[#BloombergLP-balm-MetricRegistry-setUserData-00]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/balm.adoc[balm]::xref:BloombergLP/balm/MetricRegistry.adoc[MetricRegistry]::setUserData
:relfileprefix: ../../../
:mrdocs:

Associate `value` with `key` on metrics matching `categoryName`.

== Synopsis

Declared in `<balm_metricregistry.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
setUserData(
    char const* categoryName,
    xref:BloombergLP/balm/MetricDescription/UserDataKey.adoc[MetricDescription::UserDataKey] key,
    void const* value,
    bool prefixFlag = false);
----

== Description

Associate the specified `value` with the specified `key` in any metric belonging to a category having the specified `categoryName`, or a category whose name begins with `categoryName`, as determined by the optionally specified `prefixFlag`. If `prefixFlag` is `false` or is not specified, only those metrics belonging to a category having `categoryName` will be mapped; otherwise, `value` will be associated with `key` for all metrics belonging to any category whose name begins with `categoryName`. This association applies to existing metrics as well as any subsequently created ones. When a metric is created that matches more than one registered category prefix, it is not specified which supplied value will be associated with `key`, unless only one of those values is non‐null, in which case the unique non‐null value is used. The behavior is undefined unless `key` was previously returned from `createUserDataKey`.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *categoryName*
| category name, or prefix when `prefixFlag` is true
| *key*
| user‐data key previously obtained from `createUserDataKey`
| *value*
| opaque user‐data value to associate
| *prefixFlag*
| if true, match categories by name prefix
|===


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