[#bsl-map-0a7]
= xref:bsl.adoc[bsl]::map
:relfileprefix: ../
:mrdocs:

Ordered associative container mapping unique keys to values.

== Synopsis

Declared in `<bslstl_map.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class KEY,
    class VALUE,
    class COMPARATOR = std::less<KEY>,
    class ALLOCATOR = xref:bsl/allocator-0df.adoc[allocator<pair<KEY const, VALUE>>]>
class map;
----

== Description

This class template implements a value‐semantic container type holding an ordered sequence of key‐value pairs having unique keys that provide a mapping from keys (of the template parameter type, `KEY`) 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_ * is _alias‐safe_ * is `const` _thread‐safe_ For terminology see {`bsldoc_glossary`}.

== Types

[cols="1,4"]
|===
| Name| Description
| xref:bsl/map-0a7/value_compare.adoc[`value_compare`] 
| Adaptor that compares `value_type` objects by their keys.
|===


== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:bsl/map-0a7/allocator_type.adoc[`allocator_type`] 
| Alias for the allocator type `ALLOCATOR`.
| xref:bsl/map-0a7/const_iterator.adoc[`const_iterator`] 
| Constant bidirectional iterator over `map` elements.
| xref:bsl/map-0a7/const_pointer.adoc[`const_pointer`] 
| Alias for the const pointer type supplied by the allocator traits.
| xref:bsl/map-0a7/const_reference.adoc[`const_reference`] 
| Alias for a constant reference to a map element.
| xref:bsl/map-0a7/const_reverse_iterator.adoc[`const_reverse_iterator`] 
| Reverse iterator type for traversing the map in reverse order.
| xref:bsl/map-0a7/difference_type.adoc[`difference_type`] 
| Signed integer type measuring iterator distance.
| xref:bsl/map-0a7/iterator.adoc[`iterator`] 
| Bidirectional iterator over `map` elements.
| xref:bsl/map-0a7/key_compare.adoc[`key_compare`] 
| Alias for the key‐comparison functor type `COMPARATOR`.
| xref:bsl/map-0a7/key_type.adoc[`key_type`] 
| Alias for the key type `KEY`.
| xref:bsl/map-0a7/mapped_type.adoc[`mapped_type`] 
| Alias for the mapped value type `VALUE`.
| xref:bsl/map-0a7/pointer.adoc[`pointer`] 
| Alias for the pointer type supplied by the allocator traits.
| xref:bsl/map-0a7/reference.adoc[`reference`] 
| Alias for a modifiable reference to a map element.
| xref:bsl/map-0a7/reverse_iterator.adoc[`reverse_iterator`] 
| Reverse iterator over `map` elements.
| xref:bsl/map-0a7/size_type.adoc[`size_type`] 
| Alias for the size type supplied by the allocator traits.
| xref:bsl/map-0a7/value_type.adoc[`value_type`] 
| Alias for the map element type `pair<const KEY, VALUE>`.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/map-0a7/2constructor-0bc.adoc[`map`]         [.small]#[constructor]#
| Constructors
| xref:bsl/map-0a7/2destructor.adoc[`~map`] [.small]#[destructor]#
| Destroy this object.
| xref:bsl/map-0a7/operator_assign-0c.adoc[`operator=`] 
| Assignment operators
| xref:bsl/map-0a7/at-0a.adoc[`at`] 
| `at` overloads
| xref:bsl/map-0a7/begin-0f.adoc[`begin`] 
| `begin` overloads
| xref:bsl/map-0a7/cbegin.adoc[`cbegin`] 
| Return a const iterator to the first element, or `cend` if empty.
| xref:bsl/map-0a7/cend.adoc[`cend`] 
| Return an iterator providing non‐modifiable access to the past‐the‐end element in the ordered sequence of `value_type` objects maintained by this map.
| xref:bsl/map-0a7/clear.adoc[`clear`] 
| Remove all entries from this map. Note that the map is empty after this call, but allocated memory may be retained for future use.
| xref:bsl/map-0a7/contains-06.adoc[`contains`] 
| Return whether this map contains an element equivalent to `key`.
| xref:bsl/map-0a7/count-05.adoc[`count`] 
| Return the number of elements equivalent to `key`.
| xref:bsl/map-0a7/crbegin.adoc[`crbegin`] 
| Return a const reverse iterator to the last element, or `crend` if empty.
| xref:bsl/map-0a7/crend.adoc[`crend`] 
| Return a const reverse iterator to prior‐to‐beginning.
| xref:bsl/map-0a7/emplace.adoc[`emplace`] 
| Emplace a newly constructed element into this map.
| xref:bsl/map-0a7/emplace_hint.adoc[`emplace_hint`] 
| Emplace a newly constructed element near `hint`.
| xref:bsl/map-0a7/empty.adoc[`empty`] 
| Return `true` if this map contains no elements, and `false` otherwise.
| xref:bsl/map-0a7/end-06.adoc[`end`] 
| `end` overloads
| xref:bsl/map-0a7/equal_range-0e.adoc[`equal_range`] 
| Return the half‐open range of elements equivalent to `key`.
| xref:bsl/map-0a7/erase-0d.adoc[`erase`] 
| `erase` overloads
| xref:bsl/map-0a7/find-08.adoc[`find`] 
| `find` overloads
| xref:bsl/map-0a7/get_allocator.adoc[`get_allocator`] 
| Return (a copy of) the allocator used for memory allocation by this map.
| xref:bsl/map-0a7/insert-03.adoc[`insert`] 
| `insert` overloads
| xref:bsl/map-0a7/insert_or_assign-0f.adoc[`insert_or_assign`] 
| `insert_or_assign` overloads
| xref:bsl/map-0a7/insert_range.adoc[`insert_range`] 
| Insert elements from `range` whose keys are not already present.
| xref:bsl/map-0a7/key_comp.adoc[`key_comp`] 
| Return the key‐comparison functor used by this map.
| xref:bsl/map-0a7/lower_bound-03.adoc[`lower_bound`] 
| `lower_bound` overloads
| xref:bsl/map-0a7/max_size.adoc[`max_size`] 
| Return a theoretical upper bound on the size of this map.
| xref:bsl/map-0a7/operator_subs-0e4.adoc[`operator[]`] 
| Subscript operators
| xref:bsl/map-0a7/rbegin-01.adoc[`rbegin`] 
| `rbegin` overloads
| xref:bsl/map-0a7/rend-0d8.adoc[`rend`] 
| `rend` overloads
| xref:bsl/map-0a7/size.adoc[`size`] 
| Return the number of elements in this map.
| xref:bsl/map-0a7/swap.adoc[`swap`] 
| Exchange the value and comparator with `other`.
| xref:bsl/map-0a7/try_emplace-0c.adoc[`try_emplace`] 
| `try_emplace` overloads
| xref:bsl/map-0a7/upper_bound-00.adoc[`upper_bound`] 
| `upper_bound` overloads
| xref:bsl/map-0a7/value_comp.adoc[`value_comp`] 
| Return a functor that compares two `value_type` objects by key.
|===


== Deduction Guides

[cols="1,4"]
|===
| Name| Description
| xref:bsl/map-0da.adoc[`map<KEY, VALUE>`] 
| Deduce `KEY` and `VALUE` from an initializer‐list constructor argument.
| xref:bsl/map-0b.adoc[`map<KEY, VALUE>`] 
| Deduce `KEY` and `VALUE` from iterator‐pair construction with a pointer allocator.
| xref:bsl/map-06.adoc[`map<KEY, VALUE, COMPARATOR>`] 
| Deduce `KEY`, `VALUE`, and `COMPARATOR` from initializer‐list construction.
| xref:bsl/map-0ac.adoc[`map<KEY, VALUE, COMPARATOR>`] 
| Deduce `KEY`, `VALUE`, and `COMPARATOR` from iterator‐pair construction.
| xref:bsl/map-0d4.adoc[`map<KEY, VALUE, COMPARATOR, ALLOCATOR>`] 
| Deduce `KEY`, `VALUE`, `COMPARATOR`, and `ALLOCATOR` from initializer‐list construction.
| xref:bsl/map-03.adoc[`map<KEY, VALUE, COMPARATOR, ALLOCATOR>`] 
| Deduce `KEY`, `VALUE`, `COMPARATOR`, and `ALLOCATOR` from iterator‐pair construction.
| xref:bsl/map-0cb.adoc[`map<KEY, VALUE, std::less<KEY>, ALLOCATOR>`] 
| Deduce `KEY`, `VALUE`, and `ALLOCATOR` from initializer‐list construction.
| xref:bsl/map-02.adoc[`map<KEY, VALUE, std::less<KEY>, ALLOCATOR>`] 
| Deduce `KEY`, `VALUE`, and `ALLOCATOR` from iterator‐pair construction.
|===


== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/erase_if-01.adoc[`erase_if`]
| Erase every element of `m` that satisfies `predicate`.
| xref:bsl/operator_3way-044.adoc[`operator<=>`]
| Perform a lexicographic three‐way comparison of `lhs` and `rhs`.
| xref:bsl/operator_eq-04b.adoc[`operator==`]
| Return `true` if `lhs` and `rhs` have the same value.
| xref:bsl/swap-0cc.adoc[`swap`]
| Exchange the value and comparator of `a` with those of `b`.
|===


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