STL源码剖析——关联容器之hash_multiset

浅浅的花香味﹌ 2022-08-12 14:59 130阅读 0赞

## 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：

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