[#bsl-unordered_map-02b]
= xref:bsl.adoc[bsl]::unordered_map
:relfileprefix: ../
:mrdocs:

Unordered associative container mapping unique keys to values.

== Synopsis

Declared in `<bslstl_unorderedmap.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class KEY,
    class VALUE,
    class HASH = xref:bsl/hash-06.adoc[bsl::hash<KEY>],
    class EQUAL = xref:bsl/equal_to-0d.adoc[bsl::equal_to<KEY>],
    class ALLOCATOR = xref:bsl/allocator-0df.adoc[bsl::allocator<bsl::pair<KEY const, VALUE>>]>
class unordered_map;
----

== Description

This class template implements a value‐semantic container type holding an unordered set of `KEY‐VALUE` pairs having unique keys that provide a mapping from keys (of template parameter type `KEY`) to their associated mapped values (of template parameter type `VALUE`).

This class: * supports a complete set of _value‐semantic_ operations * is _exception‐neutral_ (agnostic except for the `at` method) * is _alias‐safe_ * is `const` _thread‐safe_ For terminology see {`bsldoc_glossary`}.

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_map-02b/allocator_type.adoc[`allocator_type`] 
| This `typedef` is an alias to the (template parameter) `ALLOCATOR`.
| xref:bsl/unordered_map-02b/const_iterator.adoc[`const_iterator`] 
| This `typedef` is an alias to `HashTableIterator<const value_type>`.
| xref:bsl/unordered_map-02b/const_local_iterator.adoc[`const_local_iterator`] 
| This `typedef` is an alias to `HashTableBucketIterator<const value_type>`.
| xref:bsl/unordered_map-02b/const_pointer.adoc[`const_pointer`] 
| This `typedef` is an alias to `AllocatorTraits::const_pointer`.
| xref:bsl/unordered_map-02b/const_reference.adoc[`const_reference`] 
| This `typedef` is an alias to `const value_type&`.
| xref:bsl/unordered_map-02b/difference_type.adoc[`difference_type`] 
| This `typedef` is an alias to `AllocatorTraits::difference_type`.
| xref:bsl/unordered_map-02b/hasher.adoc[`hasher`] 
| This `typedef` is an alias to the (template parameter) `HASH`.
| xref:bsl/unordered_map-02b/iterator.adoc[`iterator`] 
| This `typedef` is an alias to `HashTableIterator<value_type>`.
| xref:bsl/unordered_map-02b/key_equal.adoc[`key_equal`] 
| This `typedef` is an alias to the (template parameter) `EQUAL`.
| xref:bsl/unordered_map-02b/key_type.adoc[`key_type`] 
| This `typedef` is an alias to the (template parameter) `KEY`.
| xref:bsl/unordered_map-02b/local_iterator.adoc[`local_iterator`] 
| This `typedef` is an alias to `HashTableBucketIterator<value_type>`.
| xref:bsl/unordered_map-02b/mapped_type.adoc[`mapped_type`] 
| This `typedef` is an alias to the (template parameter) `VALUE`.
| xref:bsl/unordered_map-02b/pointer.adoc[`pointer`] 
| This `typedef` is an alias to `AllocatorTraits::pointer`.
| xref:bsl/unordered_map-02b/reference.adoc[`reference`] 
| This `typedef` is an alias to `value_type&`.
| xref:bsl/unordered_map-02b/size_type.adoc[`size_type`] 
| This `typedef` is an alias to `AllocatorTraits::size_type`.
| xref:bsl/unordered_map-02b/value_type.adoc[`value_type`] 
| This `typedef` is an alias to `bsl::pair<const KEY, VALUE>`.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_map-02b/2constructor-0f0.adoc[`unordered_map`]         [.small]#[constructor]#
| Constructors
| xref:bsl/unordered_map-02b/2destructor.adoc[`~unordered_map`] [.small]#[destructor]#
| Destroy this object and each of its elements.
| xref:bsl/unordered_map-02b/operator_assign-08.adoc[`operator=`] 
| Assignment operators
| xref:bsl/unordered_map-02b/at-0f.adoc[`at`] 
| `at` overloads
| xref:bsl/unordered_map-02b/begin-0a.adoc[`begin`] 
| `begin` overloads
| xref:bsl/unordered_map-02b/bucket-02.adoc[`bucket`] 
| `bucket` overloads
| xref:bsl/unordered_map-02b/bucket_count.adoc[`bucket_count`] 
| Return the number of buckets in the array of buckets maintained by this unordered map.
| xref:bsl/unordered_map-02b/bucket_size.adoc[`bucket_size`] 
| Return the number of elements in the bucket at `index`.
| xref:bsl/unordered_map-02b/cbegin-03.adoc[`cbegin`] 
| `cbegin` overloads
| xref:bsl/unordered_map-02b/cend-09.adoc[`cend`] 
| `cend` overloads
| xref:bsl/unordered_map-02b/clear.adoc[`clear`] 
| Remove all entries from this unordered map.
| xref:bsl/unordered_map-02b/contains-0a.adoc[`contains`] 
| `contains` overloads
| xref:bsl/unordered_map-02b/count-08.adoc[`count`] 
| `count` overloads
| xref:bsl/unordered_map-02b/emplace.adoc[`emplace`] 
| Emplace a newly constructed element if its key is not already present.
| xref:bsl/unordered_map-02b/emplace_hint.adoc[`emplace_hint`] 
| Emplace a newly constructed element at `hint` if its key is missing.
| xref:bsl/unordered_map-02b/empty.adoc[`empty`] 
| Return `true` if this unordered map contains no elements, and `false` otherwise.
| xref:bsl/unordered_map-02b/end-07c.adoc[`end`] 
| `end` overloads
| xref:bsl/unordered_map-02b/equal_range-05.adoc[`equal_range`] 
| `equal_range` overloads
| xref:bsl/unordered_map-02b/erase-000.adoc[`erase`] 
| `erase` overloads
| xref:bsl/unordered_map-02b/find-0a.adoc[`find`] 
| `find` overloads
| xref:bsl/unordered_map-02b/get_allocator.adoc[`get_allocator`] 
| Return (a copy of) the allocator used for memory allocation by this unordered map.
| xref:bsl/unordered_map-02b/hash_function.adoc[`hash_function`] 
| Return (a copy of) the unary hash functor used by this unordered map to generate a hash value (of type `size_type`) for a `key_type` object.
| xref:bsl/unordered_map-02b/insert-03.adoc[`insert`] 
| `insert` overloads
| xref:bsl/unordered_map-02b/insert_or_assign-068.adoc[`insert_or_assign`] 
| `insert_or_assign` overloads
| xref:bsl/unordered_map-02b/insert_range.adoc[`insert_range`] 
| Insert each element of `range` whose key is not already present.
| xref:bsl/unordered_map-02b/key_eq.adoc[`key_eq`] 
| Return (a copy of) binary the key‐equality functor used by this unordered map that returns `true` if two `key_type` objects are equivalent, and `false` otherwise.
| xref:bsl/unordered_map-02b/load_factor.adoc[`load_factor`] 
| Return the current load factor of this unordered map.
| xref:bsl/unordered_map-02b/max_bucket_count.adoc[`max_bucket_count`] 
| Return a theoretical upper bound on the number of buckets.
| xref:bsl/unordered_map-02b/max_load_factor-0a.adoc[`max_load_factor`] 
| `max_load_factor` overloads
| xref:bsl/unordered_map-02b/max_size.adoc[`max_size`] 
| Return a theoretical upper bound on the size of this unordered map.
| xref:bsl/unordered_map-02b/operator_subs-01.adoc[`operator[]`] 
| Subscript operators
| xref:bsl/unordered_map-02b/rehash.adoc[`rehash`] 
| Rehash this unordered map to at least `numBuckets` buckets.
| xref:bsl/unordered_map-02b/reserve.adoc[`reserve`] 
| Reserve capacity for at least `numElements` without rehashing.
| xref:bsl/unordered_map-02b/size.adoc[`size`] 
| Return the number of elements in this unordered map.
| xref:bsl/unordered_map-02b/swap.adoc[`swap`] 
| Exchange the contents of this object with those of `other`.
| xref:bsl/unordered_map-02b/try_emplace-050.adoc[`try_emplace`] 
| `try_emplace` overloads
|===


== Deduction Guides

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_map-049.adoc[`unordered_map<KEY, VALUE>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-0c.adoc[`unordered_map<KEY, VALUE>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-0d.adoc[`unordered_map<KEY, VALUE>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-099.adoc[`unordered_map<KEY, VALUE>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-08b.adoc[`unordered_map<KEY, VALUE, HASH>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-045.adoc[`unordered_map<KEY, VALUE, HASH>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-0b4.adoc[`unordered_map<KEY, VALUE, HASH, EQUAL>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-01f.adoc[`unordered_map<KEY, VALUE, HASH, EQUAL>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-014.adoc[`unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-0ea.adoc[`unordered_map<KEY, VALUE, HASH, EQUAL, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-05d.adoc[`unordered_map<KEY, VALUE, HASH, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-0e6.adoc[`unordered_map<KEY, VALUE, HASH, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-021.adoc[`unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-09a.adoc[`unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from initializer_list `value_type`.
| xref:bsl/unordered_map-051.adoc[`unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
| xref:bsl/unordered_map-080.adoc[`unordered_map<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` and `VALUE` from iterator `value_type`.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/operator_eq-0cb.adoc[bsl::operator==]`
| Return `true` if `lhs` and `rhs` have the same value, and `false` otherwise.
|===

== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/erase_if-0a4.adoc[`erase_if`]
| Erase every element of `m` that satisfies `predicate`.
| xref:bsl/operator_eq-024.adoc[`operator==`]
| Return `true` if `lhs` and `rhs` have the same value, and `false` otherwise.
| xref:bsl/swap-04c.adoc[`swap`]
| Exchange the contents of `a` with those of `b`.
|===


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