Where does Console.WriteLine go in ASP.NET?

Question

In a J2EE application (like one running in WebSphere), when I use System.out.println(), my text goes to standard out, which is mapped to a file by the WebSphere admin console.

In an ASP.NET application (like one running in IIS), where does the output of Console.WriteLine() go? The IIS process must have a stdin, stdout and stderr; but is stdout mapped to the Windows version of /dev/null or am I missing a key concept here?

I'm not asking if I should log there (I use log4net), but where does the output go? My best info came from this discussion where they say Console.SetOut() can change the TextWriter, but it still didn't answer the question on what the initial value of the Console is, or how to set it in config/outside of runtime code.

apparently no one knows, but everyone uses it in their examples. wtf — Jason, Aug 25 '09 at 20:59
if you were looking for debugging purposes i would refer the @Greg Bernhardt reply below. — Ram, Oct 09 '15 at 06:44
It would actually go to the STDOUT of the ASP.NET Worker process. Where that is pointed to, I'm not sure. — FlySwat, Sep 26 '08 at 03:50
@KevinHakanson FWIW all these years later, stdout for any process is chosen by its parent, the process which started it. In this case, the parent would be IIS. [This might point you in the right direction](https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy/iis/troubleshoot?view=aspnetcore-2.1#aspnet-core-module-stdout-log). — jpaugh, Oct 25 '18 at 14:49

score 774 · Answer 1 · edited Oct 20 '10 at 21:12

774

If you use System.Diagnostics.Debug.WriteLine(...) instead of Console.WriteLine(), then you can see the results in the Output window of Visual Studio.

edited Oct 20 '10 at 21:12

luvieere

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answered May 18 '09 at 21:24

Greg Bernhardt

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I would've asked the same question as Kevin, but this is the answer I would've been looking for. – Zasz Jun 11 '11 at 17:04
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One more little hint; if you are printing a formatted string, use Debug.Print instead of Debug.WriteLine to avoid an argument conflict (see http://social.msdn.microsoft.com/Forums/ar/Vsexpressvcs/thread/f27bacd9-8b86-4f65-95ca-8b30c9e2e915). – Nicholas Riley Jan 09 '12 at 20:02
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Note that the debugger needs to be attached in order for the messages to be shown in the Output window. – Cosmin Aug 28 '13 at 14:20
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Does this not work for local IIS or something? I can't seem to be able to write to the output for the life of me, despite the fact that I'm starting this with F5 (so the debugger is attached). I know my code is being executed because I can write to a file fine. – Kat May 19 '15 at 19:55
@Kat Make sure the change you're trying to see is actually posting back to the server when you expect it to. I was having the same issue until I realized I didn't have my dropdownlist set to `autopostback="true"` when I was trying to write `ddl.selectedvalue` to the output window. – TylerH May 23 '19 at 14:34
It is useful to use Console.WriteLine if you use the same DLL across both IIS and console apps. That's how I ended up here ;) – Adam Jun 18 '20 at 16:13

Ruben · Accepted Answer · 2020-11-02T15:18:34.707

If you look at the Console class in .NET Reflector, you'll find that if a process doesn't have an associated console, Console.Out and Console.Error are backed by Stream.Null (wrapped inside a TextWriter), which is a dummy implementation of Stream that basically ignores all input, and gives no output.

So it is conceptually equivalent to /dev/null, but the implementation is more streamlined: there's no actual I/O taking place with the null device.

Also, apart from calling SetOut, there is no way to configure the default.

Update 2020-11-02: As this answer is still gathering votes in 2020, it should probably be noted that under ASP.NET Core, there usually is a console attached. You can configure the ASP.NET Core IIS Module to redirect all stdout and stderr output to a log file via the stdoutLogEnabled and stdoutLogFile settings:

<system.webServer>
  <aspNetCore processPath="dotnet"
              arguments=".\MyApp.dll"
              hostingModel="inprocess"
              stdoutLogEnabled="true"
              stdoutLogFile=".\logs\stdout" />
<system.webServer>

Use System.Diagnostics.Debug.WriteLine() if you actually want something to be written to the Output window, which you can view when debugging. — Ε Г И І И О, Feb 20 '19 at 11:01

score 27 · Answer 3 · answered Oct 09 '10 at 15:32

27

I've found this question by trying to change the Log output of the DataContext to the output window. So to anyone else trying to do the same, what I've done was create this:

class DebugTextWriter : System.IO.TextWriter {
   public override void Write(char[] buffer, int index, int count) {
       System.Diagnostics.Debug.Write(new String(buffer, index, count));
   }

   public override void Write(string value) {
       System.Diagnostics.Debug.Write(value);
   }

   public override Encoding Encoding {
       get { return System.Text.Encoding.Default; }
   }
}

Annd after that: dc.Log = new DebugTextWriter() and I can see all the queries in the output window (dc is the DataContext).

Have a look at this for more info: http://damieng.com/blog/2008/07/30/linq-to-sql-log-to-debug-window-file-memory-or-multiple-writers

answered Oct 09 '10 at 15:32

Artur Carvalho

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Why not just use a static wrapper, given that you're wrapping entirely static methods? Why bother extending `TextWriter`? – Kat May 19 '15 at 19:56
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You could also use `dc.Log = s => Debug.WriteLine(s);`. – Rudey Feb 16 '16 at 09:53
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Application_Start: System.Console.SetOut(new DebugTextWriter()); – Stefan Steiger Nov 23 '16 at 10:03
Even better, Console.SetOut(new DebugTextWriter()); – Alde Oct 01 '19 at 05:01

score 18 · Answer 4 · edited Jun 29 '15 at 23:15

If you are using IIS Express and launch it via a command prompt, it will leave the DOS window open, and you will see Console.Write statements there.

So for example get a command window open and type:

"C:\Program Files (x86)\IIS Express\iisexpress" /path:C:\Projects\Website1 /port:1655

This assumes you have a website directory at C:\Projects\Website1. It will start IIS Express and serve the pages in your website directory. It will leave the command windows open, and you will see output information there. Let's say you had a file there, default.aspx, with this code in it:

<%@ Page Language="C#" %>
<html>
<body>
    <form id="form1" runat="server">
    Hello!

    <% for(int i = 0; i < 6; i++) %>
       <% { Console.WriteLine(i.ToString()); }%>

    </form>
</body>
</html>

Arrange your browser and command windows so you can see them both on the screen. Now type into your browser: http://localhost:1655/. You will see Hello! on the webpage, but in the command window you will see something like

Request started: "GET" http://localhost:1655/
0
1
2
3
4
5
Request ended: http://localhost:1655/default.aspx with HTTP status 200.0

I made it simple by having the code in a code block in the markup, but any console statements in your code-behind or anywhere else in your code will show here as well.

+1 I always use IIS Express while developing for this reason. The console output is invaluable, used at the back end like the javascript console at the front end. Saves heaps of time debugging, as opposed to using a file-based server log. You don't have to override "friendly" exception handling - keep the nice "oops" browser page, and just output the exception to the console, easy to see. — ingredient_15939, Aug 21 '17 at 13:42

score 9 · Answer 5 · edited Jun 29 '15 at 23:12

9

System.Diagnostics.Debug.WriteLine(...); gets it into the Immediate Window in Visual Studio 2008.

Go to menu Debug -> Windows -> Immediate:

Enter image description here

edited Jun 29 '15 at 23:12

Peter Mortensen

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answered Sep 19 '13 at 06:34

Nik

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In my Visual Studio 2012, I followed what you said but the string appeared in the `Output` just besides the `Immediate Window` Thanks! – WTFZane Mar 14 '17 at 03:32

score 6 · Answer 6 · answered Sep 26 '08 at 14:32

6

There simply is no console listening by default. Running in debug mode there is a console attached, but in a production environment it is as you suspected, the message just doesn't go anywhere because nothing is listening.

answered Sep 26 '08 at 14:32

Craig Tyler

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score 5 · Answer 7 · edited Jun 29 '15 at 23:03

5

Unless you are in a strict console application, I wouldn't use it, because you can't really see it. I would use Trace.WriteLine() for debugging-type information that can be turned on and off in production.

edited Jun 29 '15 at 23:03

Peter Mortensen

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answered Sep 26 '08 at 04:10

Charles Graham

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Yep, here's a good place to start: http://msdn.microsoft.com/en-us/library/x5952w0c.aspx – Zhaph - Ben Duguid May 18 '09 at 21:32

score 3 · Answer 8 · edited Mar 29 '17 at 17:27

The TraceContext object in ASP.NET writes to the DefaultTraceListener which outputs to the host process’ standard output. Rather than using Console.Write(), if you use Trace.Write, output will go to the standard output of the process.

You could use the System.Diagnostics.Process object to get the ASP.NET process for your site and monitor standard output using the OutputDataRecieved event.

score 1 · Answer 9 · answered Dec 28 '18 at 02:45

if you happened to use NLog in your ASP.net project, you can add a Debugger target:

<targets>
    <target name="debugger" xsi:type="Debugger"
            layout="${date:format=HH\:mm\:ss}|${pad:padding=5:inner=${level:uppercase=true}}|${message} "/>

and writes logs to this target for the levels you want:

<rules>
    <logger name="*" minlevel="Trace" writeTo="debugger" />

now you have console output just like Jetty in "Output" window of VS, and make sure you are running in Debug Mode(F5).

score 0 · Answer 10 · answered Aug 04 '17 at 23:48

This is confusing for everyone when it comes IISExpress. There is nothing to read console messages. So for example, in the ASPCORE MVC apps it configures using appsettings.json which does nothing if you are using IISExpress.

For right now you can just add loggerFactory.AddDebug(LogLevel.Debug); in your Configure section and it will at least show you your logs in the Debug Output window.

Good news CORE 2.0 this will all be changing: https://github.com/aspnet/Announcements/issues/255

score 0 · Answer 11 · answered Mar 05 '20 at 09:37

0

Mac, In Debug mode there is a tab for the Output.

answered Mar 05 '20 at 09:37

Thushara Buddhika

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score -3 · Answer 12 · edited Jun 29 '15 at 23:02

-3

In an ASP.NET application, I think it goes to the Output or Console window which is visible during debugging.

edited Jun 29 '15 at 23:02

Peter Mortensen

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answered Sep 26 '08 at 03:57

Leon Tayson

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Where does Console.WriteLine go in ASP.NET?

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