Writing Exceptions to the Windows Log File

Question

I'd like to catch my exceptions and log them in the Windows log file. How do I go about opening and writing to the Windows log?

Answer 1

You can use the System.Diagnostics.EventLog.WriteEntry function to write entries to the event log.

System.Diagnostics.EventLog.WriteEntry("MyEventSource", exception.StackTrace,                  
                                       System.Diagnostics.EventLogEntryType.Warning);

To read event logs you can use the System.Diagnostics.EventLog.GetEventLogs function.

//here's how you get the event logs
var eventLogs = System.Diagnostics.EventLog.GetEventLogs();

foreach(var eventLog in eventLogs)
{    
    //here's how you get the event log entries
    foreach(var logEntry in eventLog.Entries)
    {
        //do something with the entry
    }    
}

Answer 2

Windows uses the Event log to trace activity. You can use the System.Diagnostics.Trace class:

var traceSwitch = new TraceSwitch("MySwitch", "");
var exception = new Exception("Exception message");

if (traceSwitch.TraceError)
{
    Trace.TraceError(exception);
}

And you can use app.config to instruct the logger where to write:

<system.diagnostics>
    <switches>
        <add name="MySwitch" value="Verbose" />
    </switches>
    <trace autoflush="true">
        <listeners>
            <add name="EventLogger"
                 type="System.Diagnostics.EventLogTraceListener"
                 initializeData="NameOfYourApplication" />
        </listeners>
    </trace>
 </system.diagnostics>

Answer 3

You can also consider using the Enterprise Library. It looks complicated to start with but an hour or two of playing will pay off. Config is stored in app.config so you can change it without recompiling - this can be really handy when you've got the same code sitting on test and live servers with different config. You can do quite a lot without loads of code.

One nice thing is that you can define Exception policies so that exceptions are automatically logged. Here's some code you might use (I'm using EntLib 4.1):

    try
    {
        //This would be where your exception might be thrown.  I'm doing it on
        //purpose so you can see it work
        throw new ArgumentNullException("param1");
    }
    catch (Exception ex)
    {
        if (ExceptionPolicy.HandleException(ex, "ExPol1")) throw;
    }

The line in the catch block will rethrow the exception IF the ExPol1 defines it. If ExPol1 is configured for rethrow, then ExceptionPolicy.HandleException will return true. If not, it returns false.

You define the rest in config. The XML looks pretty horrible (doesn't it always) but you create this using the Enterprise Library Configuration editor. I'm just supplying it for completeness.

In the loggingConfiguration section, this file defines

• the log: a rolling text log file (you can use the built in windows event logs, sql tables, email, msmq and others), with
• a text formatter that governs how the parameters are written to the log (sometimes I configure this to write everything to one line, other times spread across many),
• a single category "General"
• a Special Source which traps any errors in the config/entlib and reports them as well. I strongly advise you to do this.

In the exceptionHandling section, it defines

• a single policy: "ExPo1", which handles type ArgumentNullExceptions and specifies the postHandlingAction of None (i.e. don't rethrow).
• a handler which logs to the General category (defined above)

I don't do it in this example, but you can also replace an exception with a different type using a policy.

   <?xml version="1.0" encoding="utf-8"?>
    <configuration>
      <configSections>
        <section name="loggingConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.LoggingSettings, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
        <section name="exceptionHandling" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Configuration.ExceptionHandlingSettings, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </configSections>
      <loggingConfiguration name="Logging Application Block" tracingEnabled="true"
        defaultCategory="General" logWarningsWhenNoCategoriesMatch="true">
        <listeners>
          <add fileName="rolling.log" footer="" formatter="Text Formatter"
            header="" rollFileExistsBehavior="Overwrite" rollInterval="None"
            rollSizeKB="500" timeStampPattern="yyyy-MM-dd" listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.RollingFlatFileTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
            traceOutputOptions="None" filter="All" type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.RollingFlatFileTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
            name="Rolling Flat File Trace Listener" />
        </listeners>
        <formatters>
          <add template="Timestamp: {timestamp}; Message: {message}; Category: {category}; Priority: {priority}; EventId: {eventid}; Severity: {severity}; Title:{title}; Machine: {machine}; Application Domain: {appDomain}; Process Id: {processId}; Process Name: {processName}; Win32 Thread Id: {win32ThreadId}; Thread Name: {threadName}; &#xD;&#xA;     Extended Properties: {dictionary({key} - {value})}"
            type="Microsoft.Practices.EnterpriseLibrary.Logging.Formatters.TextFormatter, Microsoft.Practices.EnterpriseLibrary.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
            name="Text Formatter" />
        </formatters>
        <categorySources>
          <add switchValue="All" name="General">
            <listeners>
              <add name="Rolling Flat File Trace Listener" />
            </listeners>
          </add>
        </categorySources>
        <specialSources>
          <allEvents switchValue="All" name="All Events" />
          <notProcessed switchValue="All" name="Unprocessed Category" />
          <errors switchValue="All" name="Logging Errors &amp; Warnings">
            <listeners>
              <add name="Rolling Flat File Trace Listener" />
            </listeners>
          </errors>
        </specialSources>
      </loggingConfiguration>
      <exceptionHandling>
        <exceptionPolicies>
          <add name="ExPol1">
            <exceptionTypes>
              <add type="System.ArgumentNullException, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
                postHandlingAction="None" name="ArgumentNullException">
                <exceptionHandlers>
                  <add logCategory="General" eventId="100" severity="Error" title="Enterprise Library Exception Handling"
                    formatterType="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.TextExceptionFormatter, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
                    priority="0" useDefaultLogger="false" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging.LoggingExceptionHandler, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
                    name="Logging Handler" />
                </exceptionHandlers>
              </add>
            </exceptionTypes>
          </add>
        </exceptionPolicies>
      </exceptionHandling>
    </configuration>

Answer 4

These articles explain how to automatically log unhanded exceptions that might occur:

VB.NET: http://visualbasic.about.com/od/usingvbnet/a/logging.htm

C#: Where to write the functions of ApplicationEvents.vb when converting project to C#

Answer 5

Here's the simple answer on writing to the event log: http://support.microsoft.com/kb/307024

A better answer is to use something like log4net, which will handle that for you.