1// auto_ptr implementation -*- C++ -*-
2
3// Copyright (C) 2007-2019 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 } _GLIBCXX_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 template<typename _Tp>
89 class auto_ptr
90 {
91 private:
92 _Tp* _M_ptr;
93
94 public:
95 /// The pointed-to type.
96 typedef _Tp element_type;
97
98 /**
99 * @brief An %auto_ptr is usually constructed from a raw pointer.
100 * @param __p A pointer (defaults to NULL).
101 *
102 * This object now @e owns the object pointed to by @a __p.
103 */
104 explicit
105 auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
106
107 /**
108 * @brief An %auto_ptr can be constructed from another %auto_ptr.
109 * @param __a Another %auto_ptr of the same type.
110 *
111 * This object now @e owns the object previously owned by @a __a,
112 * which has given up ownership.
113 */
114 auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
115
116 /**
117 * @brief An %auto_ptr can be constructed from another %auto_ptr.
118 * @param __a Another %auto_ptr of a different but related type.
119 *
120 * A pointer-to-Tp1 must be convertible to a
121 * pointer-to-Tp/element_type.
122 *
123 * This object now @e owns the object previously owned by @a __a,
124 * which has given up ownership.
125 */
126 template<typename _Tp1>
127 auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
128
129 /**
130 * @brief %auto_ptr assignment operator.
131 * @param __a Another %auto_ptr of the same type.
132 *
133 * This object now @e owns the object previously owned by @a __a,
134 * which has given up ownership. The object that this one @e
135 * used to own and track has been deleted.
136 */
137 auto_ptr&
138 operator=(auto_ptr& __a) throw()
139 {
140 reset(__a.release());
141 return *this;
142 }
143
144 /**
145 * @brief %auto_ptr assignment operator.
146 * @param __a Another %auto_ptr of a different but related type.
147 *
148 * A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
149 *
150 * This object now @e owns the object previously owned by @a __a,
151 * which has given up ownership. The object that this one @e
152 * used to own and track has been deleted.
153 */
154 template<typename _Tp1>
155 auto_ptr&
156 operator=(auto_ptr<_Tp1>& __a) throw()
157 {
158 reset(__a.release());
159 return *this;
160 }
161
162 /**
163 * When the %auto_ptr goes out of scope, the object it owns is
164 * deleted. If it no longer owns anything (i.e., @c get() is
165 * @c NULL), then this has no effect.
166 *
167 * The C++ standard says there is supposed to be an empty throw
168 * specification here, but omitting it is standard conforming. Its
169 * presence can be detected only if _Tp::~_Tp() throws, but this is
170 * prohibited. [17.4.3.6]/2
171 */
172 ~auto_ptr() { delete _M_ptr; }
173
174 /**
175 * @brief Smart pointer dereferencing.
176 *
177 * If this %auto_ptr no longer owns anything, then this
178 * operation will crash. (For a smart pointer, <em>no longer owns
179 * anything</em> is the same as being a null pointer, and you know
180 * what happens when you dereference one of those...)
181 */
182 element_type&
183 operator*() const throw()
184 {
185 __glibcxx_assert(_M_ptr != 0);
186 return *_M_ptr;
187 }
188
189 /**
190 * @brief Smart pointer dereferencing.
191 *
192 * This returns the pointer itself, which the language then will
193 * automatically cause to be dereferenced.
194 */
195 element_type*
196 operator->() const throw()
197 {
198 __glibcxx_assert(_M_ptr != 0);
199 return _M_ptr;
200 }
201
202 /**
203 * @brief Bypassing the smart pointer.
204 * @return The raw pointer being managed.
205 *
206 * You can get a copy of the pointer that this object owns, for
207 * situations such as passing to a function which only accepts
208 * a raw pointer.
209 *
210 * @note This %auto_ptr still owns the memory.
211 */
212 element_type*
213 get() const throw() { return _M_ptr; }
214
215 /**
216 * @brief Bypassing the smart pointer.
217 * @return The raw pointer being managed.
218 *
219 * You can get a copy of the pointer that this object owns, for
220 * situations such as passing to a function which only accepts
221 * a raw pointer.
222 *
223 * @note This %auto_ptr no longer owns the memory. When this object
224 * goes out of scope, nothing will happen.
225 */
226 element_type*
227 release() throw()
228 {
229 element_type* __tmp = _M_ptr;
230 _M_ptr = 0;
231 return __tmp;
232 }
233
234 /**
235 * @brief Forcibly deletes the managed object.
236 * @param __p A pointer (defaults to NULL).
237 *
238 * This object now @e owns the object pointed to by @a __p. The
239 * previous object has been deleted.
240 */
241 void
242 reset(element_type* __p = 0) throw()
243 {
244 if (__p != _M_ptr)
245 {
246 delete _M_ptr;
247 _M_ptr = __p;
248 }
249 }
250
251 /**
252 * @brief Automatic conversions
253 *
254 * These operations are supposed to convert an %auto_ptr into and from
255 * an auto_ptr_ref automatically as needed. This would allow
256 * constructs such as
257 * @code
258 * auto_ptr<Derived> func_returning_auto_ptr(.....);
259 * ...
260 * auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
261 * @endcode
262 *
263 * But it doesn't work, and won't be fixed. For further details see
264 * http://cplusplus.github.io/LWG/lwg-closed.html#463
265 */
266 auto_ptr(auto_ptr_ref<element_type> __ref) throw()
267 : _M_ptr(__ref._M_ptr) { }
268
269 auto_ptr&
270 operator=(auto_ptr_ref<element_type> __ref) throw()
271 {
272 if (__ref._M_ptr != this->get())
273 {
274 delete _M_ptr;
275 _M_ptr = __ref._M_ptr;
276 }
277 return *this;
278 }
279
280 template<typename _Tp1>
281 operator auto_ptr_ref<_Tp1>() throw()
282 { return auto_ptr_ref<_Tp1>(this->release()); }
283
284 template<typename _Tp1>
285 operator auto_ptr<_Tp1>() throw()
286 { return auto_ptr<_Tp1>(this->release()); }
287 } _GLIBCXX_DEPRECATED;
288
289 // _GLIBCXX_RESOLVE_LIB_DEFECTS
290 // 541. shared_ptr template assignment and void
291 template<>
292 class auto_ptr<void>
293 {
294 public:
295 typedef void element_type;
296 } _GLIBCXX_DEPRECATED;
297
298#if __cplusplus >= 201103L
299 template<_Lock_policy _Lp>
300 template<typename _Tp>
301 inline
302 __shared_count<_Lp>::__shared_count(std::auto_ptr<_Tp>&& __r)
303 : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
304 { __r.release(); }
305
306 template<typename _Tp, _Lock_policy _Lp>
307 template<typename _Tp1, typename>
308 inline
309 __shared_ptr<_Tp, _Lp>::__shared_ptr(std::auto_ptr<_Tp1>&& __r)
310 : _M_ptr(__r.get()), _M_refcount()
311 {
312 __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
313 static_assert( sizeof(_Tp1) > 0, "incomplete type" );
314 _Tp1* __tmp = __r.get();
315 _M_refcount = __shared_count<_Lp>(std::move(__r));
316 _M_enable_shared_from_this_with(__tmp);
317 }
318
319 template<typename _Tp>
320 template<typename _Tp1, typename>
321 inline
322 shared_ptr<_Tp>::shared_ptr(std::auto_ptr<_Tp1>&& __r)
323 : __shared_ptr<_Tp>(std::move(__r)) { }
324
325 template<typename _Tp, typename _Dp>
326 template<typename _Up, typename>
327 inline
328 unique_ptr<_Tp, _Dp>::unique_ptr(auto_ptr<_Up>&& __u) noexcept
329 : _M_t(__u.release(), deleter_type()) { }
330#endif
331
332#pragma GCC diagnostic pop
333
334_GLIBCXX_END_NAMESPACE_VERSION
335} // namespace
336
337#endif /* _BACKWARD_AUTO_PTR_H */
338