap(__rc_string_base& __rcs)
606 if (__rcs._M_is_leaked())
607 __rcs._M_set_sharable();
609 _CharT* __tmp = _M_data();
610 _M_data(__rcs._M_data());
611 __rcs._M_data(__tmp);
613 // _GLIBCXX_RESOLVE_LIB_DEFECTS
614 // 431. Swapping containers with unequal allocators.
615 std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
616 __rcs._M_get_allocator());
619 template<typename _CharT, typename _Traits, typename _Alloc>
621 __rc_string_base<_CharT, _Traits, _Alloc>::
622 _M_assign(const __rc_string_base& __rcs)
624 if (_M_rep() != __rcs._M_rep())
626 _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
632 template<typename _CharT, typename _Traits, typename _Alloc>
634 __rc_string_base<_CharT, _Traits, _Alloc>::
635 _M_reserve(size_type __res)
637 // Make sure we don't shrink below the current size.
638 if (__res < _M_length())
641 if (__res != _M_capacity() || _M_is_shared())
643 _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
644 __res - _M_length());
650 template<typename _CharT, typename _Traits, typename _Alloc>
652 __rc_string_base<_CharT, _Traits, _Alloc>::
653 _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
656 const size_type __how_much = _M_length() - __pos - __len1;
658 _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
659 _M_capacity(), _M_get_allocator());
662 this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
664 this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
666 this->_S_copy(__r->_M_refdata() + __pos + __len2,
667 _M_data() + __pos + __len1, __how_much);
670 _M_data(__r->_M_refdata());
673 template<typename _CharT, typename _Traits, typename _Alloc>
675 __rc_string_base<_CharT, _Traits, _Alloc>::
676 _M_erase(size_type __pos, size_type __n)
678 const size_type __new_size = _M_length() - __n;
679 const size_type __how_much = _M_length() - __pos - __n;
684 _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
688 this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
690 this->_S_copy(__r->_M_refdata() + __pos,
691 _M_data() + __pos + __n, __how_much);
694 _M_data(__r->_M_refdata());
696 else if (__how_much && __n)
699 this->_S_move(_M_data() + __pos,
700 _M_data() + __pos + __n, __how_much);
703 _M_rep()->_M_set_length(__new_size);
708 __rc_string_base<char, std::char_traits<char>,
709 std::allocator<char> >::
710 _M_compare(const __rc_string_base& __rcs) const
712 if (_M_rep() == __rcs._M_rep())
717 #ifdef _GLIBCXX_USE_WCHAR_T
720 __rc_string_base<wchar_t, std::char_traits<wchar_t>,
721 std::allocator<wchar_t> >::
722 _M_compare(const __rc_string_base& __rcs) const
724 if (_M_rep() == __rcs._M_rep())
730 _GLIBCXX_END_NAMESPACE_VERSION
733 #endif /* _RC_STRING_BASE_H */