### 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
- 前言
- 空间配置器
- Traits编程技术
- STL源码剖析——迭代器
- 全局函数construct(),destroy(),uninitialized_copy(),uninitialized_fill(),uninitialized_fill_n()
- 序列容器之vector
- list容器的排序算法sort()
- 序列容器之list
- 序列容器之deque
- 容器配接器之stack
- 容器配接器之queue
- 容器配接器之priority_queue
- 最大堆heap
- 单向链表slist
- RB-Tree(红黑树)
- 关联容器之set
- stl_pair.h学习
- 关联容器之map
- 关联容器之multiset
- 关联容器之multimap
- 散列表hashtable
- stl_hash_fun.h学习
- 关联容器之hash_set
- 关联容器之hash_multiset
- 关联容器之hash_map
- 关联容器之hash_multimap
- 数值算法stl_numeric.h
- stl_relops.h学习
- 基本算法stl_algobase.h
- STL算法之set集合算法
- STL算法stl_algo.h
- STL算法之sort排序算法
- STL算法之find查找算法
- STL算法之merge合并算法
- STL算法之remove删除算法
- STL算法之permutation排列组合
- STL函数对象