std::unordered_set<Key,Hash,KeyEqual,Allocator>::extract

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

span (C++20)

 

std::unordered_set

Member functions

unordered_set::unordered_set

unordered_set::~unordered_set

unordered_set::operator=

unordered_set::get_allocator

Iterators

unordered_set::beginunordered_set::cbegin

unordered_set::endunordered_set::cend

Capacity

unordered_set::empty

unordered_set::size

unordered_set::max_size

Modifiers

unordered_set::clear

unordered_set::insert

unordered_set::emplace

unordered_set::emplace_hint

unordered_set::erase

unordered_set::swap

unordered_set::extract (C++17)

unordered_set::merge (C++17)

Lookup

unordered_set::count

unordered_set::find

unordered_set::contains (C++20)

unordered_set::equal_range

Bucket interface

unordered_set::begin(size_type)unordered_set::cbegin(size_type)

unordered_set::end(size_type)unordered_set::cend(size_type)

unordered_set::bucket_count

unordered_set::max_bucket_count

unordered_set::bucket_size

unordered_set::bucket

Hash policy

unordered_set::load_factor

unordered_set::max_load_factor

unordered_set::rehash

unordered_set::reserve

Observers

unordered_set::hash_function

unordered_set::key_eq

Deduction guides(C++17)

 

node_type extract( const_iterator position );	(1)	(since C++17)
node_type extract( const key_type& x );	(2)	(since C++17)

1) Unlinks the node that contains the element pointed to by position and returns a node handle that owns it

2) If the container has an element with key equivalent to x, unlinks the node that contains that element from the container and returns a node handle that owns it. Otherwise, returns an empty node handle.

In either case, no elements are copied or moved, only the internal pointers of the container nodes are repointed

Extracting a node invalidates only the iterators to the extracted element, and preserves the relative order of the elements that are not erased. Pointers and references to the extracted element remain valid, but cannot be used while element is owned by a node handle: they become usable if the element is inserted into a container.

Parameters

position	-	a valid iterator into this container
x	-	a key to identify the node to be extracted

Return value

A node handle that owns the extracted element, or empty node handle in case the element is not found in overload (2)

Complexity

1,2) Average case O(1), worst case O(a.size()).

Notes

extract is the only way to take a move-only object out of a set

set<move_only_type> s;
s.emplace(...);
move_only_type mot = move(s.extract(s.begin()).value());

See also

merge (C++17)	splices nodes from another container (public member function)
insert	inserts elements or nodes (since C++17) (public member function)
erase	erases elements (public member function)