C++ Unordered_map::bucket() Function

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The C++ function unordered_map::bucket() function 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. Valid range of buckets is from 0 to bucket_count - 1.

Syntax

Following is the Syntax of std::unordered_map::bucket() function.

 size_type bucket(const key_type& k) const; 

Parameters

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

Return value

Returns the unsigned integral type that is the order number of the bucket corresponding to key k.

Example 1

Following is the example, where we are going to demonstrate the usage of unordered_map::bucket() function.

 #include <iostream> #include <unordered_map> using namespace std; int main(void){ unordered_map<char, int> um = { {'a', 1}, {'b', 2}, {'c', 3}, {'d', 4}, {'e', 5} }; for (auto it = um.begin(); it != um.end(); ++it) { cout << "Element " << "[" << it->first << " : "<< it->second << "] " << "is in "<< um.bucket(it->first) << " bucket." << endl; } return 0; } 

Output

Following is the output of the above code −

 Element [e : 5] is in 3 bucket. Element [d : 4] is in 2 bucket. Element [c : 3] is in 1 bucket. Element [b : 2] is in 0 bucket. Element [a : 1] is in 6 bucket. 

Example 2

In the following example, we are creating an unordered_map that stores the only string value and counting the number of buckets assigned to each name in the current unordered_map.

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

Output

Following is the output of the above code −

 Element [Sarika : Banaras] is in 9 bucket. Element [Revathi : Wrangle] is in 10 bucket. Element [Akash : Daltonganj] is in 5 bucket. Element [Vivek : Kanpur] is in 4 bucket. Element [Aman : Ranchi] is in 8 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_map.

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

Output

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

 The bucket number of key Sarika is 9