std::_Hashtable< _Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys > Class Template Reference
Public Types
- typedef _Allocator allocator_type
-
typedef
__detail::_Node_const_iterator
< value_type,
__constant_iterators,
__cache_hash_code > const_iterator -
typedef
__detail::_Local_const_iterator
< key_type, value_type,
_ExtractKey, _H1, _H2, _Hash,
__constant_iterators,
__cache_hash_code > const_local_iterator - typedef _Allocator::const_pointer const_pointer
- typedef _Allocator::const_reference const_reference
- typedef std::ptrdiff_t difference_type
-
typedef
__detail::_Node_iterator
< value_type,
__constant_iterators,
__cache_hash_code > iterator - typedef _Equal key_equal
- typedef _Key key_type
-
typedef
__detail::_Local_iterator
< key_type, value_type,
_ExtractKey, _H1, _H2, _Hash,
__constant_iterators,
__cache_hash_code > local_iterator - typedef _Allocator::pointer pointer
- typedef _Allocator::reference reference
- typedef std::size_t size_type
- typedef _Value value_type
Public Member Functions
- _Hashtable (size_type __bucket_hint, const _H1 &, const _H2 &, const _Hash &, const _Equal &, const _ExtractKey &, const allocator_type &)
- template<typename _InputIterator > _Hashtable (_InputIterator __first, _InputIterator __last, size_type __bucket_hint, const _H1 &, const _H2 &, const _Hash &, const _Equal &, const _ExtractKey &, const allocator_type &)
- _Hashtable (_Hashtable &&)
- _Hashtable (const _Hashtable &)
- void __rehash_policy (const _RehashPolicy &)
- const _RehashPolicy & __rehash_policy () const
- iterator begin () noexcept
- const_iterator begin () const noexcept
- local_iterator begin (size_type __n)
- const_local_iterator begin (size_type __n) const
- size_type bucket (const key_type &__k) const
- size_type bucket_count () const noexcept
- size_type bucket_size (size_type __n) const
- const_iterator cbegin () const noexcept
- const_local_iterator cbegin (size_type __n) const
- const_iterator cend () const noexcept
- const_local_iterator cend (size_type __n) const
- void clear () noexcept
- size_type count (const key_type &__k) const
- template<typename... _Args> _Insert_Return_Type emplace (_Args &&...__args)
- template<typename... _Args> iterator emplace_hint (const_iterator, _Args &&...__args)
- bool empty () const noexcept
- local_iterator end (size_type __n)
- iterator end () noexcept
- const_iterator end () const noexcept
- const_local_iterator end (size_type __n) const
- std::pair< iterator, iterator > equal_range (const key_type &__k)
-
std::pair< const_iterator,
const_iterator > equal_range (const key_type &__k) const - iterator erase (iterator __it)
- size_type erase (const key_type &)
- iterator erase (const_iterator)
- iterator erase (const_iterator, const_iterator)
- const_iterator find (const key_type &__k) const
- iterator find (const key_type &__k)
- allocator_type get_allocator () const noexcept
- void insert (initializer_list< value_type > __l)
- template<typename _InputIterator > void insert (_InputIterator __first, _InputIterator __last)
- _Insert_Return_Type insert (const value_type &__v)
- iterator insert (const_iterator, const value_type &__v)
- template<typename _Pair , typename = typename std::enable_if<__and_<integral_constant<bool, !__constant_iterators>, std::is_constructible<value_type, _Pair&&>>::value>::type> iterator insert (const_iterator, _Pair &&__v)
- template<typename _Pair , typename = typename std::enable_if<__and_<integral_constant<bool, !__constant_iterators>, std::is_constructible<value_type, _Pair&&>>::value>::type> _Insert_Return_Type insert (_Pair &&__v)
- key_equal key_eq () const
- float load_factor () const noexcept
- size_type max_bucket_count () const noexcept
- size_type max_size () const noexcept
- _Hashtable & operator= (_Hashtable &&__ht)
- _Hashtable & operator= (const _Hashtable &__ht)
- void rehash (size_type __n)
- size_type size () const noexcept
- void swap (_Hashtable &)
Protected Types
Protected Member Functions
- template<typename... _Args> std::pair< iterator, bool > _M_emplace (std::true_type, _Args &&...__args)
- template<typename... _Args> iterator _M_emplace (std::false_type, _Args &&...__args)
- _Equal & _M_eq ()
- const _Equal & _M_eq () const
- bool _M_equals (const _Key &__k, _Hash_code_type __c, _Hash_node< _Value, __cache_hash_code > *__n) const
- template<typename _Arg > iterator _M_insert (_Arg &&, std::false_type)
- template<typename _Arg > std::pair< iterator, bool > _M_insert (_Arg &&, std::true_type)
- void _M_swap (_Hashtable_base &__x)
Friends
Detailed Description
template<typename _Key, typename _Value, typename _Allocator, typename _ExtractKey, typename _Equal, typename _H1, typename _H2, typename _Hash, typename _RehashPolicy, bool __cache_hash_code, bool __constant_iterators, bool __unique_keys>
class std::_Hashtable< _Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys >
Here's _Hashtable data structure, each _Hashtable has:
- _Bucket[] _M_buckets
- _Hash_node_base _M_before_begin
- size_type _M_bucket_count
- size_type _M_element_count
with _Bucket being _Hash_node* and _Hash_node containing:
- _Hash_node* _M_next
- Tp _M_value
- size_t _M_hash_code if cache_hash_code is true
In terms of Standard containers the hashtable is like the aggregation of:
- std::forward_list<_Node> containing the elements
- std::vector<std::forward_list<_Node>::iterator> representing the buckets
The non-empty buckets contain the node before the first node in the bucket. This design makes it possible to implement something like a std::forward_list::insert_after on container insertion and std::forward_list::erase_after on container erase calls. _M_before_begin is equivalent to std::foward_list::before_begin. Empty buckets contain nullptr. Note that one of the non-empty buckets contains &_M_before_begin which is not a dereferenceable node so the node pointer in a bucket shall never be dereferenced, only its next node can be.
Walking through a bucket's nodes requires a check on the hash code to see if each node is still in the bucket. Such a design assumes a quite efficient hash functor and is one of the reasons it is highly advisable to set __cache_hash_code to true.
The container iterators are simply built from nodes. This way incrementing the iterator is perfectly efficient independent of how many empty buckets there are in the container.
On insert we compute the element's hash code and use it to it find the bucket index. If the element must be inserted in an empty bucket we add it at the beginning of the singly linked list and make the bucket point to _M_before_begin. The bucket that used to point to _M_before_begin, if any, is updated to point to its new before begin node.
On erase, the simple iterator design requires using the hash functor to get the index of the bucket to update. For this reason, when __cache_hash_code is set to false, the hash functor must not throw and this is enforced by a statied assertion.
Definition at line 149 of file bits/hashtable.h.
The documentation for this class was generated from the following file:
