關聯容器之hash_map · STL源碼剖析

### 前言 ? 由于前文介紹的《[散列表](http://blog.csdn.net/chenhanzhun/article/details/39578597)[hashtable](http://blog.csdn.net/chenhanzhun/article/details/39578597)》中，可以知道hash table在查找、刪除和插入節點是常數時間，優于RB-Tree紅黑樹，所以在SGI STL中提供了底層機制基于hash table的hash_map容器，hash_map和map類似，但是不同點是hash_map容器中的元素是沒有排序的，因為hash table沒有提供排序功能。本文源碼出自SGI STL的<stl_hash_map.h>文件。? ? ? ?? ### hash_map源碼剖析 ~~~ #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的底層是基于hash table的，hash table沒有提供排序,所以hash_map容器里面的內容是沒排序的 // 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<>取出鍵值key,_Select1st<>定義在<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;//底層機制以hash table完成 public: //以下的內嵌類型均來是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相關函數 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: //構造函數 //缺省情況使用大小為100,但是實際分配的空間大小為不小于100的最小素數 //只是空的hash_map，不存儲元素節點 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()) {} //指定大小為n，且指定hash函數的hash_map hash_map(size_type __n, const hasher& __hf) : _M_ht(__n, __hf, key_equal(), allocator_type()) {} //指定大小為n，且指定hash函數和鍵值比較函數的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 //不允許有相同的鍵值插入 //用某個范圍的元素初始化hash_map對象 //相當于把某個范圍[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); }//調用hash table的插入函數 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: //以下的函數操作只是調用hash table的成員函數 //返回 hash_map 容器中元素的個數. size_type size() const { return _M_ht.size(); } //返回hash_map容器最大存儲元素的個數. 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(); } //交換兩個存儲相同元素類型的hash_map容器內容,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 ); */ //不允許有重復的鍵值 //返回pair第二個參數second若為true則插入成功 pair<iterator,bool> insert(const value_type& __obj) { return _M_ht.insert_unique(__obj); }//調用hash table的insert_unique()函數 #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. //由于不存在重復的鍵值,所以返回的個數最多為1個 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 //由于不存在重復的鍵值,所以返回的元素最多為1個 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); } //刪除元素 /* 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 ); */ //擦除指定鍵值的元素，并返回擦除的個數 //因為鍵值唯一,則該鍵值的元素最多為1個 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); } //擦除指定范圍的元素 void erase(iterator __f, iterator __l) { _M_ht.erase(__f, __l); } //清空hash_map容器 void clear() { _M_ht.clear(); } //調整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); }//返回指定桶子鍵值key中list鏈表的元素個數 }; 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_ORDER 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 == __hm2); } //交換兩個hash_map容器的內容 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 */ ~~~ 參考資料：《STL源碼剖析》侯捷