std::unordered_set::emplace

C++

Language

Headers

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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

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)

template< class... Args > std::pair<iterator,bool> emplace( Args&&... args );		(since C++11)

Inserts a new element into the container constructed in-place with the given args if there is no element with the key in the container.

Careful use of emplace allows the new element to be constructed while avoiding unnecessary copy or move operations. The constructor of the new element is called with exactly the same arguments as supplied to emplace, forwarded via std::forward<Args>(args).... The element may be constructed even if there already is an element with the key in the container, in which case the newly constructed element will be destroyed immediately.

If rehashing occurs due to the insertion, all iterators are invalidated. Otherwise iterators are not affected. References are not invalidated. Rehashing occurs only if the new number of elements is greater than max_load_factor()*bucket_count().

Parameters

args

-

arguments to forward to the constructor of the element

Return value

Returns a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a bool denoting whether the insertion took place. True for Insertion, False for No Insertion.

Exceptions

If an exception is thrown by any operation, this function has no effect.

Complexity

Amortized constant on average, worst case linear in the size of the container.

See also

emplace_hint	constructs elements in-place using a hint (public member function)
insert	inserts elements or nodes (since C++17) (public member function)