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unordered_map bucket() in C++ STL

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  • Difficulty Level : Medium
  • Last Updated : 11 Jun, 2021
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The unordered_map::bucket() is a built-in STL function in C++ which returns the bucket number where the element with the key k is located in the map. 

size_type bucket(key) 

Parameter: The function accepts one mandatory parameter key which specifies the key whose bucket number is to be returned. 
Return Value: This method returns an unsigned integral type which represents the bucket number of the key k which is passed in the parameter. 
Below program illustrate the unordered_map::bucket() function: 


// CPP program to demonstrate the
// unordered_map::bucket() function
#include <bits/stdc++.h>
using namespace std;
int main()
    // Declaration
    unordered_map<string, string> mymap;
    // Initialisation
    mymap = { { "Australia", "Canberra" },
              { "U.S.", "Washington" },
              { "France", "Paris" } };
    // prints the bucket number of the beginning element
    auto it = mymap.begin();
    // stores the bucket number of the key k
    int number = mymap.bucket(it->first);
    cout << "The bucket number of key " << it->first
                                     << " is " << number;
    return 0;


The bucket number of key France is 3


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