libstdc++
auto_ptr.h
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1 // auto_ptr implementation -*- C++ -*-
2 
3 // Copyright (C) 2007, 2008, 2009 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
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24 
25 /** @file backward/auto_ptr.h
26  * This is an internal header file, included by other library headers.
27  * You should not attempt to use it directly.
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 _GLIBCXX_BEGIN_NAMESPACE(std)
37 
38  /**
39  * A wrapper class to provide auto_ptr with reference semantics.
40  * For example, an auto_ptr can be assigned (or constructed from)
41  * the result of a function which returns an auto_ptr by value.
42  *
43  * All the auto_ptr_ref stuff should happen behind the scenes.
44  */
45  template<typename _Tp1>
46  struct auto_ptr_ref
47  {
48  _Tp1* _M_ptr;
49 
50  explicit
51  auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
52  } _GLIBCXX_DEPRECATED_ATTR;
53 
54 
55  /**
56  * @brief A simple smart pointer providing strict ownership semantics.
57  *
58  * The Standard says:
59  * <pre>
60  * An @c auto_ptr owns the object it holds a pointer to. Copying
61  * an @c auto_ptr copies the pointer and transfers ownership to the
62  * destination. If more than one @c auto_ptr owns the same object
63  * at the same time the behavior of the program is undefined.
64  *
65  * The uses of @c auto_ptr include providing temporary
66  * exception-safety for dynamically allocated memory, passing
67  * ownership of dynamically allocated memory to a function, and
68  * returning dynamically allocated memory from a function. @c
69  * auto_ptr does not meet the CopyConstructible and Assignable
70  * requirements for Standard Library <a
71  * href="tables.html#65">container</a> elements and thus
72  * instantiating a Standard Library container with an @c auto_ptr
73  * results in undefined behavior.
74  * </pre>
75  * Quoted from [20.4.5]/3.
76  *
77  * Good examples of what can and cannot be done with auto_ptr can
78  * be found in the libstdc++ testsuite.
79  *
80  * _GLIBCXX_RESOLVE_LIB_DEFECTS
81  * 127. auto_ptr<> conversion issues
82  * These resolutions have all been incorporated.
83  */
84  template<typename _Tp>
85  class auto_ptr
86  {
87  private:
88  _Tp* _M_ptr;
89 
90  public:
91  /// The pointed-to type.
92  typedef _Tp element_type;
93 
94  /**
95  * @brief An %auto_ptr is usually constructed from a raw pointer.
96  * @param p A pointer (defaults to NULL).
97  *
98  * This object now @e owns the object pointed to by @a p.
99  */
100  explicit
101  auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
102 
103  /**
104  * @brief An %auto_ptr can be constructed from another %auto_ptr.
105  * @param a Another %auto_ptr of the same type.
106  *
107  * This object now @e owns the object previously owned by @a a,
108  * which has given up ownership.
109  */
110  auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
111 
112  /**
113  * @brief An %auto_ptr can be constructed from another %auto_ptr.
114  * @param a Another %auto_ptr of a different but related type.
115  *
116  * A pointer-to-Tp1 must be convertible to a
117  * pointer-to-Tp/element_type.
118  *
119  * This object now @e owns the object previously owned by @a a,
120  * which has given up ownership.
121  */
122  template<typename _Tp1>
123  auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
124 
125  /**
126  * @brief %auto_ptr assignment operator.
127  * @param a Another %auto_ptr of the same type.
128  *
129  * This object now @e owns the object previously owned by @a a,
130  * which has given up ownership. The object that this one @e
131  * used to own and track has been deleted.
132  */
133  auto_ptr&
134  operator=(auto_ptr& __a) throw()
135  {
136  reset(__a.release());
137  return *this;
138  }
139 
140  /**
141  * @brief %auto_ptr assignment operator.
142  * @param a Another %auto_ptr of a different but related type.
143  *
144  * A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
145  *
146  * This object now @e owns the object previously owned by @a a,
147  * which has given up ownership. The object that this one @e
148  * used to own and track has been deleted.
149  */
150  template<typename _Tp1>
151  auto_ptr&
152  operator=(auto_ptr<_Tp1>& __a) throw()
153  {
154  reset(__a.release());
155  return *this;
156  }
157 
158  /**
159  * When the %auto_ptr goes out of scope, the object it owns is
160  * deleted. If it no longer owns anything (i.e., @c get() is
161  * @c NULL), then this has no effect.
162  *
163  * The C++ standard says there is supposed to be an empty throw
164  * specification here, but omitting it is standard conforming. Its
165  * presence can be detected only if _Tp::~_Tp() throws, but this is
166  * prohibited. [17.4.3.6]/2
167  */
168  ~auto_ptr() { delete _M_ptr; }
169 
170  /**
171  * @brief Smart pointer dereferencing.
172  *
173  * If this %auto_ptr no longer owns anything, then this
174  * operation will crash. (For a smart pointer, "no longer owns
175  * anything" is the same as being a null pointer, and you know
176  * what happens when you dereference one of those...)
177  */
178  element_type&
179  operator*() const throw()
180  {
181  _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
182  return *_M_ptr;
183  }
184 
185  /**
186  * @brief Smart pointer dereferencing.
187  *
188  * This returns the pointer itself, which the language then will
189  * automatically cause to be dereferenced.
190  */
191  element_type*
192  operator->() const throw()
193  {
194  _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
195  return _M_ptr;
196  }
197 
198  /**
199  * @brief Bypassing the smart pointer.
200  * @return The raw pointer being managed.
201  *
202  * You can get a copy of the pointer that this object owns, for
203  * situations such as passing to a function which only accepts
204  * a raw pointer.
205  *
206  * @note This %auto_ptr still owns the memory.
207  */
208  element_type*
209  get() const throw() { return _M_ptr; }
210 
211  /**
212  * @brief Bypassing the smart pointer.
213  * @return The raw pointer being managed.
214  *
215  * You can get a copy of the pointer that this object owns, for
216  * situations such as passing to a function which only accepts
217  * a raw pointer.
218  *
219  * @note This %auto_ptr no longer owns the memory. When this object
220  * goes out of scope, nothing will happen.
221  */
222  element_type*
223  release() throw()
224  {
225  element_type* __tmp = _M_ptr;
226  _M_ptr = 0;
227  return __tmp;
228  }
229 
230  /**
231  * @brief Forcibly deletes the managed object.
232  * @param p A pointer (defaults to NULL).
233  *
234  * This object now @e owns the object pointed to by @a p. The
235  * previous object has been deleted.
236  */
237  void
238  reset(element_type* __p = 0) throw()
239  {
240  if (__p != _M_ptr)
241  {
242  delete _M_ptr;
243  _M_ptr = __p;
244  }
245  }
246 
247  /**
248  * @brief Automatic conversions
249  *
250  * These operations convert an %auto_ptr into and from an auto_ptr_ref
251  * automatically as needed. This allows constructs such as
252  * @code
253  * auto_ptr<Derived> func_returning_auto_ptr(.....);
254  * ...
255  * auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
256  * @endcode
257  */
259  : _M_ptr(__ref._M_ptr) { }
260 
261  auto_ptr&
262  operator=(auto_ptr_ref<element_type> __ref) throw()
263  {
264  if (__ref._M_ptr != this->get())
265  {
266  delete _M_ptr;
267  _M_ptr = __ref._M_ptr;
268  }
269  return *this;
270  }
271 
272  template<typename _Tp1>
273  operator auto_ptr_ref<_Tp1>() throw()
274  { return auto_ptr_ref<_Tp1>(this->release()); }
275 
276  template<typename _Tp1>
277  operator auto_ptr<_Tp1>() throw()
278  { return auto_ptr<_Tp1>(this->release()); }
279  } _GLIBCXX_DEPRECATED_ATTR;
280 
281  // _GLIBCXX_RESOLVE_LIB_DEFECTS
282  // 541. shared_ptr template assignment and void
283  template<>
284  class auto_ptr<void>
285  {
286  public:
287  typedef void element_type;
288  } _GLIBCXX_DEPRECATED_ATTR;
289 
290 _GLIBCXX_END_NAMESPACE
291 
292 #endif /* _BACKWARD_AUTO_PTR_H */