C++ Unordered_multimap::bucket() Function

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The C++ std::unordered_multimap::bucket() function is used to returns the bucket number where element with key k is located.

Bucket is a memory space in the container's hash table to which elements are assigned based on the hash value of their key. The size of the bucket is in the range of 0 to bucket_count-1.

Syntax

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

 size_type bucket(const Key& keyval) const; 

Parameters

• k − It indicates the key whose bucket is to be located.

Return value

This function returns the unsigned integral type that is the order number of the bucket corresponding to key.

Example 1

In the following example let's see the usage of unordered_multimap::bucket() 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} }; cout << "Unordered multimap contains following elements" << endl; for (auto it = umm.begin(); it != umm.end(); ++it) { cout << "Element " << "[" << it->first << " : "<< it->second << "] " << "is in " << umm.bucket(it->first) << " bucket." << endl; } return 0; } 

Output

Let us compile and run the above program, this will produce the following result −

 Unordered multi-map contains following elements Element [e : 5] is in 1 bucket. Element [d : 4] is in 0 bucket. Element [c : 3] is in 4 bucket. Element [b : 2] is in 3 bucket. Element [a : 1] is in 2 bucket. 

Example 2

Let's look at the following example, where we are going to create a unordered_multimap that stores the string values and applying the bucket() function to count the number of buckets assigned to each other.

 #include <iostream> #include <unordered_map> using namespace std; int main(void) { unordered_multimap<string, string> umm = { {"Aman", "Ranchi"}, {"Vivek", "Kanpur"}, {"Akash", "Daltonganj"}, {"Aman", "Ranchi"}, {"Vivek", "Kanpur"}, }; for (auto it = umm.begin(); it != umm.end(); ++it) { cout << "Element " << "[" << it->first << " : " << it->second << "] " << "is in " << umm.bucket(it->first) << " bucket." << endl; } return 0; } 

Output

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

 Element [Akash : Daltonganj] is in 4 bucket. Element [Vivek : Kanpur] is in 4 bucket. Element [Vivek : Kanpur] is in 4 bucket. Element [Aman : Ranchi] is in 3 bucket. Element [Aman : Ranchi] is in 3 bucket. 

Example 3

Consider the following example, where we are going to displaying the number of buckets of the iteration pointing to the first element of the container from unordered_multimap.

 #include <iostream> #include <unordered_map> using namespace std; int main(void) { unordered_multimap<string, string> umm = { {"Aman", "Ranchi"}, {"Vivek", "Kanpur"}, {"Akash", "Daltonganj"}, {"Aman", "Ranchi"}, {"Vivek", "Kanpur"}, }; // prints the bucket number of the beginning element auto it = umm.begin(); // stores the bucket number of the key k int number = umm.bucket(it->first); cout << "The bucket number of key " << it->first << " is " << number; return 0; } 

Output

Following is the output of the above code −

 The bucket number of key Akash is 4 

Example 4

Following is the example, where we are going to display the bucket number of the specified key from the current unordered_multimap.

 #include <iostream> #include <unordered_map> using namespace std; int main(void) { unordered_multimap<char, int> umm = { {'A', 1}, {'B', 2}, {'C', 3}, {'A', 1}, {'D', 4}, {'A', 1}, {'E', 5}, {'D', 4}, }; cout<<umm.bucket('A')<<endl; cout<<umm.bucket('D')<<endl; return 0; } 

Output

Output of the above code is as follows −

 10 2