Redirect stdout+stderr on a C# Windows service

Question

I've written a Windows service in C# using the ServiceBase helper. During its execution, some procedures in an external native DLL are called. Annoyingly, those procedures write to stdout and/or stderr in an uncontrolled manner as no sources are given for this DLL.

Is it possible to redirect those outputs from the C# service to a log file?

is it starting up the DLL as a Process? or simply referencing the DLL? — Agent_9191, Oct 16 '09 at 16:40

score 31 · Accepted Answer · edited Dec 08 '20 at 00:07

31

You can do this via PInvoke to SetStdHandle:

[DllImport("Kernel32.dll", SetLastError = true) ]
public static extern int SetStdHandle(int device, IntPtr handle); 

// in your service, dispose on shutdown..
FileStream filestream;
StreamWriter streamwriter;

void Redirect()
{   
    int status;
    IntPtr handle;
    filestream = new FileStream("logfile.txt", FileMode.Create);
    streamwriter = new StreamWriter(filestream);
    streamwriter.AutoFlush = true;
    Console.SetOut(streamwriter);
    Console.SetError(streamwriter);

    handle = filestream.Handle;
    status = SetStdHandle(-11, handle); // set stdout
    // Check status as needed
    status = SetStdHandle(-12, handle); // set stderr
    // Check status as needed
}

edited Dec 08 '20 at 00:07

Pang

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answered Oct 16 '09 at 16:42

Reed Copsey

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I've changed the line handle = filestream.Handler; by handle = filestream.SafeFileHandle.DangerousGetHandle(); because filestream.Handler is deprecated. – Herchu Oct 19 '09 at 15:36
1

Any way to use this without a FileStream? (i.e. MemoryStream or similar)? – Steve Dec 18 '11 at 21:27
@ReedCopsey - Please see my reply to a similar comment on my new question: http://stackoverflow.com/questions/8555002/redirecting-native-dlls-stdout-to-memory-stream – Steve Dec 18 '11 at 22:18
@Herchu you did realise the "Dangerous" in DangerousGetHandle? It is there for a reason: http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.safehandle.dangerousgethandle%28v=vs.100%29.aspx – Rui Marques Sep 01 '14 at 11:42
@RuiMarques Yeah, they call me Danger for a reason! :) Seriously now; that was 2009. If I happen to need it again I'll write it following Steve's solution. – Herchu Sep 03 '14 at 08:37
Regretfully, it does not work on Windows 10. The file is empty. I made sure that I Close() on both streamwriter and filestream when done. – eugen_nw Jul 12 '23 at 21:42

score 0 · Answer 2 · edited Dec 08 '20 at 00:07

0

Check out the Console.SetOut method.

It will allow you to redirect console output to a TextWriter.

edited Dec 08 '20 at 00:07

Pang

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answered Oct 16 '09 at 16:42

Jay Riggs

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Depending on how the DLL is written, that won't redirect the DLLs output to the console, though. Typically, it works, but not always. – Reed Copsey Oct 16 '09 at 16:44
2

Reed, so what does it depend on? – Stiefel Jul 19 '10 at 11:13
To my recent experience, captures only the output that the C# code writes to the Console. – eugen_nw Jul 12 '23 at 21:35

Redirect stdout+stderr on a C# Windows service

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