1 // Reference-counted versatile string base -*- C++ -*-
3 // Copyright (C) 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
25 /** @file ext/rc_string_base.h
26 * This file is a GNU extension to the Standard C++ Library.
27 * This is an internal header file, included by other library headers.
28 * You should not attempt to use it directly.
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 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx
)
40 * Documentation? What's that?
41 * Nathan Myers <ncm@cantrip.org>.
43 * A string looks like this:
48 * [__rc_string_base<char_type>] _M_capacity
49 * _M_dataplus _M_refcount
50 * _M_p ----------------> unnamed array of char_type
53 * Where the _M_p points to the first character in the string, and
54 * you cast it to a pointer-to-_Rep and subtract 1 to get a
55 * pointer to the header.
57 * This approach has the enormous advantage that a string object
58 * requires only one allocation. All the ugliness is confined
59 * within a single pair of inline functions, which each compile to
60 * a single "add" instruction: _Rep::_M_refdata(), and
61 * __rc_string_base::_M_rep(); and the allocation function which gets a
62 * block of raw bytes and with room enough and constructs a _Rep
63 * object at the front.
65 * The reason you want _M_data pointing to the character array and
66 * not the _Rep is so that the debugger can see the string
67 * contents. (Probably we should add a non-inline member to get
68 * the _Rep for the debugger to use, so users can check the actual
71 * Note that the _Rep object is a POD so that you can have a
72 * static "empty string" _Rep object already "constructed" before
73 * static constructors have run. The reference-count encoding is
74 * chosen so that a 0 indicates one reference, so you never try to
75 * destroy the empty-string _Rep object.
77 * All but the last paragraph is considered pretty conventional
78 * for a C++ string implementation.
80 template<typename _CharT
, typename _Traits
, typename _Alloc
>
81 class __rc_string_base
82 : protected __vstring_utility
<_CharT
, _Traits
, _Alloc
>
85 typedef _Traits traits_type
;
86 typedef typename
_Traits::char_type value_type
;
87 typedef _Alloc allocator_type
;
89 typedef __vstring_utility
<_CharT
, _Traits
, _Alloc
> _Util_Base
;
90 typedef typename
_Util_Base::_CharT_alloc_type _CharT_alloc_type
;
91 typedef typename
_CharT_alloc_type::size_type size_type
;
94 // _Rep: string representation
96 // 1. String really contains _M_length + 1 characters: due to 21.3.4
97 // must be kept null-terminated.
98 // 2. _M_capacity >= _M_length
99 // Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
100 // 3. _M_refcount has three states:
101 // -1: leaked, one reference, no ref-copies allowed, non-const.
102 // 0: one reference, non-const.
103 // n>0: n + 1 references, operations require a lock, const.
104 // 4. All fields == 0 is an empty string, given the extra storage
105 // beyond-the-end for a null terminator; thus, the shared
106 // empty string representation needs no constructor.
114 size_type _M_capacity
;
115 _Atomic_word _M_refcount
;
118 // Only for alignment purposes.
122 typedef typename
_Alloc::template rebind
<_Rep
>::other _Rep_alloc_type
;
126 { return reinterpret_cast<_CharT
*>(this + 1); }
131 __atomic_add_dispatch(&_M_info
._M_refcount
, 1);
136 _M_set_length(size_type __n
)
138 _M_info
._M_refcount
= 0; // One reference.
139 _M_info
._M_length
= __n
;
140 // grrr. (per 21.3.4)
141 // You cannot leave those LWG people alone for a second.
142 traits_type::assign(_M_refdata()[__n
], _CharT());
147 _S_create(size_type
, size_type
, const _Alloc
&);
150 _M_destroy(const _Alloc
&) throw();
153 _M_clone(const _Alloc
&, size_type __res
= 0);
162 static _Rep_empty _S_empty_rep
;
164 // The maximum number of individual char_type elements of an
165 // individual string is determined by _S_max_size. This is the
166 // value that will be returned by max_size(). (Whereas npos
167 // is the maximum number of bytes the allocator can allocate.)
168 // If one was to divvy up the theoretical largest size string,
169 // with a terminating character and m _CharT elements, it'd
171 // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
172 // + sizeof(_Rep) - 1
173 // (NB: last two terms for rounding reasons, see _M_create below)
175 // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
176 // In addition, this implementation halves this amount.
177 enum { _S_max_size
= (((static_cast<size_type
>(-1) - 2 * sizeof(_Rep
)
178 + 1) / sizeof(_CharT
)) - 1) / 2 };
180 // Data Member (private):
181 mutable typename
_Util_Base::template _Alloc_hider
<_Alloc
> _M_dataplus
;
185 { _M_dataplus
._M_p
= __p
; }
189 { return &((reinterpret_cast<_Rep
*>(_M_data()))[-1]); }
192 _M_grab(const _Alloc
& __alloc
) const
194 return (!_M_is_leaked() && _M_get_allocator() == __alloc
)
195 ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc
);
201 if (__exchange_and_add_dispatch(&_M_rep()->_M_info
._M_refcount
,
203 _M_rep()->_M_destroy(_M_get_allocator());
208 { return _M_rep()->_M_info
._M_refcount
< 0; }
212 { _M_rep()->_M_info
._M_refcount
= 0; }
217 // _S_construct_aux is used to implement the 21.3.1 para 15 which
218 // requires special behaviour if _InIterator is an integral type
219 template<typename _InIterator
>
221 _S_construct_aux(_InIterator __beg
, _InIterator __end
,
222 const _Alloc
& __a
, std::__false_type
)
224 typedef typename iterator_traits
<_InIterator
>::iterator_category _Tag
;
225 return _S_construct(__beg
, __end
, __a
, _Tag());
228 // _GLIBCXX_RESOLVE_LIB_DEFECTS
229 // 438. Ambiguity in the "do the right thing" clause
230 template<typename _Integer
>
232 _S_construct_aux(_Integer __beg
, _Integer __end
,
233 const _Alloc
& __a
, std::__true_type
)
234 { return _S_construct_aux_2(static_cast<size_type
>(__beg
),
238 _S_construct_aux_2(size_type __req
, _CharT __c
, const _Alloc
& __a
)
239 { return _S_construct(__req
, __c
, __a
); }
241 template<typename _InIterator
>
243 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
)
245 typedef typename
std::__is_integer
<_InIterator
>::__type _Integral
;
246 return _S_construct_aux(__beg
, __end
, __a
, _Integral());
249 // For Input Iterators, used in istreambuf_iterators, etc.
250 template<typename _InIterator
>
252 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
,
253 std::input_iterator_tag
);
255 // For forward_iterators up to random_access_iterators, used for
256 // string::iterator, _CharT*, etc.
257 template<typename _FwdIterator
>
259 _S_construct(_FwdIterator __beg
, _FwdIterator __end
, const _Alloc
& __a
,
260 std::forward_iterator_tag
);
263 _S_construct(size_type __req
, _CharT __c
, const _Alloc
& __a
);
268 { return size_type(_S_max_size
); }
272 { return _M_dataplus
._M_p
; }
276 { return _M_rep()->_M_info
._M_length
; }
280 { return _M_rep()->_M_info
._M_capacity
; }
284 { return _M_rep()->_M_info
._M_refcount
> 0; }
288 { _M_rep()->_M_info
._M_refcount
= -1; }
291 _M_leak() // for use in begin() & non-const op[]
298 _M_set_length(size_type __n
)
299 { _M_rep()->_M_set_length(__n
); }
302 : _M_dataplus(_S_empty_rep
._M_refcopy()) { }
304 __rc_string_base(const _Alloc
& __a
);
306 __rc_string_base(const __rc_string_base
& __rcs
);
308 #ifdef __GXX_EXPERIMENTAL_CXX0X__
309 __rc_string_base(__rc_string_base
&& __rcs
)
310 : _M_dataplus(__rcs
._M_get_allocator(), __rcs
._M_data())
311 { __rcs
._M_data(_S_empty_rep
._M_refcopy()); }
314 __rc_string_base(size_type __n
, _CharT __c
, const _Alloc
& __a
);
316 template<typename _InputIterator
>
317 __rc_string_base(_InputIterator __beg
, _InputIterator __end
,
325 { return _M_dataplus
; }
327 const allocator_type
&
328 _M_get_allocator() const
329 { return _M_dataplus
; }
332 _M_swap(__rc_string_base
& __rcs
);
335 _M_assign(const __rc_string_base
& __rcs
);
338 _M_reserve(size_type __res
);
341 _M_mutate(size_type __pos
, size_type __len1
, const _CharT
* __s
,
345 _M_erase(size_type __pos
, size_type __n
);
349 { _M_erase(size_type(0), _M_length()); }
352 _M_compare(const __rc_string_base
&) const
356 template<typename _CharT
, typename _Traits
, typename _Alloc
>
357 typename __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep_empty
358 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_S_empty_rep
;
360 template<typename _CharT
, typename _Traits
, typename _Alloc
>
361 typename __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep
*
362 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep::
363 _S_create(size_type __capacity
, size_type __old_capacity
,
364 const _Alloc
& __alloc
)
366 // _GLIBCXX_RESOLVE_LIB_DEFECTS
367 // 83. String::npos vs. string::max_size()
368 if (__capacity
> size_type(_S_max_size
))
369 std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
371 // The standard places no restriction on allocating more memory
372 // than is strictly needed within this layer at the moment or as
373 // requested by an explicit application call to reserve().
375 // Many malloc implementations perform quite poorly when an
376 // application attempts to allocate memory in a stepwise fashion
377 // growing each allocation size by only 1 char. Additionally,
378 // it makes little sense to allocate less linear memory than the
379 // natural blocking size of the malloc implementation.
380 // Unfortunately, we would need a somewhat low-level calculation
381 // with tuned parameters to get this perfect for any particular
382 // malloc implementation. Fortunately, generalizations about
383 // common features seen among implementations seems to suffice.
385 // __pagesize need not match the actual VM page size for good
386 // results in practice, thus we pick a common value on the low
387 // side. __malloc_header_size is an estimate of the amount of
388 // overhead per memory allocation (in practice seen N * sizeof
389 // (void*) where N is 0, 2 or 4). According to folklore,
390 // picking this value on the high side is better than
391 // low-balling it (especially when this algorithm is used with
392 // malloc implementations that allocate memory blocks rounded up
393 // to a size which is a power of 2).
394 const size_type __pagesize
= 4096;
395 const size_type __malloc_header_size
= 4 * sizeof(void*);
397 // The below implements an exponential growth policy, necessary to
398 // meet amortized linear time requirements of the library: see
399 // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
400 if (__capacity
> __old_capacity
&& __capacity
< 2 * __old_capacity
)
402 __capacity
= 2 * __old_capacity
;
403 // Never allocate a string bigger than _S_max_size.
404 if (__capacity
> size_type(_S_max_size
))
405 __capacity
= size_type(_S_max_size
);
408 // NB: Need an array of char_type[__capacity], plus a terminating
409 // null char_type() element, plus enough for the _Rep data structure,
410 // plus sizeof(_Rep) - 1 to upper round to a size multiple of
412 // Whew. Seemingly so needy, yet so elemental.
413 size_type __size
= ((__capacity
+ 1) * sizeof(_CharT
)
414 + 2 * sizeof(_Rep
) - 1);
416 const size_type __adj_size
= __size
+ __malloc_header_size
;
417 if (__adj_size
> __pagesize
&& __capacity
> __old_capacity
)
419 const size_type __extra
= __pagesize
- __adj_size
% __pagesize
;
420 __capacity
+= __extra
/ sizeof(_CharT
);
421 if (__capacity
> size_type(_S_max_size
))
422 __capacity
= size_type(_S_max_size
);
423 __size
= (__capacity
+ 1) * sizeof(_CharT
) + 2 * sizeof(_Rep
) - 1;
426 // NB: Might throw, but no worries about a leak, mate: _Rep()
428 _Rep
* __place
= _Rep_alloc_type(__alloc
).allocate(__size
/ sizeof(_Rep
));
429 _Rep
* __p
= new (__place
) _Rep
;
430 __p
->_M_info
._M_capacity
= __capacity
;
434 template<typename _CharT
, typename _Traits
, typename _Alloc
>
436 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep::
437 _M_destroy(const _Alloc
& __a
) throw ()
439 const size_type __size
= ((_M_info
._M_capacity
+ 1) * sizeof(_CharT
)
440 + 2 * sizeof(_Rep
) - 1);
441 _Rep_alloc_type(__a
).deallocate(this, __size
/ sizeof(_Rep
));
444 template<typename _CharT
, typename _Traits
, typename _Alloc
>
446 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep::
447 _M_clone(const _Alloc
& __alloc
, size_type __res
)
449 // Requested capacity of the clone.
450 const size_type __requested_cap
= _M_info
._M_length
+ __res
;
451 _Rep
* __r
= _Rep::_S_create(__requested_cap
, _M_info
._M_capacity
,
454 if (_M_info
._M_length
)
455 _S_copy(__r
->_M_refdata(), _M_refdata(), _M_info
._M_length
);
457 __r
->_M_set_length(_M_info
._M_length
);
458 return __r
->_M_refdata();
461 template<typename _CharT
, typename _Traits
, typename _Alloc
>
462 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
463 __rc_string_base(const _Alloc
& __a
)
464 : _M_dataplus(__a
, _S_construct(size_type(), _CharT(), __a
)) { }
466 template<typename _CharT
, typename _Traits
, typename _Alloc
>
467 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
468 __rc_string_base(const __rc_string_base
& __rcs
)
469 : _M_dataplus(__rcs
._M_get_allocator(),
470 __rcs
._M_grab(__rcs
._M_get_allocator())) { }
472 template<typename _CharT
, typename _Traits
, typename _Alloc
>
473 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
474 __rc_string_base(size_type __n
, _CharT __c
, const _Alloc
& __a
)
475 : _M_dataplus(__a
, _S_construct(__n
, __c
, __a
)) { }
477 template<typename _CharT
, typename _Traits
, typename _Alloc
>
478 template<typename _InputIterator
>
479 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
480 __rc_string_base(_InputIterator __beg
, _InputIterator __end
,
482 : _M_dataplus(__a
, _S_construct(__beg
, __end
, __a
)) { }
484 template<typename _CharT
, typename _Traits
, typename _Alloc
>
486 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
494 // NB: This is the special case for Input Iterators, used in
495 // istreambuf_iterators, etc.
496 // Input Iterators have a cost structure very different from
497 // pointers, calling for a different coding style.
498 template<typename _CharT
, typename _Traits
, typename _Alloc
>
499 template<typename _InIterator
>
501 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
502 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
,
503 std::input_iterator_tag
)
505 if (__beg
== __end
&& __a
== _Alloc())
506 return _S_empty_rep
._M_refcopy();
508 // Avoid reallocation for common case.
511 while (__beg
!= __end
&& __len
< sizeof(__buf
) / sizeof(_CharT
))
513 __buf
[__len
++] = *__beg
;
516 _Rep
* __r
= _Rep::_S_create(__len
, size_type(0), __a
);
517 _S_copy(__r
->_M_refdata(), __buf
, __len
);
520 while (__beg
!= __end
)
522 if (__len
== __r
->_M_info
._M_capacity
)
524 // Allocate more space.
525 _Rep
* __another
= _Rep::_S_create(__len
+ 1, __len
, __a
);
526 _S_copy(__another
->_M_refdata(), __r
->_M_refdata(), __len
);
527 __r
->_M_destroy(__a
);
530 __r
->_M_refdata()[__len
++] = *__beg
;
536 __r
->_M_destroy(__a
);
537 __throw_exception_again
;
539 __r
->_M_set_length(__len
);
540 return __r
->_M_refdata();
543 template<typename _CharT
, typename _Traits
, typename _Alloc
>
544 template<typename _InIterator
>
546 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
547 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
,
548 std::forward_iterator_tag
)
550 if (__beg
== __end
&& __a
== _Alloc())
551 return _S_empty_rep
._M_refcopy();
553 // NB: Not required, but considered best practice.
554 if (__is_null_pointer(__beg
) && __beg
!= __end
)
555 std::__throw_logic_error(__N("__rc_string_base::"
556 "_S_construct NULL not valid"));
558 const size_type __dnew
= static_cast<size_type
>(std::distance(__beg
,
560 // Check for out_of_range and length_error exceptions.
561 _Rep
* __r
= _Rep::_S_create(__dnew
, size_type(0), __a
);
563 { _S_copy_chars(__r
->_M_refdata(), __beg
, __end
); }
566 __r
->_M_destroy(__a
);
567 __throw_exception_again
;
569 __r
->_M_set_length(__dnew
);
570 return __r
->_M_refdata();
573 template<typename _CharT
, typename _Traits
, typename _Alloc
>
575 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
576 _S_construct(size_type __n
, _CharT __c
, const _Alloc
& __a
)
578 if (__n
== 0 && __a
== _Alloc())
579 return _S_empty_rep
._M_refcopy();
581 // Check for out_of_range and length_error exceptions.
582 _Rep
* __r
= _Rep::_S_create(__n
, size_type(0), __a
);
584 _S_assign(__r
->_M_refdata(), __n
, __c
);
586 __r
->_M_set_length(__n
);
587 return __r
->_M_refdata();
590 template<typename _CharT
, typename _Traits
, typename _Alloc
>
592 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
593 _M_swap(__rc_string_base
& __rcs
)
597 if (__rcs
._M_is_leaked())
598 __rcs
._M_set_sharable();
600 _CharT
* __tmp
= _M_data();
601 _M_data(__rcs
._M_data());
602 __rcs
._M_data(__tmp
);
604 // _GLIBCXX_RESOLVE_LIB_DEFECTS
605 // 431. Swapping containers with unequal allocators.
606 std::__alloc_swap
<allocator_type
>::_S_do_it(_M_get_allocator(),
607 __rcs
._M_get_allocator());
610 template<typename _CharT
, typename _Traits
, typename _Alloc
>
612 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
613 _M_assign(const __rc_string_base
& __rcs
)
615 if (_M_rep() != __rcs
._M_rep())
617 _CharT
* __tmp
= __rcs
._M_grab(_M_get_allocator());
623 template<typename _CharT
, typename _Traits
, typename _Alloc
>
625 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
626 _M_reserve(size_type __res
)
628 // Make sure we don't shrink below the current size.
629 if (__res
< _M_length())
632 if (__res
!= _M_capacity() || _M_is_shared())
634 _CharT
* __tmp
= _M_rep()->_M_clone(_M_get_allocator(),
635 __res
- _M_length());
641 template<typename _CharT
, typename _Traits
, typename _Alloc
>
643 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
644 _M_mutate(size_type __pos
, size_type __len1
, const _CharT
* __s
,
647 const size_type __how_much
= _M_length() - __pos
- __len1
;
649 _Rep
* __r
= _Rep::_S_create(_M_length() + __len2
- __len1
,
650 _M_capacity(), _M_get_allocator());
653 _S_copy(__r
->_M_refdata(), _M_data(), __pos
);
655 _S_copy(__r
->_M_refdata() + __pos
, __s
, __len2
);
657 _S_copy(__r
->_M_refdata() + __pos
+ __len2
,
658 _M_data() + __pos
+ __len1
, __how_much
);
661 _M_data(__r
->_M_refdata());
664 template<typename _CharT
, typename _Traits
, typename _Alloc
>
666 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
667 _M_erase(size_type __pos
, size_type __n
)
669 const size_type __new_size
= _M_length() - __n
;
670 const size_type __how_much
= _M_length() - __pos
- __n
;
675 _Rep
* __r
= _Rep::_S_create(__new_size
, _M_capacity(),
679 _S_copy(__r
->_M_refdata(), _M_data(), __pos
);
681 _S_copy(__r
->_M_refdata() + __pos
,
682 _M_data() + __pos
+ __n
, __how_much
);
685 _M_data(__r
->_M_refdata());
687 else if (__how_much
&& __n
)
690 _S_move(_M_data() + __pos
,
691 _M_data() + __pos
+ __n
, __how_much
);
694 _M_rep()->_M_set_length(__new_size
);
699 __rc_string_base
<char, std::char_traits
<char>,
700 std::allocator
<char> >::
701 _M_compare(const __rc_string_base
& __rcs
) const
703 if (_M_rep() == __rcs
._M_rep())
708 #ifdef _GLIBCXX_USE_WCHAR_T
711 __rc_string_base
<wchar_t, std::char_traits
<wchar_t>,
712 std::allocator
<wchar_t> >::
713 _M_compare(const __rc_string_base
& __rcs
) const
715 if (_M_rep() == __rcs
._M_rep())
721 _GLIBCXX_END_NAMESPACE
723 #endif /* _RC_STRING_BASE_H */