C++ Unordered_multimap::bucket_size() Function

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The C++ std::unordered_multimap::bucket_size() function is used to returns the number of elements presents in the n^th bucket. 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. It has a range from 0 to bucket_count - 1.

Syntax

Following is the syntax of std::unordered_multimap::bucket_size().

size_type bucket_size(size_type n) const;

Parameters

• n − It indicates the bucket number that should be lower than bucket_count.

Return value

This function returns the total number of elements from current bucket.

Example 1

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

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm = {
      {'a', 1},
      {'b', 2},
      {'c', 3},
      {'d', 4},
      {'e', 5}
   };
   for (int i = 0; i < umm.bucket_count(); ++i)
      cout << "Bucket " << i << " contains "<< umm.bucket_size(i) << " elements." << endl;
   return 0;
}

Output

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

Bucket 0 contains 2 elements.
Bucket 1 contains 2 elements.
Bucket 2 contains 0 elements.
Bucket 3 contains 0 elements.
Bucket 4 contains 0 elements.
Bucket 5 contains 0 elements.
Bucket 6 contains 2 elements.

Example 2

Consider the following example, where we are going to use the bucket_size() function to get the count of elements present in each bucket.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm;
   umm.insert({ {'a', 10}, {'b', 20}, {'a', 10}, {'b', 30}, {'c', 40} });
   
   for (int i = 0; i < umm.bucket_count(); ++i)
      cout << "Bucket " << i << " contains "<< umm.bucket_size(i) << " elements." << endl;
   return 0;
}

Output

Following is the output of the above code −

Bucket 0 contains 0 elements.
Bucket 1 contains 0 elements.
Bucket 2 contains 0 elements.
Bucket 3 contains 0 elements.
Bucket 4 contains 0 elements.
Bucket 5 contains 0 elements.
Bucket 6 contains 2 elements.
Bucket 7 contains 2 elements.
Bucket 8 contains 1 elements.
Bucket 9 contains 0 elements.
Bucket 10 contains 0 elements.
Bucket 11 contains 0 elements.
Bucket 12 contains 0 elements.

Example 3

Let's look at the following example, where we are going to use the bucket_size() function.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm;
   umm.insert({ {'a', 10}, {'b', 20}, {'a', 10}, {'b', 30}, {'c', 40} });
   for (int i = 0; i < umm.bucket_count(); ++i){
      if(i%2!=0){
         cout << "Bucket " << i << " contains "<< umm.bucket_size(i) << " elements." << endl;
      }
   }
   return 0;
}

Output

Output of the above code is as follows −

Bucket 1 contains 0 elements.
Bucket 3 contains 0 elements.
Bucket 5 contains 0 elements.
Bucket 7 contains 2 elements.
Bucket 9 contains 0 elements.
Bucket 11 contains 0 elements.