5.10 hash_multiset

       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hashtable，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 */