[#BloombergLP-balm-MetricDescription-userData]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/balm.adoc[balm]::xref:BloombergLP/balm/MetricDescription.adoc[MetricDescription]::userData
:relfileprefix: ../../../
:mrdocs:

Return the non‐modifiable value associated with the specified user‐data `key`. If the data for `key` has not been set, a value of 0 is returned, which is indistinguishable from a valid `key` with a 0 value. The behavior is undefined unless `key >= 0`. Note that this method allows clients of `balm` to access the (opaque) application‐specific information that they have previously associated with a metric (via `setUserData`).

== Synopsis

Declared in `<balm_metricdescription.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void const*
userData(xref:BloombergLP/balm/MetricDescription/UserDataKey.adoc[UserDataKey] key) const;
----


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