libstdc++: auto_ptr.h Source File

libstdc++

auto_ptr.h
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1// auto_ptr implementation -*- C++ -*-
2
3// Copyright (C) 2007-2026 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 backward/auto_ptr.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 _BACKWARD_AUTO_PTR_H
31#define _BACKWARD_AUTO_PTR_H 1
32
33#include <bits/c++config.h>
34#include <debug/debug.h>
35
36namespace std _GLIBCXX_VISIBILITY(default)
37{
38_GLIBCXX_BEGIN_NAMESPACE_VERSION
39
40 /**
41 * A wrapper class to provide auto_ptr with reference semantics.
42 * For example, an auto_ptr can be assigned (or constructed from)
43 * the result of a function which returns an auto_ptr by value.
44 *
45 * All the auto_ptr_ref stuff should happen behind the scenes.
46 */
47 template<typename _Tp1>
48 struct auto_ptr_ref
49 {
50 _Tp1* _M_ptr;
51
52 explicit
53 auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
54 } _GLIBCXX11_DEPRECATED;
55
56#pragma GCC diagnostic push
57#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
58
59 /**
60 * @brief A simple smart pointer providing strict ownership semantics.
61 *
62 * The Standard says:
63 * <pre>
64 * An @c auto_ptr owns the object it holds a pointer to. Copying
65 * an @c auto_ptr copies the pointer and transfers ownership to the
66 * destination. If more than one @c auto_ptr owns the same object
67 * at the same time the behavior of the program is undefined.
68 *
69 * The uses of @c auto_ptr include providing temporary
70 * exception-safety for dynamically allocated memory, passing
71 * ownership of dynamically allocated memory to a function, and
72 * returning dynamically allocated memory from a function. @c
73 * auto_ptr does not meet the CopyConstructible and Assignable
74 * requirements for Standard Library <a
75 * href="tables.html#65">container</a> elements and thus
76 * instantiating a Standard Library container with an @c auto_ptr
77 * results in undefined behavior.
78 * </pre>
79 * Quoted from [20.4.5]/3.
80 *
81 * Good examples of what can and cannot be done with auto_ptr can
82 * be found in the libstdc++ testsuite.
83 *
84 * _GLIBCXX_RESOLVE_LIB_DEFECTS
85 * 127. auto_ptr<> conversion issues
86 * These resolutions have all been incorporated.
87 *
88 * @headerfile memory
89 * @deprecated Deprecated in C++11, no longer in the standard since C++17.
90 * Use `unique_ptr` instead.
91 */
92 template<typename _Tp>
93 class auto_ptr
94 {
95 private:
96 _Tp* _M_ptr;
97
98 public:
99 /// The pointed-to type.
100 typedef _Tp element_type;
101
102 /**
103 * @brief An %auto_ptr is usually constructed from a raw pointer.
104 * @param __p A pointer (defaults to NULL).
105 *
106 * This object now @e owns the object pointed to by @a __p.
107 */
108 explicit
109 auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
110
111 /**
112 * @brief An %auto_ptr can be constructed from another %auto_ptr.
113 * @param __a Another %auto_ptr of the same type.
114 *
115 * This object now @e owns the object previously owned by @a __a,
116 * which has given up ownership.
117 */
118 auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
119
120 /**
121 * @brief An %auto_ptr can be constructed from another %auto_ptr.
122 * @param __a Another %auto_ptr of a different but related type.
123 *
124 * A pointer-to-Tp1 must be convertible to a
125 * pointer-to-Tp/element_type.
126 *
127 * This object now @e owns the object previously owned by @a __a,
128 * which has given up ownership.
129 */
130 template<typename _Tp1>
131 auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
132
133 /**
134 * @brief %auto_ptr assignment operator.
135 * @param __a Another %auto_ptr of the same type.
136 *
137 * This object now @e owns the object previously owned by @a __a,
138 * which has given up ownership. The object that this one @e
139 * used to own and track has been deleted.
140 */
141 auto_ptr&
142 operator=(auto_ptr& __a) throw()
143 {
144 reset(__a.release());
145 return *this;
146 }
147
148 /**
149 * @brief %auto_ptr assignment operator.
150 * @param __a Another %auto_ptr of a different but related type.
151 *
152 * A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
153 *
154 * This object now @e owns the object previously owned by @a __a,
155 * which has given up ownership. The object that this one @e
156 * used to own and track has been deleted.
157 */
158 template<typename _Tp1>
159 auto_ptr&
160 operator=(auto_ptr<_Tp1>& __a) throw()
161 {
162 reset(__a.release());
163 return *this;
164 }
165
166 /**
167 * When the %auto_ptr goes out of scope, the object it owns is
168 * deleted. If it no longer owns anything (i.e., @c get() is
169 * @c NULL), then this has no effect.
170 *
171 * The C++ standard says there is supposed to be an empty throw
172 * specification here, but omitting it is standard conforming. Its
173 * presence can be detected only if _Tp::~_Tp() throws, but this is
174 * prohibited. [17.4.3.6]/2
175 */
176 ~auto_ptr() { delete _M_ptr; }
177
178 /**
179 * @brief Smart pointer dereferencing.
180 *
181 * If this %auto_ptr no longer owns anything, then this
182 * operation will crash. (For a smart pointer, <em>no longer owns
183 * anything</em> is the same as being a null pointer, and you know
184 * what happens when you dereference one of those...)
185 */
186 element_type&
187 operator*() const throw()
188 {
189 __glibcxx_assert(_M_ptr != 0);
190 return *_M_ptr;
191 }
192
193 /**
194 * @brief Smart pointer dereferencing.
195 *
196 * This returns the pointer itself, which the language then will
197 * automatically cause to be dereferenced.
198 */
199 element_type*
200 operator->() const throw()
201 {
202 __glibcxx_assert(_M_ptr != 0);
203 return _M_ptr;
204 }
205
206 /**
207 * @brief Bypassing the smart pointer.
208 * @return The raw pointer being managed.
209 *
210 * You can get a copy of the pointer that this object owns, for
211 * situations such as passing to a function which only accepts
212 * a raw pointer.
213 *
214 * @note This %auto_ptr still owns the memory.
215 */
216 element_type*
217 get() const throw() { return _M_ptr; }
218
219 /**
220 * @brief Bypassing the smart pointer.
221 * @return The raw pointer being managed.
222 *
223 * You can get a copy of the pointer that this object owns, for
224 * situations such as passing to a function which only accepts
225 * a raw pointer.
226 *
227 * @note This %auto_ptr no longer owns the memory. When this object
228 * goes out of scope, nothing will happen.
229 */
230 element_type*
231 release() throw()
232 {
233 element_type* __tmp = _M_ptr;
234 _M_ptr = 0;
235 return __tmp;
236 }
237
238 /**
239 * @brief Forcibly deletes the managed object.
240 * @param __p A pointer (defaults to NULL).
241 *
242 * This object now @e owns the object pointed to by @a __p. The
243 * previous object has been deleted.
244 */
245 void
246 reset(element_type* __p = 0) throw()
247 {
248 if (__p != _M_ptr)
249 {
250 delete _M_ptr;
251 _M_ptr = __p;
252 }
253 }
254
255 /**
256 * @brief Automatic conversions
257 *
258 * These operations are supposed to convert an %auto_ptr into and from
259 * an auto_ptr_ref automatically as needed. This would allow
260 * constructs such as
261 * @code
262 * auto_ptr<Derived> func_returning_auto_ptr(.....);
263 * ...
264 * auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
265 * @endcode
266 *
267 * But it doesn't work, and won't be fixed. For further details see
268 * https://cplusplus.github.io/LWG/lwg-closed.html#463
269 */
270 auto_ptr(auto_ptr_ref<element_type> __ref) throw()
271 : _M_ptr(__ref._M_ptr) { }
272
273 auto_ptr&
274 operator=(auto_ptr_ref<element_type> __ref) throw()
275 {
276 if (__ref._M_ptr != this->get())
277 {
278 delete _M_ptr;
279 _M_ptr = __ref._M_ptr;
280 }
281 return *this;
282 }
283
284 template<typename _Tp1>
285 operator auto_ptr_ref<_Tp1>() throw()
286 { return auto_ptr_ref<_Tp1>(this->release()); }
287
288 template<typename _Tp1>
289 operator auto_ptr<_Tp1>() throw()
290 { return auto_ptr<_Tp1>(this->release()); }
291 } _GLIBCXX11_DEPRECATED_SUGGEST("std::unique_ptr");
292
293 // _GLIBCXX_RESOLVE_LIB_DEFECTS
294 // 541. shared_ptr template assignment and void
295 template<>
296 class auto_ptr<void>
297 {
298 public:
299 typedef void element_type;
300 } _GLIBCXX11_DEPRECATED;
301
302#if __cplusplus >= 201103L
303#if _GLIBCXX_HOSTED
304 template<_Lock_policy _Lp>
305 template<typename _Tp>
306 inline
307 __shared_count<_Lp>::__shared_count(std::auto_ptr<_Tp>&& __r)
308 : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
309 { __r.release(); }
310
311 template<typename _Tp, _Lock_policy _Lp>
312 template<typename _Tp1, typename>
313 inline
314 __shared_ptr<_Tp, _Lp>::__shared_ptr(std::auto_ptr<_Tp1>&& __r)
315 : _M_ptr(__r.get()), _M_refcount()
316 {
317 __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
318 static_assert( sizeof(_Tp1) > 0, "incomplete type" );
319 _Tp1* __tmp = __r.get();
320 _M_refcount = __shared_count<_Lp>(std::move(__r));
321 _M_enable_shared_from_this_with(__tmp);
322 }
323
324 template<typename _Tp>
325 template<typename _Tp1, typename>
326 inline
327 shared_ptr<_Tp>::shared_ptr(std::auto_ptr<_Tp1>&& __r)
328 : __shared_ptr<_Tp>(std::move(__r)) { }
329#endif // HOSTED
330
331 template<typename _Tp, typename _Dp>
332 template<typename _Up, typename>
333 inline
334 unique_ptr<_Tp, _Dp>::unique_ptr(auto_ptr<_Up>&& __u) noexcept
335 : _M_t(__u.release(), deleter_type()) { }
336#endif // C++11
337
338#pragma GCC diagnostic pop
339
340_GLIBCXX_END_NAMESPACE_VERSION
341} // namespace
342
343#endif /* _BACKWARD_AUTO_PTR_H */
c++config.h
debug.h
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std
ISO C++ entities toplevel namespace is std.
std::shared_ptr::shared_ptr
constexpr shared_ptr() noexcept
Construct an empty shared_ptr.
Definition bits/shared_ptr.h:201
std::auto_ptr
A simple smart pointer providing strict ownership semantics.
Definition auto_ptr.h:94
std::auto_ptr::operator->
element_type * operator->() const
Smart pointer dereferencing.
Definition auto_ptr.h:200
std::auto_ptr::operator=
auto_ptr & operator=(auto_ptr< _Tp1 > &__a)
auto_ptr assignment operator.
Definition auto_ptr.h:160
std::auto_ptr::auto_ptr
auto_ptr(auto_ptr< _Tp1 > &__a)
An auto_ptr can be constructed from another auto_ptr.
Definition auto_ptr.h:131
std::auto_ptr::operator=
auto_ptr & operator=(auto_ptr &__a)
auto_ptr assignment operator.
Definition auto_ptr.h:142
std::auto_ptr::auto_ptr
auto_ptr(element_type *__p=0)
An auto_ptr is usually constructed from a raw pointer.
Definition auto_ptr.h:109
std::auto_ptr::~auto_ptr
~auto_ptr()
Definition auto_ptr.h:176
std::auto_ptr::element_type
_Tp element_type
The pointed-to type.
Definition auto_ptr.h:100
std::auto_ptr::reset
void reset(element_type *__p=0)
Forcibly deletes the managed object.
Definition auto_ptr.h:246
std::auto_ptr::auto_ptr
auto_ptr(auto_ptr_ref< element_type > __ref)
Automatic conversions.
Definition auto_ptr.h:270
std::auto_ptr::release
element_type * release()
Bypassing the smart pointer.
Definition auto_ptr.h:231
std::auto_ptr::auto_ptr
auto_ptr(auto_ptr &__a)
An auto_ptr can be constructed from another auto_ptr.
Definition auto_ptr.h:118
std::auto_ptr::get
element_type * get() const
Bypassing the smart pointer.
Definition auto_ptr.h:217
std::auto_ptr::operator*
element_type & operator*() const
Smart pointer dereferencing.
Definition auto_ptr.h:187
std::unique_ptr::unique_ptr
constexpr unique_ptr() noexcept
Default constructor, creates a unique_ptr that owns nothing.
Definition unique_ptr.h:297
std::auto_ptr_ref
Definition auto_ptr.h:49