标签：c++ stl 源码 hash table 散列表哈希表
在前面介绍的RB-tree红黑树中，可以看出红黑树的插入、查找、删除的平均时间复杂度为O(nlogn)。但这是基于一个假设：输入数据具有随机性。而哈希表/散列表hash table在插入、删除、查找上具有“平均常数时间复杂度”O(1)；且不依赖输入数据的随机性。
hash table的实现有线性探测、二次探测、二次散列等实现，SGI的STL是采用开链法(separate chaining)来实现的。大概原理就是在hash table的每一项都是个指针（指向一个链表），叫做bucket。这样的话如果多个key值散列到同一位置，那么就存储到这个位置对应的链表中。如下图所示：
hash table使用了vector来做buckets的容器，容器大小是质数（因为散列函数好多情况下是取余数），实现代码如下：
G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_hashtable.h 完整列表
/*
* Copyright (c) 1996,1997
* Silicon Graphics Computer Systems, Inc.
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Silicon Graphics makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*
*
* Copyright (c) 1994
* Hewlett-Packard Company
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Hewlett-Packard Company makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*
*/
/* NOTE: This is an internal header file, included by other STL headers.
* You should not attempt to use it directly.
*/
#ifndef __SGI_STL_INTERNAL_HASHTABLE_H
#define __SGI_STL_INTERNAL_HASHTABLE_H
// Hashtable class 用來實作 hashed associative containers
// hash_set, hash_map, hash_multiset, 和 hash_multimap.
#include <stl_algobase.h>
#include <stl_alloc.h>
#include <stl_construct.h>
#include <stl_tempbuf.h>
#include <stl_algo.h>
#include <stl_uninitialized.h>
#include <stl_function.h>
#include <stl_vector.h>
#include <stl_hash_fun.h>
__STL_BEGIN_NAMESPACE
//hash table中节点的定义，都是public
template <class Value>
struct __hashtable_node
{
/*
用vector来做hash table，为什么还需要next指针？
因为SGI 实现的hash table使用了开链法/链接法。
hash table中的节点可能代表一系列节点。它们以链形式连接。
这是所谓的 separate chaining 技巧。
*/
__hashtable_node* next;
Value val;
};
//先声明 hash table，在 iterator中有用到。
template <class Value, class Key, class HashFcn,
class ExtractKey, class EqualKey, class Alloc = alloc>
class hashtable;
// 由与 __hashtable_iterator 和 __hashtable_const_iterator 两者会
// 互相使用，因此必须在下面先做声明，否则编译出错。
template <class Value, class Key, class HashFcn,
class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_iterator;
template <class Value, class Key, class HashFcn,
class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_const_iterator;
//hash table中的迭代器
template <class Value, class Key, class HashFcn,
class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_iterator {
typedef hashtable<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>
hashtable;
typedef __hashtable_iterator<Value, Key, HashFcn,
ExtractKey, EqualKey, Alloc>
iterator;
typedef __hashtable_const_iterator<Value, Key, HashFcn,
ExtractKey, EqualKey, Alloc>
const_iterator;
typedef __hashtable_node<Value> node;
//迭代器类型，只能向前
typedef forward_iterator_tag iterator_category;
typedef Value value_type;
typedef ptrdiff_t difference_type;
typedef size_t size_type;
typedef Value& reference;
typedef Value* pointer;
node* cur; // 迭代器目前所指之节点
hashtable* ht; // 保持对容器的连接关系，因为可能需要从bucket跳到bucket
__hashtable_iterator(node* n, hashtable* tab) : cur(n), ht(tab) {}
//默认构造函数什么也没做
__hashtable_iterator() {}
reference operator*() const { return cur->val; }
#ifndef __SGI_STL_NO_ARROW_OPERATOR
pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */
iterator& operator++();
iterator operator++(int);
bool operator==(const iterator& it) const { return cur == it.cur; }
bool operator!=(const iterator& it) const { return cur != it.cur; }
};
template <class Value, class Key, class HashFcn,
class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_const_iterator {
typedef hashtable<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>
hashtable;
typedef __hashtable_iterator<Value, Key, HashFcn,
ExtractKey, EqualKey, Alloc>
iterator;
typedef __hashtable_const_iterator<Value, Key, HashFcn,
ExtractKey, EqualKey, Alloc>
const_iterator;
typedef __hashtable_node<Value> node;
typedef forward_iterator_tag iterator_category; // 注意
typedef Value value_type;
typedef ptrdiff_t difference_type;
typedef size_t size_type;
typedef const Value& reference;
typedef const Value* pointer;
const node* cur;
const hashtable* ht;
__hashtable_const_iterator(const node* n, const hashtable* tab)
: cur(n), ht(tab) {}
__hashtable_const_iterator() {}
__hashtable_const_iterator(const iterator& it) : cur(it.cur), ht(it.ht) {}
reference operator*() const { return cur->val; }
#ifndef __SGI_STL_NO_ARROW_OPERATOR
pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */
const_iterator& operator++();
const_iterator operator++(int);
bool operator==(const const_iterator& it) const { return cur == it.cur; }
bool operator!=(const const_iterator& it) const { return cur != it.cur; }
};
// 注意：假设 long 至少有 32 bits。
//定义28个素数（大概是2倍关系增长），用来做hash table的大小
static const int __stl_num_primes = 28;
static const unsigned long __stl_prime_list[__stl_num_primes] =
{
53, 97, 193, 389, 769,
1543, 3079, 6151, 12289, 24593,
49157, 98317, 196613, 393241, 786433,
1572869, 3145739, 6291469, 12582917, 25165843,
50331653, 100663319, 201326611, 402653189, 805306457,
1610612741, 3221225473ul, 4294967291ul
};
//找出28个素数中，最接近n且大于n的那个数
inline unsigned long __stl_next_prime(unsigned long n)
{
const unsigned long* first = __stl_prime_list;
const unsigned long* last = __stl_prime_list + __stl_num_primes;
const unsigned long* pos = lower_bound(first, last, n);
// 以上，lower_bound() 是泛型算法
// 使用 lower_bound()，序列需先排序。上述数组以排序
return pos == last ? *(last - 1) : *pos;
}
/*
Value 节点的实值类型
Key 节点的键值类型
HashFcn hash function的类型
EqualKey从节点中取出键值的方法（函数或仿函数）
EqualKey判断键值是否相同的方法（函数或仿函数）
*/
template <class Value, class Key, class HashFcn,
class ExtractKey, class EqualKey,
class Alloc> // 最上面已经说明：默认使用 alloc 空间配置器。
class hashtable {
public:
//为 template 类型参数重新定义一个名称（貌似没必要）
typedef Key key_type;
typedef Value value_type;
typedef HashFcn hasher;//hash函数
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 hash; }
key_equal key_eq() const { return equals; }
private:
//以下三个都是 function objects。。、<stl_hash_fun.h>中定义了几个
//标准类型(如int,c-style string等)的 hasher。
hasher hash;
key_equal equals;
ExtractKey get_key;
typedef __hashtable_node<Value> node;
typedef simple_alloc<node, Alloc> node_allocator;
vector<node*,Alloc> buckets; // 以 vector 完成
size_type num_elements;//hash table中节点的个数
public:
typedef __hashtable_iterator<Value, Key, HashFcn, ExtractKey, EqualKey,
Alloc>
iterator;
typedef __hashtable_const_iterator<Value, Key, HashFcn, ExtractKey, EqualKey,
Alloc>
const_iterator;
friend struct
__hashtable_iterator<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>;
friend struct
__hashtable_const_iterator<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>;
public:
//没有默认的构造函数
hashtable(size_type n,
const HashFcn& hf,
const EqualKey& eql,
const ExtractKey& ext)
: hash(hf), equals(eql), get_key(ext), num_elements(0)
{
initialize_buckets(n);
}
hashtable(size_type n,
const HashFcn& hf,
const EqualKey& eql)
: hash(hf), equals(eql), get_key(ExtractKey()), num_elements(0)
{
initialize_buckets(n);
}
hashtable(const hashtable& ht)
: hash(ht.hash), equals(ht.equals), get_key(ht.get_key), num_elements(0)
{
copy_from(ht);
}
hashtable& operator= (const hashtable& ht)
{
if (&ht != this) { //防止自身赋值
clear(); // 先清除自己
hash = ht.hash; // 以下三个动作，将三份data members 复制过来。
equals = ht.equals;
get_key = ht.get_key;
copy_from(ht); // 完整赋值整个 hash table的内容。
}
return *this;
}
~hashtable() { clear(); }
size_type size() const { return num_elements; }
size_type max_size() const { return size_type(-1); }
bool empty() const { return size() == 0; }
void swap(hashtable& ht)
{
__STD::swap(hash, ht.hash);
__STD::swap(equals, ht.equals);
__STD::swap(get_key, ht.get_key);
buckets.swap(ht.buckets);
__STD::swap(num_elements, ht.num_elements);
}
iterator begin()
{
for (size_type n = 0; n < buckets.size(); ++n)
//找出第一个被使用的节点，此即 begin iterator。
if (buckets[n])
return iterator(buckets[n], this);
return end();
}
//最后被使用节点的下个位置，所以使用0来初始化迭代器
iterator end() { return iterator(0, this); }
const_iterator begin() const
{
for (size_type n = 0; n < buckets.size(); ++n)
if (buckets[n])
return const_iterator(buckets[n], this);
return end();
}
const_iterator end() const { return const_iterator(0, this); }
friend bool
operator== __STL_NULL_TMPL_ARGS (const hashtable&, const hashtable&);
public:
// bucket 个数即 buckets vector 的大小
size_type bucket_count() const { return buckets.size(); }
//以目前情况（不重建表格），总共可以有多少个 buckets
size_type max_bucket_count() const
{ return __stl_prime_list[__stl_num_primes - 1]; }
// 某一个 bucket （内含一个list） 容纳多少个元素
size_type elems_in_bucket(size_type bucket) const
{
size_type result = 0;
for (node* cur = buckets[bucket]; cur; cur = cur->next)
result += 1;
return result;
}
//安插元素，不允许重复
pair<iterator, bool> insert_unique(const value_type& obj)
{
resize(num_elements + 1); // 判断是否需要重建表格，如果需要就填充
return insert_unique_noresize(obj);
}
// 安插元素，允许重复
iterator insert_equal(const value_type& obj)
{
resize(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);
#ifdef __STL_MEMBER_TEMPLATES
//插入两个迭代器之间的元素[f l)
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);//判断两个迭代器的距离，n是引用传递
resize(num_elements + n); // 判断（并实施）表格的重建
for ( ; n > 0; --n, ++f)
insert_unique_noresize(*f); // 一一安插新元素
}
template <class ForwardIterator>
void insert_equal(ForwardIterator f, ForwardIterator l,
forward_iterator_tag)
{
size_type n = 0;
distance(f, l, n);
resize(num_elements + n);
for ( ; n > 0; --n, ++f)
insert_equal_noresize(*f); // 一一安插新元素
}
#else /* __STL_MEMBER_TEMPLATES */
void insert_unique(const value_type* f, const value_type* l)
{
//可以直接计算迭代器之间的距离，应该是rando access iterator
size_type n = l - f;
resize(num_elements + n);
for ( ; n > 0; --n, ++f)
insert_unique_noresize(*f);
}
void insert_equal(const value_type* f, const value_type* l)
{
size_type n = l - f;
resize(num_elements + n);
for ( ; n > 0; --n, ++f)
insert_equal_noresize(*f);
}
void insert_unique(const_iterator f, const_iterator l)
{
size_type n = 0;
distance(f, l, n);
resize(num_elements + n);
for ( ; n > 0; --n, ++f)
insert_unique_noresize(*f);
}
void insert_equal(const_iterator f, const_iterator l)
{
size_type n = 0;
distance(f, l, n);
resize(num_elements + n);
for ( ; n > 0; --n, ++f)
insert_equal_noresize(*f);
}
#endif /*__STL_MEMBER_TEMPLATES */
reference find_or_insert(const value_type& obj);
iterator find(const key_type& key)
{
size_type n = bkt_num_key(key); // 首先找到落在哪个bucket内
node* first;
//从bucket list的头开始，一一对比每个元素的键值。
for ( first = buckets[n];
first && !equals(get_key(first->val), key);
first = first->next)
{}
return iterator(first, this);
}
const_iterator find(const key_type& key) const
{
size_type n = bkt_num_key(key);
const node* first;
for ( first = buckets[n];
first && !equals(get_key(first->val), key);
first = first->next)
{}
return const_iterator(first, this);
}
//查看hash table中含有多少个值为key的元素
size_type count(const key_type& key) const
{
const size_type n = bkt_num_key(key);
size_type result = 0;
// 以下，从bucket list 的头开始，一一比对每个素的键值。比对成功就累加1。
for (const node* cur = buckets[n]; cur; cur = cur->next)
if (equals(get_key(cur->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:
// 寻找STL中提供的下一个质数
size_type next_size(size_type n) const { return __stl_next_prime(n); }
// 注意，hash_vec 和 hash_map 都將其底層的 hash table 的初始大小預設為 100
// hash_vec 和 hash_map 都将底层的 hash table初始化大小预设为100
void initialize_buckets(size_type n)
{
//例如：传入100,返回193。以下首先保留193个元素空间，然后将其全部填0。
//例如：传入50,返回53。以下首先保留53个元素空间，然后将其全部填0。
const size_type n_buckets = next_size(n);
buckets.reserve(n_buckets);
buckets.insert(buckets.end(), n_buckets, (node*) 0);
num_elements = 0;
}
size_type bkt_num_key(const key_type& key) const
{
return bkt_num_key(key, buckets.size());
}
size_type bkt_num(const value_type& obj) const
{
return bkt_num_key(get_key(obj));
}
size_type bkt_num_key(const key_type& key, size_t n) const
{
return hash(key) % n;
}
size_type bkt_num(const value_type& obj, size_t n) const
{
return bkt_num_key(get_key(obj), n);
}
node* new_node(const value_type& obj)
{
node* n = node_allocator::allocate();//配置空间
n->next = 0;//指针next设置为NULL
__STL_TRY {
construct(&n->val, obj);//构建元素
return n;
}
//commit or rollback
__STL_UNWIND(node_allocator::deallocate(n));
}
void delete_node(node* n)
{
destroy(&n->val);//析构
node_allocator::deallocate(n);//释放空间
}
void erase_bucket(const size_type n, node* first, node* last);
void erase_bucket(const size_type n, node* last);
void copy_from(const hashtable& ht);
};
template <class V, class K, class HF, class ExK, class EqK, class A>
__hashtable_iterator<V, K, HF, ExK, EqK, A>&
__hashtable_iterator<V, K, HF, ExK, EqK, A>::operator++()
{
const node* old = cur;
cur = cur->next; // 如果存在，就是它。否则进入以下 if 流程
if (!cur) {
// 根据原值，重新定位。从该位置(bucket)的下一个位置找起。
size_type bucket = ht->bkt_num(old->val);
while (!cur && ++bucket < ht->buckets.size()) // 注意，prefix operator++
cur = ht->buckets[bucket];
}
return *this;
}
template <class V, class K, class HF, class ExK, class EqK, class A>
inline __hashtable_iterator<V, K, HF, ExK, EqK, A>
__hashtable_iterator<V, K, HF, ExK, EqK, A>::operator++(int)
{
iterator tmp = *this;
++*this; // 调用 operator++()
return tmp;
}
template <class V, class K, class HF, class ExK, class EqK, class A>
__hashtable_const_iterator<V, K, HF, ExK, EqK, A>&
__hashtable_const_iterator<V, K, HF, ExK, EqK, A>::operator++()
{
const node* old = cur;
cur = cur->next;
if (!cur) {
size_type bucket = ht->bkt_num(old->val);
while (!cur && ++bucket < ht->buckets.size())
cur = ht->buckets[bucket];
}
return *this;
}
template <class V, class K, class HF, class ExK, class EqK, class A>
inline __hashtable_const_iterator<V, K, HF, ExK, EqK, A>
__hashtable_const_iterator<V, K, HF, ExK, EqK, A>::operator++(int)
{
const_iterator tmp = *this;
++*this;
return tmp;
}
#ifndef __STL_CLASS_PARTIAL_SPECIALIZATION
template <class V, class K, class HF, class ExK, class EqK, class All>
inline forward_iterator_tag
iterator_category(const __hashtable_iterator<V, K, HF, ExK, EqK, All>&)
{
return forward_iterator_tag();
}
template <class V, class K, class HF, class ExK, class EqK, class All>
inline V* value_type(const __hashtable_iterator<V, K, HF, ExK, EqK, All>&)
{
return (V*) 0;
}
template <class V, class K, class HF, class ExK, class EqK, class All>
inline hashtable<V, K, HF, ExK, EqK, All>::difference_type*
distance_type(const __hashtable_iterator<V, K, HF, ExK, EqK, All>&)
{
return (hashtable<V, K, HF, ExK, EqK, All>::difference_type*) 0;
}
template <class V, class K, class HF, class ExK, class EqK, class All>
inline forward_iterator_tag
iterator_category(const __hashtable_const_iterator<V, K, HF, ExK, EqK, All>&)
{
return forward_iterator_tag();
}
template <class V, class K, class HF, class ExK, class EqK, class All>
inline V*
value_type(const __hashtable_const_iterator<V, K, HF, ExK, EqK, All>&)
{
return (V*) 0;
}
template <class V, class K, class HF, class ExK, class EqK, class All>
inline hashtable<V, K, HF, ExK, EqK, All>::difference_type*
distance_type(const __hashtable_const_iterator<V, K, HF, ExK, EqK, All>&)
{
return (hashtable<V, K, HF, ExK, EqK, All>::difference_type*) 0;
}
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */
//判断两个hash table是否相等（两个hasn table的 buckets相同，且
//bucket对应的list相同)
template <class V, class K, class HF, class Ex, class Eq, class A>
bool operator==(const hashtable<V, K, HF, Ex, Eq, A>& ht1,
const hashtable<V, K, HF, Ex, Eq, A>& ht2)
{
typedef typename hashtable<V, K, HF, Ex, Eq, A>::node node;
if (ht1.buckets.size() != ht2.buckets.size())
return false;
for (int n = 0; n < ht1.buckets.size(); ++n) {
node* cur1 = ht1.buckets[n];
node* cur2 = ht2.buckets[n];
for ( ; cur1 && cur2 && cur1->val == cur2->val;
cur1 = cur1->next, cur2 = cur2->next)
{}
if (cur1 || cur2)//如果cur1或cur2有一个不等于0（没有指向最后位置的下一个位置）
return false;
}
return true;
}
#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
template <class Val, class Key, class HF, class Extract, class EqKey, class A>
inline void swap(hashtable<Val, Key, HF, Extract, EqKey, A>& ht1,
hashtable<Val, Key, HF, Extract, EqKey, A>& ht2) {
ht1.swap(ht2);
}
#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */
//在不重建表格的情况下安插新节点。键值不允许重复。返回pair。第二个参数指出
//插入是否成功
template <class V, class K, class HF, class Ex, class Eq, class A>
pair<typename hashtable<V, K, HF, Ex, Eq, A>::iterator, bool>
hashtable<V, K, HF, Ex, Eq, A>::insert_unique_noresize(const value_type& obj)
{
const size_type n = bkt_num(obj); // 決定obj位于哪个buckets中
node* first = buckets[n]; // 令 first 指向 bucket 对应串列头部
// 如果 buckets[n] 已被占用，此时first 将不为0，于是进入以下循环，
// 遍历bucket对应的整个链表
for (node* cur = first; cur; cur = cur->next)
if (equals(get_key(cur->val), get_key(obj)))
// 如果发现链表中的某键值相同，就不安插，立刻回返。
return pair<iterator, bool>(iterator(cur, this), false);
//离开以上循环（或没进入循环），first指向指向bucket所指链表的头部节点
node* tmp = new_node(obj); // 生成新节点并赋值
tmp->next = first; //更改新节点指针
buckets[n] = tmp; // 新节点称为bucket链表第一个节点
++num_elements; // 节点个诉累加1
return pair<iterator, bool>(iterator(tmp, this), true);
}
//在不重建表格的情况下安插新节点。键值不允许重复。
template <class V, class K, class HF, class Ex, class Eq, class A>
typename hashtable<V, K, HF, Ex, Eq, A>::iterator
hashtable<V, K, HF, Ex, Eq, A>::insert_equal_noresize(const value_type& obj)
{
const size_type n = bkt_num(obj);
node* first = buckets[n];
// 如果 buckets[n] 已被佔用，此時first 將不為0，於是進入以下迴圈，
// 走過 bucket 所對應的整個串列。
for (node* cur = first; cur; cur = cur->next)
if (equals(get_key(cur->val), get_key(obj))) {
// 如果发现链表中键值相同，马上插入，然后返回
//插到键值相同节点的后面
node* tmp = new_node(obj);
tmp->next = cur->next;
cur->next = tmp;
++num_elements;
return iterator(tmp, this); // 返回迭代器，指向新插入的节点
}
// 运行到此处，没有键值重复。
node* tmp = new_node(obj);
tmp->next = first;
buckets[n] = tmp;
++num_elements;
return iterator(tmp, this);
}
//如果存在obj节点则返回指向其节点的迭代器，否则插入
template <class V, class K, class HF, class Ex, class Eq, class A>
typename hashtable<V, K, HF, Ex, Eq, A>::reference
hashtable<V, K, HF, Ex, Eq, A>::find_or_insert(const value_type& obj)
{
resize(num_elements + 1);
size_type n = bkt_num(obj);
node* first = buckets[n];
for (node* cur = first; cur; cur = cur->next)
if (equals(get_key(cur->val), get_key(obj)))
return cur->val;
node* tmp = new_node(obj);
tmp->next = first;
buckets[n] = tmp;
++num_elements;
return tmp->val;
}
template <class V, class K, class HF, class Ex, class Eq, class A>
pair<typename hashtable<V, K, HF, Ex, Eq, A>::iterator,
typename hashtable<V, K, HF, Ex, Eq, A>::iterator>
hashtable<V, K, HF, Ex, Eq, A>::equal_range(const key_type& key)
{
typedef pair<iterator, iterator> pii;
const size_type n = bkt_num_key(key);
for (node* first = buckets[n]; first; first = first->next) {
if (equals(get_key(first->val), key)) {
for (node* cur = first->next; cur; cur = cur->next)
if (!equals(get_key(cur->val), key))
return pii(iterator(first, this), iterator(cur, this));
for (size_type m = n + 1; m < buckets.size(); ++m)
if (buckets[m])
return pii(iterator(first, this),
iterator(buckets[m], this));
return pii(iterator(first, this), end());
}
}
return pii(end(), end());
}
//查找键值等于key的区间。pair两个元素类型都是迭代器类型
//一个指向区间起始位置，一个指向区间结束的下一个位置。
template <class V, class K, class HF, class Ex, class Eq, class A>
pair<typename hashtable<V, K, HF, Ex, Eq, A>::const_iterator,
typename hashtable<V, K, HF, Ex, Eq, A>::const_iterator>
hashtable<V, K, HF, Ex, Eq, A>::equal_range(const key_type& key) const
{
typedef pair<const_iterator, const_iterator> pii;
const size_type n = bkt_num_key(key);//先找到在哪个 buckets
//bucket对应的链表中查找
for (const node* first = buckets[n] ; first; first = first->next) {
if (equals(get_key(first->val), key)) {//找到键值为key的起始位置
for (const node* cur = first->next; cur; cur = cur->next)
if (!equals(get_key(cur->val), key))
return pii(const_iterator(first, this),
const_iterator(cur, this));
//运行到此处，说明bucket对应的链表中尾节点也是键值为key节点
//那么下一个位置就是 buckets中可用的bucket链表头节点
for (size_type m = n + 1; m < buckets.size(); ++m)
if (buckets[m])
return pii(const_iterator(first, this),
const_iterator(buckets[m], this));
//后面的 buckets都没用
return pii(const_iterator(first, this), end());
}
}
// hash table没有key值节点
return pii(end(), end());
}
//擦除键值为key的节点
template <class V, class K, class HF, class Ex, class Eq, class A>
typename hashtable<V, K, HF, Ex, Eq, A>::size_type
hashtable<V, K, HF, Ex, Eq, A>::erase(const key_type& key)
{
const size_type n = bkt_num_key(key);
node* first = buckets[n];//找到对应bucket链表头节点
size_type erased = 0;
if (first) {
node* cur = first;//这里要保存前一个节点，因为是单向链表
node* next = cur->next;
//如果链表中多于一个节点
while (next) {
if (equals(get_key(next->val), key)) {
cur->next = next->next;
delete_node(next);
next = cur->next;
++erased;
--num_elements;
}
else {
cur = next;
next = cur->next;
}
}
//链表中只有一个节点
if (equals(get_key(first->val), key)) {
buckets[n] = first->next;
delete_node(first);
++erased;
--num_elements;
}
}
return erased;
}
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::erase(const iterator& it)
{
if (node* const p = it.cur) {
const size_type n = bkt_num(p->val);
node* cur = buckets[n];
if (cur == p) {
buckets[n] = cur->next;
delete_node(cur);
--num_elements;
}
else {
node* next = cur->next;
while (next) {
if (next == p) {
cur->next = next->next;
delete_node(next);
--num_elements;
break;
}
else {
cur = next;
next = cur->next;
}
}
}
}
}
//擦除两个迭代器之间的元素
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::erase(iterator first, iterator last)
{
size_type f_bucket = first.cur ? bkt_num(first.cur->val) : buckets.size();
size_type l_bucket = last.cur ? bkt_num(last.cur->val) : buckets.size();
if (first.cur == last.cur)
return;
else if (f_bucket == l_bucket)
erase_bucket(f_bucket, first.cur, last.cur);
else {
erase_bucket(f_bucket, first.cur, 0);
for (size_type n = f_bucket + 1; n < l_bucket; ++n)
erase_bucket(n, 0);
if (l_bucket != buckets.size())
erase_bucket(l_bucket, last.cur);
}
}
template <class V, class K, class HF, class Ex, class Eq, class A>
inline void
hashtable<V, K, HF, Ex, Eq, A>::erase(const_iterator first,
const_iterator last)
{
erase(iterator(const_cast<node*>(first.cur),
const_cast<hashtable*>(first.ht)),
iterator(const_cast<node*>(last.cur),
const_cast<hashtable*>(last.ht)));
}
template <class V, class K, class HF, class Ex, class Eq, class A>
inline void
hashtable<V, K, HF, Ex, Eq, A>::erase(const const_iterator& it)
{
erase(iterator(const_cast<node*>(it.cur),
const_cast<hashtable*>(it.ht)));
}
//重新配置 hash table的大小
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::resize(size_type num_elements_hint)
{
const size_type old_n = buckets.size();//原来hash table大小
if (num_elements_hint > old_n) { // 确定真的需要重新配置
const size_type n = next_size(num_elements_hint); // 找出下一个质数
//下个这个判断没必要了吧？因为n>=num_elements_hint，而num_elements_hint>=old_n
if (n > old_n) {
vector<node*, A> tmp(n, (node*) 0); // 设立新的 buckets
__STL_TRY {
// 下面处理每一个旧的bucket
for (size_type bucket = 0; bucket < old_n; ++bucket) {
node* first = buckets[bucket]; // 指向节点所对应链表的起始节点
// 以下處理每一個舊bucket 所含（串列）的每一個節點
// 一下处理bucketliability的每一个节点
while (first) { // 链表没结束
// 以下找出节点落在哪一个新bucket 內
size_type new_bucket = bkt_num(first->val, n);
// 以下四个动作颇为巧妙
// (1) 令旧 bucket 指向其所对应之链表的下一个节点（以便迭代处理）
buckets[bucket] = first->next;
// (2)(3) 将当前节点安插到新的bucket内，成为其对应链表的第一个节点。
first->next = tmp[new_bucket];
tmp[new_bucket] = first;
// (4) 回到旧bucket 所指的待处理链表，准备处理下一个节点
first = buckets[bucket];
}
}
buckets.swap(tmp); // vector::swap。新旧 buckets 对调。
// 注意，对调两方如果大小不同，大的会变小，小的会变大。
// tmp为局部作用域，离开其作用域自动释放
}
# ifdef __STL_USE_EXCEPTIONS
//commit or rollback
catch(...) {
for (size_type bucket = 0; bucket < tmp.size(); ++bucket) {
while (tmp[bucket]) {
node* next = tmp[bucket]->next;
delete_node(tmp[bucket]);
tmp[bucket] = next;
}
}
throw;
}
# endif /* __STL_USE_EXCEPTIONS */
}
}
}
//擦除hash table对应第n个bucket中的一段元素[first last)
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::erase_bucket(const size_type n,
node* first, node* last)
{
node* cur = buckets[n];
if (cur == first)
erase_bucket(n, last);
else {
node* next;
for (next = cur->next; next != first; cur = next, next = cur->next)
;
//下面应该是 while(next!=last)吧？否则last在这没用
while (next) {
cur->next = next->next;
delete_node(next);
next = cur->next;
--num_elements;
}
}
}
////擦除hash table对应第n个bucket中的一段元素[buckets[n] last)
template <class V, class K, class HF, class Ex, class Eq, class A>
void
hashtable<V, K, HF, Ex, Eq, A>::erase_bucket(const size_type n, node* last)
{
node* cur = buckets[n];
while (cur != last) {
node* next = cur->next;
delete_node(cur);
cur = next;
buckets[n] = cur;
--num_elements;
}
}
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::clear()
{
// 针对每一个 bucket.
for (size_type i = 0; i < buckets.size(); ++i) {
node* cur = buckets[i];
// 将 bucket list 中的每一个节点刪除掉
while (cur != 0) {
node* next = cur->next;
delete_node(cur);
cur = next;
}
buckets[i] = 0; // 令bucket 內容为 null 指针
}
num_elements = 0; // 令总节点个数0
// 注意，buckets vector 并未释放掉，仍保有原来大小。
}
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::copy_from(const hashtable& ht)
{
// 先清除己方的buckets vector. 调用vector::clear.
buckets.clear();
//如果己方空间大于对方，就不懂，否则增大己方空间等于对方
buckets.reserve(ht.buckets.size());
//从己方的buckets vector尾端开始，安插n个元素，其值为NULL指针。
//注意，此时buckets vector为空，所以所谓尾端就是起始处
buckets.insert(buckets.end(), ht.buckets.size(), (node*) 0);
__STL_TRY {
// 针对 buckets vector
for (size_type i = 0; i < ht.buckets.size(); ++i) {
//复制 vector 的每一个元素（是个指针，指向hash table节点）
//注意下面if语句，是先赋值再判断，它等价于
//const node* cur = ht.buckets[i]; if(cur)
if (const node* cur = ht.buckets[i]) {
node* copy = new_node(cur->val);
buckets[i] = copy;
// 针对每一个 bucket list，复制每一个节点
for (node* next = cur->next; next; cur = next, next = cur->next) {
copy->next = new_node(next->val);
copy = copy->next;
}
}
}
num_elements = ht.num_elements; // 重新设置节点个数（hashtable 的大小）
}
__STL_UNWIND(clear());
}
__STL_END_NAMESPACE
#endif /* __SGI_STL_INTERNAL_HASHTABLE_H */
// Local Variables:
// mode:C++
// End:
《STL源码剖析》---stl_hashtable.h阅读笔记,布布扣,bubuko.com
《STL源码剖析》---stl_hashtable.h阅读笔记
标签：c++ stl 源码 hash table 散列表哈希表
原文地址：http://blog.csdn.net/kangroger/article/details/38640943
