std::unordered_map::reserve

void reserve( size_type count );

Sets the number of buckets to the number needed to accomodate at least count elements without exceeding maximum load factor and rehashes the container, i.e. puts the elements into appropriate buckets considering that total number of buckets has changed. Effectively calls rehash(std::ceil(count / max_load_factor())).

Parameters

Return value

(none).

Complexity

Average case linear in the size of the container, worst case quadratic.

See also