C++ STL源码学习（之hash_table篇）

stl_hash_table.h

这不属于C++标准，是SGI STL标准的一部分，用于辅助实现hash_map和hash_set

/// Hashtable class, used to implement the hashed associative containers/// hash_set, hash_map, hash_multiset, and hash_multimap.///STL HashTable采用的是所谓的开链哈希法,依靠一个类似vector<list<T>>来实现.///先通过哈希函数确定所需处理元素应当在vector中的那个位置(可以一步找到),vector///中的每个元素我们称之为一个桶,则这个过程即是寻找桶的过程,每个桶实际是一个///list<T>元素,若要处理的元素存在,则必然在这个桶之中,然后顺序遍历这个list即///可确定该元素是否存在或者所在位置.由于第一步的哈希使得桶中存放的元素一///般很少,因此遍历查询过程比较高效.template <class _Val>struct _Hashtable_node{  _Hashtable_node* _M_next;  _Val _M_val;};///val:存储的值///key:对应的键///_HashFcn:所采用的hash函数类型///_ExtractKey:用于从存储对象值中抽出键对象的函数,当hash_table中///存储pair类型实现hash_map时最有用.///_EqualKey:用于确定两个键值是否相等的函数template <class _Val, class _Key, class _HashFcn,          class _ExtractKey, class _EqualKey, class _Alloc = alloc>class hashtable;template <class _Val, class _Key, class _HashFcn,          class _ExtractKey, class _EqualKey, class _Alloc>struct _Hashtable_iterator;template <class _Val, class _Key, class _HashFcn,          class _ExtractKey, class _EqualKey, class _Alloc>struct _Hashtable_const_iterator;template <class _Val, class _Key, class _HashFcn,          class _ExtractKey, class _EqualKey, class _Alloc>struct _Hashtable_iterator {  typedef hashtable<_Val,_Key,_HashFcn,_ExtractKey,_EqualKey,_Alloc>          _Hashtable;  typedef _Hashtable_iterator<_Val, _Key, _HashFcn,                              _ExtractKey, _EqualKey, _Alloc>          iterator;  typedef _Hashtable_const_iterator<_Val, _Key, _HashFcn,                                    _ExtractKey, _EqualKey, _Alloc>          const_iterator;  typedef _Hashtable_node<_Val> _Node;  typedef forward_iterator_tag iterator_category;  typedef _Val value_type;  typedef ptrdiff_t difference_type;  typedef size_t size_type;  typedef _Val& reference;  typedef _Val* pointer;  _Node* _M_cur;  _Hashtable* _M_ht;  _Hashtable_iterator(_Node* __n, _Hashtable* __tab)    : _M_cur(__n), _M_ht(__tab) {}  _Hashtable_iterator() {}  reference operator*() const { return _M_cur->_M_val; }  pointer operator->() const { return &(operator*()); }  iterator& operator++();  iterator operator++(int);  bool operator==(const iterator& __it) const    { return _M_cur == __it._M_cur; }  bool operator!=(const iterator& __it) const    { return _M_cur != __it._M_cur; }};template <class _Val, class _Key, class _HashFcn,          class _ExtractKey, class _EqualKey, class _Alloc>struct _Hashtable_const_iterator {  typedef hashtable<_Val,_Key,_HashFcn,_ExtractKey,_EqualKey,_Alloc>          _Hashtable;  typedef _Hashtable_iterator<_Val,_Key,_HashFcn,                              _ExtractKey,_EqualKey,_Alloc>          iterator;  typedef _Hashtable_const_iterator<_Val, _Key, _HashFcn,                                    _ExtractKey, _EqualKey, _Alloc>          const_iterator;  typedef _Hashtable_node<_Val> _Node;  typedef forward_iterator_tag iterator_category;  typedef _Val value_type;  typedef ptrdiff_t difference_type;  typedef size_t size_type;  typedef const _Val& reference;  typedef const _Val* pointer;  const _Node* _M_cur;  const _Hashtable* _M_ht;  _Hashtable_const_iterator(const _Node* __n, const _Hashtable* __tab)    : _M_cur(__n), _M_ht(__tab) {}  _Hashtable_const_iterator() {}  _Hashtable_const_iterator(const iterator& __it)    : _M_cur(__it._M_cur), _M_ht(__it._M_ht) {}  reference operator*() const { return _M_cur->_M_val; }  pointer operator->() const { return &(operator*()); }  const_iterator& operator++();  const_iterator operator++(int);  bool operator==(const const_iterator& __it) const    { return _M_cur == __it._M_cur; }  bool operator!=(const const_iterator& __it) const    { return _M_cur != __it._M_cur; }};///HashTable的vector长度是有讲究的,为了尽量减少冲突(过多的元素被散列///到同一个桶中),我们的桶个数一般应为质数个(由于我们是通过hash函数得到///的值与桶数做mod运算得到需处理元素所在的桶号).这里取53开始的后28个///质数,他们中的最大质数大于32位内存可存储的值./// Note: assumes long is at least 32 bits.enum { __stl_num_primes = 28 };static const unsigned long __stl_prime_list[__stl_num_primes] ={  53ul,         97ul,         193ul,       389ul,       769ul,  1543ul,       3079ul,       6151ul,      12289ul,     24593ul,  49157ul,      98317ul,      196613ul,    393241ul,    786433ul,  1572869ul,    3145739ul,    6291469ul,   12582917ul,  25165843ul,  50331653ul,   100663319ul,  201326611ul, 402653189ul, 805306457ul,  1610612741ul, 3221225473ul, 4294967291ul};///给定一个值(实际即HashTable中所要存储的元素个数)得到大于等于///它的最小质数(实际即HashTable中Array的长度/桶的个数).inline unsigned long __stl_next_prime(unsigned long __n){  const unsigned long* __first = __stl_prime_list;  const unsigned long* __last = __stl_prime_list + (int)__stl_num_primes;  const unsigned long* pos = lower_bound(__first, __last, __n);  return pos == __last ? *(__last - 1) : *pos;}/// Forward declaration of operator==.template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>class hashtable;template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>bool operator==(const hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>& __ht1,                const hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>& __ht2);/// Hashtables handle allocators a bit differently than other containers///  do.  If we're using standard-conforming allocators, then a hashtable///  unconditionally has a member variable to hold its allocator, even if///  it so happens that all instances of the allocator type are identical./// This is because, for hashtables, this extra storage is negligible.///  Additionally, a base class wouldn't serve any other purposes; it///  wouldn't, for example, simplify the exception-handling code.template <class _Val, class _Key, class _HashFcn,          class _ExtractKey, class _EqualKey, class _Alloc>class hashtable {public:  typedef _Key key_type;  typedef _Val value_type;  typedef _HashFcn hasher;  typedef _EqualKey key_equal;  typedef size_t            size_type;  typedef ptrdiff_t         difference_type;  typedef value_type*       pointer;  typedef const value_type* const_pointer;  typedef value_type&       reference;  typedef const value_type& const_reference;  hasher hash_funct() const { return _M_hash; }  key_equal key_eq() const { return _M_equals; }private:  typedef _Hashtable_node<_Val> _Node;public:  typedef _Alloc allocator_type;  allocator_type get_allocator() const { return allocator_type(); }private:  typedef simple_alloc<_Node, _Alloc> _M_node_allocator_type;  ///分配和回收桶中的一个节点  _Node* _M_get_node() { return _M_node_allocator_type::allocate(1); }  void _M_put_node(_Node* __p) { _M_node_allocator_type::deallocate(__p, 1); }private:  hasher                _M_hash;  key_equal             _M_equals;  _ExtractKey           _M_get_key;  vector<_Node*,_Alloc> _M_buckets;  size_type             _M_num_elements;public:  typedef _Hashtable_iterator<_Val,_Key,_HashFcn,_ExtractKey,_EqualKey,_Alloc>          iterator;  typedef _Hashtable_const_iterator<_Val,_Key,_HashFcn,_ExtractKey,_EqualKey,                                    _Alloc>          const_iterator;  friend struct  _Hashtable_iterator<_Val,_Key,_HashFcn,_ExtractKey,_EqualKey,_Alloc>;  friend struct  _Hashtable_const_iterator<_Val,_Key,_HashFcn,_ExtractKey,_EqualKey,_Alloc>;public:  hashtable(size_type __n,            const _HashFcn&    __hf,            const _EqualKey&   __eql,            const _ExtractKey& __ext,            const allocator_type& __a = allocator_type())    : _M_hash(__hf),      _M_equals(__eql),      _M_get_key(__ext),      _M_buckets(__a),      _M_num_elements(0)  {    _M_initialize_buckets(__n);  }  hashtable(size_type __n,            const _HashFcn&    __hf,            const _EqualKey&   __eql,            const allocator_type& __a = allocator_type())    :_M_hash(__hf),      _M_equals(__eql),      _M_get_key(_ExtractKey()),      _M_buckets(__a),      _M_num_elements(0)  {    _M_initialize_buckets(__n);  }  hashtable(const hashtable& __ht)    : _M_hash(__ht._M_hash),      _M_equals(__ht._M_equals),      _M_get_key(__ht._M_get_key),      _M_buckets(__ht.get_allocator()),      _M_num_elements(0)  {    _M_copy_from(__ht);  }  hashtable& operator= (const hashtable& __ht)  {    if (&__ht != this) {      clear();      _M_hash = __ht._M_hash;      _M_equals = __ht._M_equals;      _M_get_key = __ht._M_get_key;      _M_copy_from(__ht);    }    return *this;  }  ~hashtable() { clear(); }  size_type size() const { return _M_num_elements; }  size_type max_size() const { return size_type(-1); }  bool empty() const { return size() == 0; }  ///STL容器自身的swap成员函数一般都比较高效,HashTable也不例外  void swap(hashtable& __ht)  {    __STD::swap(_M_hash, __ht._M_hash);    __STD::swap(_M_equals, __ht._M_equals);    __STD::swap(_M_get_key, __ht._M_get_key);    _M_buckets.swap(__ht._M_buckets);    __STD::swap(_M_num_elements, __ht._M_num_elements);  }  iterator begin()  {      ///找到第一个非空的桶,得到其第一个元素    for (size_type __n = 0; __n < _M_buckets.size(); ++__n)      if (_M_buckets[__n])        return iterator(_M_buckets[__n], this);    return end();  }  iterator end() { return iterator(0, this); }  const_iterator begin() const  {    for (size_type __n = 0; __n < _M_buckets.size(); ++__n)      if (_M_buckets[__n])        return const_iterator(_M_buckets[__n], this);    return end();  }  const_iterator end() const { return const_iterator(0, this); }  friend bool operator==<> (const hashtable&,const hashtable&);public:  size_type bucket_count() const { return _M_buckets.size(); }  size_type max_bucket_count() const    { return __stl_prime_list[(int)__stl_num_primes - 1]; }  ///得到第__bucket个桶中的元素个数  size_type elems_in_bucket(size_type __bucket) const  {    size_type __result = 0;    for (_Node* __cur = _M_buckets[__bucket]; __cur; __cur = __cur->_M_next)      __result += 1;    return __result;  }  pair<iterator, bool> insert_unique(const value_type& __obj)  {    resize(_M_num_elements + 1);    return insert_unique_noresize(__obj);  }  iterator insert_equal(const value_type& __obj)  {    resize(_M_num_elements + 1);    return insert_equal_noresize(__obj);  }  pair<iterator, bool> insert_unique_noresize(const value_type& __obj);  iterator insert_equal_noresize(const value_type& __obj);  ///下面insert_*中使用到的型别推导技法在STL中很常见  template <class _InputIterator>  void insert_unique(_InputIterator __f, _InputIterator __l)  {    insert_unique(__f, __l, __ITERATOR_CATEGORY(__f));  }  template <class _InputIterator>  void insert_equal(_InputIterator __f, _InputIterator __l)  {    insert_equal(__f, __l, __ITERATOR_CATEGORY(__f));  }  template <class _InputIterator>  void insert_unique(_InputIterator __f, _InputIterator __l,                     input_iterator_tag)  {    for ( ; __f != __l; ++__f)      insert_unique(*__f);  }  template <class _InputIterator>  void insert_equal(_InputIterator __f, _InputIterator __l,                    input_iterator_tag)  {    for ( ; __f != __l; ++__f)      insert_equal(*__f);  }  template <class _ForwardIterator>  void insert_unique(_ForwardIterator __f, _ForwardIterator __l,                     forward_iterator_tag)  {    size_type __n = 0;    distance(__f, __l, __n);    resize(_M_num_elements + __n);    for ( ; __n > 0; --__n, ++__f)      insert_unique_noresize(*__f);  }  template <class _ForwardIterator>  void insert_equal(_ForwardIterator __f, _ForwardIterator __l,                    forward_iterator_tag)  {    size_type __n = 0;    distance(__f, __l, __n);    resize(_M_num_elements + __n);    for ( ; __n > 0; --__n, ++__f)      insert_equal_noresize(*__f);  }  reference find_or_insert(const value_type& __obj);  iterator find(const key_type& __key)  {    size_type __n = _M_bkt_num_key(__key);  ///计算键所在的桶序号    ///在应在的桶中顺序查找    _Node* __first;    for ( __first = _M_buckets[__n];          __first && !_M_equals(_M_get_key(__first->_M_val), __key);          __first = __first->_M_next)      {}    return iterator(__first, this);  }  const_iterator find(const key_type& __key) const  {    size_type __n = _M_bkt_num_key(__key);    const _Node* __first;    for ( __first = _M_buckets[__n];          __first && !_M_equals(_M_get_key(__first->_M_val), __key);          __first = __first->_M_next)      {}    return const_iterator(__first, this);  }  size_type count(const key_type& __key) const  {    const size_type __n = _M_bkt_num_key(__key);    size_type __result = 0;    for (const _Node* __cur = _M_buckets[__n]; __cur; __cur = __cur->_M_next)      if (_M_equals(_M_get_key(__cur->_M_val), __key))        ++__result;    return __result;  }  pair<iterator, iterator>  equal_range(const key_type& __key);  pair<const_iterator, const_iterator>  equal_range(const key_type& __key) const;  size_type erase(const key_type& __key);  void erase(const iterator& __it);  void erase(iterator __first, iterator __last);  void erase(const const_iterator& __it);  void erase(const_iterator __first, const_iterator __last);  void resize(size_type __num_elements_hint);  void clear();private:  size_type _M_next_size(size_type __n) const    { return __stl_next_prime(__n); }  void _M_initialize_buckets(size_type __n)  {    const size_type __n_buckets = _M_next_size(__n); ///计算应分配的桶个数    _M_buckets.reserve(__n_buckets);    ///分配桶    ///将每个桶清空    _M_buckets.insert(_M_buckets.end(), __n_buckets, (_Node*) 0);    _M_num_elements = 0;  }   ///计算键所在的桶序号  size_type _M_bkt_num_key(const key_type& __key) const  {    return _M_bkt_num_key(__key, _M_buckets.size());  }   ///计算值所在的桶序号  size_type _M_bkt_num(const value_type& __obj) const  {    return _M_bkt_num_key(_M_get_key(__obj));  }  size_type _M_bkt_num_key(const key_type& __key, size_t __n) const  {      ///通过hash_fun得到的值在和桶个数做mod运算得到    return _M_hash(__key) % __n;  }  size_type _M_bkt_num(const value_type& __obj, size_t __n) const  {    return _M_bkt_num_key(_M_get_key(__obj), __n);  }  _Node* _M_new_node(const value_type& __obj)  {    _Node* __n = _M_get_node();    __n->_M_next = 0;   try {      construct(&__n->_M_val, __obj);      return __n;    }catch(...){        _M_put_node(__n);    }  }  void _M_delete_node(_Node* __n)  {    destroy(&__n->_M_val);    _M_put_node(__n);  }  void _M_erase_bucket(const size_type __n, _Node* __first, _Node* __last);  void _M_erase_bucket(const size_type __n, _Node* __last);  void _M_copy_from(const hashtable& __ht);};template <class _Val, class _Key, class _HF, class _ExK, class _EqK,          class _All>_Hashtable_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>&_Hashtable_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>::operator++(){  const _Node* __old = _M_cur;  _M_cur = _M_cur->_M_next;  if (!_M_cur) {   ///当前迭代器所指元素为当前桶中的最后一个元素    ///得到当前桶序号    size_type __bucket = _M_ht->_M_bkt_num(__old->_M_val);    ///从下一个桶开始查找非空桶,查找的的第一个非空桶的第一个元素    ///即为所求    while (!_M_cur && ++__bucket < _M_ht->_M_buckets.size())      _M_cur = _M_ht->_M_buckets[__bucket];  }  return *this;}template <class _Val, class _Key, class _HF, class _ExK, class _EqK, class _All>inline _Hashtable_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>_Hashtable_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>::operator++(int){  iterator __tmp = *this;  ++*this;  return __tmp;}template <class _Val, class _Key, class _HF, class _ExK, class _EqK,          class _All>_Hashtable_const_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>&_Hashtable_const_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>::operator++(){  const _Node* __old = _M_cur;  _M_cur = _M_cur->_M_next;  if (!_M_cur) {    size_type __bucket = _M_ht->_M_bkt_num(__old->_M_val);    while (!_M_cur && ++__bucket < _M_ht->_M_buckets.size())      _M_cur = _M_ht->_M_buckets[__bucket];  }  return *this;}template <class _Val, class _Key, class _HF, class _ExK, class _EqK,          class _All>inline _Hashtable_const_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>_Hashtable_const_iterator<_Val,_Key,_HF,_ExK,_EqK,_All>::operator++(int){  const_iterator __tmp = *this;  ++*this;  return __tmp;}///判断两个HashTable是否相等template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>bool operator==(const hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>& __ht1,                const hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>& __ht2){  typedef typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::_Node _Node;  ///(1)桶个数必须相等  if (__ht1._M_buckets.size() != __ht2._M_buckets.size())    return false;  ///(2)每个相同桶序号的相同位置的元素必须相等  for (int __n = 0; __n < __ht1._M_buckets.size(); ++__n) {    _Node* __cur1 = __ht1._M_buckets[__n];    _Node* __cur2 = __ht2._M_buckets[__n];    for ( ; __cur1 && __cur2 && __cur1->_M_val == __cur2->_M_val;          __cur1 = __cur1->_M_next, __cur2 = __cur2->_M_next)      {}    if (__cur1 || __cur2)      return false;  }  return true;}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>pair<typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::iterator, bool>hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::insert_unique_noresize(const value_type& __obj){  const size_type __n = _M_bkt_num(__obj);   ///计算应在桶序号  _Node* __first = _M_buckets[__n];  ///遍历该桶,如果已有键相同元素,返回  for (_Node* __cur = __first; __cur; __cur = __cur->_M_next)    if (_M_equals(_M_get_key(__cur->_M_val), _M_get_key(__obj)))      return pair<iterator, bool>(iterator(__cur, this), false);  ///需要插入  _Node* __tmp = _M_new_node(__obj);   ///构建对应值的插入结点   ///插入应在桶头部  __tmp->_M_next = __first;  _M_buckets[__n] = __tmp;  ++_M_num_elements;  return pair<iterator, bool>(iterator(__tmp, this), true);}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::iteratorhashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::insert_equal_noresize(const value_type& __obj){  const size_type __n = _M_bkt_num(__obj);  _Node* __first = _M_buckets[__n];  for (_Node* __cur = __first; __cur; __cur = __cur->_M_next)    if (_M_equals(_M_get_key(__cur->_M_val), _M_get_key(__obj))) {    ///如果应在桶中已有键相同元素,相同元素的最前面      _Node* __tmp = _M_new_node(__obj);      __tmp->_M_next = __cur->_M_next;      __cur->_M_next = __tmp;      ++_M_num_elements;      return iterator(__tmp, this);    }  ///所在桶中无键相同元素  _Node* __tmp = _M_new_node(__obj);  __tmp->_M_next = __first;  _M_buckets[__n] = __tmp;  ++_M_num_elements;  return iterator(__tmp, this);}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::referencehashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::find_or_insert(const value_type& __obj){    ///首先调整hashtable,为了防止桶个数太少以至于冲突太多  resize(_M_num_elements + 1);  size_type __n = _M_bkt_num(__obj);  _Node* __first = _M_buckets[__n];  for (_Node* __cur = __first; __cur; __cur = __cur->_M_next)    if (_M_equals(_M_get_key(__cur->_M_val), _M_get_key(__obj)))      return __cur->_M_val;  _Node* __tmp = _M_new_node(__obj);  __tmp->_M_next = __first;  _M_buckets[__n] = __tmp;  ++_M_num_elements;  return __tmp->_M_val;}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>pair<typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::iterator,     typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::iterator>hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::equal_range(const key_type& __key){  typedef pair<iterator, iterator> _Pii;  const size_type __n = _M_bkt_num_key(__key);  for (_Node* __first = _M_buckets[__n]; __first; __first = __first->_M_next)    if (_M_equals(_M_get_key(__first->_M_val), __key)) {  ///找到一个键与__key相同的元素      ///继续从当前位置遍历该桶,若遇到一个与之不同的键即可得到所求      for (_Node* __cur = __first->_M_next; __cur; __cur = __cur->_M_next)        if (!_M_equals(_M_get_key(__cur->_M_val), __key))          return _Pii(iterator(__first, this), iterator(__cur, this));        ///该桶中键与__key相同的元素为最后一波元素      for (size_type __m = __n + 1; __m < _M_buckets.size(); ++__m)        if (_M_buckets[__m])          return _Pii(iterator(__first, this),iterator(_M_buckets[__m], this));      return _Pii(iterator(__first, this), end());    }  return _Pii(end(), end());}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>pair<typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::const_iterator,     typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::const_iterator>hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::equal_range(const key_type& __key) const{  typedef pair<const_iterator, const_iterator> _Pii;  const size_type __n = _M_bkt_num_key(__key);  for (const _Node* __first = _M_buckets[__n] ;       __first;       __first = __first->_M_next) {    if (_M_equals(_M_get_key(__first->_M_val), __key)) {      for (const _Node* __cur = __first->_M_next;           __cur;           __cur = __cur->_M_next)        if (!_M_equals(_M_get_key(__cur->_M_val), __key))          return _Pii(const_iterator(__first, this),                      const_iterator(__cur, this));      for (size_type __m = __n + 1; __m < _M_buckets.size(); ++__m)        if (_M_buckets[__m])          return _Pii(const_iterator(__first, this),                      const_iterator(_M_buckets[__m], this));      return _Pii(const_iterator(__first, this), end());    }  }  return _Pii(end(), end());}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::size_typehashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::erase(const key_type& __key){ ///找到对应桶以后的删除操作和单链表中删除元素相同, ///最后记着对头结点需另行处理  const size_type __n = _M_bkt_num_key(__key);  _Node* __first = _M_buckets[__n];  size_type __erased = 0;  if (__first) {    _Node* __cur = __first;    _Node* __next = __cur->_M_next;    while (__next) {      if (_M_equals(_M_get_key(__next->_M_val), __key)) {        __cur->_M_next = __next->_M_next;        _M_delete_node(__next);        __next = __cur->_M_next;        ++__erased;        --_M_num_elements;      }      else {        __cur = __next;        __next = __cur->_M_next;      }    }    if (_M_equals(_M_get_key(__first->_M_val), __key)) {      _M_buckets[__n] = __first->_M_next;      _M_delete_node(__first);      ++__erased;      --_M_num_elements;    }  }  return __erased;}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::erase(const iterator& __it){    ///同样找到对应桶后和单链表删除操作相同  _Node* __p = __it._M_cur;  if (__p) {    const size_type __n = _M_bkt_num(__p->_M_val);    _Node* __cur = _M_buckets[__n];    if (__cur == __p) {      _M_buckets[__n] = __cur->_M_next;      _M_delete_node(__cur);      --_M_num_elements;    }    else {      _Node* __next = __cur->_M_next;      while (__next) {        if (__next == __p) {          __cur->_M_next = __next->_M_next;          _M_delete_node(__next);          --_M_num_elements;          break;        }        else {          __cur = __next;          __next = __cur->_M_next;        }      }    }  }}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::erase(iterator __first, iterator __last){  size_type __f_bucket = __first._M_cur ?    _M_bkt_num(__first._M_cur->_M_val) : _M_buckets.size();  size_type __l_bucket = __last._M_cur ?    _M_bkt_num(__last._M_cur->_M_val) : _M_buckets.size();  if (__first._M_cur == __last._M_cur)    return;  else if (__f_bucket == __l_bucket)   ///删除区间位于同一个桶内    _M_erase_bucket(__f_bucket, __first._M_cur, __last._M_cur);  else {      ///区间内的每个桶分别作合适的删除    _M_erase_bucket(__f_bucket, __first._M_cur, 0);    for (size_type __n = __f_bucket + 1; __n < __l_bucket; ++__n)      _M_erase_bucket(__n, 0);    if (__l_bucket != _M_buckets.size())      _M_erase_bucket(__l_bucket, __last._M_cur);  }}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>inline voidhashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::erase(const_iterator __first,                                             const_iterator __last){  erase(iterator(const_cast<_Node*>(__first._M_cur),                 const_cast<hashtable*>(__first._M_ht)),        iterator(const_cast<_Node*>(__last._M_cur),                 const_cast<hashtable*>(__last._M_ht)));}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>inline voidhashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::erase(const const_iterator& __it){  erase(iterator(const_cast<_Node*>(__it._M_cur),                 const_cast<hashtable*>(__it._M_ht)));}///对hashtable的重新调整,为了避免桶个数太少以至于冲突太多.这是整个///hashtable中最关键也最复杂的一个成员函数.template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::resize(size_type __num_elements_hint){  const size_type __old_n = _M_buckets.size();  if (__num_elements_hint > __old_n) {    const size_type __n = _M_next_size(__num_elements_hint);///得到下一个质数    if (__n > __old_n) {      vector<_Node*, _All> __tmp(__n, (_Node*)(0),                                 _M_buckets.get_allocator());   ///重新分配合适大小的vector<list>      try {        ///按序号遍历每个桶        for (size_type __bucket = 0; __bucket < __old_n; ++__bucket) {            ///得到桶中第一个元素          _Node* __first = _M_buckets[__bucket];          ///依次将该桶中的元素插入到新hashtable中对应的桶中,直到该桶为空          while (__first) {            ///或得该元素在新的hashtable内应在的桶序号            size_type __new_bucket = _M_bkt_num(__first->_M_val, __n);            ///将该元素从旧的位置摘下,插入新的hashtable应在的桶内            _M_buckets[__bucket] = __first->_M_next;            __first->_M_next = __tmp[__new_bucket];            __tmp[__new_bucket] = __first;            ///将first指向旧桶中的第一个元素            __first = _M_buckets[__bucket];          }        }        ///将得到的新hashtable和原有hashtable替换        _M_buckets.swap(__tmp);      }      catch(...) {          ///如果操作失败,需要依次删除所有新hashtable内的元素,          ///以防内存泄露        for (size_type __bucket = 0; __bucket < __tmp.size(); ++__bucket) {          while (__tmp[__bucket]) {            _Node* __next = __tmp[__bucket]->_M_next;            _M_delete_node(__tmp[__bucket]);            __tmp[__bucket] = __next;          }        }        throw;      }    }  }}///删除序号为__n的桶内[first,last)区间内的元素template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::_M_erase_bucket(const size_type __n, _Node* __first, _Node* __last){  _Node* __cur = _M_buckets[__n];  ///从头结点开始删除,需要特殊处理  if (__cur == __first)    _M_erase_bucket(__n, __last);  else {    _Node* __next;    ///找到需要删除的起点    for (__next = __cur->_M_next;         __next != __first;         __cur = __next, __next = __cur->_M_next)      ;    ///类似单链表删除    while (__next != __last) {      __cur->_M_next = __next->_M_next;      _M_delete_node(__next);      __next = __cur->_M_next;      --_M_num_elements;    }  }}///删除序号为__n的桶内自头结点至__last的元素,不包括__lasttemplate <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::_M_erase_bucket(const size_type __n, _Node* __last){  _Node* __cur = _M_buckets[__n];  while (__cur != __last) {    _Node* __next = __cur->_M_next;    _M_delete_node(__cur);    __cur = __next;    _M_buckets[__n] = __cur;   ///记着调整_M_buckets[__n]的指向    --_M_num_elements;  }}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::clear(){    ///挨个清空单链表,并将桶清空  for (size_type __i = 0; __i < _M_buckets.size(); ++__i) {    _Node* __cur = _M_buckets[__i];    while (__cur != 0) {      _Node* __next = __cur->_M_next;      _M_delete_node(__cur);      __cur = __next;    }    _M_buckets[__i] = 0;  }  _M_num_elements = 0;}template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All>void hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>  ::_M_copy_from(const hashtable& __ht){    ///挨个复制单链表  _M_buckets.clear();  _M_buckets.reserve(__ht._M_buckets.size());  _M_buckets.insert(_M_buckets.end(), __ht._M_buckets.size(), (_Node*) 0);  try {    for (size_type __i = 0; __i < __ht._M_buckets.size(); ++__i) {      const _Node* __cur = __ht._M_buckets[__i];      if (__cur) {        _Node* __copy = _M_new_node(__cur->_M_val);        _M_buckets[__i] = __copy;        for (_Node* __next = __cur->_M_next;             __next;             __cur = __next, __next = __cur->_M_next) {          __copy->_M_next = _M_new_node(__next->_M_val);          __copy = __copy->_M_next;        }      }    }    _M_num_elements = __ht._M_num_elements;  }catch(...){      clear();      throw;  }}

hash_table是STL中hash_map 和 hash_set 的内部数据结构，hash_table的插入/删除/查找的时间复杂度都为O(1),是查找速度最快的一种数据结构，但是hash_table中的数据是无序的，一般也只有在数据不需要排序，只需要满足快速查找/插入/删除的时候使用hash_table。hash_table的扩展是将原hash_table中的数据摘下来插入到一个临时的hash_table中，因为每个桶都使用list来实现的，因此插入删除都不存在内存copy，所以也是很高效的，最后再将临时hash_table和原来的hash_table（此时已经为空）交换。