Defined in header
<unordered_set> | ||
---|---|---|
template< class Key, class Hash = std::hash<Key>, class KeyEqual = std::equal_to<Key>, class Allocator = std::allocator<Key> > class unordered_set; | (1) | (since C++11) |
namespace pmr { template <class Key, class Hash = std::hash<Key>, class Pred = std::equal_to<Key>> using unordered_set = std::unordered_set<Key, Hash, Pred, std::polymorphic_allocator<Key>>; } | (2) | (since C++17) |
Unordered set is an associative container that contains a set of 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 a hash is computed, it refers to the exact bucket the element is placed into.
Container elements may not be modified (even by non const iterators) since modification could change an element's hash and corrupt the container.
std::unordered_set
meets the requirements of Container
, AllocatorAwareContainer
, UnorderedAssociativeContainer
.
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 forward iterator |
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 | a specialization of node handle representing a container node (since C++17) |
insert_return_type | type describing the result of inserting a node_type in a container of type X with at least three non-static public data members: bool inserted; X::iterator position; , X::node_type node; . This type is MoveConstructible , MoveAssignable , DefaultConstructible , Destructible , and Swappable (since C++17) |
constructs the unordered_set (public member function) |
|
destructs the unordered_set (public member function) |
|
assigns values to the container (public member function) |
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returns the associated allocator (public member function) |
|
Iterators |
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returns an iterator to the beginning (public member function) |
|
returns an iterator to the end (public member function) |
|
Capacity |
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checks whether the container is empty (public member function) |
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returns the number of elements (public member function) |
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returns the maximum possible number of elements (public member function) |
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Modifiers |
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clears the contents (public member function) |
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inserts elements or nodes (since C++17) (public member function) |
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constructs element in-place (public member function) |
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constructs elements in-place using a hint (public member function) |
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erases elements (public member function) |
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swaps the contents (public member function) |
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(C++17)
| extracts nodes from the container (public member function) |
(C++17)
| splices nodes from another container (public member function) |
Lookup |
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returns the number of elements matching specific key (public member function) |
|
finds element with specific key (public member function) |
|
returns range of elements matching a specific key (public member function) |
|
Bucket interface |
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returns an iterator to the beginning of the specified bucket (public member function) |
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returns an iterator to the end of the specified bucket (public member function) |
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returns the number of buckets (public member function) |
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returns the maximum number of buckets (public member function) |
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returns the number of elements in specific bucket (public member function) |
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returns the bucket for specific key (public member function) |
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Hash policy |
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returns average number of elements per bucket (public member function) |
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manages maximum average number of elements per bucket (public member function) |
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reserves at least the specified number of buckets. This regenerates the hash table. (public member function) |
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reserves space for at least the specified number of elements. This regenerates the hash table. (public member function) |
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Observers |
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returns function used to hash the keys (public member function) |
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returns the function used to compare keys for equality (public member function) |
compares the values in the unordered_set (function template) |
|
(C++11)
| specializes the std::swap algorithm (function template) |
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.
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