[#BloombergLP-bdlc-FlatHashSet-count-04]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlc.adoc[bdlc]::xref:BloombergLP/bdlc/FlatHashSet.adoc[FlatHashSet]::count
:relfileprefix: ../../../
:mrdocs:

Return the number of elements equivalent to the specified `key`.

== Synopsis

Declared in `<bdlc_flathashset.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class LOOKUP_KEY>
std::size_t
count(LOOKUP_KEY const& key) const
requires BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
         && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value;
----

== Description

The behavior is undefined unless `key` is equivalent to at most one element in this unordered set. Note that since an unordered set maintains unique keys, the returned value will be either 0 or 1.

== Return Value

1 if `key` is present, and 0 otherwise

== Parameters

[cols="1,4"]
|===
| Name| Description
| *key*
| key to count
|===


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