C++ Unordered_multimap::bucket_count() Function

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The C++ std::unordered_multimap::bucket_count() function is used returns the total number of buckets present in unordered_multimap container. 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. They have numbers ranging from 0 to bucket_count - 1.

Syntax

Following is the syntax of std::unordered_multimap::bucket_count() function.

size_type bucket_count() const noexcept;

Parameters

This function does not accepts any parameter.

Return value

This function returns the total number of bucket present in the unordered_multimap.

Example 1

In the following example, let's see the usage of unordered_multimap::bucket_count() function.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm = {
      {'a', 1},
      {'b', 2},
      {'c', 3},
      {'b', 2},
      {'c', 3},
      {'e', 5}
   };
   cout << "Number of buckets = " << umm.bucket_count() << endl;
   return 0;
}

Output

If we run the above code it will generate the following output −

Number of buckets = 7

Example 2

Consider the following example, where we are going to use the bucket_count() to get the total number of buckets and no.of items in each bucket.

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main () {
   unordered_multimap<string, string> UnorderMmap={
      {"Aman","Akash"},
      {"Gautam","Garav"},
      {"Anil","Sunil"},
      {"Raja","Roja"},
      {"Gautam","Garav"},
      {"Anil","Sunil"},
   };
   unsigned n = UnorderMmap.bucket_count();
   cout << "map has " << n << " buckets.\n";

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

Output

Following is the output of the above code −

map has 7 buckets.
bucket #0 contains: 
bucket #1 contains: [Gautam:Garav] [Gautam:Garav] [Aman:Akash] 
bucket #2 contains: 
bucket #3 contains: 
bucket #4 contains: [Anil:Sunil] [Anil:Sunil] 
bucket #5 contains: [Raja:Roja] 
bucket #6 contains: 

Example 3

Let's look at the following example, where we are going to use the unordered_multimap that stores the duplicate key and value, and applying the bucket_count() function to get the total no.of buckets.

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main () {
   unordered_multimap<char, int> UnorderMmap={ {'A', 2}, {'B', 2}, {'A', 1}, {'A', 2}, {'B', 1} };
   unsigned n = UnorderMmap.bucket_count();
   cout << "unordered_multimap has total: " << n << " buckets.\n";
   return 0;
}

Output

Output of the above code is as follows −

unordered_multimap has total: 5 buckets.