public member function
<unordered_map>

std::unordered_map::bucket

size_type bucket ( const key_type& k ) const;
Locate element's bucket
Returns the bucket number where the element with key k is located.

A bucket is a slot in the container's internal hash table to which elements are assigned based on the hash value of their key. Buckets are numbered from 0 to (bucket_count-1).

Individual elements in a bucket can be accessed by means of the range iterators returned by unordered_map::begin and unordered_map::end.

Parameters

k
Key whose bucket is to be located.
Member type key_type is the type of the keys for the elements in the container, defined in unordered_map as an alias of its first template parameter (Key).

Return value

The order number of the bucket corresponding to k.

Member type size_type is an unsigned integral type.

Example

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// unordered_map::bucket
#include <iostream>
#include <string>
#include <unordered_map>

int main ()
{
  std::unordered_map<std::string,std::string> mymap = {
    {"us","United States"},
    {"uk","United Kingdom"},
    {"fr","France"},
    {"de","Germany"}
  };

  for (auto& x: mymap) {
    std::cout << "Element [" << x.first << ":" << x.second << "]";
    std::cout << " is in bucket #" << mymap.bucket (x.first) << std::endl;
  }

  return 0;
}


Possible output:
Element [us:United States] is in bucket #1
Element [de:Germany] is in bucket #2
Element [fr:France] is in bucket #2
Element [uk:United Kingdom] is in bucket #4

Complexity

Constant.

Iterator validity

No changes.

See also

unordered_map::find
Get iterator to element (public member function)
unordered_map::bucket_size
Return bucket size (public member type)
unordered_map::bucket_count
Return number of buckets (public member function)

C++