libstdc++
auto_ptr.h
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00001 // auto_ptr implementation -*- C++ -*-
00002 
00003 // Copyright (C) 2007-2019 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 #pragma GCC diagnostic push
00057 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
00058 
00059   /**
00060    *  @brief  A simple smart pointer providing strict ownership semantics.
00061    *
00062    *  The Standard says:
00063    *  <pre>
00064    *  An @c auto_ptr owns the object it holds a pointer to.  Copying
00065    *  an @c auto_ptr copies the pointer and transfers ownership to the
00066    *  destination.  If more than one @c auto_ptr owns the same object
00067    *  at the same time the behavior of the program is undefined.
00068    *
00069    *  The uses of @c auto_ptr include providing temporary
00070    *  exception-safety for dynamically allocated memory, passing
00071    *  ownership of dynamically allocated memory to a function, and
00072    *  returning dynamically allocated memory from a function.  @c
00073    *  auto_ptr does not meet the CopyConstructible and Assignable
00074    *  requirements for Standard Library <a
00075    *  href="tables.html#65">container</a> elements and thus
00076    *  instantiating a Standard Library container with an @c auto_ptr
00077    *  results in undefined behavior.
00078    *  </pre>
00079    *  Quoted from [20.4.5]/3.
00080    *
00081    *  Good examples of what can and cannot be done with auto_ptr can
00082    *  be found in the libstdc++ testsuite.
00083    *
00084    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
00085    *  127.  auto_ptr<> conversion issues
00086    *  These resolutions have all been incorporated.
00087    */
00088   template<typename _Tp>
00089     class auto_ptr
00090     {
00091     private:
00092       _Tp* _M_ptr;
00093       
00094     public:
00095       /// The pointed-to type.
00096       typedef _Tp element_type;
00097       
00098       /**
00099        *  @brief  An %auto_ptr is usually constructed from a raw pointer.
00100        *  @param  __p  A pointer (defaults to NULL).
00101        *
00102        *  This object now @e owns the object pointed to by @a __p.
00103        */
00104       explicit
00105       auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
00106 
00107       /**
00108        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
00109        *  @param  __a  Another %auto_ptr of the same type.
00110        *
00111        *  This object now @e owns the object previously owned by @a __a,
00112        *  which has given up ownership.
00113        */
00114       auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
00115 
00116       /**
00117        *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
00118        *  @param  __a  Another %auto_ptr of a different but related type.
00119        *
00120        *  A pointer-to-Tp1 must be convertible to a
00121        *  pointer-to-Tp/element_type.
00122        *
00123        *  This object now @e owns the object previously owned by @a __a,
00124        *  which has given up ownership.
00125        */
00126       template<typename _Tp1>
00127         auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
00128 
00129       /**
00130        *  @brief  %auto_ptr assignment operator.
00131        *  @param  __a  Another %auto_ptr of the same type.
00132        *
00133        *  This object now @e owns the object previously owned by @a __a,
00134        *  which has given up ownership.  The object that this one @e
00135        *  used to own and track has been deleted.
00136        */
00137       auto_ptr&
00138       operator=(auto_ptr& __a) throw()
00139       {
00140         reset(__a.release());
00141         return *this;
00142       }
00143 
00144       /**
00145        *  @brief  %auto_ptr assignment operator.
00146        *  @param  __a  Another %auto_ptr of a different but related type.
00147        *
00148        *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
00149        *
00150        *  This object now @e owns the object previously owned by @a __a,
00151        *  which has given up ownership.  The object that this one @e
00152        *  used to own and track has been deleted.
00153        */
00154       template<typename _Tp1>
00155         auto_ptr&
00156         operator=(auto_ptr<_Tp1>& __a) throw()
00157         {
00158           reset(__a.release());
00159           return *this;
00160         }
00161 
00162       /**
00163        *  When the %auto_ptr goes out of scope, the object it owns is
00164        *  deleted.  If it no longer owns anything (i.e., @c get() is
00165        *  @c NULL), then this has no effect.
00166        *
00167        *  The C++ standard says there is supposed to be an empty throw
00168        *  specification here, but omitting it is standard conforming.  Its
00169        *  presence can be detected only if _Tp::~_Tp() throws, but this is
00170        *  prohibited.  [17.4.3.6]/2
00171        */
00172       ~auto_ptr() { delete _M_ptr; }
00173       
00174       /**
00175        *  @brief  Smart pointer dereferencing.
00176        *
00177        *  If this %auto_ptr no longer owns anything, then this
00178        *  operation will crash.  (For a smart pointer, <em>no longer owns
00179        *  anything</em> is the same as being a null pointer, and you know
00180        *  what happens when you dereference one of those...)
00181        */
00182       element_type&
00183       operator*() const throw() 
00184       {
00185         __glibcxx_assert(_M_ptr != 0);
00186         return *_M_ptr; 
00187       }
00188       
00189       /**
00190        *  @brief  Smart pointer dereferencing.
00191        *
00192        *  This returns the pointer itself, which the language then will
00193        *  automatically cause to be dereferenced.
00194        */
00195       element_type*
00196       operator->() const throw() 
00197       {
00198         __glibcxx_assert(_M_ptr != 0);
00199         return _M_ptr; 
00200       }
00201       
00202       /**
00203        *  @brief  Bypassing the smart pointer.
00204        *  @return  The raw pointer being managed.
00205        *
00206        *  You can get a copy of the pointer that this object owns, for
00207        *  situations such as passing to a function which only accepts
00208        *  a raw pointer.
00209        *
00210        *  @note  This %auto_ptr still owns the memory.
00211        */
00212       element_type*
00213       get() const throw() { return _M_ptr; }
00214       
00215       /**
00216        *  @brief  Bypassing the smart pointer.
00217        *  @return  The raw pointer being managed.
00218        *
00219        *  You can get a copy of the pointer that this object owns, for
00220        *  situations such as passing to a function which only accepts
00221        *  a raw pointer.
00222        *
00223        *  @note  This %auto_ptr no longer owns the memory.  When this object
00224        *  goes out of scope, nothing will happen.
00225        */
00226       element_type*
00227       release() throw()
00228       {
00229         element_type* __tmp = _M_ptr;
00230         _M_ptr = 0;
00231         return __tmp;
00232       }
00233       
00234       /**
00235        *  @brief  Forcibly deletes the managed object.
00236        *  @param  __p  A pointer (defaults to NULL).
00237        *
00238        *  This object now @e owns the object pointed to by @a __p.  The
00239        *  previous object has been deleted.
00240        */
00241       void
00242       reset(element_type* __p = 0) throw()
00243       {
00244         if (__p != _M_ptr)
00245           {
00246             delete _M_ptr;
00247             _M_ptr = __p;
00248           }
00249       }
00250       
00251       /** 
00252        *  @brief  Automatic conversions
00253        *
00254        *  These operations are supposed to convert an %auto_ptr into and from
00255        *  an auto_ptr_ref automatically as needed.  This would allow
00256        *  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        *  But it doesn't work, and won't be fixed. For further details see
00264        *  http://cplusplus.github.io/LWG/lwg-closed.html#463
00265        */
00266       auto_ptr(auto_ptr_ref<element_type> __ref) throw()
00267       : _M_ptr(__ref._M_ptr) { }
00268       
00269       auto_ptr&
00270       operator=(auto_ptr_ref<element_type> __ref) throw()
00271       {
00272         if (__ref._M_ptr != this->get())
00273           {
00274             delete _M_ptr;
00275             _M_ptr = __ref._M_ptr;
00276           }
00277         return *this;
00278       }
00279       
00280       template<typename _Tp1>
00281         operator auto_ptr_ref<_Tp1>() throw()
00282         { return auto_ptr_ref<_Tp1>(this->release()); }
00283 
00284       template<typename _Tp1>
00285         operator auto_ptr<_Tp1>() throw()
00286         { return auto_ptr<_Tp1>(this->release()); }
00287     } _GLIBCXX_DEPRECATED;
00288 
00289   // _GLIBCXX_RESOLVE_LIB_DEFECTS
00290   // 541. shared_ptr template assignment and void
00291   template<>
00292     class auto_ptr<void>
00293     {
00294     public:
00295       typedef void element_type;
00296     } _GLIBCXX_DEPRECATED;
00297 
00298 #if __cplusplus >= 201103L
00299   template<_Lock_policy _Lp>
00300   template<typename _Tp>
00301     inline
00302     __shared_count<_Lp>::__shared_count(std::auto_ptr<_Tp>&& __r)
00303     : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
00304     { __r.release(); }
00305 
00306   template<typename _Tp, _Lock_policy _Lp>
00307   template<typename _Tp1, typename>
00308     inline
00309     __shared_ptr<_Tp, _Lp>::__shared_ptr(std::auto_ptr<_Tp1>&& __r)
00310     : _M_ptr(__r.get()), _M_refcount()
00311     {
00312       __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
00313       static_assert( sizeof(_Tp1) > 0, "incomplete type" );
00314       _Tp1* __tmp = __r.get();
00315       _M_refcount = __shared_count<_Lp>(std::move(__r));
00316       _M_enable_shared_from_this_with(__tmp);
00317     }
00318 
00319   template<typename _Tp>
00320   template<typename _Tp1, typename>
00321     inline
00322     shared_ptr<_Tp>::shared_ptr(std::auto_ptr<_Tp1>&& __r)
00323     : __shared_ptr<_Tp>(std::move(__r)) { }
00324 
00325   template<typename _Tp, typename _Dp>
00326   template<typename _Up, typename>
00327     inline
00328     unique_ptr<_Tp, _Dp>::unique_ptr(auto_ptr<_Up>&& __u) noexcept
00329     : _M_t(__u.release(), deleter_type()) { }
00330 #endif
00331 
00332 #pragma GCC diagnostic pop
00333 
00334 _GLIBCXX_END_NAMESPACE_VERSION
00335 } // namespace
00336 
00337 #endif /* _BACKWARD_AUTO_PTR_H */