The unordered_set::reserve() method is a builtin function in C++ STL which is used to request capacity change of unordered_set. It sets the number of buckets in the container to contain at least n elements. If n is greater than the current bucket_count multiplied by the max_load_factor, the container’s bucket_count is increased and a rehash is forced. If n is lower than the bucket_count, then the function has no effect on it.
Parameter: The function accepts a single mandatory parameter n which sets the number of buckets in the container (bucket_count) to the most appropriate to contain at least n elements.
Return Value: This function doesn’t returns anything.
Below programs illustrate the unordered_set::reserve() function:
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