1 // Reference-counted versatile string base -*- C++ -*-
3 // Copyright (C) 2005-2020 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 is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{ext/vstring.h}
30 #ifndef _RC_STRING_BASE_H
31 #define _RC_STRING_BASE_H 1
33 #include <ext/atomicity.h>
34 #include <ext/alloc_traits.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_traits
<_Alloc
>::template rebind
<_Rep
>::other
129 { return reinterpret_cast<_CharT
*>(this + 1); }
134 __atomic_add_dispatch(&_M_info
._M_refcount
, 1);
139 _M_set_length(size_type __n
)
141 _M_info
._M_refcount
= 0; // One reference.
142 _M_info
._M_length
= __n
;
143 // grrr. (per 21.3.4)
144 // You cannot leave those LWG people alone for a second.
145 traits_type::assign(_M_refdata()[__n
], _CharT());
150 _S_create(size_type
, size_type
, const _Alloc
&);
153 _M_destroy(const _Alloc
&) throw();
156 _M_clone(const _Alloc
&, size_type __res
= 0);
165 static _Rep_empty _S_empty_rep
;
167 // The maximum number of individual char_type elements of an
168 // individual string is determined by _S_max_size. This is the
169 // value that will be returned by max_size(). (Whereas npos
170 // is the maximum number of bytes the allocator can allocate.)
171 // If one was to divvy up the theoretical largest size string,
172 // with a terminating character and m _CharT elements, it'd
174 // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
175 // + sizeof(_Rep) - 1
176 // (NB: last two terms for rounding reasons, see _M_create below)
178 // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
179 // In addition, this implementation halves this amount.
180 enum { _S_max_size
= (((static_cast<size_type
>(-1) - 2 * sizeof(_Rep
)
181 + 1) / sizeof(_CharT
)) - 1) / 2 };
183 // Data Member (private):
184 mutable typename
_Util_Base::template _Alloc_hider
<_Alloc
> _M_dataplus
;
188 { _M_dataplus
._M_p
= __p
; }
192 { return &((reinterpret_cast<_Rep
*>(_M_data()))[-1]); }
195 _M_grab(const _Alloc
& __alloc
) const
197 return (!_M_is_leaked() && _M_get_allocator() == __alloc
)
198 ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc
);
204 // Be race-detector-friendly. For more info see bits/c++config.
205 _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info
.
207 if (__exchange_and_add_dispatch(&_M_rep()->_M_info
._M_refcount
,
210 _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info
.
212 _M_rep()->_M_destroy(_M_get_allocator());
218 { return _M_rep()->_M_info
._M_refcount
< 0; }
222 { _M_rep()->_M_info
._M_refcount
= 0; }
227 // _S_construct_aux is used to implement the 21.3.1 para 15 which
228 // requires special behaviour if _InIterator is an integral type
229 template<typename _InIterator
>
231 _S_construct_aux(_InIterator __beg
, _InIterator __end
,
232 const _Alloc
& __a
, std::__false_type
)
234 typedef typename
std::iterator_traits
<_InIterator
>::iterator_category
236 return _S_construct(__beg
, __end
, __a
, _Tag());
239 // _GLIBCXX_RESOLVE_LIB_DEFECTS
240 // 438. Ambiguity in the "do the right thing" clause
241 template<typename _Integer
>
243 _S_construct_aux(_Integer __beg
, _Integer __end
,
244 const _Alloc
& __a
, std::__true_type
)
245 { return _S_construct_aux_2(static_cast<size_type
>(__beg
),
249 _S_construct_aux_2(size_type __req
, _CharT __c
, const _Alloc
& __a
)
250 { return _S_construct(__req
, __c
, __a
); }
252 template<typename _InIterator
>
254 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
)
256 typedef typename
std::__is_integer
<_InIterator
>::__type _Integral
;
257 return _S_construct_aux(__beg
, __end
, __a
, _Integral());
260 // For Input Iterators, used in istreambuf_iterators, etc.
261 template<typename _InIterator
>
263 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
,
264 std::input_iterator_tag
);
266 // For forward_iterators up to random_access_iterators, used for
267 // string::iterator, _CharT*, etc.
268 template<typename _FwdIterator
>
270 _S_construct(_FwdIterator __beg
, _FwdIterator __end
, const _Alloc
& __a
,
271 std::forward_iterator_tag
);
274 _S_construct(size_type __req
, _CharT __c
, const _Alloc
& __a
);
279 { return size_type(_S_max_size
); }
283 { return _M_dataplus
._M_p
; }
287 { return _M_rep()->_M_info
._M_length
; }
291 { return _M_rep()->_M_info
._M_capacity
; }
295 { return _M_rep()->_M_info
._M_refcount
> 0; }
299 { _M_rep()->_M_info
._M_refcount
= -1; }
302 _M_leak() // for use in begin() & non-const op[]
309 _M_set_length(size_type __n
)
310 { _M_rep()->_M_set_length(__n
); }
313 : _M_dataplus(_S_empty_rep
._M_refcopy()) { }
315 __rc_string_base(const _Alloc
& __a
);
317 __rc_string_base(const __rc_string_base
& __rcs
);
319 #if __cplusplus >= 201103L
320 __rc_string_base(__rc_string_base
&& __rcs
)
321 : _M_dataplus(__rcs
._M_dataplus
)
322 { __rcs
._M_data(_S_empty_rep
._M_refcopy()); }
325 __rc_string_base(size_type __n
, _CharT __c
, const _Alloc
& __a
);
327 template<typename _InputIterator
>
328 __rc_string_base(_InputIterator __beg
, _InputIterator __end
,
336 { return _M_dataplus
; }
338 const allocator_type
&
339 _M_get_allocator() const
340 { return _M_dataplus
; }
343 _M_swap(__rc_string_base
& __rcs
);
346 _M_assign(const __rc_string_base
& __rcs
);
349 _M_reserve(size_type __res
);
352 _M_mutate(size_type __pos
, size_type __len1
, const _CharT
* __s
,
356 _M_erase(size_type __pos
, size_type __n
);
362 _M_data(_S_empty_rep
._M_refcopy());
366 _M_compare(const __rc_string_base
&) const
370 template<typename _CharT
, typename _Traits
, typename _Alloc
>
371 typename __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep_empty
372 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_S_empty_rep
;
374 template<typename _CharT
, typename _Traits
, typename _Alloc
>
375 typename __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep
*
376 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep::
377 _S_create(size_type __capacity
, size_type __old_capacity
,
378 const _Alloc
& __alloc
)
380 // _GLIBCXX_RESOLVE_LIB_DEFECTS
381 // 83. String::npos vs. string::max_size()
382 if (__capacity
> size_type(_S_max_size
))
383 std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
385 // The standard places no restriction on allocating more memory
386 // than is strictly needed within this layer at the moment or as
387 // requested by an explicit application call to reserve().
389 // Many malloc implementations perform quite poorly when an
390 // application attempts to allocate memory in a stepwise fashion
391 // growing each allocation size by only 1 char. Additionally,
392 // it makes little sense to allocate less linear memory than the
393 // natural blocking size of the malloc implementation.
394 // Unfortunately, we would need a somewhat low-level calculation
395 // with tuned parameters to get this perfect for any particular
396 // malloc implementation. Fortunately, generalizations about
397 // common features seen among implementations seems to suffice.
399 // __pagesize need not match the actual VM page size for good
400 // results in practice, thus we pick a common value on the low
401 // side. __malloc_header_size is an estimate of the amount of
402 // overhead per memory allocation (in practice seen N * sizeof
403 // (void*) where N is 0, 2 or 4). According to folklore,
404 // picking this value on the high side is better than
405 // low-balling it (especially when this algorithm is used with
406 // malloc implementations that allocate memory blocks rounded up
407 // to a size which is a power of 2).
408 const size_type __pagesize
= 4096;
409 const size_type __malloc_header_size
= 4 * sizeof(void*);
411 // The below implements an exponential growth policy, necessary to
412 // meet amortized linear time requirements of the library: see
413 // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
414 if (__capacity
> __old_capacity
&& __capacity
< 2 * __old_capacity
)
416 __capacity
= 2 * __old_capacity
;
417 // Never allocate a string bigger than _S_max_size.
418 if (__capacity
> size_type(_S_max_size
))
419 __capacity
= size_type(_S_max_size
);
422 // NB: Need an array of char_type[__capacity], plus a terminating
423 // null char_type() element, plus enough for the _Rep data structure,
424 // plus sizeof(_Rep) - 1 to upper round to a size multiple of
426 // Whew. Seemingly so needy, yet so elemental.
427 size_type __size
= ((__capacity
+ 1) * sizeof(_CharT
)
428 + 2 * sizeof(_Rep
) - 1);
430 const size_type __adj_size
= __size
+ __malloc_header_size
;
431 if (__adj_size
> __pagesize
&& __capacity
> __old_capacity
)
433 const size_type __extra
= __pagesize
- __adj_size
% __pagesize
;
434 __capacity
+= __extra
/ sizeof(_CharT
);
435 if (__capacity
> size_type(_S_max_size
))
436 __capacity
= size_type(_S_max_size
);
437 __size
= (__capacity
+ 1) * sizeof(_CharT
) + 2 * sizeof(_Rep
) - 1;
440 // NB: Might throw, but no worries about a leak, mate: _Rep()
442 _Rep
* __place
= _Rep_alloc_type(__alloc
).allocate(__size
/ sizeof(_Rep
));
443 _Rep
* __p
= new (__place
) _Rep
;
444 __p
->_M_info
._M_capacity
= __capacity
;
448 template<typename _CharT
, typename _Traits
, typename _Alloc
>
450 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep::
451 _M_destroy(const _Alloc
& __a
) throw ()
453 const size_type __size
= ((_M_info
._M_capacity
+ 1) * sizeof(_CharT
)
454 + 2 * sizeof(_Rep
) - 1);
455 _Rep_alloc_type(__a
).deallocate(this, __size
/ sizeof(_Rep
));
458 template<typename _CharT
, typename _Traits
, typename _Alloc
>
460 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::_Rep::
461 _M_clone(const _Alloc
& __alloc
, size_type __res
)
463 // Requested capacity of the clone.
464 const size_type __requested_cap
= _M_info
._M_length
+ __res
;
465 _Rep
* __r
= _Rep::_S_create(__requested_cap
, _M_info
._M_capacity
,
468 if (_M_info
._M_length
)
469 __rc_string_base::_S_copy(__r
->_M_refdata(), _M_refdata(), _M_info
._M_length
);
471 __r
->_M_set_length(_M_info
._M_length
);
472 return __r
->_M_refdata();
475 template<typename _CharT
, typename _Traits
, typename _Alloc
>
476 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
477 __rc_string_base(const _Alloc
& __a
)
478 : _M_dataplus(__a
, _S_construct(size_type(), _CharT(), __a
)) { }
480 template<typename _CharT
, typename _Traits
, typename _Alloc
>
481 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
482 __rc_string_base(const __rc_string_base
& __rcs
)
483 : _M_dataplus(__rcs
._M_get_allocator(),
484 __rcs
._M_grab(__rcs
._M_get_allocator())) { }
486 template<typename _CharT
, typename _Traits
, typename _Alloc
>
487 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
488 __rc_string_base(size_type __n
, _CharT __c
, const _Alloc
& __a
)
489 : _M_dataplus(__a
, _S_construct(__n
, __c
, __a
)) { }
491 template<typename _CharT
, typename _Traits
, typename _Alloc
>
492 template<typename _InputIterator
>
493 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
494 __rc_string_base(_InputIterator __beg
, _InputIterator __end
,
496 : _M_dataplus(__a
, _S_construct(__beg
, __end
, __a
)) { }
498 template<typename _CharT
, typename _Traits
, typename _Alloc
>
500 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
508 // NB: This is the special case for Input Iterators, used in
509 // istreambuf_iterators, etc.
510 // Input Iterators have a cost structure very different from
511 // pointers, calling for a different coding style.
512 template<typename _CharT
, typename _Traits
, typename _Alloc
>
513 template<typename _InIterator
>
515 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
516 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
,
517 std::input_iterator_tag
)
519 if (__beg
== __end
&& __a
== _Alloc())
520 return _S_empty_rep
._M_refcopy();
522 // Avoid reallocation for common case.
525 while (__beg
!= __end
&& __len
< sizeof(__buf
) / sizeof(_CharT
))
527 __buf
[__len
++] = *__beg
;
530 _Rep
* __r
= _Rep::_S_create(__len
, size_type(0), __a
);
531 _S_copy(__r
->_M_refdata(), __buf
, __len
);
534 while (__beg
!= __end
)
536 if (__len
== __r
->_M_info
._M_capacity
)
538 // Allocate more space.
539 _Rep
* __another
= _Rep::_S_create(__len
+ 1, __len
, __a
);
540 _S_copy(__another
->_M_refdata(), __r
->_M_refdata(), __len
);
541 __r
->_M_destroy(__a
);
544 __r
->_M_refdata()[__len
++] = *__beg
;
550 __r
->_M_destroy(__a
);
551 __throw_exception_again
;
553 __r
->_M_set_length(__len
);
554 return __r
->_M_refdata();
557 template<typename _CharT
, typename _Traits
, typename _Alloc
>
558 template<typename _InIterator
>
560 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
561 _S_construct(_InIterator __beg
, _InIterator __end
, const _Alloc
& __a
,
562 std::forward_iterator_tag
)
564 if (__beg
== __end
&& __a
== _Alloc())
565 return _S_empty_rep
._M_refcopy();
567 // NB: Not required, but considered best practice.
568 if (__is_null_pointer(__beg
) && __beg
!= __end
)
569 std::__throw_logic_error(__N("__rc_string_base::"
570 "_S_construct null not valid"));
572 const size_type __dnew
= static_cast<size_type
>(std::distance(__beg
,
574 // Check for out_of_range and length_error exceptions.
575 _Rep
* __r
= _Rep::_S_create(__dnew
, size_type(0), __a
);
577 { __rc_string_base::_S_copy_chars(__r
->_M_refdata(), __beg
, __end
); }
580 __r
->_M_destroy(__a
);
581 __throw_exception_again
;
583 __r
->_M_set_length(__dnew
);
584 return __r
->_M_refdata();
587 template<typename _CharT
, typename _Traits
, typename _Alloc
>
589 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
590 _S_construct(size_type __n
, _CharT __c
, const _Alloc
& __a
)
592 if (__n
== 0 && __a
== _Alloc())
593 return _S_empty_rep
._M_refcopy();
595 // Check for out_of_range and length_error exceptions.
596 _Rep
* __r
= _Rep::_S_create(__n
, size_type(0), __a
);
598 __rc_string_base::_S_assign(__r
->_M_refdata(), __n
, __c
);
600 __r
->_M_set_length(__n
);
601 return __r
->_M_refdata();
604 template<typename _CharT
, typename _Traits
, typename _Alloc
>
606 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
607 _M_swap(__rc_string_base
& __rcs
)
611 if (__rcs
._M_is_leaked())
612 __rcs
._M_set_sharable();
614 _CharT
* __tmp
= _M_data();
615 _M_data(__rcs
._M_data());
616 __rcs
._M_data(__tmp
);
618 // _GLIBCXX_RESOLVE_LIB_DEFECTS
619 // 431. Swapping containers with unequal allocators.
620 std::__alloc_swap
<allocator_type
>::_S_do_it(_M_get_allocator(),
621 __rcs
._M_get_allocator());
624 template<typename _CharT
, typename _Traits
, typename _Alloc
>
626 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
627 _M_assign(const __rc_string_base
& __rcs
)
629 if (_M_rep() != __rcs
._M_rep())
631 _CharT
* __tmp
= __rcs
._M_grab(_M_get_allocator());
637 template<typename _CharT
, typename _Traits
, typename _Alloc
>
639 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
640 _M_reserve(size_type __res
)
642 // Make sure we don't shrink below the current size.
643 if (__res
< _M_length())
646 if (__res
!= _M_capacity() || _M_is_shared())
648 _CharT
* __tmp
= _M_rep()->_M_clone(_M_get_allocator(),
649 __res
- _M_length());
655 template<typename _CharT
, typename _Traits
, typename _Alloc
>
657 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
658 _M_mutate(size_type __pos
, size_type __len1
, const _CharT
* __s
,
661 const size_type __how_much
= _M_length() - __pos
- __len1
;
663 _Rep
* __r
= _Rep::_S_create(_M_length() + __len2
- __len1
,
664 _M_capacity(), _M_get_allocator());
667 this->_S_copy(__r
->_M_refdata(), _M_data(), __pos
);
669 this->_S_copy(__r
->_M_refdata() + __pos
, __s
, __len2
);
671 this->_S_copy(__r
->_M_refdata() + __pos
+ __len2
,
672 _M_data() + __pos
+ __len1
, __how_much
);
675 _M_data(__r
->_M_refdata());
678 template<typename _CharT
, typename _Traits
, typename _Alloc
>
680 __rc_string_base
<_CharT
, _Traits
, _Alloc
>::
681 _M_erase(size_type __pos
, size_type __n
)
683 const size_type __new_size
= _M_length() - __n
;
684 const size_type __how_much
= _M_length() - __pos
- __n
;
689 _Rep
* __r
= _Rep::_S_create(__new_size
, _M_capacity(),
693 this->_S_copy(__r
->_M_refdata(), _M_data(), __pos
);
695 this->_S_copy(__r
->_M_refdata() + __pos
,
696 _M_data() + __pos
+ __n
, __how_much
);
699 _M_data(__r
->_M_refdata());
701 else if (__how_much
&& __n
)
704 this->_S_move(_M_data() + __pos
,
705 _M_data() + __pos
+ __n
, __how_much
);
708 _M_rep()->_M_set_length(__new_size
);
713 __rc_string_base
<char, std::char_traits
<char>,
714 std::allocator
<char> >::
715 _M_compare(const __rc_string_base
& __rcs
) const
717 if (_M_rep() == __rcs
._M_rep())
722 #ifdef _GLIBCXX_USE_WCHAR_T
725 __rc_string_base
<wchar_t, std::char_traits
<wchar_t>,
726 std::allocator
<wchar_t> >::
727 _M_compare(const __rc_string_base
& __rcs
) const
729 if (_M_rep() == __rcs
._M_rep())
735 _GLIBCXX_END_NAMESPACE_VERSION
738 #endif /* _RC_STRING_BASE_H */