libstdc++: extptr_allocator.h Source File

libstdc++

extptr_allocator.h
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1// <extptr_allocator.h> -*- C++ -*-
2
3// Copyright (C) 2008-2026 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/**
26 * @file ext/extptr_allocator.h
27 * This file is a GNU extension to the Standard C++ Library.
28 *
29 * @author Bob Walters
30 *
31 * An example allocator which uses an alternative pointer type from
32 * bits/pointer.h. Supports test cases which confirm container support
33 * for alternative pointers.
34 */
35
36#ifndef _EXTPTR_ALLOCATOR_H
37#define _EXTPTR_ALLOCATOR_H 1
38
39#include <bits/requires_hosted.h> // GNU extensions are currently omitted
40
41#include <memory>
42#include <ext/numeric_traits.h>
43#include <ext/pointer.h>
44
45namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
46{
47_GLIBCXX_BEGIN_NAMESPACE_VERSION
48
49 /**
50 * @brief An example allocator which uses a non-standard pointer type.
51 * @ingroup allocators
52 *
53 * This allocator specifies that containers use a 'relative pointer' as it's
54 * pointer type. (See ext/pointer.h) Memory allocation in this example
55 * is still performed using std::allocator.
56 */
57 template<typename _Tp>
58 class _ExtPtr_allocator
59 {
60 public:
61 typedef std::size_t size_type;
62 typedef std::ptrdiff_t difference_type;
63
64 // Note the non-standard pointer types.
65 typedef _Pointer_adapter<_Relative_pointer_impl<_Tp> > pointer;
66 typedef _Pointer_adapter<_Relative_pointer_impl<const _Tp> >
67 const_pointer;
68
69 typedef _Tp& reference;
70 typedef const _Tp& const_reference;
71 typedef _Tp value_type;
72
73 template<typename _Up>
74 struct rebind
75 { typedef _ExtPtr_allocator<_Up> other; };
76
77 _ExtPtr_allocator() _GLIBCXX_USE_NOEXCEPT
78 : _M_real_alloc() { }
79
80 _ExtPtr_allocator(const _ExtPtr_allocator& __rarg) _GLIBCXX_USE_NOEXCEPT
81 : _M_real_alloc(__rarg._M_real_alloc) { }
82
83 template<typename _Up>
84 _ExtPtr_allocator(const _ExtPtr_allocator<_Up>& __rarg)
85 _GLIBCXX_USE_NOEXCEPT
86 : _M_real_alloc(__rarg._M_getUnderlyingImp()) { }
87
88 ~_ExtPtr_allocator() _GLIBCXX_USE_NOEXCEPT
89 { }
90
91 pointer address(reference __x) const _GLIBCXX_NOEXCEPT
92 { return std::__addressof(__x); }
93
94 const_pointer address(const_reference __x) const _GLIBCXX_NOEXCEPT
95 { return std::__addressof(__x); }
96
97 _GLIBCXX_NODISCARD pointer allocate(size_type __n, const void* = 0)
98 { return _M_real_alloc.allocate(__n); }
99
100 void deallocate(pointer __p, size_type __n)
101 { _M_real_alloc.deallocate(__p.get(), __n); }
102
103 size_type max_size() const _GLIBCXX_USE_NOEXCEPT
104 { return __numeric_traits<size_type>::__max / sizeof(_Tp); }
105
106#if __cplusplus >= 201103L
107 template<typename _Up, typename... _Args>
108 void
109 construct(_Up* __p, _Args&&... __args)
110 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
111
112 template<typename... _Args>
113 void
114 construct(pointer __p, _Args&&... __args)
115 { construct(__p.get(), std::forward<_Args>(__args)...); }
116
117 template<typename _Up>
118 void
119 destroy(_Up* __p)
120 { __p->~_Up(); }
121
122 void destroy(pointer __p)
123 { destroy(__p.get()); }
124
125#else
126
127 void construct(pointer __p, const _Tp& __val)
128 { ::new(__p.get()) _Tp(__val); }
129
130 void destroy(pointer __p)
131 { __p->~_Tp(); }
132#endif
133
134 template<typename _Up>
135 inline bool
136 operator==(const _ExtPtr_allocator<_Up>& __rarg) const
137 { return _M_real_alloc == __rarg._M_getUnderlyingImp(); }
138
139 inline bool
140 operator==(const _ExtPtr_allocator& __rarg) const
141 { return _M_real_alloc == __rarg._M_real_alloc; }
142
143#if __cpp_impl_three_way_comparison < 201907L
144 template<typename _Up>
145 inline bool
146 operator!=(const _ExtPtr_allocator<_Up>& __rarg) const
147 { return _M_real_alloc != __rarg._M_getUnderlyingImp(); }
148
149 inline bool
150 operator!=(const _ExtPtr_allocator& __rarg) const
151 { return _M_real_alloc != __rarg._M_real_alloc; }
152#endif
153
154 template<typename _Up>
155 inline friend void
156 swap(_ExtPtr_allocator<_Up>&, _ExtPtr_allocator<_Up>&);
157
158 // A method specific to this implementation.
159 const std::allocator<_Tp>&
160 _M_getUnderlyingImp() const
161 { return _M_real_alloc; }
162
163 private:
164 std::allocator<_Tp> _M_real_alloc;
165 };
166
167 // _ExtPtr_allocator<void> specialization.
168 template<>
169 class _ExtPtr_allocator<void>
170 {
171 public:
172 typedef std::size_t size_type;
173 typedef std::ptrdiff_t difference_type;
174 typedef void value_type;
175
176 // Note the non-standard pointer types
177 typedef _Pointer_adapter<_Relative_pointer_impl<void> > pointer;
178 typedef _Pointer_adapter<_Relative_pointer_impl<const void> >
179 const_pointer;
180
181 _ExtPtr_allocator() { }
182
183 template<typename _Up>
184 _ExtPtr_allocator(const _ExtPtr_allocator<_Up>&) { }
185
186 template<typename _Up>
187 struct rebind
188 { typedef _ExtPtr_allocator<_Up> other; };
189
190 private:
191 std::allocator<void> _M_real_alloc;
192 };
193
194 template<typename _Tp>
195 inline void
196 swap(_ExtPtr_allocator<_Tp>& __larg, _ExtPtr_allocator<_Tp>& __rarg)
197 {
198 std::allocator<_Tp> __tmp( __rarg._M_real_alloc );
199 __rarg._M_real_alloc = __larg._M_real_alloc;
200 __larg._M_real_alloc = __tmp;
201 }
202
203_GLIBCXX_END_NAMESPACE_VERSION
204} // namespace
205
206#endif /* _EXTPTR_ALLOCATOR_H */
requires_hosted.h
pointer.h
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::allocator
The standard allocator, as per C++03 [20.4.1].
Definition allocator.h:134
__gnu_cxx::other
__gnu_cxx::_ExtPtr_allocator
An example allocator which uses a non-standard pointer type.
Definition extptr_allocator.h:59
__gnu_cxx::_Pointer_adapter
Definition pointer.h:280
numeric_traits.h
memory