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<concept id="GUID-D14CD452-BFCE-5EBA-B73B-61AA045D23E4" xml:lang="en"><title>Log

Engine Overview</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>This topic describes the key concepts of Log Engine. </p>

<section id="GUID-ECD7C71D-F465-48FC-8478-65E5D09E6124"><title>Purpose</title> <p>Used to record events of interest to the

user, of which they may not be immediately aware, or of high importance as

costs are incurred, such as telephone calls. These events can be retrieved

by a viewer application and displayed to the user. </p> </section>

<section id="GUID-44BF0863-2E2B-4E2B-A04A-03956C9A64BA"><title>Architectural relationships</title> <p>The Log Engine is split

into a wrapper (a stub interface) that is present on all UI variants, and

an actual logging DLL that may or may not be present. On UI variants on which

the actual logging engine is not present, calls to the wrapper will have no

effect. Programs written for multiple UI variants should use the wrapper only.

Programs for a particular UI variant on which the log engine is present can

use it directly. </p> </section>

<section id="GUID-D2D4E2AA-1842-4394-B916-3B473C578DBE"><title>Description</title> <p>The API has five key concepts: log

engine wrapper, log client, event, view, and filter. </p> <p><b>Log

engine wrapper</b> </p> <p>The log engine wrapper provides simple interfaces

to record events, and is present on all UI variants. The wrapper interfaces

are <xref href="GUID-146D719E-BDD6-3F20-80B1-EDE09081A6EA.dita"><apiname>CLogWrapper</apiname></xref> and <xref href="GUID-4A7D312F-A8C6-3663-8455-13FA73F1CFB5.dita"><apiname>CLogBase</apiname></xref>. </p> <p><b>Log client</b> </p> <p>The log client is the main direct interface on

the log engine. It is used to add, delete, and change log events, and allows

log administration. It is also used to create filtered views of events. </p> <p>The

log client interface is <xref href="GUID-51C67545-12BA-326D-BD8F-662B24C68ED2.dita"><apiname>CLogClient</apiname></xref>. </p> <p><b>Event</b> </p> <p>A log event is an entry in the log. Events have a fixed

number of data fields, though some fields do not apply to all events. </p> <p>The

event interface is <xref href="GUID-CDFB61A7-1C74-3F63-9FDF-5A3B8603A010.dita"><apiname>CLogEvent</apiname></xref>. </p> <p><b>View</b> </p> <p>A view allows a filtered list of events to be accessed.

Views are provided for the main event log (<codeph>CLogViewEvent</codeph>)

and for recent events only (<xref href="GUID-F40F9556-F223-36A5-9812-6EF6FF3F5156.dita"><apiname>CLogViewRecent</apiname></xref>). </p> <p><b>Filter </b> </p> <p>A filter specifies the type of events that appear

in a view. The filter interface is <xref href="GUID-99144BA6-F79A-3D3C-B1D3-272B3723C42C.dita"><apiname>CLogFilter</apiname></xref>. </p> </section>

</conbody><related-links>

<link href="GUID-B0D76734-1DB7-5465-91AE-BB3521599A75.dita"><linktext>How To Use

the Log Engine</linktext></link>

<link href="GUID-F3770B99-5228-5D29-8CA6-71028A327714.dita"><linktext> Log Engine

Using Central Repository</linktext></link>

</related-links></concept>