[#absl-linked_hash_map]
= xref:absl.adoc[absl]::linked_hash_map
:relfileprefix: ../
:mrdocs:

An insertion‐ordered map.

== Synopsis

Declared in `<absl/container/linked_hash_map.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename Key,
    typename Value,
    typename KeyHash = absl::flat_hash_set<Key>::hasher,
    typename KeyEq = absl::flat_hash_set<Key, KeyHash>::key_equal,
    typename Alloc = std::allocator<std::pair<Key const, Value>>>
class linked_hash_map;
----

== Description

Provides O(1) amortized insertions and lookups, as well as iteration over the map in the insertion order. This class is thread‐compatible, but not exception‐safe. It supports heterogeneous lookups.

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:absl/linked_hash_map/allocator_type.adoc[`allocator_type`] 
| The allocator type.
| xref:absl/linked_hash_map/const_iterator.adoc[`const_iterator`] 
| The const iterator type, iterating in insertion order.
| xref:absl/linked_hash_map/const_pointer.adoc[`const_pointer`] 
| A const pointer to an element.
| xref:absl/linked_hash_map/const_reference.adoc[`const_reference`] 
| A const reference to an element.
| xref:absl/linked_hash_map/const_reverse_iterator.adoc[`const_reverse_iterator`] 
| The const reverse iterator type.
| xref:absl/linked_hash_map/difference_type.adoc[`difference_type`] 
| The signed integer type for iterator differences.
| xref:absl/linked_hash_map/hasher.adoc[`hasher`] 
| The hash function type for keys.
| xref:absl/linked_hash_map/insert_return_type.adoc[`insert_return_type`] 
| The return type of node‐handle insertions.
| xref:absl/linked_hash_map/iterator.adoc[`iterator`] 
| The iterator type, iterating in insertion order.
| xref:absl/linked_hash_map/key_equal.adoc[`key_equal`] 
| The equality comparison type for keys.
| xref:absl/linked_hash_map/key_type.adoc[`key_type`] 
| The key type.
| xref:absl/linked_hash_map/mapped_type.adoc[`mapped_type`] 
| The mapped value type.
| xref:absl/linked_hash_map/node_type.adoc[`node_type`] 
| The node handle type used to extract and reinsert elements.
| xref:absl/linked_hash_map/pointer.adoc[`pointer`] 
| A pointer to an element.
| xref:absl/linked_hash_map/reference.adoc[`reference`] 
| A reference to an element.
| xref:absl/linked_hash_map/reverse_iterator.adoc[`reverse_iterator`] 
| The reverse iterator type.
| xref:absl/linked_hash_map/size_type.adoc[`size_type`] 
| The unsigned integer type for sizes.
| xref:absl/linked_hash_map/value_type.adoc[`value_type`] 
| The stored element type, a key/value pair.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:absl/linked_hash_map/2constructor-031.adoc[`linked_hash_map`]         [.small]#[constructor]#
| Constructors
| xref:absl/linked_hash_map/operator_assign-04.adoc[`operator=`] 
| Assignment operators
| xref:absl/linked_hash_map/at-07.adoc[`at`] 
| `at` overloads
| xref:absl/linked_hash_map/back-0d.adoc[`back`] 
| `back` overloads
| xref:absl/linked_hash_map/begin-06.adoc[`begin`] 
| `begin` overloads
| xref:absl/linked_hash_map/bucket_count.adoc[`bucket_count`] 
| Returns the number of buckets in the underlying hash set.
| xref:absl/linked_hash_map/capacity.adoc[`capacity`] 
| Returns the number of elements the map can hold without rehashing.
| xref:absl/linked_hash_map/cbegin.adoc[`cbegin`] 
| Returns a const iterator to the first element.
| xref:absl/linked_hash_map/cend.adoc[`cend`] 
| Returns a const iterator past the last element.
| xref:absl/linked_hash_map/clear.adoc[`clear`] 
| Removes all elements from the map.
| xref:absl/linked_hash_map/contains.adoc[`contains`] 
| Returns whether the map contains an element with the given key.
| xref:absl/linked_hash_map/count.adoc[`count`] 
| Returns the number of elements with the given key.
| xref:absl/linked_hash_map/crbegin.adoc[`crbegin`] 
| Returns a const reverse iterator to the last element.
| xref:absl/linked_hash_map/crend.adoc[`crend`] 
| Returns a const reverse iterator before the first element.
| xref:absl/linked_hash_map/emplace.adoc[`emplace`] 
| Constructs an element in place if the key is not already present.
| xref:absl/linked_hash_map/emplace_hint.adoc[`emplace_hint`] 
| Constructs an element in place if the key is not present, ignoring the position hint.
| xref:absl/linked_hash_map/empty.adoc[`empty`] 
| Returns whether the map is empty.
| xref:absl/linked_hash_map/end-0f.adoc[`end`] 
| `end` overloads
| xref:absl/linked_hash_map/equal_range-034.adoc[`equal_range`] 
| Returns the range of elements matching the given key.
| xref:absl/linked_hash_map/erase-01.adoc[`erase`] 
| `erase` overloads
| xref:absl/linked_hash_map/extract-01.adoc[`extract`] 
| `extract` overloads
| xref:absl/linked_hash_map/find-04.adoc[`find`] 
| Finds the element with the given key.
| xref:absl/linked_hash_map/front-00.adoc[`front`] 
| `front` overloads
| xref:absl/linked_hash_map/get_allocator.adoc[`get_allocator`] 
| Returns the allocator used by the map.
| xref:absl/linked_hash_map/hash_function.adoc[`hash_function`] 
| Returns the hash function used by the map.
| xref:absl/linked_hash_map/insert-00.adoc[`insert`] 
| `insert` overloads
| xref:absl/linked_hash_map/insert_or_assign-0c.adoc[`insert_or_assign`] 
| `insert_or_assign` overloads
| xref:absl/linked_hash_map/key_eq.adoc[`key_eq`] 
| Returns the key equality comparison used by the map.
| xref:absl/linked_hash_map/load_factor.adoc[`load_factor`] 
| Returns the current load factor of the underlying hash set.
| xref:absl/linked_hash_map/max_size.adoc[`max_size`] 
| Returns the maximum number of elements the map can hold.
| xref:absl/linked_hash_map/merge-03.adoc[`merge`] 
| Merges the elements of another map into this one.
| xref:absl/linked_hash_map/operator_subs-0a.adoc[`operator[]`] 
| Returns a reference to the value mapped to the given key, inserting a default‐constructed value if the key is not present.
| xref:absl/linked_hash_map/pop_back.adoc[`pop_back`] 
| Removes the last element from the map.
| xref:absl/linked_hash_map/pop_front.adoc[`pop_front`] 
| Removes the first element from the map.
| xref:absl/linked_hash_map/rbegin-0a.adoc[`rbegin`] 
| `rbegin` overloads
| xref:absl/linked_hash_map/rehash.adoc[`rehash`] 
| Rehashes the map so it can hold at least `n` elements without rehashing.
| xref:absl/linked_hash_map/rend-0f.adoc[`rend`] 
| `rend` overloads
| xref:absl/linked_hash_map/reserve.adoc[`reserve`] 
| Reserves capacity for at least `n` elements.
| xref:absl/linked_hash_map/size.adoc[`size`] 
| Returns the number of elements in the map.
| xref:absl/linked_hash_map/splice.adoc[`splice`] 
| Moves an element from another map into this one at the given position.
| xref:absl/linked_hash_map/swap.adoc[`swap`] 
| Swaps the contents of this map with another.
| xref:absl/linked_hash_map/try_emplace-0f.adoc[`try_emplace`] 
| `try_emplace` overloads
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:absl/operator_not_eq-069.adoc[absl::operator!=]`
| Returns whether two maps differ in their key/value pairs.
| `xref:absl/operator_eq-040.adoc[absl::operator==]`
| Returns whether two maps contain the same key/value pairs.
|===


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