std::unordered_set::emplace

 

C++

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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::erase

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

Lookup

unordered_set::count

unordered_set::find

unordered_set::equal_range

Bucket interface

unordered_set::begin2

unordered_set::end2

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

 

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

Inserts a new element into the container by constructing it 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)....

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 equal to or 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 a bool denoting whether the insertion took place and an iterator to the inserted element, or the already-existing element if no insertion happened.

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 (public member function)