std::multimap::extract

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators 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

 

std::multimap

Member functions

multimap::multimap

multimap::~multimap

multimap::operator=

multimap::get_allocator

Iterators

multimap::beginmultimap::cbegin (C++11)

multimap::endmultimap::cend (C++11)

multimap::rbeginmultimap::crbegin (C++11)

multimap::rendmultimap::crend (C++11)

Capacity

multimap::erase

multimap::size

multimap::max_size

Modifiers

multimap::clear

multimap::insert

multimap::emplace (C++11)

multimap::emplace_hint (C++11)

multimap::erase

multimap::swap

multimap::extract (C++17)

multimap::merge (C++17)

Lookup

multimap::count

multimap::find

multimap::equal_range

multimap::lower_bound

multimap::upper_bound

Observers

multimap::key_comp

multimap::value_comp

 

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 the first such 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 (rebalancing may occur, as with erase())

Extracting a node invalidates the iterators to the extracted element. 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) amortized constant

2) log(a.size())

Notes

extract is the only way to change a key of a map element without reallocation:

map<int, string> m{{1,”mango”}, {2,”papaya”}, {3,”guava”}};
auto nh = m.extract(2);
nh.key() = 4;
m.insert(move(nh));
// m == {{1,”mango”}, {3,”guava”}, {4,”papaya”}}

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)