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 container.
   std::unordered_set meets the requirements of Container, AllocatorAwareContainer,
   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 assignment is forced by
       incompatible allocators, references, pointers, and iterators (other than the end
       iterator) to moved-from container remain valid, but refer to elements 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<Allocator>::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_iterator. 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 representing 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 iterator 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 specific 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 specified 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 unordered_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 specific 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.