[#bsl-unordered_multimap-0b0]
= xref:bsl.adoc[bsl]::unordered_multimap
:relfileprefix: ../
:mrdocs:

Unordered associative container mapping keys to values, allowing duplicates.

== Synopsis

Declared in `<bslstl_unorderedmultimap.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_multimap;
----

== Description

This class template implements a value‐semantic container type holding a collection of (possibly equivalent) keys (of the template parameter type `KEY`), each mapped to their associated values (of another template parameter type `VALUE`).

This class: * supports a complete set of _value‐semantic_ operations

* except for BDEX serialization * 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_multimap-0b0/allocator_type.adoc[`allocator_type`] 
| This `typedef` is an alias for `allocator_type`.
| xref:bsl/unordered_multimap-0b0/const_iterator.adoc[`const_iterator`] 
| This `typedef` is an alias for `const_iterator`.
| xref:bsl/unordered_multimap-0b0/const_local_iterator.adoc[`const_local_iterator`] 
| This `typedef` is an alias for `const_local_iterator`.
| xref:bsl/unordered_multimap-0b0/const_pointer.adoc[`const_pointer`] 
| This `typedef` is an alias to `AllocatorTraits::const_pointer`.
| xref:bsl/unordered_multimap-0b0/const_reference.adoc[`const_reference`] 
| This `typedef` is an alias for `const_reference`.
| xref:bsl/unordered_multimap-0b0/difference_type.adoc[`difference_type`] 
| This `typedef` is an alias for `difference_type`.
| xref:bsl/unordered_multimap-0b0/hasher.adoc[`hasher`] 
| This `typedef` is an alias to the (template parameter) `HASH`.
| xref:bsl/unordered_multimap-0b0/iterator.adoc[`iterator`] 
| This `typedef` is an alias for `iterator`.
| xref:bsl/unordered_multimap-0b0/key_equal.adoc[`key_equal`] 
| This `typedef` is an alias for `key_equal`.
| xref:bsl/unordered_multimap-0b0/key_type.adoc[`key_type`] 
| This `typedef` is an alias for `key_type`.
| xref:bsl/unordered_multimap-0b0/local_iterator.adoc[`local_iterator`] 
| This `typedef` is an alias for `local_iterator`.
| xref:bsl/unordered_multimap-0b0/mapped_type.adoc[`mapped_type`] 
| This `typedef` is an alias for `mapped_type`.
| xref:bsl/unordered_multimap-0b0/pointer.adoc[`pointer`] 
| This `typedef` is an alias for `pointer`.
| xref:bsl/unordered_multimap-0b0/reference.adoc[`reference`] 
| This `typedef` is an alias to `value_type&`.
| xref:bsl/unordered_multimap-0b0/size_type.adoc[`size_type`] 
| This `typedef` is an alias for `size_type`.
| xref:bsl/unordered_multimap-0b0/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_multimap-0b0/2constructor-06.adoc[`unordered_multimap`]         [.small]#[constructor]#
| Constructors
| xref:bsl/unordered_multimap-0b0/2destructor.adoc[`~unordered_multimap`] [.small]#[destructor]#
| Destroy this object.
| xref:bsl/unordered_multimap-0b0/operator_assign-0b.adoc[`operator=`] 
| Assignment operators
| xref:bsl/unordered_multimap-0b0/begin-096.adoc[`begin`] 
| `begin` overloads
| xref:bsl/unordered_multimap-0b0/bucket-00d.adoc[`bucket`] 
| `bucket` overloads
| xref:bsl/unordered_multimap-0b0/bucket_count.adoc[`bucket_count`] 
| Return the number of buckets in the array of buckets maintained by this unordered multimap.
| xref:bsl/unordered_multimap-0b0/bucket_size.adoc[`bucket_size`] 
| Return the number of elements in the bucket at `index`.
| xref:bsl/unordered_multimap-0b0/cbegin-01.adoc[`cbegin`] 
| `cbegin` overloads
| xref:bsl/unordered_multimap-0b0/cend-03.adoc[`cend`] 
| `cend` overloads
| xref:bsl/unordered_multimap-0b0/clear.adoc[`clear`] 
| Remove all entries from this unordered multimap. Note that this object will be empty after this call, but allocated memory may be retained for future use.
| xref:bsl/unordered_multimap-0b0/contains-0e.adoc[`contains`] 
| Return `true` if this container has an element with key equivalent to `key`.
| xref:bsl/unordered_multimap-0b0/count-09.adoc[`count`] 
| Return the number of elements with a key equivalent to `key`.
| xref:bsl/unordered_multimap-0b0/emplace.adoc[`emplace`] 
| Emplace a newly constructed element into this container.
| xref:bsl/unordered_multimap-0b0/emplace_hint.adoc[`emplace_hint`] 
| Emplace a newly constructed element near `hint`.
| xref:bsl/unordered_multimap-0b0/empty.adoc[`empty`] 
| Return `true` if this unordered multimap contains no elements, and `false` otherwise.
| xref:bsl/unordered_multimap-0b0/end-0d.adoc[`end`] 
| `end` overloads
| xref:bsl/unordered_multimap-0b0/equal_range-0c.adoc[`equal_range`] 
| Return an iterator pair covering elements with key equivalent to `key`.
| xref:bsl/unordered_multimap-0b0/erase-0b5.adoc[`erase`] 
| `erase` overloads
| xref:bsl/unordered_multimap-0b0/find-00.adoc[`find`] 
| Return an iterator to the first element with key equivalent to `key`.
| xref:bsl/unordered_multimap-0b0/get_allocator.adoc[`get_allocator`] 
| Return (a copy of) the allocator used for memory allocation by this unordered multimap.
| xref:bsl/unordered_multimap-0b0/hash_function.adoc[`hash_function`] 
| Return (a copy of) the hash unary functor used by this unordered multimap to generate a hash value (of type `size_type`) for a `key_type` object.
| xref:bsl/unordered_multimap-0b0/insert-0a.adoc[`insert`] 
| `insert` overloads
| xref:bsl/unordered_multimap-0b0/insert_range.adoc[`insert_range`] 
| Insert each element from the specified `range`.
| xref:bsl/unordered_multimap-0b0/key_eq.adoc[`key_eq`] 
| Return (a copy of) the key‐equivalence binary functor that returns `true` if the value of two `key_type` objects are equivalent, and `false` otherwise.
| xref:bsl/unordered_multimap-0b0/load_factor.adoc[`load_factor`] 
| Return the current load factor of this container.
| xref:bsl/unordered_multimap-0b0/max_bucket_count.adoc[`max_bucket_count`] 
| Return a theoretical upper bound on the number of buckets.
| xref:bsl/unordered_multimap-0b0/max_load_factor-0f.adoc[`max_load_factor`] 
| `max_load_factor` overloads
| xref:bsl/unordered_multimap-0b0/max_size.adoc[`max_size`] 
| Return a theoretical upper bound on the number of elements.
| xref:bsl/unordered_multimap-0b0/rehash.adoc[`rehash`] 
| Rehash this container to have at least `numBuckets` buckets.
| xref:bsl/unordered_multimap-0b0/reserve.adoc[`reserve`] 
| Reserve capacity for at least `numElements` without rehashing.
| xref:bsl/unordered_multimap-0b0/size.adoc[`size`] 
| Return the number of elements in this unordered multimap.
| xref:bsl/unordered_multimap-0b0/swap.adoc[`swap`] 
| Exchange the contents of this object with those of `other`.
|===


== Deduction Guides

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_multimap-0d8.adoc[`unordered_multimap<KEY, VALUE>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-02.adoc[`unordered_multimap<KEY, VALUE>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-048a.adoc[`unordered_multimap<KEY, VALUE>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-07.adoc[`unordered_multimap<KEY, VALUE>`] 
| Deduce template arguments from iterators with size and `bslma` allocator.
| xref:bsl/unordered_multimap-044.adoc[`unordered_multimap<KEY, VALUE, HASH>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-08f.adoc[`unordered_multimap<KEY, VALUE, HASH>`] 
| Deduce template arguments from a constructor taking a `bslma` allocator.
| xref:bsl/unordered_multimap-00.adoc[`unordered_multimap<KEY, VALUE, HASH, EQUAL>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-06.adoc[`unordered_multimap<KEY, VALUE, HASH, EQUAL>`] 
| Deduce template arguments from a constructor taking a `bslma` allocator.
| xref:bsl/unordered_multimap-0e.adoc[`unordered_multimap<KEY, VALUE, HASH, EQUAL, ALLOCATOR>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-0d6.adoc[`unordered_multimap<KEY, VALUE, HASH, EQUAL, ALLOCATOR>`] 
| Deduce template arguments for an `unordered_multimap` constructor.
| xref:bsl/unordered_multimap-048e.adoc[`unordered_multimap<KEY, VALUE, HASH, bsl::equal_to<KEY>, ALLOCATOR>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-084.adoc[`unordered_multimap<KEY, VALUE, HASH, bsl::equal_to<KEY>, ALLOCATOR>`] 
| Deduce template arguments for an `unordered_multimap` constructor.
| xref:bsl/unordered_multimap-04c.adoc[`unordered_multimap<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-0b8.adoc[`unordered_multimap<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| Deduce template arguments from an initializer‐list constructor.
| xref:bsl/unordered_multimap-0b6.adoc[`unordered_multimap<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| Deduce template arguments for an `unordered_multimap` constructor.
| xref:bsl/unordered_multimap-04e.adoc[`unordered_multimap<KEY, VALUE, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| Deduce template arguments for an `unordered_multimap` constructor.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/operator_eq-068.adoc[bsl::operator==]`
| Return `true` if `lhs` and `rhs` have the same value.
|===

== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/erase_if-0aa.adoc[`erase_if`]
| Erase every element of `m` that satisfies `predicate`.
| xref:bsl/operator_eq-08a.adoc[`operator==`]
| Return `true` if `lhs` and `rhs` have the same value.
| xref:bsl/swap-08c.adoc[`swap`]
| Exchange the value of `a` with that of `b`.
|===


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