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Showing content from https://cplusplus.com/reference/unordered_map/unordered_multimap/bucket_count/ below:

public member function

<unordered_map>

size_type bucket_count() const noexcept;

Return number of buckets

A bucket is a slot in the container's internal hash table to which elements are assigned based on the hash value of their key.

The number of buckets influences directly the load factor of the container's hash table (and thus the probability of collision). The container automatically increases the number of buckets to keep the load factor below a specific threshold (its max_load_factor), causing a rehash each time the number of buckets needs to be increased.

Member type size_type is an unsigned integral type.

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// unordered_multimap::bucket_count
#include <iostream>
#include <string>
#include <unordered_map>

int main ()
{
  std::unordered_multimap<std::string,std::string> myumm = {
       {"bed","bedroom"},
       {"oven","kitchen"},
       {"towel","bathroom"},
       {"towel","beach"},
       {"plant","garden"}
  };

  unsigned n = myumm.bucket_count();

  std::cout << "myumm has " << n << " buckets.\n";

  for (unsigned i=0; i<n; ++i) {
    std::cout << "bucket #" << i << " contains: ";
    for (auto it = myumm.begin(i); it!=myumm.end(i); ++it)
      std::cout << "[" << it->first << ":" << it->second << "] ";
    std::cout << "\n";
  }

  return 0;
}

myumm has 5 buckets.
bucket #0 contains: [towel:bathroom] [towel:beach]
bucket #1 contains: [plant:garden]
bucket #2 contains: 
bucket #3 contains: 
bucket #4 contains: [oven:kitchen] [bed:bedroom]

unordered_multimap::bucket

Locate element's bucket (public member function)

unordered_multimap::bucket_size

Return bucket_size (public member type)

unordered_multimap::load_factor

Return load factor (public member function)

unordered_multimap::max_bucket_count

Return maximum number of buckets (public member function)

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