How can I add (simple) tracing in C#?

I want to introduce some tracing to a C# application I am writing. Sadly, I can never really remember how it works and would like a tutorial with reference qualities to check up on every now and then. It should include:

• App.config / Web.config stuff to add for registering TraceListeners
• how to set it up in the calling application

Do you know the über tutorial that we should link to?

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Glenn Slaven pointed me in the right direction. Add this to your App.config/Web.config inside <configuration/>:

<system.diagnostics>
    <trace autoflush="true">
      <listeners>
        <add type="System.Diagnostics.TextWriterTraceListener" name="TextWriter"
             initializeData="trace.log" />
      </listeners>
    </trace>
</system.diagnostics>

This will add a TextWriterTraceListener that will catch everything you send to with Trace.WriteLine, etc.

@DanEsparza pointed out that you should use Trace.TraceInformation, Trace.TraceWarning and Trace.TraceError instead of Trace.WriteLine, as they allow you to format messages the same way as string.Format.

Tip: If you don't add any listeners, then you can still see the trace output with the Sysinternals program DebugView (Dbgview.exe):

I followed around five different answers as well as all the blog posts in the previous answers and still had problems. I was trying to add a listener to some existing code that was tracing using the TraceSource.TraceEvent(TraceEventType, Int32, String) method where the TraceSource object was initialised with a string making it a 'named source'.

For me the issue was not creating a valid combination of source and switch elements to target this source. Here is an example that will log to a file called tracelog.txt. For the following code:

TraceSource source = new TraceSource("sourceName");
source.TraceEvent(TraceEventType.Verbose, 1, "Trace message");

I successfully managed to log with the following diagnostics configuration:

<system.diagnostics>
    <sources>
        <source name="sourceName" switchName="switchName">
            <listeners>
                <add
                    name="textWriterTraceListener"
                    type="System.Diagnostics.TextWriterTraceListener"
                    initializeData="tracelog.txt" />
            </listeners>
        </source>
    </sources>

    <switches>
        <add name="switchName" value="Verbose" />
    </switches>
</system.diagnostics>

DotNetCoders has a starter article on it: <http://www.dotnetcoders.com/web/Articles/ShowArticle.aspx?article=50>;. They talk about how to set up the switches in the configuration file and how to write the code, but it is pretty old (2002).

There's another article on CodeProject: A Treatise on Using Debug and Trace classes, including Exception Handling, but it's the same age.

CodeGuru has another article on custom TraceListeners: Implementing a Custom TraceListener