libstdc++: ptr_traits.h Source File

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ptr_traits.h
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1// Pointer Traits -*- C++ -*-
2
3// Copyright (C) 2011-2026 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/ptr_traits.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 _PTR_TRAITS_H
31#define _PTR_TRAITS_H 1
32
33#if __cplusplus >= 201103L
34
35#include <bits/move.h>
36
37#if __cplusplus > 201703L
38#include <concepts>
39namespace __gnu_debug { class _Safe_iterator_base; }
40#endif
41
42namespace std _GLIBCXX_VISIBILITY(default)
43{
44_GLIBCXX_BEGIN_NAMESPACE_VERSION
45
46 /// @cond undocumented
47
48 class __undefined;
49
50 // For a specialization `SomeTemplate<T, Types...>` the member `type` is T,
51 // otherwise `type` is `__undefined`.
52 template<typename _Tp>
53 struct __get_first_arg
54 { using type = __undefined; };
55
56 template<template<typename, typename...> class _SomeTemplate, typename _Tp,
57 typename... _Types>
58 struct __get_first_arg<_SomeTemplate<_Tp, _Types...>>
59 { using type = _Tp; };
60
61 // For a specialization `SomeTemplate<T, Args...>` and a type `U` the member
62 // `type` is `SomeTemplate<U, Args...>`, otherwise there is no member `type`.
63 template<typename _Tp, typename _Up>
64 struct __replace_first_arg
65 { };
66
67 template<template<typename, typename...> class _SomeTemplate, typename _Up,
68 typename _Tp, typename... _Types>
69 struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up>
70 { using type = _SomeTemplate<_Up, _Types...>; };
71
72 // Detect the element type of a pointer-like type.
73 template<typename _Ptr, typename = void>
74 struct __ptr_traits_elem : __get_first_arg<_Ptr>
75 { };
76
77 // Use _Ptr::element_type if is a valid type.
78#if __cpp_concepts
79 template<typename _Ptr> requires requires { typename _Ptr::element_type; }
80 struct __ptr_traits_elem<_Ptr, void>
81 { using type = typename _Ptr::element_type; };
82#else
83 template<typename _Ptr>
84 struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
85 { using type = typename _Ptr::element_type; };
86#endif
87
88 template<typename _Ptr>
89 using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type;
90
91 /// @endcond
92
93 // Define pointer_traits<P>::pointer_to.
94 template<typename _Ptr, typename _Elt, bool = is_void<_Elt>::value>
95 struct __ptr_traits_ptr_to
96 {
97 using pointer = _Ptr;
98 using element_type = _Elt;
99
100 /**
101 * @brief Obtain a pointer to an object
102 * @param __r A reference to an object of type `element_type`
103 * @return `pointer::pointer_to(__r)`
104 * @pre `pointer::pointer_to(__r)` is a valid expression.
105 */
106 static pointer
107 pointer_to(element_type& __r)
108#if __cpp_lib_concepts
109 requires requires {
110 { pointer::pointer_to(__r) } -> convertible_to<pointer>;
111 }
112#endif
113 { return pointer::pointer_to(__r); }
114 };
115
116 // Do not define pointer_traits<P>::pointer_to if element type is void.
117 template<typename _Ptr, typename _Elt>
118 struct __ptr_traits_ptr_to<_Ptr, _Elt, true>
119 { };
120
121 // Partial specialization defining pointer_traits<T*>::pointer_to(T&).
122 template<typename _Tp>
123 struct __ptr_traits_ptr_to<_Tp*, _Tp, false>
124 {
125 using pointer = _Tp*;
126 using element_type = _Tp;
127
128 /**
129 * @brief Obtain a pointer to an object
130 * @param __r A reference to an object of type `element_type`
131 * @return `addressof(__r)`
132 */
133 static _GLIBCXX20_CONSTEXPR pointer
134 pointer_to(element_type& __r) noexcept
135 { return std::addressof(__r); }
136 };
137
138 template<typename _Ptr, typename _Elt>
139 struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
140 {
141 private:
142 template<typename _Tp>
143 using __diff_t = typename _Tp::difference_type;
144
145 template<typename _Tp, typename _Up>
146 using __rebind = __type_identity<typename _Tp::template rebind<_Up>>;
147
148 public:
149 /// The pointer type.
150 using pointer = _Ptr;
151
152 /// The type pointed to.
153 using element_type = _Elt;
154
155 /// The type used to represent the difference between two pointers.
156 using difference_type = __detected_or_t<ptrdiff_t, __diff_t, _Ptr>;
157
158 /// A pointer to a different type.
159 template<typename _Up>
160 using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>,
161 __rebind, _Ptr, _Up>::type;
162 };
163
164 // _GLIBCXX_RESOLVE_LIB_DEFECTS
165 // 3545. std::pointer_traits should be SFINAE-friendly
166 template<typename _Ptr>
167 struct __ptr_traits_impl<_Ptr, __undefined>
168 { };
169
170 /**
171 * @brief Uniform interface to all pointer-like types
172 * @headerfile memory
173 * @ingroup pointer_abstractions
174 * @since C++11
175 */
176 template<typename _Ptr>
177 struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>>
178 { };
179
180 /**
181 * @brief Partial specialization for built-in pointers.
182 * @headerfile memory
183 * @ingroup pointer_abstractions
184 * @since C++11
185 */
186 template<typename _Tp>
187 struct pointer_traits<_Tp*> : __ptr_traits_ptr_to<_Tp*, _Tp>
188 {
189 /// The pointer type
190 typedef _Tp* pointer;
191 /// The type pointed to
192 typedef _Tp element_type;
193 /// Type used to represent the difference between two pointers
194 typedef ptrdiff_t difference_type;
195 /// A pointer to a different type.
196 template<typename _Up> using rebind = _Up*;
197 };
198
199 /// Convenience alias for rebinding pointers.
200 template<typename _Ptr, typename _Tp>
201 using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
202
203#ifndef __glibcxx_to_address // C++ < 20
204 template<typename _Tp>
205 [[__gnu__::__always_inline__]]
206 constexpr _Tp*
207 __to_address(_Tp* __ptr) noexcept
208 {
209 static_assert(!std::is_function<_Tp>::value, "std::to_address argument "
210 "must not be a function pointer");
211 return __ptr;
212 }
213
214 // This should only be used for pointer-like types (e.g. allocator pointers)
215 // and (in C++20 and later) for types satisfying std::contiguous_iterator.
216 // It should not be used for arbitrary random access iterators, because
217 // they might not be contiguous iterators (e.g. deque::iterator isn't).
218 template<typename _Ptr>
219 constexpr typename std::pointer_traits<_Ptr>::element_type*
220 __to_address(const _Ptr& __ptr)
221 { return std::__to_address(__ptr.operator->()); }
222#else
223 /**
224 * @brief Obtain address referenced by a pointer to an object
225 * @param __ptr A pointer to an object
226 * @return `__ptr`
227 * @ingroup pointer_abstractions
228 */
229 template<typename _Tp>
230 [[__gnu__::__always_inline__]]
231 constexpr _Tp*
232 to_address(_Tp* __ptr) noexcept
233 {
234 static_assert(!is_function_v<_Tp>, "std::to_address argument "
235 "must not be a function pointer");
236 return __ptr;
237 }
238
239 /**
240 * @brief Obtain address referenced by a pointer to an object
241 * @param __ptr A pointer to an object
242 * @return `pointer_traits<_Ptr>::to_address(__ptr)` if that expression is
243 * well-formed, otherwise `to_address(__ptr.operator->())`.
244 * @ingroup pointer_abstractions
245 */
246 template<typename _Ptr>
247 constexpr auto
248 to_address(const _Ptr& __ptr) noexcept
249 {
250 if constexpr (requires { pointer_traits<_Ptr>::to_address(__ptr); })
251 return pointer_traits<_Ptr>::to_address(__ptr);
252 else if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
253 return std::to_address(__ptr.base().operator->());
254 else
255 return std::to_address(__ptr.operator->());
256 }
257
258 /// @cond undocumented
259 /// Compatibility for use in code that is also compiled as pre-C++20.
260 template<typename _Ptr>
261 [[__gnu__::__always_inline__]]
262 constexpr auto
263 __to_address(const _Ptr& __ptr) noexcept
264 { return std::to_address(__ptr); }
265 /// @endcond
266#endif // __glibcxx_to_address
267
268_GLIBCXX_END_NAMESPACE_VERSION
269} // namespace std
270
271#endif
272
273#endif
concepts
move.h
std::to_address
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition ptr_traits.h:232
std::addressof
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition move.h:176
std
ISO C++ entities toplevel namespace is std.
std::__ptr_rebind
typename pointer_traits< _Ptr >::template rebind< _Tp > __ptr_rebind
Convenience alias for rebinding pointers.
Definition ptr_traits.h:201
__gnu_debug
GNU debug classes for public use.
Definition boost_concept_check.h:60
std::is_function
is_function
Definition type_traits:742
std::pointer_traits
Uniform interface to all pointer-like types.
Definition ptr_traits.h:178
std::pointer_traits< _Tp * >::pointer
_Tp * pointer
The pointer type.
Definition ptr_traits.h:190
std::pointer_traits< _Tp * >::difference_type
ptrdiff_t difference_type
Type used to represent the difference between two pointers.
Definition ptr_traits.h:194
std::pointer_traits< _Tp * >::element_type
_Tp element_type
The type pointed to.
Definition ptr_traits.h:192
std::pointer_traits< _Tp * >::rebind
_Up * rebind
A pointer to a different type.
Definition ptr_traits.h:196
__gnu_debug::_Safe_iterator_base
Basic functionality for a safe iterator.
Definition safe_base.h:51