[#nlohmann-ordered_map]
= xref:nlohmann.adoc[nlohmann]::ordered_map
:relfileprefix: ../
:mrdocs:

a minimal map‐like container that preserves insertion order

== Synopsis

Declared in `<nlohmann/ordered_map.hpp>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class Key,
    class T,
    class IgnoredLess = std::less<Key>,
    class Allocator = std::allocator<std::pair<Key const, T>>>
struct ordered_map
    : std::vector<std::pair<Key const, T>, Allocator>
----

== Description

ordered_map: a minimal map‐like container that preserves insertion order for use within nlohmann::basic_json<ordered_map>

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `std::vector<std::pair<Key const, T>, Allocator>`
| A standard container which offers fixed time access to  individual elements in any order.
|===

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:nlohmann/ordered_map/Container.adoc[`Container`] 
| the underlying container type used to store the key‐value pairs
| xref:nlohmann/ordered_map/const_iterator.adoc[`const_iterator`] 
| a const iterator over the underlying container
| xref:nlohmann/ordered_map/iterator.adoc[`iterator`] 
| an iterator over the underlying container
| xref:nlohmann/ordered_map/key_compare.adoc[`key_compare`] 
| the comparison function used to determine whether two keys are equal
| xref:nlohmann/ordered_map/key_type.adoc[`key_type`] 
| the type of the keys stored in the map
| xref:nlohmann/ordered_map/mapped_type.adoc[`mapped_type`] 
| the type of the values mapped to each key
| xref:nlohmann/ordered_map/require_input_iter.adoc[`require_input_iter`] 
| helper type that is only defined if _InputIt_ qualifies as an input iterator, used to constrain the iterator‐range overload of xref:nlohmann/ordered_map/insert-0e.adoc[`insert`]
| xref:nlohmann/ordered_map/size_type.adoc[`size_type`] 
| an unsigned integer type used to represent sizes and counts
| xref:nlohmann/ordered_map/value_type.adoc[`value_type`] 
| the type of the key‐value pairs stored in the underlying container
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:nlohmann/ordered_map/2constructor-03.adoc[`ordered_map`]         [.small]#[constructor]#
| Constructors
| xref:nlohmann/ordered_map/2destructor.adoc[`~ordered_map`] [.small]#[destructor]#
| destructor
| xref:nlohmann/ordered_map/operator_assign-05.adoc[`operator=`] 
| Assignment operators
| xref:nlohmann/ordered_map/at-07.adoc[`at`] 
| accesses the element with the given key, with bounds checking
| xref:nlohmann/ordered_map/count-0d.adoc[`count`] 
| returns the number of elements matching the given key
| xref:nlohmann/ordered_map/emplace-01.adoc[`emplace`] 
| inserts a new element constructed from _key_ and _t_ if the key does not already exist
| xref:nlohmann/ordered_map/erase-0f.adoc[`erase`] 
| `erase` overloads
| xref:nlohmann/ordered_map/find-08.adoc[`find`] 
| finds an element with the given key
| xref:nlohmann/ordered_map/insert-0e.adoc[`insert`] 
| `insert` overloads
| xref:nlohmann/ordered_map/operator_subs-0e.adoc[`operator[]`] 
| Subscript operators
|===



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