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### 前言      hash_multiset和hash_set的区别就像multiset与set的区别一样,hash_multiset的底层机制是基于hash table,它可以存在重复的键值,所以插入函数使用insert_equal(),hash_multiset和hash_set一样,容器的内容不自动排序。本文源码出自SGI STL的<stl_hash_set.h>文件。 ### hash_multiset源码剖析 ~~~ //以下是hash_multiset的定义 /* hash_multiset是基于底层机制为hash table,hash_multiset的元素不会自动排序,其他功能与multiset类似, hash_multiset与hash_set的区别和multiset与set区别一样, hash_multiset的插入函数是hash table的insert_equal() */ template <class _Value, class _HashFcn __STL_DEPENDENT_DEFAULT_TMPL(hash<_Value>), class _EqualKey __STL_DEPENDENT_DEFAULT_TMPL(equal_to<_Value>), class _Alloc = __STL_DEFAULT_ALLOCATOR(_Value) > class hash_multiset; template <class _Val, class _HashFcn, class _EqualKey, class _Alloc> inline bool operator==(const hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs1, const hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs2); template <class _Value, class _HashFcn, class _EqualKey, class _Alloc> class hash_multiset { // requirements: __STL_CLASS_REQUIRES(_Value, _Assignable); __STL_CLASS_UNARY_FUNCTION_CHECK(_HashFcn, size_t, _Value); __STL_CLASS_BINARY_FUNCTION_CHECK(_EqualKey, bool, _Value, _Value); private: //_Identity获取value值,在hash_set中也是键值,_Identity<>定义在<stl_function.h> /* template <class _Arg, class _Result> struct unary_function { typedef _Arg argument_type; typedef _Result result_type; }; template <class _Tp> struct _Identity : public unary_function<_Tp,_Tp> { const _Tp& operator()(const _Tp& __x) const { return __x; } }; */ typedef hashtable<_Value, _Value, _HashFcn, _Identity<_Value>, _EqualKey, _Alloc> _Ht; _Ht _M_ht;//底层机制是hashtable public: typedef typename _Ht::key_type key_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; // 注意: 不能修改hash table内部的元素,reference, pointer, iterator都为const typedef typename _Ht::const_pointer pointer; typedef typename _Ht::const_pointer const_pointer; typedef typename _Ht::const_reference reference; typedef typename _Ht::const_reference const_reference; typedef typename _Ht::const_iterator iterator; typedef typename _Ht::const_iterator const_iterator; typedef typename _Ht::allocator_type allocator_type; //返回hash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: //构造函数和hash_set一样,具体可以参照hash_set的讲解 //唯一的区别就是插入函数是insert_equal() hash_multiset() : _M_ht(100, hasher(), key_equal(), allocator_type()) {} explicit hash_multiset(size_type __n) : _M_ht(__n, hasher(), key_equal(), allocator_type()) {} hash_multiset(size_type __n, const hasher& __hf) : _M_ht(__n, __hf, key_equal(), allocator_type()) {} hash_multiset(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 template <class _InputIterator> hash_multiset(_InputIterator __f, _InputIterator __l) : _M_ht(100, hasher(), key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } template <class _InputIterator> hash_multiset(_InputIterator __f, _InputIterator __l, size_type __n) : _M_ht(__n, hasher(), key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } template <class _InputIterator> hash_multiset(_InputIterator __f, _InputIterator __l, size_type __n, const hasher& __hf) : _M_ht(__n, __hf, key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } template <class _InputIterator> hash_multiset(_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_equal(__f, __l); } #else hash_multiset(const value_type* __f, const value_type* __l) : _M_ht(100, hasher(), key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } hash_multiset(const value_type* __f, const value_type* __l, size_type __n) : _M_ht(__n, hasher(), key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } hash_multiset(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_equal(__f, __l); } hash_multiset(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_equal(__f, __l); } hash_multiset(const_iterator __f, const_iterator __l) : _M_ht(100, hasher(), key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } hash_multiset(const_iterator __f, const_iterator __l, size_type __n) : _M_ht(__n, hasher(), key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } hash_multiset(const_iterator __f, const_iterator __l, size_type __n, const hasher& __hf) : _M_ht(__n, __hf, key_equal(), allocator_type()) { _M_ht.insert_equal(__f, __l); } hash_multiset(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_equal(__f, __l); } #endif /*__STL_MEMBER_TEMPLATES */ public: //Returns the number of elements in the hash_multiset container size_type size() const { return _M_ht.size(); } //Returns the maximum number of elements that the hash_multiset container can hold. size_type max_size() const { return _M_ht.max_size(); } //Returns a bool value indicating whether the hash_multiset container is empty, //i.e. whether its size is 0. bool empty() const { return _M_ht.empty(); } //交换两个hash_multiset的内容 void swap(hash_multiset& hs) { _M_ht.swap(hs._M_ht); } #ifdef __STL_MEMBER_TEMPLATES template <class _Val, class _HF, class _EqK, class _Al> friend bool operator== (const hash_multiset<_Val, _HF, _EqK, _Al>&, const hash_multiset<_Val, _HF, _EqK, _Al>&); #else /* __STL_MEMBER_TEMPLATES */ friend bool __STD_QUALIFIER operator== __STL_NULL_TMPL_ARGS (const hash_multiset&,const hash_multiset&); #endif /* __STL_MEMBER_TEMPLATES */ iterator begin() const { return _M_ht.begin(); } iterator end() const { return _M_ht.end(); } public: //插入元素 /* iterator insert ( const value_type& val ); template <class InputIterator> void insert ( InputIterator first, InputIterator last ); */ iterator insert(const value_type& __obj) { return _M_ht.insert_equal(__obj); } #ifdef __STL_MEMBER_TEMPLATES template <class _InputIterator> void insert(_InputIterator __f, _InputIterator __l) { _M_ht.insert_equal(__f,__l); } #else void insert(const value_type* __f, const value_type* __l) { _M_ht.insert_equal(__f,__l); } void insert(const_iterator __f, const_iterator __l) { _M_ht.insert_equal(__f, __l); } #endif /*__STL_MEMBER_TEMPLATES */ iterator insert_noresize(const value_type& __obj) { return _M_ht.insert_equal_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_multiset::end (the element past the end of the container). iterator find(const key_type& __key) const { return _M_ht.find(__key); } //Searches the container for elements with a value of k and returns the number of elements found 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 that compare equal to k. pair<iterator, 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 ); */ size_type erase(const key_type& __key) {return _M_ht.erase(__key); } void erase(iterator __it) { _M_ht.erase(__it); } void erase(iterator __f, iterator __l) { _M_ht.erase(__f, __l); } //清空容器 void clear() { _M_ht.clear(); } public: void resize(size_type __hint) { _M_ht.resize(__hint); } size_type bucket_count() const { return _M_ht.bucket_count(); } size_type max_bucket_count() const { return _M_ht.max_bucket_count(); } size_type elems_in_bucket(size_type __n) const { return _M_ht.elems_in_bucket(__n); } }; template <class _Val, class _HashFcn, class _EqualKey, class _Alloc> inline bool operator==(const hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs1, const hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs2) { return __hs1._M_ht == __hs2._M_ht; } #ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER template <class _Val, class _HashFcn, class _EqualKey, class _Alloc> inline bool operator!=(const hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs1, const hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs2) { return !(__hs1 == __hs2); } template <class _Val, class _HashFcn, class _EqualKey, class _Alloc> inline void swap(hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs1, hash_multiset<_Val,_HashFcn,_EqualKey,_Alloc>& __hs2) { __hs1.swap(__hs2); } #endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */ ~~~ 参考资料: 《STL源码剖析》侯捷