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
– Agent_9191, Commented Oct 16, 2009 at 16:40

Pang · Accepted Answer · 2020-12-08 00:07:48Z

32

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 8, 2020 at 0:07

Pang

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answered Oct 16, 2009 at 16:42

Reed Copsey

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6 Comments

Herchu Over a year ago

I've changed the line handle = filestream.Handler; by handle = filestream.SafeFileHandle.DangerousGetHandle(); because filestream.Handler is deprecated.

Steve Over a year ago

Any way to use this without a FileStream? (i.e. MemoryStream or similar)?

Steve Over a year ago

@ReedCopsey - Please see my reply to a similar comment on my new question: stackoverflow.com/questions/8555002/…

Rui Marques Over a year ago

@Herchu you did realise the "Dangerous" in DangerousGetHandle? It is there for a reason: msdn.microsoft.com/en-us/library/…

Herchu Over a year ago

@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.

|

Pang · Accepted Answer · 2020-12-08 00:07:06Z

0

Check out the Console.SetOut method.

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

edited Dec 8, 2020 at 0:07

Pang

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answered Oct 16, 2009 at 16:42

Jay Riggs

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3 Comments

Reed Copsey Over a year ago

Depending on how the DLL is written, that won't redirect the DLLs output to the console, though. Typically, it works, but not always.

Stiefel Over a year ago

Reed, so what does it depend on?

eugen_nw Over a year ago

To my recent experience, captures only the output that the C# code writes to the Console.

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