Error While writing to a file

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Hi guys,

Please look at the code below:

System.IO.FileStream oFS = new System.IO.FileStream("c:\\tt.csv",System.IO.FileMode.Append, System.IO.FileAccess.Write, System.IO.FileShare.Read);
int i = 0;
while (true)
{
    string str;
    byte[] oByte;
    str="5886A," + "Program,"+ "Main,"+ "This is a Test :" + i.ToString();
    oByte = System.Text.Encoding.ASCII.GetBytes(str);
    oFS.Write(oByte, 0, oByte.Length);
    oFS.Write(new byte[]{13,10}, 0, 2);
    oFS.Flush();
    i++;
    str = "5886A," + "Program," + "Main," + "This is a Test :" + i.ToString();
    oByte = System.Text.Encoding.ASCII.GetBytes(str);
    oFS.Write(oByte, 0, oByte.Length);
    oFS.Write(new byte[] { 13, 10 }, 0, 2);
    oFS.Flush();
    i++;
    str = "5886A," + "Program," + "Main," + "This is a Test :" + i.ToString();
    oByte = System.Text.Encoding.ASCII.GetBytes(str);
    oFS.Write(oByte, 0, oByte.Length);
    oFS.Write(new byte[] { 13, 10 }, 0, 2);
    oFS.Flush();
    i++;
    str = "5886A," + "Program," + "Main," + "This is a Test :" + i.ToString();
    oByte = System.Text.Encoding.ASCII.GetBytes(str);
    oFS.Write(oByte, 0, oByte.Length);
    oFS.Write(new byte[] { 13, 10 }, 0, 2);
    oFS.Flush();
    System.Threading.Thread.Sleep(10);
    if (i > 56000) break;
}
oFS.Close();

This code simply create or open a csv (text) file and start writing in it.
If I open the csv file with Microsoft Excel (2003 or 2007) while the program is writing in this file, most of the times I get this Error:

The process cannot access the file because another process has locked a portion of the file.

Note:
Microsoft Excel ask to open the file as readonly. and when I confirm that, I get the Error.
( I have not tested this with Excel 2010)

Can anyone please tell me what is going on?!!!

Thanks.

(I had asked this question before, but now I simplified my question with a very simple source code.)

Posted 2-Nov-10 7:51am

aidin Tajadod

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Comments

Toli Cuturicu 2-Nov-10 14:31pm

Don't put the file in the root directory!

aidin Tajadod 2-Nov-10 14:44pm

I did it just for test. In real it is not.

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Keith Barrow · Answer 1 · 2010-11-02T09:42:00

When you write to the file, the OS locks it. This prevents other applications from accessing it and causing problems. I hacked this code to test:

C++

FileStream fs = new FileStream(@"c:\foobar.txt", FileMode.Append, FileAccess.Write);
while (true)
{
    fs.WriteByte((byte)'*');
    fs.Flush();
}

I opened the file in text pad several times without incident while the file was being written.
Excel seems to work in a pretty strange way:

Open file: Excel reports the file is already locked. The code then throws and error as Excel has locked it while it isn't being written. Excel must repeatedly try to lock the file.
Open as Readonly: Excel does not display the error popup, but it does lock when it isn't being written the file as the code throws the next time it tries to write

I have no idea why Excel needs to lock the file in readonly mode, but it does, so there it is. I doubt there is much you can do about this, other than re-design or work around the problem.

You can verify that you application has the file open using the unlocking tool available here:

http://ccollomb.free.fr/unlocker/[^] it lists the process locking the file.