[#XLOG_IS_ON_IMPL_HELPER]
= XLOG&lowbar;IS&lowbar;ON&lowbar;IMPL&lowbar;HELPER
:mrdocs:

Helper macro to implement of XLOG&lowbar;IS&lowbar;ON()

== Synopsis

Declared in `&lt;folly&sol;logging&sol;xlog&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
#define XLOG&lowbar;IS&lowbar;ON&lowbar;IMPL&lowbar;HELPER(level)

----

== Description

This macro is used in the XLOG() implementation, and therefore must be as cheap as possible&period; It stores the category&apos;s LogLevel as a local static variable&period; The very first time this macro is evaluated it will look up the correct LogCategory and initialize the LogLevel&period; Subsequent calls then are only a single conditional log level check&period;

The LogCategory object keeps track of this local LogLevel variable and automatically keeps it up&hyphen;to&hyphen;date when the category&apos;s effective level is changed&period;

See XlogLevelInfo for the implementation details&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *level*
| A fully qualified `folly&colon;&colon;LogLevel` value&period;
|===


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