libstdc++: new_allocator.h Source File

libstdc++

bits/new_allocator.h
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1// Allocator that wraps operator new -*- C++ -*-
2
3// Copyright (C) 2001-2026 Free Software Foundation, Inc.
4//
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)
9// any later version.
10
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.
15
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.
19
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/>.
24
25/** @file bits/new_allocator.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{memory}
28 */
29
30#ifndef _STD_NEW_ALLOCATOR_H
31#define _STD_NEW_ALLOCATOR_H 1
32
33#include <bits/c++config.h>
34#include <new>
35#include <bits/new_throw.h>
36#include <bits/move.h>
37#if __cplusplus >= 201103L
38#include <type_traits>
39#endif
40
41namespace std _GLIBCXX_VISIBILITY(default)
42{
43_GLIBCXX_BEGIN_NAMESPACE_VERSION
44
45 /**
46 * @brief An allocator that uses global `new`, as per C++03 [20.4.1].
47 * @ingroup allocators
48 *
49 * This is precisely the allocator defined in the C++ Standard.
50 * - all allocation calls `operator new`
51 * - all deallocation calls `operator delete`
52 *
53 * This is the default base-class implementation of `std::allocator`,
54 * and is also the base-class of the `__gnu_cxx::new_allocator` extension.
55 * You should use either `std::allocator` or `__gnu_cxx::new_allocator`
56 * instead of using this directly.
57 *
58 * @tparam _Tp Type of allocated object.
59 *
60 * @headerfile memory
61 */
62 template<typename _Tp>
63 class __new_allocator
64 {
65 public:
66 typedef _Tp value_type;
67 typedef std::size_t size_type;
68 typedef std::ptrdiff_t difference_type;
69#if __cplusplus <= 201703L
70 typedef _Tp* pointer;
71 typedef const _Tp* const_pointer;
72 typedef _Tp& reference;
73 typedef const _Tp& const_reference;
74
75 template<typename _Tp1>
76 struct rebind
77 { typedef __new_allocator<_Tp1> other; };
78#endif
79
80#if __cplusplus >= 201103L
81 // _GLIBCXX_RESOLVE_LIB_DEFECTS
82 // 2103. propagate_on_container_move_assignment
83 typedef std::true_type propagate_on_container_move_assignment;
84#endif
85
86 __attribute__((__always_inline__))
87 _GLIBCXX20_CONSTEXPR
88 __new_allocator() _GLIBCXX_USE_NOEXCEPT { }
89
90 __attribute__((__always_inline__))
91 _GLIBCXX20_CONSTEXPR
92 __new_allocator(const __new_allocator&) _GLIBCXX_USE_NOEXCEPT { }
93
94 template<typename _Tp1>
95 __attribute__((__always_inline__))
96 _GLIBCXX20_CONSTEXPR
97 __new_allocator(const __new_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
98
99#if __cplusplus >= 201103L
100 __new_allocator& operator=(const __new_allocator&) = default;
101#endif
102
103#if __cplusplus <= 201703L
104 ~__new_allocator() _GLIBCXX_USE_NOEXCEPT { }
105
106 pointer
107 address(reference __x) const _GLIBCXX_NOEXCEPT
108 { return std::__addressof(__x); }
109
110 const_pointer
111 address(const_reference __x) const _GLIBCXX_NOEXCEPT
112 { return std::__addressof(__x); }
113#endif
114
115#if __has_builtin(__builtin_operator_new) >= 201802L
116# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new
117# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete
118#else
119# define _GLIBCXX_OPERATOR_NEW ::operator new
120# define _GLIBCXX_OPERATOR_DELETE ::operator delete
121#endif
122
123#pragma GCC diagnostic push
124#pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
125
126 // NB: __n is permitted to be 0. The C++ standard says nothing
127 // about what the return value is when __n == 0.
128 _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR _Tp*
129 allocate(size_type __n, const void* = static_cast<const void*>(0))
130 {
131#if __cplusplus >= 201103L
132 // _GLIBCXX_RESOLVE_LIB_DEFECTS
133 // 3308. std::allocator<void>().allocate(n)
134#if ! __cpp_concepts
135 static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
136#else
137 static_assert(requires { sizeof(_Tp); },
138 "cannot allocate incomplete types");
139
140 if constexpr (!requires { sizeof(_Tp); })
141 return nullptr; // static_assert already failed
142 else
143#endif
144#endif
145 if (__builtin_expect(__n > this->_M_max_size(), false))
146 {
147 // _GLIBCXX_RESOLVE_LIB_DEFECTS
148 // 3190. allocator::allocate sometimes returns too little storage
149 if (__n > (std::size_t(-1) / sizeof(_Tp)))
150 std::__throw_bad_array_new_length();
151 std::__throw_bad_alloc();
152 }
153#if __cpp_aligned_new && __cplusplus >= 201103L
154 else if constexpr (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
155 {
156 std::align_val_t __al = std::align_val_t(alignof(_Tp));
157 return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp),
158 __al));
159 }
160#endif
161 else
162 return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp)));
163 }
164
165 // __p is not permitted to be a null pointer.
166 _GLIBCXX20_CONSTEXPR void
167 deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__)))
168 {
169#if __cpp_sized_deallocation
170# define _GLIBCXX_SIZED_DEALLOC(p, n) (p), (n) * sizeof(_Tp)
171#else
172# define _GLIBCXX_SIZED_DEALLOC(p, n) (p)
173#endif
174
175#if __cpp_aligned_new && __cplusplus >= 201103L
176 if constexpr (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
177 {
178 _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n),
179 std::align_val_t(alignof(_Tp)));
180 return;
181 }
182#endif
183 _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n));
184 }
185
186#pragma GCC diagnostic pop
187#undef _GLIBCXX_SIZED_DEALLOC
188#undef _GLIBCXX_OPERATOR_DELETE
189#undef _GLIBCXX_OPERATOR_NEW
190
191#if __cplusplus <= 201703L
192 __attribute__((__always_inline__))
193 size_type
194 max_size() const _GLIBCXX_USE_NOEXCEPT
195 { return _M_max_size(); }
196
197#if __cplusplus >= 201103L
198 template<typename _Up, typename... _Args>
199 __attribute__((__always_inline__))
200 void
201 construct(_Up* __p, _Args&&... __args)
202 noexcept(__is_nothrow_new_constructible<_Up, _Args...>)
203 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
204
205 template<typename _Up>
206 __attribute__((__always_inline__))
207 void
208 destroy(_Up* __p)
209 noexcept(std::is_nothrow_destructible<_Up>::value)
210 { __p->~_Up(); }
211#else
212 // _GLIBCXX_RESOLVE_LIB_DEFECTS
213 // 402. wrong new expression in [some_] allocator::construct
214 __attribute__((__always_inline__))
215 void
216 construct(pointer __p, const _Tp& __val)
217 { ::new((void *)__p) _Tp(__val); }
218
219 __attribute__((__always_inline__))
220 void
221 destroy(pointer __p) { __p->~_Tp(); }
222#endif
223#endif // ! C++20
224
225 template<typename _Up>
226 friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR bool
227 operator==(const __new_allocator&, const __new_allocator<_Up>&)
228 _GLIBCXX_NOTHROW
229 { return true; }
230
231#if __cpp_impl_three_way_comparison < 201907L
232 template<typename _Up>
233 friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR bool
234 operator!=(const __new_allocator&, const __new_allocator<_Up>&)
235 _GLIBCXX_NOTHROW
236 { return false; }
237#endif
238
239 private:
240 __attribute__((__always_inline__))
241 _GLIBCXX_CONSTEXPR size_type
242 _M_max_size() const _GLIBCXX_USE_NOEXCEPT
243 {
244#if __PTRDIFF_MAX__ < __SIZE_MAX__
245 return std::size_t(__PTRDIFF_MAX__) / sizeof(_Tp);
246#else
247 return std::size_t(-1) / sizeof(_Tp);
248#endif
249 }
250 };
251
252_GLIBCXX_END_NAMESPACE_VERSION
253} // namespace
254
255#endif
new
type_traits
new_throw.h
move.h
c++config.h
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
std
ISO C++ entities toplevel namespace is std.
std::is_nothrow_destructible
is_nothrow_destructible
Definition type_traits:1171