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std::unordered_map

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< cpp‎ | container
Revision as of 06:29, 16 October 2013 by Eendy (Talk | contribs)

Defined in header <unordered_map>
template<

    class Key,
    class T,
    class Hash = std::hash<Key>,
    class KeyEqual = std::equal_to<Key>,
    class Allocator = std::allocator< std::pair<const Key, T> >

> class unordered_map;
(since C++11)

Unordered map is an associative container that contains key-value pairs with unique keys. Search, insertion, and removal of elements have average constant-time complexity.

Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its key. This allows fast access to individual elements, since once hash is computed, it refers to the exact bucket the element is placed into.

std::unordered_map meets the requirements of Container, AllocatorAwareContainer, UnorderedAssociativeContainer.

Contents

Member types

Member type Definition
key_type Key [edit]
mapped_type T [edit]
value_type std::pair<const Key, T> [edit]
size_type Unsigned integral type (usually std::size_t) [edit]
difference_type Signed integer type (usually std::ptrdiff_t) [edit]
hasher Hash [edit]
key_equal KeyEqual [edit]
allocator_type Allocator [edit]
reference value_type& [edit]
const_reference const value_type& [edit]
pointer std::allocator_traits<Allocator>::pointer [edit]
const_pointer std::allocator_traits<Allocator>::const_pointer [edit]
iterator ForwardIterator [edit]
const_iterator Constant forward iterator [edit]
local_iterator An iterator type whose category, value, difference, pointer and
reference types are the same as iterator. This iterator
can be used to iterate through a single bucket but not across buckets[edit]
const_local_iterator An iterator type whose category, value, difference, pointer and
reference types are the same as const_iterator. This iterator
can be used to iterate through a single bucket but not across buckets[edit]

Member functions

constructs the unordered_map
(public member function) [edit]
destructs the unordered_map
(public member function) [edit]
assigns values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Iterators
returns an iterator to the beginning
(public member function) [edit]
returns an iterator to the end
(public member function) [edit]
Capacity
checks whether the container is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
returns the maximum possible number of elements
(public member function) [edit]
Modifiers
clears the contents
(public member function) [edit]
inserts elements
(public member function) [edit]
constructs element in-place
(public member function) [edit]
constructs elements in-place using a hint
(public member function) [edit]
erases elements
(public member function) [edit]
swaps the contents
(public member function) [edit]
Lookup
access specified element with bounds checking
(public member function) [edit]
access specified element
(public member function) [edit]
returns the number of elements matching specific key
(public member function) [edit]
finds element with specific key
(public member function) [edit]
returns range of elements matching a specific key
(public member function) [edit]
Bucket interface
returns an iterator to the beginning of the specified bucket
(public member function) [edit]
returns an iterator to the end of the specified bucket
(public member function) [edit]
returns the number of buckets
(public member function) [edit]
returns the maximum number of buckets
(public member function) [edit]
returns the number of elements in specific bucket
(public member function) [edit]
returns the bucket for specific key
(public member function) [edit]
Hash policy
returns average number of elements per bucket
(public member function) [edit]
manages maximum average number of elements per bucket
(public member function) [edit]
reserves at least the specified number of buckets.
This regenerates the hash table.
(public member function) [edit]
reserves space for at least the specified number of elements.
This regenerates the hash table.
(public member function) [edit]
Observers
returns function used to hash the keys
(public member function) [edit]
returns the function used to compare keys for equality
(public member function) [edit]

Non-member functions

compares the values in the unordered_map
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]