C++ Unordered_set::bucket_size() Function

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The C++ unordered_set::bucket_size() function is used to return the number of elements present in the n the bucket. A bucket is a slot in the unordered_set container's internal hash table to which elements are assigned based on the hash value. Buckets have numbers ranging from 0 to (bucket_count - 1).

Syntax

Following is the syntax of std::unordered_set::bucket_size() function.

size_type bucket_size ( size_type n ) const;

Parameters

• n − It indicates the bucket number that must be less than the bucket_count.

Return Value

This function returns the number of elements in the bucket.

Example 1

Let's look at the following example, where we are going to demonstrte the usage of unordered_set::bucket_size() function.

#include <iostream>
#include <string>
#include <unordered_set>

int main () {
   std::unordered_set<std::string> myUset = { "sai", "ram", "krishna", "prasad", "tutorials", "point" };
   unsigned nbuckets = myUset.bucket_count();

   std::cout << "myset has " << nbuckets << " buckets:\n";
   for (unsigned i = 0; i < nbuckets; ++i) {
      std::cout << "bucket #" << i << " has " << myUset.bucket_size(i) << " elements.\n";
   }
   return 0;
}

Output

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

myset has 13 buckets:
bucket #0 has 0 elements.
bucket #1 has 0 elements.
bucket #2 has 0 elements.
bucket #3 has 1 elements.
bucket #4 has 0 elements.
bucket #5 has 1 elements.
bucket #6 has 0 elements.
bucket #7 has 0 elements.
bucket #8 has 1 elements.
bucket #9 has 2 elements.
bucket #10 has 0 elements.
bucket #11 has 1 elements.
bucket #12 has 0 elements.

Example 2

Consider the following example, where we are going to find the number of elements that specified bucket contains.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<string> myUset = { "sai", "ram", "krishna", "prasad", "tutorials", "point" };
   unsigned nbuckets = myUset.bucket_count();

   cout << "myUset has " << nbuckets << " buckets:\n";
   cout<<"bucket 5 contains: "<<myUset.bucket_size(5);
   return 0;
}

Output

Following is the output of the above code −

myUset has 13 buckets:
bucket 5 contains: 1

Example 3

In the following example, we are going to consider the unordered_set of string type and applying the bucket_size() function to count the number of elements in each bucket and displaying them.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<string> uSet = { "red", "green", "blue", "yellow", "purple", "pink" };

   unsigned nbuckets = uSet.bucket_count();

   cout << "uSet has " << nbuckets << " buckets:\n";

   for (unsigned i=0; i<nbuckets; ++i) {
      cout << "bucket #" << i << " has " << uSet.bucket_size(i) << " elements: ";
      for (auto it = uSet.begin(i); it!=uSet.end(i); ++it)
         cout << "[" << *it<< "] ";
      cout << "\n";
   }

   return 0;
}

Output

Output of the above code is as follows −

uSet has 13 buckets:
bucket #0 has 2 elements: [purple] [red] 
bucket #1 has 0 elements: 
bucket #2 has 1 elements: [blue] 
bucket #3 has 1 elements: [green] 
bucket #4 has 0 elements: 
bucket #5 has 0 elements: 
bucket #6 has 1 elements: [yellow] 
bucket #7 has 0 elements: 
bucket #8 has 0 elements: 
bucket #9 has 0 elements: 
bucket #10 has 1 elements: [pink] 
bucket #11 has 0 elements: 
bucket #12 has 0 elements: