unordered_multimap bucket_count() function in C++ STL

The unordered_multimap::bucket_count() is a built-in function in C++ STL which returns the total number of buckets in the unordered_multimap container. A bucket is a slot in the container’s internal hash table to which elements are assigned based on their hash value.

Syntax:

unordered_multimap_name.bucket_count()

Parameters: The function does not accept any parameter.

Return Value: It returns an unsigned integral type which denotes the total count of buckets.

Below programs illustrate the above function:

Program 1:

// C++ program to illustrate the
// unordered_multimap::bucket_count()
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<int, int> sample;

    // inserts key and element
    sample.insert({ 10, 100 });
    sample.insert({ 10, 100 });
    sample.insert({ 20, 200 });
    sample.insert({ 30, 300 });
    sample.insert({ 15, 150 });

    cout << "The total count of buckets: "
         << sample.bucket_count();

    // prints all element bucket wise
    for (int i = 0; i < sample.bucket_count(); i++) {

        cout << "\nBucket " << i << ": ";

        // if bucket is empty
        if (sample.bucket_size(i) == 0)
            cout << "empty";

        for (auto it = sample.cbegin(i);
                  it != sample.cend(i); it++)
            cout << "{" << it->first << ", "
                 << it->second << "}, ";
    }
    return 0;
}

Output:

The total count of buckets: 7
Bucket 0: empty
Bucket 1: {15, 150}, 
Bucket 2: {30, 300}, 
Bucket 3: {10, 100}, {10, 100}, 
Bucket 4: empty
Bucket 5: empty
Bucket 6: {20, 200},

Program 2:

// C++ program to illustrate the
// unordered_multimap::bucket_count()
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<char, char> sample;

    // inserts key and element
    sample.insert({ 'a', 'b' });
    sample.insert({ 'a', 'b' });
    sample.insert({ 'b', 'c' });
    sample.insert({ 'r', 'a' });
    sample.insert({ 'c', 'b' });

    cout << "The total count of buckets: "
         << sample.bucket_count();

    // prints all element bucket wise
    for (int i = 0; i < sample.bucket_count(); i++) {

        cout << "\nBucket " << i << ": ";

        // if bucket is empty
        if (sample.bucket_size(i) == 0)
            cout << "empty";

        for (auto it = sample.cbegin(i);
                    it != sample.cend(i); it++)
            cout << "{" << it->first << ", "
                 << it->second << "}, ";
    }
    return 0;
}

Output:

The total count of buckets: 7
Bucket 0: {b, c}, 
Bucket 1: {c, b}, 
Bucket 2: {r, a}, 
Bucket 3: empty
Bucket 4: empty
Bucket 5: empty
Bucket 6: {a, b}, {a, b},