Comments on: How To User StreamReader to Open A File ReadOnly in C# (.NET)

By: Rajesh

Rajesh — Mon, 02 Apr 2012 11:07:10 +0000

Bob,

I managed to get my requirement coded – which was to read from a file that was continuously getting updated by other process. I think you are looking for similar one… Here’s what I did.

FileStream fs = new FileStream(“myfile.txt”, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
StreamReader streamReader = new StreamReader(fs);
string line;
while ((line = streamReader.ReadLine()) != null)
{
// do something
}

The FileShare.ReadWrite in fs object is important to let your program know that the file is being updated by another process. This way it reads the new contents that are written while it was already opened for reading. Hope this helps!

Cheers.

By: Rajesh

Rajesh — Mon, 02 Apr 2012 09:36:04 +0000

The code looks good to me, but When I manually opened a file and edited it but didn’t save it yet!, Then ran my program with the above code to open it in ReadOnly mode and read the stream. While it is reading the stream, I tried to save the file which I manually updated earlier. This doesn’t allow me to save it saying there is a Sharing violation and cannot save the file. Any ideas why this issue arises even when the file is being opened in File.OpenRead(file) method.

By: Peter Kellner

Peter Kellner — Mon, 05 Mar 2012 16:34:20 +0000

hmm. It looks to me like OpenRead is there, all the way back to .net 2.0 http://msdn.microsoft.com/en-US/library/system.io.file_methods(v=vs.80).aspx

By: Bob

Bob — Mon, 05 Mar 2012 16:18:23 +0000

Ben, that still gives me an error that the file is in use by another process, even though I can open it in Windows.

By: Ben

Ben — Thu, 06 Oct 2011 21:46:28 +0000

I beleive that you want to do something like this

using( FileStream s = File.OpenRead(filename))
{
using(TextReader reader = new StreamReader(s))
{
// Do smoething
}
}

This ensures the both streams get closed properly.

Cheers
Ben

By: MarkJoel60

MarkJoel60 — Wed, 17 Aug 2011 19:47:18 +0000

@Ash: I believe you are incorrect. I am using VS2010, and this works:

System.IO.StreamReader streamReader = new System.IO.StreamReader(System.IO.File.OpenRead(“myfile.txt”));

By: Ash

Ash — Fri, 23 Jul 2010 18:27:44 +0000

File.OpenRead(file) .. doesn’t seem to work in VS 2010 C#. The only option (in Intellisense) I get is file.OpenFile no file.openRead. Any thoughts?

By: Peter

Peter — Tue, 08 Dec 2009 20:06:55 +0000

Hi Ryan,
Sorry, don’t know about performance, but I’d guess opening in ReadOnly has not perf impact.
-Peter

By: Ryan

Ryan — Tue, 08 Dec 2009 20:06:03 +0000

Nice, I did not know of that static method.

Do you know if it improves performance/memory if opening a file for reading purposes only vs. opening it in RW mode?

By: Bartek

Bartek — Tue, 08 Dec 2009 12:03:21 +0000

Thanks Peter, I was just looking for something like this!