std::unordered_multiset
| Defined in header <unordered_set>
|
||
| template< class Key, |
(1) | (since C++11) |
| namespace pmr { template <class Key, |
(2) | (since C++17) |
Unordered multiset is an associative container that contains set of possibly non-unique objects of type Key. Search, insertion, and removal have average constant-time complexity.
Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its value. This allows fast access to individual elements, since once hash is computed, it refers to the exact bucket the element is placed into.
The iteration order of this container is not required to be stable (so, for example, std::equal cannot be used to compare two std::unordered_multisets), except that every group of elements whose keys compare equivalent (compare equal with key_eq() as the comparator) forms a contiguous subrange in the iteration order, also accessible with equal_range().
std::unordered_multiset meets the requirements of Container, AllocatorAwareContainer, UnorderedAssociativeContainer.
Member types
| Member type | Definition |
key_type
|
Key |
value_type
|
Key |
size_type
|
Unsigned integer type (usually std::size_t) |
difference_type
|
Signed integer type (usually std::ptrdiff_t) |
hasher
|
Hash |
key_equal
|
KeyEqual |
allocator_type
|
Allocator |
reference
|
value_type& |
const_reference
|
const value_type& |
pointer
|
std::allocator_traits<Allocator>::pointer |
const_pointer
|
std::allocator_traits<Allocator>::const_pointer |
iterator
|
Constant ForwardIterator |
const_iterator
|
Constant ForwardIterator |
local_iterator
|
An iterator type whose category, value, difference, pointer and reference types are the same as iterator. This iteratorcan be used to iterate through a single bucket but not across buckets |
const_local_iterator
|
An iterator type whose category, value, difference, pointer and reference types are the same as const_iterator. This iteratorcan be used to iterate through a single bucket but not across buckets |
node_type(since C++17)
|
a specialization of node handle representing a container node |
Member functions
constructs the unordered_multiset (public member function) | |
destructs the unordered_multiset (public member function) | |
| assigns values to the container (public member function) | |
| returns the associated allocator (public member function) | |
Iterators | |
| returns an iterator to the beginning (public member function) | |
| returns an iterator to the end (public member function) | |
Capacity | |
| checks whether the container is empty (public member function) | |
| returns the number of elements (public member function) | |
| returns the maximum possible number of elements (public member function) | |
Modifiers | |
| clears the contents (public member function) | |
| inserts elements or nodes (since C++17) (public member function) | |
| constructs element in-place (public member function) | |
| constructs elements in-place using a hint (public member function) | |
| erases elements (public member function) | |
| swaps the contents (public member function) | |
| (C++17) |
extracts nodes from the container (public member function) |
| (C++17) |
splices nodes from another container (public member function) |
Lookup | |
| returns the number of elements matching specific key (public member function) | |
| finds element with specific key (public member function) | |
| (C++20) |
checks if the container contains element with specific key (public member function) |
| returns range of elements matching a specific key (public member function) | |
Bucket interface | |
| returns an iterator to the beginning of the specified bucket (public member function) | |
| returns an iterator to the end of the specified bucket (public member function) | |
| returns the number of buckets (public member function) | |
| returns the maximum number of buckets (public member function) | |
| returns the number of elements in specific bucket (public member function) | |
| returns the bucket for specific key (public member function) | |
Hash policy | |
| returns average number of elements per bucket (public member function) | |
| manages maximum average number of elements per bucket (public member function) | |
| reserves at least the specified number of buckets. This regenerates the hash table. (public member function) | |
| reserves space for at least the specified number of elements. This regenerates the hash table. (public member function) | |
Observers | |
| returns function used to hash the keys (public member function) | |
| returns the function used to compare keys for equality (public member function) | |
Non-member functions
| compares the values in the unordered_multiset (function template) | |
| specializes the std::swap algorithm (function template) |
Deduction guides(since C++17)
Notes
The member types iterator and const_iterator may be aliases to the same type. Since iterator is convertible to const_iterator, const_iterator should be used in function parameter lists to avoid violations of the One Definition Rule.