STL中的構造器

頭檔案

c++/5/ext/new_allocator.h
c++/5/ext/allocator_traits.h
x86_64-linux-gnu/c++/5/bits/c++allocator.h
c++/5/bits/allocator.h
           

作用

為基本資料類及定義類 類型 構造記憶體空間。

源代碼解析

new_allocator.h

//new_allocator.h
template<typename _Tp>
    class new_allocator
    {
    public:
      typedef size_t     size_type;
      typedef ptrdiff_t  difference_type;
      typedef _Tp*       pointer;
      typedef const _Tp* const_pointer;
      typedef _Tp&       reference;
      typedef const _Tp& const_reference;
      typedef _Tp        value_type;

      template<typename _Tp1>
        struct rebind
        { typedef new_allocator<_Tp1> other; };

#if __cplusplus >= 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2103. propagate_on_container_move_assignment
      typedef std::true_type propagate_on_container_move_assignment;
#endif

      //構造函數
      new_allocator() _GLIBCXX_USE_NOEXCEPT { }
      
      //拷貝構造函數  
      new_allocator(const new_allocator&) _GLIBCXX_USE_NOEXCEPT { }

      template<typename _Tp1>
        new_allocator(const new_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
      
      //析構函數
      ~new_allocator() _GLIBCXX_USE_NOEXCEPT { }
       
      //擷取 _Tp 類型 變量的位址
      pointer
      address(reference __x) const _GLIBCXX_NOEXCEPT
      { return std::__addressof(__x); }
     
      //擷取 _Tp 類型 變量的位址
      const_pointer
      address(const_reference __x) const _GLIBCXX_NOEXCEPT
      { return std::__addressof(__x); }

      // NB: __n is permitted to be 0.  The C++ standard says nothing
      // about what the return value is when __n == 0.
      
      //申請類型為 _Tp ，數量為n， 的記憶體，即數組
      pointer
      allocate(size_type __n, const void* = 0)
      { 
	if (__n > this->max_size())
	  std::__throw_bad_alloc();

	return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
      }

      // __p is not permitted to be a null pointer.
      // 釋放 _Tp* 記憶體
      void
      deallocate(pointer __p, size_type)
      { ::operator delete(__p); }
      
      //擷取 最大的容量
      size_type
      max_size() const _GLIBCXX_USE_NOEXCEPT
      { return size_t(-1) / sizeof(_Tp); }

#if __cplusplus >= 201103L
      template<typename _Up, typename... _Args>
        void
        construct(_Up* __p, _Args&&... __args)
	{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }

      template<typename _Up>
        void 
        destroy(_Up* __p) { __p->~_Up(); }
#else
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 402. wrong new expression in [some_] allocator::construct
      void 
      construct(pointer __p, const _Tp& __val) 
      { ::new((void *)__p) _Tp(__val); }
    
      //調用 _Tp* 的析構函數，并沒有釋放記憶體
      void 
      destroy(pointer __p) { __p->~_Tp(); }
#endif
    };
           

c++allocator.h

#if __cplusplus >= 201103L
namespace std
{
  /**
   *  @brief  An alias to the base class for std::allocator.
   *  @ingroup allocators
   *
   *  Used to set the std::allocator base class to
   *  __gnu_cxx::new_allocator.
   *
   *  @tparam  _Tp  Type of allocated object.
    */
  template<typename _Tp>
    using __allocator_base = __gnu_cxx::new_allocator<_Tp>;
}
#else
// Define new_allocator as the base class to std::allocator.
# define __allocator_base  __gnu_cxx::new_allocator
#endif
           

allocator.h

template<typename _Tp>
    class allocator: public __allocator_base<_Tp>
    {
   public:
      typedef size_t     size_type;
      typedef ptrdiff_t  difference_type;
      typedef _Tp*       pointer;
      typedef const _Tp* const_pointer;
      typedef _Tp&       reference;
      typedef const _Tp& const_reference;
      typedef _Tp        value_type;

      template<typename _Tp1>
        struct rebind
        { typedef allocator<_Tp1> other; };

#if __cplusplus >= 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2103. std::allocator propagate_on_container_move_assignment
      typedef true_type propagate_on_container_move_assignment;
#endif

      allocator() throw() { }

      allocator(const allocator& __a) throw()
      : __allocator_base<_Tp>(__a) { }

      template<typename _Tp1>
        allocator(const allocator<_Tp1>&) throw() { }

      ~allocator() throw() { }

      // Inherit everything else.
    };
           

alloc_traits.h

template<typename _Alloc>
  struct __alloc_traits
#if __cplusplus >= 201103L
  : std::allocator_traits<_Alloc>
#endif
  {
    typedef _Alloc allocator_type;
#if __cplusplus >= 201103L
    typedef std::allocator_traits<_Alloc>           _Base_type;
    typedef typename _Base_type::value_type         value_type;
    typedef typename _Base_type::pointer            pointer;
    typedef typename _Base_type::const_pointer      const_pointer;
    typedef typename _Base_type::size_type          size_type;
    typedef typename _Base_type::difference_type    difference_type;
    // C++11 allocators do not define reference or const_reference
    typedef value_type&                             reference;
    typedef const value_type&                       const_reference;
    using _Base_type::allocate;
    using _Base_type::deallocate;
    using _Base_type::construct;
    using _Base_type::destroy;
    using _Base_type::max_size;

  private:
    template<typename _Ptr>
      using __is_custom_pointer
	= std::__and_<std::is_same<pointer, _Ptr>,
		      std::__not_<std::is_pointer<_Ptr>>>;

  public:
    // overload construct for non-standard pointer types
    template<typename _Ptr, typename... _Args>
      static typename std::enable_if<__is_custom_pointer<_Ptr>::value>::type
      construct(_Alloc& __a, _Ptr __p, _Args&&... __args)
      {
	_Base_type::construct(__a, std::addressof(*__p),
			      std::forward<_Args>(__args)...);
      }

    // overload destroy for non-standard pointer types
    template<typename _Ptr>
      static typename std::enable_if<__is_custom_pointer<_Ptr>::value>::type
      destroy(_Alloc& __a, _Ptr __p)
      { _Base_type::destroy(__a, std::addressof(*__p)); }

    static _Alloc _S_select_on_copy(const _Alloc& __a)
    { return _Base_type::select_on_container_copy_construction(__a); }

    static void _S_on_swap(_Alloc& __a, _Alloc& __b)
    { std::__alloc_on_swap(__a, __b); }

    static constexpr bool _S_propagate_on_copy_assign()
    { return _Base_type::propagate_on_container_copy_assignment::value; }

    static constexpr bool _S_propagate_on_move_assign()
    { return _Base_type::propagate_on_container_move_assignment::value; }

    static constexpr bool _S_propagate_on_swap()
    { return _Base_type::propagate_on_container_swap::value; }

    static constexpr bool _S_always_equal()
    { return __allocator_always_compares_equal<_Alloc>::value; }

    static constexpr bool _S_nothrow_move()
    { return _S_propagate_on_move_assign() || _S_always_equal(); }

    static constexpr bool _S_nothrow_swap()
    {
      using std::swap;
      return !_S_propagate_on_swap()
       	|| noexcept(swap(std::declval<_Alloc&>(), std::declval<_Alloc&>()));
    }

    template<typename _Tp>
      struct rebind
      { typedef typename _Base_type::template rebind_alloc<_Tp> other; };
#else

    typedef typename _Alloc::pointer                pointer;
    typedef typename _Alloc::const_pointer          const_pointer;
    typedef typename _Alloc::value_type             value_type;
    typedef typename _Alloc::reference              reference;
    typedef typename _Alloc::const_reference        const_reference;
    typedef typename _Alloc::size_type              size_type;
    typedef typename _Alloc::difference_type        difference_type;

    static pointer
    allocate(_Alloc& __a, size_type __n)
    { return __a.allocate(__n); }

    static void deallocate(_Alloc& __a, pointer __p, size_type __n)
    { __a.deallocate(__p, __n); }

    template<typename _Tp>
      static void construct(_Alloc& __a, pointer __p, const _Tp& __arg)
      { __a.construct(__p, __arg); }

    static void destroy(_Alloc& __a, pointer __p)
    { __a.destroy(__p); }

    static size_type max_size(const _Alloc& __a)
    { return __a.max_size(); }

    static const _Alloc& _S_select_on_copy(const _Alloc& __a) { return __a; }

    static void _S_on_swap(_Alloc& __a, _Alloc& __b)
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 431. Swapping containers with unequal allocators.
      std::__alloc_swap<_Alloc>::_S_do_it(__a, __b);
    }

    template<typename _Tp>
      struct rebind
      { typedef typename _Alloc::template rebind<_Tp>::other other; };
#endif
  };