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<unordered_map>

C++11
unordered_map
C++11
unordered_multimap

unordered_map

C++11
unordered_map::~unordered_map
C++11
unordered_map::unordered_map
member functions
- C++11
  unordered_map::at
- C++11
  unordered_map::begin
- C++11
  unordered_map::bucket
- C++11
  unordered_map::bucket_count
- C++11
  unordered_map::bucket_size
- C++11
  unordered_map::cbegin
- C++11
  unordered_map::cend
- C++11
  unordered_map::clear
- C++11
  unordered_map::count
- C++11
  unordered_map::emplace
- C++11
  unordered_map::emplace_hint
- C++11
  unordered_map::empty
- C++11
  unordered_map::end
- C++11
  unordered_map::equal_range
- C++11
  unordered_map::erase
- C++11
  unordered_map::find
- C++11
  unordered_map::get_allocator
- C++11
  unordered_map::hash_function
- C++11
  unordered_map::insert
- C++11
  unordered_map::key_eq
- C++11
  unordered_map::load_factor
- C++11
  unordered_map::max_bucket_count
- C++11
  unordered_map::max_load_factor
- C++11
  unordered_map::max_size
- C++11
  unordered_map::operator[]
- C++11
  unordered_map::operator=
- C++11
  unordered_map::rehash
- C++11
  unordered_map::reserve
- C++11
  unordered_map::size
- C++11
  unordered_map::swap
non-member overloads
- C++11
  operators (unordered_map)
- C++11
  swap (unordered_map)

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

// 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)

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