auto_ptr.h

Go to the documentation of this file.
00001 // auto_ptr implementation -*- C++ -*-
00002 
00003 // Copyright (C) 2007, 2008 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 2, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // You should have received a copy of the GNU General Public License
00017 // along with this library; see the file COPYING.  If not, write to
00018 // the Free Software Foundation, 51 Franklin Street, Fifth Floor,
00019 // Boston, MA 02110-1301, USA.
00020 
00021 // As a special exception, you may use this file as part of a free software
00022 // library without restriction.  Specifically, if other files instantiate
00023 // templates or use macros or inline functions from this file, or you compile
00024 // this file and link it with other files to produce an executable, this
00025 // file does not by itself cause the resulting executable to be covered by
00026 // the GNU General Public License.  This exception does not however
00027 // invalidate any other reasons why the executable file might be covered by
00028 // the GNU General Public License.
00029 
00030 /** @file backward/auto_ptr.h
00031  *  This is an internal header file, included by other library headers.
00032  *  You should not attempt to use it directly.
00033  */
00034 
00035 #ifndef _STL_AUTO_PTR_H
00036 #define _STL_AUTO_PTR_H 1
00037 
00038 #include <bits/c++config.h>
00039 #include <debug/debug.h>
00040 
00041 _GLIBCXX_BEGIN_NAMESPACE(std)
00042 
00043   /**
00044    *  A wrapper class to provide auto_ptr with reference semantics.
00045    *  For example, an auto_ptr can be assigned (or constructed from)
00046    *  the result of a function which returns an auto_ptr by value.
00047    *
00048    *  All the auto_ptr_ref stuff should happen behind the scenes.
00049    */
00050   template<typename _Tp1>
00051     struct auto_ptr_ref
00052     {
00053       _Tp1* _M_ptr;
00054       
00055       explicit
00056       auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
00057     } _GLIBCXX_DEPRECATED_ATTR;
00058 
00059 
00060   /**
00061    *  @brief  A simple smart pointer providing strict ownership semantics.
00062    *
00063    *  The Standard says:
00064    *  <pre>
00065    *  An @c auto_ptr owns the object it holds a pointer to.  Copying
00066    *  an @c auto_ptr copies the pointer and transfers ownership to the
00067    *  destination.  If more than one @c auto_ptr owns the same object
00068    *  at the same time the behavior of the program is undefined.
00069    *
00070    *  The uses of @c auto_ptr include providing temporary
00071    *  exception-safety for dynamically allocated memory, passing
00072    *  ownership of dynamically allocated memory to a function, and
00073    *  returning dynamically allocated memory from a function.  @c
00074    *  auto_ptr does not meet the CopyConstructible and Assignable
00075    *  requirements for Standard Library <a
00076    *  href="tables.html#65">container</a> elements and thus
00077    *  instantiating a Standard Library container with an @c auto_ptr
00078    *  results in undefined behavior.
00079    *  </pre>
00080    *  Quoted from [20.4.5]/3.
00081    *
00082    *  Good examples of what can and cannot be done with auto_ptr can
00083    *  be found in the libstdc++ testsuite.
00084    *
00085    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
00086    *  127.  auto_ptr<> conversion issues
00087    *  These resolutions have all been incorporated.
00088    */
00089   template<typename _Tp>
00090     class auto_ptr
00091     {
00092     private:
00093       _Tp* _M_ptr;
00094       
00095     public:
00096       /// The pointed-to type.
00097       typedef _Tp element_type;
00098       
00099       /**
00100        *  @brief  An %auto_ptr is usually constructed from a raw pointer.
00101        *  @param  p  A pointer (defaults to NULL).
00102        *
00103        *  This object now @e owns the object pointed to by @a p.
00104        */
00105       explicit
00106       auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
00107 
00108       /**
00109        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
00110        *  @param  a  Another %auto_ptr of the same type.
00111        *
00112        *  This object now @e owns the object previously owned by @a a,
00113        *  which has given up ownership.
00114        */
00115       auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
00116 
00117       /**
00118        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
00119        *  @param  a  Another %auto_ptr of a different but related type.
00120        *
00121        *  A pointer-to-Tp1 must be convertible to a
00122        *  pointer-to-Tp/element_type.
00123        *
00124        *  This object now @e owns the object previously owned by @a a,
00125        *  which has given up ownership.
00126        */
00127       template<typename _Tp1>
00128         auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
00129 
00130       /**
00131        *  @brief  %auto_ptr assignment operator.
00132        *  @param  a  Another %auto_ptr of the same type.
00133        *
00134        *  This object now @e owns the object previously owned by @a a,
00135        *  which has given up ownership.  The object that this one @e
00136        *  used to own and track has been deleted.
00137        */
00138       auto_ptr&
00139       operator=(auto_ptr& __a) throw()
00140       {
00141     reset(__a.release());
00142     return *this;
00143       }
00144 
00145       /**
00146        *  @brief  %auto_ptr assignment operator.
00147        *  @param  a  Another %auto_ptr of a different but related type.
00148        *
00149        *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
00150        *
00151        *  This object now @e owns the object previously owned by @a a,
00152        *  which has given up ownership.  The object that this one @e
00153        *  used to own and track has been deleted.
00154        */
00155       template<typename _Tp1>
00156         auto_ptr&
00157         operator=(auto_ptr<_Tp1>& __a) throw()
00158         {
00159       reset(__a.release());
00160       return *this;
00161     }
00162 
00163       /**
00164        *  When the %auto_ptr goes out of scope, the object it owns is
00165        *  deleted.  If it no longer owns anything (i.e., @c get() is
00166        *  @c NULL), then this has no effect.
00167        *
00168        *  The C++ standard says there is supposed to be an empty throw
00169        *  specification here, but omitting it is standard conforming.  Its
00170        *  presence can be detected only if _Tp::~_Tp() throws, but this is
00171        *  prohibited.  [17.4.3.6]/2
00172        */
00173       ~auto_ptr() { delete _M_ptr; }
00174       
00175       /**
00176        *  @brief  Smart pointer dereferencing.
00177        *
00178        *  If this %auto_ptr no longer owns anything, then this
00179        *  operation will crash.  (For a smart pointer, "no longer owns
00180        *  anything" is the same as being a null pointer, and you know
00181        *  what happens when you dereference one of those...)
00182        */
00183       element_type&
00184       operator*() const throw() 
00185       {
00186     _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
00187     return *_M_ptr; 
00188       }
00189       
00190       /**
00191        *  @brief  Smart pointer dereferencing.
00192        *
00193        *  This returns the pointer itself, which the language then will
00194        *  automatically cause to be dereferenced.
00195        */
00196       element_type*
00197       operator->() const throw() 
00198       {
00199     _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
00200     return _M_ptr; 
00201       }
00202       
00203       /**
00204        *  @brief  Bypassing the smart pointer.
00205        *  @return  The raw pointer being managed.
00206        *
00207        *  You can get a copy of the pointer that this object owns, for
00208        *  situations such as passing to a function which only accepts
00209        *  a raw pointer.
00210        *
00211        *  @note  This %auto_ptr still owns the memory.
00212        */
00213       element_type*
00214       get() const throw() { return _M_ptr; }
00215       
00216       /**
00217        *  @brief  Bypassing the smart pointer.
00218        *  @return  The raw pointer being managed.
00219        *
00220        *  You can get a copy of the pointer that this object owns, for
00221        *  situations such as passing to a function which only accepts
00222        *  a raw pointer.
00223        *
00224        *  @note  This %auto_ptr no longer owns the memory.  When this object
00225        *  goes out of scope, nothing will happen.
00226        */
00227       element_type*
00228       release() throw()
00229       {
00230     element_type* __tmp = _M_ptr;
00231     _M_ptr = 0;
00232     return __tmp;
00233       }
00234       
00235       /**
00236        *  @brief  Forcibly deletes the managed object.
00237        *  @param  p  A pointer (defaults to NULL).
00238        *
00239        *  This object now @e owns the object pointed to by @a p.  The
00240        *  previous object has been deleted.
00241        */
00242       void
00243       reset(element_type* __p = 0) throw()
00244       {
00245     if (__p != _M_ptr)
00246       {
00247         delete _M_ptr;
00248         _M_ptr = __p;
00249       }
00250       }
00251       
00252       /** 
00253        *  @brief  Automatic conversions
00254        *
00255        *  These operations convert an %auto_ptr into and from an auto_ptr_ref
00256        *  automatically as needed.  This allows constructs such as
00257        *  @code
00258        *    auto_ptr<Derived>  func_returning_auto_ptr(.....);
00259        *    ...
00260        *    auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
00261        *  @endcode
00262        */
00263       auto_ptr(auto_ptr_ref<element_type> __ref) throw()
00264       : _M_ptr(__ref._M_ptr) { }
00265       
00266       auto_ptr&
00267       operator=(auto_ptr_ref<element_type> __ref) throw()
00268       {
00269     if (__ref._M_ptr != this->get())
00270       {
00271         delete _M_ptr;
00272         _M_ptr = __ref._M_ptr;
00273       }
00274     return *this;
00275       }
00276       
00277       template<typename _Tp1>
00278         operator auto_ptr_ref<_Tp1>() throw()
00279         { return auto_ptr_ref<_Tp1>(this->release()); }
00280 
00281       template<typename _Tp1>
00282         operator auto_ptr<_Tp1>() throw()
00283         { return auto_ptr<_Tp1>(this->release()); }
00284     } _GLIBCXX_DEPRECATED_ATTR;
00285 
00286   // _GLIBCXX_RESOLVE_LIB_DEFECTS
00287   // 541. shared_ptr template assignment and void
00288   template<>
00289     class auto_ptr<void>
00290     {
00291     public:
00292       typedef void element_type;
00293     } _GLIBCXX_DEPRECATED_ATTR;
00294 
00295 _GLIBCXX_END_NAMESPACE
00296 
00297 #endif /* _STL_AUTO_PTR_H */

Generated on Sat Oct 25 05:08:58 2008 for libstdc++ by  doxygen 1.5.6