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std::unordered_set(3) C++ Standard Libary std::unordered_set(3) NAME std::unordered_set - std::unordered_set Synopsis Defined in header <unordered_set> template< class Key, class Hash = std::hash<Key>, (1) (since C++11) class KeyEqual = std::equal_to<Key>, class Allocator = std::allocator<Key> > class unordered_set; namespace pmr { template <class Key, class Hash = std::hash<Key>, class Pred = std::equal_to<Key>> (2) (since C++17) using unordered_set = std::unordered_set<Key, Hash, Pred, std::pmr::polymorphic_allocator<Key>>; } 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 con- tainer. std::unordered_set meets the requirements of Container, Alloca- torAwareContainer, UnorderedAssociativeContainer. Iterator invalidation Operations Invalidated All read only operations, swap, std::swap Never clear, rehash, reserve, operator= Always insert, emplace, emplace_hint Only if causes rehash erase Only to the element erased Notes * The swap functions do not invalidate any of the iterators inside the container, but they do invalidate the iterator marking the end of the swap region. * References and pointers to data stored in the container are only invalidated by erasing that element, even when the corresponding iterator is invalidated. * After container move assignment, unless elementwise move assign- ment is forced by incompatible allocators, references, pointers, and iterators (other than the end iterator) to moved-from container remain valid, but refer to el- ements that are now in *this. 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<Alloca- tor>::const_pointer iterator Constant LegacyForwardIterator to value_type const_iterator LegacyForwardIterator to const value_type An iterator type whose category, value, difference, pointer and local_iterator reference types are the same as iterator. This iterator can be used to iterate through a single bucket but not across buckets An iterator type whose category, value, difference, pointer and const_local_iterator reference types are the same as const_it- erator. This iterator can be used to iterate through a single bucket but not across buckets node_type (since C++17) a specialization of node handle represent- ing a container node type describing the result of inserting a node_type, a specialization of template <class Iter, class NodeType> insert_return_type (since struct /*unspecified*/ { C++17) Iter position; bool inserted; NodeType node; }; instantiated with template arguments iter- ator and node_type. Member functions constructor constructs the unordered_set (C++11) (public member function) destructor destructs the unordered_set (C++11) (public member function) operator= assigns values to the container (C++11) (public member function) get_allocator returns the associated allocator (C++11) (public member function) Iterators begin returns an iterator to the beginning cbegin (public member function) (C++11) end returns an iterator to the end cend (public member function) (C++11) Capacity empty checks whether the container is empty (C++11) (public member function) size returns the number of elements (C++11) (public member function) max_size returns the maximum possible number of elements (C++11) (public member function) Modifiers clear clears the contents (C++11) (public member function) inserts elements insert or nodes (C++11) (since C++17) (public member function) emplace constructs element in-place (C++11) (public member function) emplace_hint constructs elements in-place using a hint (C++11) (public member function) erase erases elements (C++11) (public member function) swap swaps the contents (C++11) (public member function) extract extracts nodes from the container (C++17) (public member function) merge splices nodes from another container (C++17) (public member function) Lookup count returns the number of elements matching specific key (C++11) (public member function) find finds element with specific key (C++11) (public member function) contains checks if the container contains element with spe- cific key (C++20) (public member function) equal_range returns range of elements matching a specific key (C++11) (public member function) Bucket interface begin(size_type) returns an iterator to the beginning of the speci- fied bucket cbegin(size_type) (public member function) (C++11) end(size_type) returns an iterator to the end of the specified bucket cend(size_type) (public member function) (C++11) bucket_count returns the number of buckets (C++11) (public member function) max_bucket_count returns the maximum number of buckets (C++11) (public member function) bucket_size returns the number of elements in specific bucket (C++11) (public member function) bucket returns the bucket for specific key (C++11) (public member function) Hash policy load_factor returns average number of elements per bucket (C++11) (public member function) max_load_factor manages maximum average number of elements per bucket (C++11) (public member function) rehash reserves at least the specified number of buckets and regenerates (C++11) the hash table (public member function) reserve reserves space for at least the specified number of elements and (C++11) regenerates the hash table (public member function) Observers hash_function returns function used to hash the keys (C++11) (public member function) key_eq returns the function used to compare keys for equality (C++11) (public member function) Non-member functions operator== compares the values in the un- ordered_set operator!= (function template) (removed in C++20) std::swap(std::unordered_set) specializes the std::swap algorithm (C++11) (function template) erase_if(std::unordered_set) Erases all elements satisfying spe- cific criteria (C++20) (function template) Deduction guides(since C++17) Notes The member types iterator and const_iterator may be aliases to the same type. This means defining a pair of function overloads using the two types as parameter types may violate the One Definition Rule. Since iterator is convertible to const_iterator, a single function with a const_iterator as parameter type will work instead. http://cppreference.com 2022.07.31 std::unordered_set(3)
NAME | Synopsis | Notes | Member types | Member functions | Iterators | Capacity | Modifiers | Lookup | Bucket interface | Hash policy | Observers | Non-member functions | Notes
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