libstdc++
auto_ptr.h
Go to the documentation of this file.
1 // auto_ptr implementation -*- C++ -*-
2 
3 // Copyright (C) 2007, 2008, 2009, 2010, 2011 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 
36 namespace 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 
57  /**
58  * @brief A simple smart pointer providing strict ownership semantics.
59  *
60  * The Standard says:
61  * <pre>
62  * An @c auto_ptr owns the object it holds a pointer to. Copying
63  * an @c auto_ptr copies the pointer and transfers ownership to the
64  * destination. If more than one @c auto_ptr owns the same object
65  * at the same time the behavior of the program is undefined.
66  *
67  * The uses of @c auto_ptr include providing temporary
68  * exception-safety for dynamically allocated memory, passing
69  * ownership of dynamically allocated memory to a function, and
70  * returning dynamically allocated memory from a function. @c
71  * auto_ptr does not meet the CopyConstructible and Assignable
72  * requirements for Standard Library <a
73  * href="tables.html#65">container</a> elements and thus
74  * instantiating a Standard Library container with an @c auto_ptr
75  * results in undefined behavior.
76  * </pre>
77  * Quoted from [20.4.5]/3.
78  *
79  * Good examples of what can and cannot be done with auto_ptr can
80  * be found in the libstdc++ testsuite.
81  *
82  * _GLIBCXX_RESOLVE_LIB_DEFECTS
83  * 127. auto_ptr<> conversion issues
84  * These resolutions have all been incorporated.
85  */
86  template<typename _Tp>
87  class auto_ptr
88  {
89  private:
90  _Tp* _M_ptr;
91 
92  public:
93  /// The pointed-to type.
94  typedef _Tp element_type;
95 
96  /**
97  * @brief An %auto_ptr is usually constructed from a raw pointer.
98  * @param __p A pointer (defaults to NULL).
99  *
100  * This object now @e owns the object pointed to by @a __p.
101  */
102  explicit
103  auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
104 
105  /**
106  * @brief An %auto_ptr can be constructed from another %auto_ptr.
107  * @param __a Another %auto_ptr of the same type.
108  *
109  * This object now @e owns the object previously owned by @a __a,
110  * which has given up ownership.
111  */
112  auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
113 
114  /**
115  * @brief An %auto_ptr can be constructed from another %auto_ptr.
116  * @param __a Another %auto_ptr of a different but related type.
117  *
118  * A pointer-to-Tp1 must be convertible to a
119  * pointer-to-Tp/element_type.
120  *
121  * This object now @e owns the object previously owned by @a __a,
122  * which has given up ownership.
123  */
124  template<typename _Tp1>
125  auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
126 
127  /**
128  * @brief %auto_ptr assignment operator.
129  * @param __a Another %auto_ptr of the same type.
130  *
131  * This object now @e owns the object previously owned by @a __a,
132  * which has given up ownership. The object that this one @e
133  * used to own and track has been deleted.
134  */
135  auto_ptr&
136  operator=(auto_ptr& __a) throw()
137  {
138  reset(__a.release());
139  return *this;
140  }
141 
142  /**
143  * @brief %auto_ptr assignment operator.
144  * @param __a Another %auto_ptr of a different but related type.
145  *
146  * A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
147  *
148  * This object now @e owns the object previously owned by @a __a,
149  * which has given up ownership. The object that this one @e
150  * used to own and track has been deleted.
151  */
152  template<typename _Tp1>
153  auto_ptr&
154  operator=(auto_ptr<_Tp1>& __a) throw()
155  {
156  reset(__a.release());
157  return *this;
158  }
159 
160  /**
161  * When the %auto_ptr goes out of scope, the object it owns is
162  * deleted. If it no longer owns anything (i.e., @c get() is
163  * @c NULL), then this has no effect.
164  *
165  * The C++ standard says there is supposed to be an empty throw
166  * specification here, but omitting it is standard conforming. Its
167  * presence can be detected only if _Tp::~_Tp() throws, but this is
168  * prohibited. [17.4.3.6]/2
169  */
170  ~auto_ptr() { delete _M_ptr; }
171 
172  /**
173  * @brief Smart pointer dereferencing.
174  *
175  * If this %auto_ptr no longer owns anything, then this
176  * operation will crash. (For a smart pointer, <em>no longer owns
177  * anything</em> is the same as being a null pointer, and you know
178  * what happens when you dereference one of those...)
179  */
180  element_type&
181  operator*() const throw()
182  {
183  _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
184  return *_M_ptr;
185  }
186 
187  /**
188  * @brief Smart pointer dereferencing.
189  *
190  * This returns the pointer itself, which the language then will
191  * automatically cause to be dereferenced.
192  */
193  element_type*
194  operator->() const throw()
195  {
196  _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
197  return _M_ptr;
198  }
199 
200  /**
201  * @brief Bypassing the smart pointer.
202  * @return The raw pointer being managed.
203  *
204  * You can get a copy of the pointer that this object owns, for
205  * situations such as passing to a function which only accepts
206  * a raw pointer.
207  *
208  * @note This %auto_ptr still owns the memory.
209  */
210  element_type*
211  get() const throw() { return _M_ptr; }
212 
213  /**
214  * @brief Bypassing the smart pointer.
215  * @return The raw pointer being managed.
216  *
217  * You can get a copy of the pointer that this object owns, for
218  * situations such as passing to a function which only accepts
219  * a raw pointer.
220  *
221  * @note This %auto_ptr no longer owns the memory. When this object
222  * goes out of scope, nothing will happen.
223  */
224  element_type*
225  release() throw()
226  {
227  element_type* __tmp = _M_ptr;
228  _M_ptr = 0;
229  return __tmp;
230  }
231 
232  /**
233  * @brief Forcibly deletes the managed object.
234  * @param __p A pointer (defaults to NULL).
235  *
236  * This object now @e owns the object pointed to by @a __p. The
237  * previous object has been deleted.
238  */
239  void
240  reset(element_type* __p = 0) throw()
241  {
242  if (__p != _M_ptr)
243  {
244  delete _M_ptr;
245  _M_ptr = __p;
246  }
247  }
248 
249  /**
250  * @brief Automatic conversions
251  *
252  * These operations convert an %auto_ptr into and from an auto_ptr_ref
253  * automatically as needed. This allows constructs such as
254  * @code
255  * auto_ptr<Derived> func_returning_auto_ptr(.....);
256  * ...
257  * auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
258  * @endcode
259  */
261  : _M_ptr(__ref._M_ptr) { }
262 
263  auto_ptr&
265  {
266  if (__ref._M_ptr != this->get())
267  {
268  delete _M_ptr;
269  _M_ptr = __ref._M_ptr;
270  }
271  return *this;
272  }
273 
274  template<typename _Tp1>
275  operator auto_ptr_ref<_Tp1>() throw()
276  { return auto_ptr_ref<_Tp1>(this->release()); }
277 
278  template<typename _Tp1>
279  operator auto_ptr<_Tp1>() throw()
280  { return auto_ptr<_Tp1>(this->release()); }
281  } _GLIBCXX_DEPRECATED;
282 
283  // _GLIBCXX_RESOLVE_LIB_DEFECTS
284  // 541. shared_ptr template assignment and void
285  template<>
286  class auto_ptr<void>
287  {
288  public:
289  typedef void element_type;
290  } _GLIBCXX_DEPRECATED;
291 
292 _GLIBCXX_END_NAMESPACE_VERSION
293 } // namespace
294 
295 #endif /* _BACKWARD_AUTO_PTR_H */