libstdc++: malloc_allocator.h Source File

libstdc++

malloc_allocator.h
Go to the documentation of this file.
1// Allocator that wraps "C" malloc -*- 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 ext/malloc_allocator.h
26 * This file is a GNU extension to the Standard C++ Library.
27 */
28
29#ifndef _MALLOC_ALLOCATOR_H
30#define _MALLOC_ALLOCATOR_H 1
31
32#include <bits/requires_hosted.h> // malloc
33
34#include <cstdlib>
35#include <cstddef>
36#include <new>
37#include <bits/new_throw.h>
38#include <bits/move.h>
39#if __cplusplus >= 201103L
40#include <type_traits>
41#endif
42
43namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
44{
45_GLIBCXX_BEGIN_NAMESPACE_VERSION
46
47 /**
48 * @brief An allocator that uses malloc.
49 * @ingroup allocators
50 *
51 * This is precisely the allocator defined in the C++ Standard.
52 * - all allocation calls malloc
53 * - all deallocation calls free
54 */
55 template<typename _Tp>
56 class malloc_allocator
57 {
58 public:
59 typedef _Tp value_type;
60 typedef std::size_t size_type;
61 typedef std::ptrdiff_t difference_type;
62#if __cplusplus <= 201703L
63 typedef _Tp* pointer;
64 typedef const _Tp* const_pointer;
65 typedef _Tp& reference;
66 typedef const _Tp& const_reference;
67
68 template<typename _Tp1>
69 struct rebind
70 { typedef malloc_allocator<_Tp1> other; };
71#endif
72
73#if __cplusplus >= 201103L
74 // _GLIBCXX_RESOLVE_LIB_DEFECTS
75 // 2103. propagate_on_container_move_assignment
76 typedef std::true_type propagate_on_container_move_assignment;
77#endif
78
79 _GLIBCXX20_CONSTEXPR
80 malloc_allocator() _GLIBCXX_USE_NOEXCEPT { }
81
82 _GLIBCXX20_CONSTEXPR
83 malloc_allocator(const malloc_allocator&) _GLIBCXX_USE_NOEXCEPT { }
84
85 template<typename _Tp1>
86 _GLIBCXX20_CONSTEXPR
87 malloc_allocator(const malloc_allocator<_Tp1>&)
88 _GLIBCXX_USE_NOEXCEPT { }
89
90#if __cplusplus <= 201703L
91 ~malloc_allocator() _GLIBCXX_USE_NOEXCEPT { }
92
93 pointer
94 address(reference __x) const _GLIBCXX_NOEXCEPT
95 { return std::__addressof(__x); }
96
97 const_pointer
98 address(const_reference __x) const _GLIBCXX_NOEXCEPT
99 { return std::__addressof(__x); }
100#endif
101
102 // NB: __n is permitted to be 0. The C++ standard says nothing
103 // about what the return value is when __n == 0.
104 _GLIBCXX_NODISCARD _Tp*
105 allocate(size_type __n, const void* = 0)
106 {
107#if __cplusplus >= 201103L
108 // _GLIBCXX_RESOLVE_LIB_DEFECTS
109 // 3308. std::allocator<void>().allocate(n)
110 static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
111#endif
112
113 if (__builtin_expect(__n > this->_M_max_size(), false))
114 {
115 // _GLIBCXX_RESOLVE_LIB_DEFECTS
116 // 3190. allocator::allocate sometimes returns too little storage
117 if (__n > (std::size_t(-1) / sizeof(_Tp)))
118 std::__throw_bad_array_new_length();
119 std::__throw_bad_alloc();
120 }
121
122 _Tp* __ret = 0;
123#if __cpp_aligned_new && __cplusplus >= 201103L
124#if __cplusplus > 201402L && _GLIBCXX_HAVE_ALIGNED_ALLOC
125 if (alignof(_Tp) > alignof(std::max_align_t))
126 {
127 __ret = static_cast<_Tp*>(::aligned_alloc(alignof(_Tp),
128 __n * sizeof(_Tp)));
129 }
130#else
131# define _GLIBCXX_CHECK_MALLOC_RESULT
132#endif
133#endif
134 if (!__ret)
135 __ret = static_cast<_Tp*>(std::malloc(__n * sizeof(_Tp)));
136 if (!__ret)
137 std::__throw_bad_alloc();
138#ifdef _GLIBCXX_CHECK_MALLOC_RESULT
139#undef _GLIBCXX_CHECK_MALLOC_RESULT
140 if (reinterpret_cast<std::size_t>(__ret) % alignof(_Tp))
141 {
142 // Memory returned by malloc is not suitably aligned for _Tp.
143 deallocate(__ret, __n);
144 std::__throw_bad_alloc();
145 }
146#endif
147 return __ret;
148 }
149
150 // __p is not permitted to be a null pointer.
151 void
152 deallocate(_Tp* __p, size_type)
153 { std::free(static_cast<void*>(__p)); }
154
155#if __cplusplus <= 201703L
156 size_type
157 max_size() const _GLIBCXX_USE_NOEXCEPT
158 { return _M_max_size(); }
159
160#if __cplusplus >= 201103L
161 template<typename _Up, typename... _Args>
162 void
163 construct(_Up* __p, _Args&&... __args)
164 noexcept(std::__is_nothrow_new_constructible<_Up, _Args...>)
165 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
166
167 template<typename _Up>
168 void
169 destroy(_Up* __p)
170 noexcept(std::is_nothrow_destructible<_Up>::value)
171 { __p->~_Up(); }
172#else
173 // _GLIBCXX_RESOLVE_LIB_DEFECTS
174 // 402. wrong new expression in [some_] allocator::construct
175 void
176 construct(pointer __p, const _Tp& __val)
177 { ::new((void *)__p) value_type(__val); }
178
179 void
180 destroy(pointer __p) { __p->~_Tp(); }
181#endif
182#endif // ! C++20
183
184 template<typename _Up>
185 friend _GLIBCXX20_CONSTEXPR bool
186 operator==(const malloc_allocator&, const malloc_allocator<_Up>&)
187 _GLIBCXX_NOTHROW
188 { return true; }
189
190#if __cpp_impl_three_way_comparison < 201907L
191 template<typename _Up>
192 friend _GLIBCXX20_CONSTEXPR bool
193 operator!=(const malloc_allocator&, const malloc_allocator<_Up>&)
194 _GLIBCXX_NOTHROW
195 { return false; }
196#endif
197
198 private:
199 _GLIBCXX_CONSTEXPR size_type
200 _M_max_size() const _GLIBCXX_USE_NOEXCEPT
201 {
202#if __PTRDIFF_MAX__ < __SIZE_MAX__
203 return std::size_t(__PTRDIFF_MAX__) / sizeof(_Tp);
204#else
205 return std::size_t(-1) / sizeof(_Tp);
206#endif
207 }
208 };
209
210_GLIBCXX_END_NAMESPACE_VERSION
211} // namespace
212
213#endif
new
type_traits
cstddef
cstdlib
new_throw.h
move.h
requires_hosted.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
__gnu_cxx
GNU extensions for public use.
std::is_nothrow_destructible
is_nothrow_destructible
Definition type_traits:1175
__gnu_cxx::pointer