C++ 智能指针

template<typename _Tp>
    class auto_ptr
    {
    private:
      _Tp* _M_ptr;
      
    public:
      /// The pointed-to type.
      typedef _Tp element_type;
      
      /**
       *  @brief  An %auto_ptr is usually constructed from a raw pointer.
       *  @param  p  A pointer (defaults to NULL).
       *
       *  This object now @e owns the object pointed to by @a p.
       */
      explicit
      auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }


      /**
       *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
       *  @param  a  Another %auto_ptr of the same type.
       *
       *  This object now @e owns the object previously owned by @a a,
       *  which has given up ownsership.
       */
      auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }


      /**
       *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
       *  @param  a  Another %auto_ptr of a different but related type.
       *
       *  A pointer-to-Tp1 must be convertible to a
       *  pointer-to-Tp/element_type.
       *
       *  This object now @e owns the object previously owned by @a a,
       *  which has given up ownsership.
       */
      template<typename _Tp1>
        auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }


      /**
       *  @brief  %auto_ptr assignment operator.
       *  @param  a  Another %auto_ptr of the same type.
       *
       *  This object now @e owns the object previously owned by @a a,
       *  which has given up ownsership.  The object that this one @e
       *  used to own and track has been deleted.
       */
      auto_ptr&
      operator=(auto_ptr& __a) throw()
      {
reset(__a.release());
return *this;
      }


      /**
       *  @brief  %auto_ptr assignment operator.
       *  @param  a  Another %auto_ptr of a different but related type.
       *
       *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
       *
       *  This object now @e owns the object previously owned by @a a,
       *  which has given up ownsership.  The object that this one @e
       *  used to own and track has been deleted.
       */
      template<typename _Tp1>
        auto_ptr&
        operator=(auto_ptr<_Tp1>& __a) throw()
        {
 reset(__a.release());
 return *this;
}


      /**
       *  When the %auto_ptr goes out of scope, the object it owns is
       *  deleted.  If it no longer owns anything (i.e., @c get() is
       *  @c NULL), then this has no effect.
       *
       *  @if maint
       *  The C++ standard says there is supposed to be an empty throw
       *  specification here, but omitting it is standard conforming.  Its
       *  presence can be detected only if _Tp::~_Tp() throws, but this is
       *  prohibited.  [17.4.3.6]/2
       *  @end maint
       */
      ~auto_ptr() { delete _M_ptr; }
      
      /**
       *  @brief  Smart pointer dereferencing.
       *
       *  If this %auto_ptr no longer owns anything, then this
       *  operation will crash.  (For a smart pointer, "no longer owns
       *  anything" is the same as being a null pointer, and you know
       *  what happens when you dereference one of those...)
       */
      element_type&
      operator*() const throw() 
      {
_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
return *_M_ptr; 
      }
      
      /**
       *  @brief  Smart pointer dereferencing.
       *
       *  This returns the pointer itself, which the language then will
       *  automatically cause to be dereferenced.
       */
      element_type*
      operator->() const throw() 
      {
_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
return _M_ptr; 
      }
      
      /**
       *  @brief  Bypassing the smart pointer.
       *  @return  The raw pointer being managed.
       *
       *  You can get a copy of the pointer that this object owns, for
       *  situations such as passing to a function which only accepts
       *  a raw pointer.
       *
       *  @note  This %auto_ptr still owns the memory.
       */
      element_type*
      get() const throw() { return _M_ptr; }
      
      /**
       *  @brief  Bypassing the smart pointer.
       *  @return  The raw pointer being managed.
       *
       *  You can get a copy of the pointer that this object owns, for
       *  situations such as passing to a function which only accepts
       *  a raw pointer.
       *
       *  @note  This %auto_ptr no longer owns the memory.  When this object
       *  goes out of scope, nothing will happen.
       */
      element_type*
      release() throw()
      {
element_type* __tmp = _M_ptr;
_M_ptr = 0;
return __tmp;
      }
      
      /**
       *  @brief  Forcibly deletes the managed object.
       *  @param  p  A pointer (defaults to NULL).
       *
       *  This object now @e owns the object pointed to by @a p.  The
       *  previous object has been deleted.
       */
      void
      reset(element_type* __p = 0) throw()
      {
if (__p != _M_ptr)
 {
   delete _M_ptr;
   _M_ptr = __p;
 }
      }
      
      /** @{
       *  @brief  Automatic conversions
       *
       *  These operations convert an %auto_ptr into and from an auto_ptr_ref
       *  automatically as needed.  This allows constructs such as
       *  @code
       *    auto_ptr<Derived>  func_returning_auto_ptr(.....);
       *    ...
       *    auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
       *  @endcode
       */
      auto_ptr(auto_ptr_ref<element_type> __ref) throw()
      : _M_ptr(__ref._M_ptr) { }
      
      auto_ptr&
      operator=(auto_ptr_ref<element_type> __ref) throw()
      {
if (__ref._M_ptr != this->get())
 {
   delete _M_ptr;
   _M_ptr = __ref._M_ptr;
 }
return *this;
      }
      
      template<typename _Tp1>
        operator auto_ptr_ref<_Tp1>() throw()
        { return auto_ptr_ref<_Tp1>(this->release()); }


      template<typename _Tp1>
        operator auto_ptr<_Tp1>() throw()
        { return auto_ptr<_Tp1>(this->release()); }
      /** @}  */
  };
} // namespace std