libstdc++-v3/include/backward/auto_ptr.h

   1 // auto_ptr implementation -*- C++ -*-
   2
   3 // Copyright (C) 2007 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 2, 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 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING.  If not, write to
  18 // the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  19 // Boston, MA 02110-1301, USA.
  20
  21 // As a special exception, you may use this file as part of a free software
  22 // library without restriction.  Specifically, if other files instantiate
  23 // templates or use macros or inline functions from this file, or you compile
  24 // this file and link it with other files to produce an executable, this
  25 // file does not by itself cause the resulting executable to be covered by
  26 // the GNU General Public License.  This exception does not however
  27 // invalidate any other reasons why the executable file might be covered by
  28 // the GNU General Public License.
  29
  30 /** @file backward/auto_ptr.h
  31  *  This is an internal header file, included by other library headers.
  32  *  You should not attempt to use it directly.
  33  */
  34
  35 #ifndef _STL_AUTO_PTR_H
  36 #define _STL_AUTO_PTR_H 1
  37
  38 #include <bits/c++config.h>
  39 #include <debug/debug.h>
  40
  41 _GLIBCXX_BEGIN_NAMESPACE(std)
  42
  43   /**
  44    *  A wrapper class to provide auto_ptr with reference semantics.
  45    *  For example, an auto_ptr can be assigned (or constructed from)
  46    *  the result of a function which returns an auto_ptr by value.
  47    *
  48    *  All the auto_ptr_ref stuff should happen behind the scenes.
  49    */
  50   template<typename _Tp1>
  51     struct auto_ptr_ref
  52     {
  53       _Tp1* _M_ptr;
  54
  55       explicit
  56       auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
  57     } _GLIBCXX_DEPRECATED_ATTR;
  58
  59
  60   /**
  61    *  @brief  A simple smart pointer providing strict ownership semantics.
  62    *
  63    *  The Standard says:
  64    *  <pre>
  65    *  An @c auto_ptr owns the object it holds a pointer to.  Copying
  66    *  an @c auto_ptr copies the pointer and transfers ownership to the
  67    *  destination.  If more than one @c auto_ptr owns the same object
  68    *  at the same time the behavior of the program is undefined.
  69    *
  70    *  The uses of @c auto_ptr include providing temporary
  71    *  exception-safety for dynamically allocated memory, passing
  72    *  ownership of dynamically allocated memory to a function, and
  73    *  returning dynamically allocated memory from a function.  @c
  74    *  auto_ptr does not meet the CopyConstructible and Assignable
  75    *  requirements for Standard Library <a
  76    *  href="tables.html#65">container</a> elements and thus
  77    *  instantiating a Standard Library container with an @c auto_ptr
  78    *  results in undefined behavior.
  79    *  </pre>
  80    *  Quoted from [20.4.5]/3.
  81    *
  82    *  Good examples of what can and cannot be done with auto_ptr can
  83    *  be found in the libstdc++ testsuite.
  84    *
  85    *  @if maint
  86    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
  87    *  127.  auto_ptr<> conversion issues
  88    *  These resolutions have all been incorporated.
  89    *  @endif
  90    */
  91   template<typename _Tp>
  92     class auto_ptr
  93     {
  94     private:
  95       _Tp* _M_ptr;
  96
  97     public:
  98       /// The pointed-to type.
  99       typedef _Tp element_type;
 100
 101       /**
 102        *  @brief  An %auto_ptr is usually constructed from a raw pointer.
 103        *  @param  p  A pointer (defaults to NULL).
 104        *
 105        *  This object now @e owns the object pointed to by @a p.
 106        */
 107       explicit
 108       auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
 109
 110       /**
 111        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
 112        *  @param  a  Another %auto_ptr of the same type.
 113        *
 114        *  This object now @e owns the object previously owned by @a a,
 115        *  which has given up ownsership.
 116        */
 117       auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
 118
 119       /**
 120        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
 121        *  @param  a  Another %auto_ptr of a different but related type.
 122        *
 123        *  A pointer-to-Tp1 must be convertible to a
 124        *  pointer-to-Tp/element_type.
 125        *
 126        *  This object now @e owns the object previously owned by @a a,
 127        *  which has given up ownsership.
 128        */
 129       template<typename _Tp1>
 130         auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
 131
 132       /**
 133        *  @brief  %auto_ptr assignment operator.
 134        *  @param  a  Another %auto_ptr of the same type.
 135        *
 136        *  This object now @e owns the object previously owned by @a a,
 137        *  which has given up ownsership.  The object that this one @e
 138        *  used to own and track has been deleted.
 139        */
 140       auto_ptr&
 141       operator=(auto_ptr& __a) throw()
 142       {
 143         reset(__a.release());
 144         return *this;
 145       }
 146
 147       /**
 148        *  @brief  %auto_ptr assignment operator.
 149        *  @param  a  Another %auto_ptr of a different but related type.
 150        *
 151        *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
 152        *
 153        *  This object now @e owns the object previously owned by @a a,
 154        *  which has given up ownsership.  The object that this one @e
 155        *  used to own and track has been deleted.
 156        */
 157       template<typename _Tp1>
 158         auto_ptr&
 159         operator=(auto_ptr<_Tp1>& __a) throw()
 160         {
 161           reset(__a.release());
 162           return *this;
 163         }
 164
 165       /**
 166        *  When the %auto_ptr goes out of scope, the object it owns is
 167        *  deleted.  If it no longer owns anything (i.e., @c get() is
 168        *  @c NULL), then this has no effect.
 169        *
 170        *  @if maint
 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        *  @endif
 176        */
 177       ~auto_ptr() { delete _M_ptr; }
 178
 179       /**
 180        *  @brief  Smart pointer dereferencing.
 181        *
 182        *  If this %auto_ptr no longer owns anything, then this
 183        *  operation will crash.  (For a smart pointer, "no longer owns
 184        *  anything" is the same as being a null pointer, and you know
 185        *  what happens when you dereference one of those...)
 186        */
 187       element_type&
 188       operator*() const throw()
 189       {
 190         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 191         return *_M_ptr;
 192       }
 193
 194       /**
 195        *  @brief  Smart pointer dereferencing.
 196        *
 197        *  This returns the pointer itself, which the language then will
 198        *  automatically cause to be dereferenced.
 199        */
 200       element_type*
 201       operator->() const throw()
 202       {
 203         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
 204         return _M_ptr;
 205       }
 206
 207       /**
 208        *  @brief  Bypassing the smart pointer.
 209        *  @return  The raw pointer being managed.
 210        *
 211        *  You can get a copy of the pointer that this object owns, for
 212        *  situations such as passing to a function which only accepts
 213        *  a raw pointer.
 214        *
 215        *  @note  This %auto_ptr still owns the memory.
 216        */
 217       element_type*
 218       get() const throw() { return _M_ptr; }
 219
 220       /**
 221        *  @brief  Bypassing the smart pointer.
 222        *  @return  The raw pointer being managed.
 223        *
 224        *  You can get a copy of the pointer that this object owns, for
 225        *  situations such as passing to a function which only accepts
 226        *  a raw pointer.
 227        *
 228        *  @note  This %auto_ptr no longer owns the memory.  When this object
 229        *  goes out of scope, nothing will happen.
 230        */
 231       element_type*
 232       release() throw()
 233       {
 234         element_type* __tmp = _M_ptr;
 235         _M_ptr = 0;
 236         return __tmp;
 237       }
 238
 239       /**
 240        *  @brief  Forcibly deletes the managed object.
 241        *  @param  p  A pointer (defaults to NULL).
 242        *
 243        *  This object now @e owns the object pointed to by @a p.  The
 244        *  previous object has been deleted.
 245        */
 246       void
 247       reset(element_type* __p = 0) throw()
 248       {
 249         if (__p != _M_ptr)
 250           {
 251             delete _M_ptr;
 252             _M_ptr = __p;
 253           }
 254       }
 255
 256       /**
 257        *  @brief  Automatic conversions
 258        *
 259        *  These operations convert an %auto_ptr into and from an auto_ptr_ref
 260        *  automatically as needed.  This allows 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       auto_ptr(auto_ptr_ref<element_type> __ref) throw()
 268       : _M_ptr(__ref._M_ptr) { }
 269
 270       auto_ptr&
 271       operator=(auto_ptr_ref<element_type> __ref) throw()
 272       {
 273         if (__ref._M_ptr != this->get())
 274           {
 275             delete _M_ptr;
 276             _M_ptr = __ref._M_ptr;
 277           }
 278         return *this;
 279       }
 280
 281       template<typename _Tp1>
 282         operator auto_ptr_ref<_Tp1>() throw()
 283         { return auto_ptr_ref<_Tp1>(this->release()); }
 284
 285       template<typename _Tp1>
 286         operator auto_ptr<_Tp1>() throw()
 287         { return auto_ptr<_Tp1>(this->release()); }
 288     } _GLIBCXX_DEPRECATED_ATTR;
 289
 290   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 291   // 541. shared_ptr template assignment and void
 292   template<>
 293     class auto_ptr<void>
 294     {
 295     public:
 296       typedef void element_type;
 297     } _GLIBCXX_DEPRECATED_ATTR;
 298
 299 _GLIBCXX_END_NAMESPACE
 300
 301 #endif /* _STL_AUTO_PTR_H */