std::unordered_map::emplace

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

Inserts a new element to the container. The element is constructed in-place, i.e. no copy or move operations are performed. The constructor of the element type (value_type) is called as follows: the first argument is used to construct the key, the rest of the arguments are used to construct the value.

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 higher than max_load_factor()*bucket_count().

Contents

[edit] Parameters

args - arguments to forward to the constructor of the element

[edit] Return value

returns a pair consisting of a bool denoting whether the insertion took place and an iterator to the inserted element.

[edit] Complexity

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

[edit] See also

constructs elements in-place using a hint
(public member function)
inserts elements
(public member function)