NAME¶

std::unordered_set::emplace - std::unordered_set::emplace

Synopsis¶

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

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 if insertion happened, false if it did not).

Exceptions¶

If an exception is thrown by any operation, this function has no effect (strong
exception guarantee).

Complexity¶

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

Example¶

This section is incomplete
Reason: no example

See also¶

emplace_hint constructs elements in-place using a hint
(C++11) (public member function)
inserts elements
insert or nodes
(C++11) (since C++17)
(public member function)