libstdc++
auto_ptr.h
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00001 // auto_ptr implementation -*- C++ -*-
00002 
00003 // Copyright (C) 2007, 2008, 2009, 2010, 2011 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 3, 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 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file backward/auto_ptr.h
00026  *  This is an internal header file, included by other library headers.
00027  *  Do not attempt to use it directly. @headername{memory}
00028  */
00029 
00030 #ifndef _BACKWARD_AUTO_PTR_H
00031 #define _BACKWARD_AUTO_PTR_H 1
00032 
00033 #include <bits/c++config.h>
00034 #include <debug/debug.h>
00035 
00036 namespace std _GLIBCXX_VISIBILITY(default)
00037 {
00038 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00039 
00040   /**
00041    *  A wrapper class to provide auto_ptr with reference semantics.
00042    *  For example, an auto_ptr can be assigned (or constructed from)
00043    *  the result of a function which returns an auto_ptr by value.
00044    *
00045    *  All the auto_ptr_ref stuff should happen behind the scenes.
00046    */
00047   template<typename _Tp1>
00048     struct auto_ptr_ref
00049     {
00050       _Tp1* _M_ptr;
00051       
00052       explicit
00053       auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
00054     } _GLIBCXX_DEPRECATED;
00055 
00056 
00057   /**
00058    *  @brief  A simple smart pointer providing strict ownership semantics.
00059    *
00060    *  The Standard says:
00061    *  <pre>
00062    *  An @c auto_ptr owns the object it holds a pointer to.  Copying
00063    *  an @c auto_ptr copies the pointer and transfers ownership to the
00064    *  destination.  If more than one @c auto_ptr owns the same object
00065    *  at the same time the behavior of the program is undefined.
00066    *
00067    *  The uses of @c auto_ptr include providing temporary
00068    *  exception-safety for dynamically allocated memory, passing
00069    *  ownership of dynamically allocated memory to a function, and
00070    *  returning dynamically allocated memory from a function.  @c
00071    *  auto_ptr does not meet the CopyConstructible and Assignable
00072    *  requirements for Standard Library <a
00073    *  href="tables.html#65">container</a> elements and thus
00074    *  instantiating a Standard Library container with an @c auto_ptr
00075    *  results in undefined behavior.
00076    *  </pre>
00077    *  Quoted from [20.4.5]/3.
00078    *
00079    *  Good examples of what can and cannot be done with auto_ptr can
00080    *  be found in the libstdc++ testsuite.
00081    *
00082    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
00083    *  127.  auto_ptr<> conversion issues
00084    *  These resolutions have all been incorporated.
00085    */
00086   template<typename _Tp>
00087     class auto_ptr
00088     {
00089     private:
00090       _Tp* _M_ptr;
00091       
00092     public:
00093       /// The pointed-to type.
00094       typedef _Tp element_type;
00095       
00096       /**
00097        *  @brief  An %auto_ptr is usually constructed from a raw pointer.
00098        *  @param  __p  A pointer (defaults to NULL).
00099        *
00100        *  This object now @e owns the object pointed to by @a __p.
00101        */
00102       explicit
00103       auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
00104 
00105       /**
00106        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
00107        *  @param  __a  Another %auto_ptr of the same type.
00108        *
00109        *  This object now @e owns the object previously owned by @a __a,
00110        *  which has given up ownership.
00111        */
00112       auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
00113 
00114       /**
00115        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
00116        *  @param  __a  Another %auto_ptr of a different but related type.
00117        *
00118        *  A pointer-to-Tp1 must be convertible to a
00119        *  pointer-to-Tp/element_type.
00120        *
00121        *  This object now @e owns the object previously owned by @a __a,
00122        *  which has given up ownership.
00123        */
00124       template<typename _Tp1>
00125         auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
00126 
00127       /**
00128        *  @brief  %auto_ptr assignment operator.
00129        *  @param  __a  Another %auto_ptr of the same type.
00130        *
00131        *  This object now @e owns the object previously owned by @a __a,
00132        *  which has given up ownership.  The object that this one @e
00133        *  used to own and track has been deleted.
00134        */
00135       auto_ptr&
00136       operator=(auto_ptr& __a) throw()
00137       {
00138     reset(__a.release());
00139     return *this;
00140       }
00141 
00142       /**
00143        *  @brief  %auto_ptr assignment operator.
00144        *  @param  __a  Another %auto_ptr of a different but related type.
00145        *
00146        *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
00147        *
00148        *  This object now @e owns the object previously owned by @a __a,
00149        *  which has given up ownership.  The object that this one @e
00150        *  used to own and track has been deleted.
00151        */
00152       template<typename _Tp1>
00153         auto_ptr&
00154         operator=(auto_ptr<_Tp1>& __a) throw()
00155         {
00156       reset(__a.release());
00157       return *this;
00158     }
00159 
00160       /**
00161        *  When the %auto_ptr goes out of scope, the object it owns is
00162        *  deleted.  If it no longer owns anything (i.e., @c get() is
00163        *  @c NULL), then this has no effect.
00164        *
00165        *  The C++ standard says there is supposed to be an empty throw
00166        *  specification here, but omitting it is standard conforming.  Its
00167        *  presence can be detected only if _Tp::~_Tp() throws, but this is
00168        *  prohibited.  [17.4.3.6]/2
00169        */
00170       ~auto_ptr() { delete _M_ptr; }
00171       
00172       /**
00173        *  @brief  Smart pointer dereferencing.
00174        *
00175        *  If this %auto_ptr no longer owns anything, then this
00176        *  operation will crash.  (For a smart pointer, <em>no longer owns
00177        *  anything</em> is the same as being a null pointer, and you know
00178        *  what happens when you dereference one of those...)
00179        */
00180       element_type&
00181       operator*() const throw() 
00182       {
00183     _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
00184     return *_M_ptr; 
00185       }
00186       
00187       /**
00188        *  @brief  Smart pointer dereferencing.
00189        *
00190        *  This returns the pointer itself, which the language then will
00191        *  automatically cause to be dereferenced.
00192        */
00193       element_type*
00194       operator->() const throw() 
00195       {
00196     _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
00197     return _M_ptr; 
00198       }
00199       
00200       /**
00201        *  @brief  Bypassing the smart pointer.
00202        *  @return  The raw pointer being managed.
00203        *
00204        *  You can get a copy of the pointer that this object owns, for
00205        *  situations such as passing to a function which only accepts
00206        *  a raw pointer.
00207        *
00208        *  @note  This %auto_ptr still owns the memory.
00209        */
00210       element_type*
00211       get() const throw() { return _M_ptr; }
00212       
00213       /**
00214        *  @brief  Bypassing the smart pointer.
00215        *  @return  The raw pointer being managed.
00216        *
00217        *  You can get a copy of the pointer that this object owns, for
00218        *  situations such as passing to a function which only accepts
00219        *  a raw pointer.
00220        *
00221        *  @note  This %auto_ptr no longer owns the memory.  When this object
00222        *  goes out of scope, nothing will happen.
00223        */
00224       element_type*
00225       release() throw()
00226       {
00227     element_type* __tmp = _M_ptr;
00228     _M_ptr = 0;
00229     return __tmp;
00230       }
00231       
00232       /**
00233        *  @brief  Forcibly deletes the managed object.
00234        *  @param  __p  A pointer (defaults to NULL).
00235        *
00236        *  This object now @e owns the object pointed to by @a __p.  The
00237        *  previous object has been deleted.
00238        */
00239       void
00240       reset(element_type* __p = 0) throw()
00241       {
00242     if (__p != _M_ptr)
00243       {
00244         delete _M_ptr;
00245         _M_ptr = __p;
00246       }
00247       }
00248       
00249       /** 
00250        *  @brief  Automatic conversions
00251        *
00252        *  These operations convert an %auto_ptr into and from an auto_ptr_ref
00253        *  automatically as needed.  This allows constructs such as
00254        *  @code
00255        *    auto_ptr<Derived>  func_returning_auto_ptr(.....);
00256        *    ...
00257        *    auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
00258        *  @endcode
00259        */
00260       auto_ptr(auto_ptr_ref<element_type> __ref) throw()
00261       : _M_ptr(__ref._M_ptr) { }
00262       
00263       auto_ptr&
00264       operator=(auto_ptr_ref<element_type> __ref) throw()
00265       {
00266     if (__ref._M_ptr != this->get())
00267       {
00268         delete _M_ptr;
00269         _M_ptr = __ref._M_ptr;
00270       }
00271     return *this;
00272       }
00273       
00274       template<typename _Tp1>
00275         operator auto_ptr_ref<_Tp1>() throw()
00276         { return auto_ptr_ref<_Tp1>(this->release()); }
00277 
00278       template<typename _Tp1>
00279         operator auto_ptr<_Tp1>() throw()
00280         { return auto_ptr<_Tp1>(this->release()); }
00281     } _GLIBCXX_DEPRECATED;
00282 
00283   // _GLIBCXX_RESOLVE_LIB_DEFECTS
00284   // 541. shared_ptr template assignment and void
00285   template<>
00286     class auto_ptr<void>
00287     {
00288     public:
00289       typedef void element_type;
00290     } _GLIBCXX_DEPRECATED;
00291 
00292 _GLIBCXX_END_NAMESPACE_VERSION
00293 } // namespace
00294 
00295 #endif /* _BACKWARD_AUTO_PTR_H */