STL源码剖析——关联容器之hash_map

前言

    由于前文介绍的《散列表hashtable》中，可以知道hash table在查找、删除和插入节点是常数时间，优于RB-Tree红黑树，所以在SGI STL中提供了底层机制基于hash table的hash_map容器，hash_map和map类似，但是不同点是hash_map容器中的元素是没有排序的，因为hash table没有提供排序功能。本文源码出自SGI STL的<stl_hash_map.h>文件。        

hash_map源码剖析

#ifndef __SGI_STL_INTERNAL_HASH_MAP_H#define __SGI_STL_INTERNAL_HASH_MAP_H#include <concept_checks.h>__STL_BEGIN_NAMESPACE#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)#pragma set woff 1174#pragma set woff 1375#endif//hash_map的底层是基于hash table的，hash table没有提供排序,所以hash_map容器里面的内容是没排序的// Forward declaration of equality operator; needed for friend declaration.template <class _Key, class _Tp,          class _HashFcn  __STL_DEPENDENT_DEFAULT_TMPL(hash<_Key>),          class _EqualKey __STL_DEPENDENT_DEFAULT_TMPL(equal_to<_Key>),          class _Alloc =  __STL_DEFAULT_ALLOCATOR(_Tp) >class hash_map;template <class _Key, class _Tp, class _HashFn, class _EqKey, class _Alloc>inline bool operator==(const hash_map<_Key, _Tp, _HashFn, _EqKey, _Alloc>&,                       const hash_map<_Key, _Tp, _HashFn, _EqKey, _Alloc>&);template <class _Key, class _Tp, class _HashFcn, class _EqualKey,          class _Alloc>class hash_map{  // requirements:  __STL_CLASS_REQUIRES(_Key, _Assignable);  __STL_CLASS_REQUIRES(_Tp, _Assignable);  __STL_CLASS_UNARY_FUNCTION_CHECK(_HashFcn, size_t, _Key);  __STL_CLASS_BINARY_FUNCTION_CHECK(_EqualKey, bool, _Key, _Key);private://_Select1st<>取出键值key,_Select1st<>定义在<stl_function.h>/*template <class _Arg, class _Result>struct unary_function {  typedef _Arg argument_type;  typedef _Result result_type;};template <class _Pair>struct _Select1st : public unary_function<_Pair, typename _Pair::first_type> {  const typename _Pair::first_type& operator()(const _Pair& __x) const {return __x.first;  }};*/  typedef hashtable<pair<const _Key,_Tp>,_Key,_HashFcn,                    _Select1st<pair<const _Key,_Tp> >,_EqualKey,_Alloc> _Ht;  _Ht _M_ht;//底层机制以hash table完成public://以下的内嵌类型均来是hash table  typedef typename _Ht::key_type key_type;  typedef _Tp data_type;  typedef _Tp mapped_type;  typedef typename _Ht::value_type value_type;  typedef typename _Ht::hasher hasher;  typedef typename _Ht::key_equal key_equal;    typedef typename _Ht::size_type size_type;  typedef typename _Ht::difference_type difference_type;  typedef typename _Ht::pointer pointer;  typedef typename _Ht::const_pointer const_pointer;  typedef typename _Ht::reference reference;  typedef typename _Ht::const_reference const_reference;  typedef typename _Ht::iterator iterator;  typedef typename _Ht::const_iterator const_iterator;  typedef typename _Ht::allocator_type allocator_type;  //返回hash相关函数  hasher hash_funct() const { return _M_ht.hash_funct(); }  key_equal key_eq() const { return _M_ht.key_eq(); }  allocator_type get_allocator() const { return _M_ht.get_allocator(); }public://构造函数//缺省情况使用大小为100,但是实际分配的空间大小为不小于100的最小素数//只是空的hash_map，不存储元素节点  hash_map() : _M_ht(100, hasher(), key_equal(), allocator_type()) {}  //指定大小n的hash_map表  explicit hash_map(size_type __n)    : _M_ht(__n, hasher(), key_equal(), allocator_type()) {}  //指定大小为n，且指定hash函数的hash_map  hash_map(size_type __n, const hasher& __hf)    : _M_ht(__n, __hf, key_equal(), allocator_type()) {}  //指定大小为n，且指定hash函数和键值比较函数的hash_map  hash_map(size_type __n, const hasher& __hf, const key_equal& __eql,           const allocator_type& __a = allocator_type())    : _M_ht(__n, __hf, __eql, __a) {}#ifdef __STL_MEMBER_TEMPLATES  //以下hash_map的插入操作使用hash table的insert_unique插入  //不允许有相同的键值插入  //用某个范围的元素初始化hash_map对象  //相当于把某个范围[f,l)插入到空的hash_map  template <class _InputIterator>  hash_map(_InputIterator __f, _InputIterator __l)    : _M_ht(100, hasher(), key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }//调用hash table的插入函数  template <class _InputIterator>  hash_map(_InputIterator __f, _InputIterator __l, size_type __n)    : _M_ht(__n, hasher(), key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  template <class _InputIterator>  hash_map(_InputIterator __f, _InputIterator __l, size_type __n,           const hasher& __hf)    : _M_ht(__n, __hf, key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  template <class _InputIterator>  hash_map(_InputIterator __f, _InputIterator __l, size_type __n,           const hasher& __hf, const key_equal& __eql,           const allocator_type& __a = allocator_type())    : _M_ht(__n, __hf, __eql, __a)    { _M_ht.insert_unique(__f, __l); }#else  hash_map(const value_type* __f, const value_type* __l)    : _M_ht(100, hasher(), key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  hash_map(const value_type* __f, const value_type* __l, size_type __n)    : _M_ht(__n, hasher(), key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  hash_map(const value_type* __f, const value_type* __l, size_type __n,           const hasher& __hf)    : _M_ht(__n, __hf, key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  hash_map(const value_type* __f, const value_type* __l, size_type __n,           const hasher& __hf, const key_equal& __eql,           const allocator_type& __a = allocator_type())    : _M_ht(__n, __hf, __eql, __a)    { _M_ht.insert_unique(__f, __l); }  hash_map(const_iterator __f, const_iterator __l)    : _M_ht(100, hasher(), key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  hash_map(const_iterator __f, const_iterator __l, size_type __n)    : _M_ht(__n, hasher(), key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  hash_map(const_iterator __f, const_iterator __l, size_type __n,           const hasher& __hf)    : _M_ht(__n, __hf, key_equal(), allocator_type())    { _M_ht.insert_unique(__f, __l); }  hash_map(const_iterator __f, const_iterator __l, size_type __n,           const hasher& __hf, const key_equal& __eql,           const allocator_type& __a = allocator_type())    : _M_ht(__n, __hf, __eql, __a)    { _M_ht.insert_unique(__f, __l); }#endif /*__STL_MEMBER_TEMPLATES */public://以下的函数操作只是调用hash table的成员函数//返回 hash_map 容器中元素的个数.  size_type size() const { return _M_ht.size(); }//返回hash_map容器最大存储元素的个数.  size_type max_size() const { return _M_ht.max_size(); }//Returns a bool value indicating whether the hash_map container is empty,//i.e. whether its size is 0.  bool empty() const { return _M_ht.empty(); }  //交换两个存储相同元素类型的hash_map容器内容,但是hash_map容器大小可以不同  void swap(hash_map& __hs) { _M_ht.swap(__hs._M_ht); }#ifdef __STL_MEMBER_TEMPLATES  template <class _K1, class _T1, class _HF, class _EqK, class _Al>  friend bool operator== (const hash_map<_K1, _T1, _HF, _EqK, _Al>&,                          const hash_map<_K1, _T1, _HF, _EqK, _Al>&);#else /* __STL_MEMBER_TEMPLATES */  friend bool __STD_QUALIFIER  operator== __STL_NULL_TMPL_ARGS (const hash_map&, const hash_map&);#endif /* __STL_MEMBER_TEMPLATES */  iterator begin() { return _M_ht.begin(); }  iterator end() { return _M_ht.end(); }  const_iterator begin() const { return _M_ht.begin(); }  const_iterator end() const { return _M_ht.end(); }public://插入元素/*(1)pair<iterator,bool> insert ( const value_type& val );(2)template <class InputIterator>void insert ( InputIterator first, InputIterator last );*///不允许有重复的键值//返回pair第二个参数second若为true则插入成功  pair<iterator,bool> insert(const value_type& __obj)    { return _M_ht.insert_unique(__obj); }//调用hash table的insert_unique()函数#ifdef __STL_MEMBER_TEMPLATES  template <class _InputIterator>  void insert(_InputIterator __f, _InputIterator __l)    { _M_ht.insert_unique(__f,__l); }#else  void insert(const value_type* __f, const value_type* __l) {    _M_ht.insert_unique(__f,__l);  }  void insert(const_iterator __f, const_iterator __l)    { _M_ht.insert_unique(__f, __l); }#endif /*__STL_MEMBER_TEMPLATES */  pair<iterator,bool> insert_noresize(const value_type& __obj)    { return _M_ht.insert_unique_noresize(__obj); }      //Searches the container for an element with k as key and returns an iterator to it if found,   //otherwise it returns an iterator to hash_map::end   iterator find(const key_type& __key) { return _M_ht.find(__key); }  const_iterator find(const key_type& __key) const     { return _M_ht.find(__key); }  //If k matches the key of an element in the container, the function returns a reference to its mapped value.  _Tp& operator[](const key_type& __key) {    return _M_ht.find_or_insert(value_type(__key, _Tp())).second;  }  //Searches the container for elements whose key is k and returns the number of elements found.   //由于不存在重复的键值,所以返回的个数最多为1个  size_type count(const key_type& __key) const { return _M_ht.count(__key); }   //Returns the bounds of a range that includes all the elements in the container with a key that compares equal to k  //由于不存在重复的键值,所以返回的元素最多为1个  pair<iterator, iterator> equal_range(const key_type& __key)    { return _M_ht.equal_range(__key); }  pair<const_iterator, const_iterator>  equal_range(const key_type& __key) const    { return _M_ht.equal_range(__key); }  //删除元素  /*by position (1)iterator erase ( const_iterator position );by key (2)size_type erase ( const key_type& k );range (3)iterator erase ( const_iterator first, const_iterator last );  */  //擦除指定键值的元素，并返回擦除的个数  //因为键值唯一,则该键值的元素最多为1个  size_type erase(const key_type& __key) {return _M_ht.erase(__key); }  //擦除指定位置的元素  void erase(iterator __it) { _M_ht.erase(__it); }  //擦除指定范围的元素  void erase(iterator __f, iterator __l) { _M_ht.erase(__f, __l); }  //清空hash_map容器  void clear() { _M_ht.clear(); }  //调整hash_set容器的容量  void resize(size_type __hint) { _M_ht.resize(__hint); }  //Returns the number of buckets in the hash_map container.  size_type bucket_count() const { return _M_ht.bucket_count(); }  //Returns the maximum number of buckets that the hash_map container can have.  size_type max_bucket_count() const { return _M_ht.max_bucket_count(); }  //Returns the number of elements in bucket n  size_type elems_in_bucket(size_type __n) const    { return _M_ht.elems_in_bucket(__n); }//返回指定桶子键值key中list链表的元素个数};template <class _Key, class _Tp, class _HashFcn, class _EqlKey, class _Alloc>inline bool operator==(const hash_map<_Key,_Tp,_HashFcn,_EqlKey,_Alloc>& __hm1,           const hash_map<_Key,_Tp,_HashFcn,_EqlKey,_Alloc>& __hm2){  return __hm1._M_ht == __hm2._M_ht;}#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDERtemplate <class _Key, class _Tp, class _HashFcn, class _EqlKey, class _Alloc>inline bool operator!=(const hash_map<_Key,_Tp,_HashFcn,_EqlKey,_Alloc>& __hm1,           const hash_map<_Key,_Tp,_HashFcn,_EqlKey,_Alloc>& __hm2) {  return !(__hm1 == __hm2);}//交换两个hash_map容器的内容template <class _Key, class _Tp, class _HashFcn, class _EqlKey, class _Alloc>inline void swap(hash_map<_Key,_Tp,_HashFcn,_EqlKey,_Alloc>& __hm1,     hash_map<_Key,_Tp,_HashFcn,_EqlKey,_Alloc>& __hm2){  __hm1.swap(__hm2);}#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */

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《STL源码剖析》侯捷