How should I check "dynamic" file accessibility (e.g., in use)

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How should I check if a file can be opened for Read, including cases like the file is in use in another process?
I can catch the IOException where I get:
"The process cannot access the file 'C:\...' because it is being used by another process."
but I'd rather check for Read-ability in advance, and control the error message.
(I know this leaves a "window of opportunity" between the checking and the file opening, but in this case the nature of the file is that the user may have opened it manually, so pre-checking should catch most cases, and catching the exception will handle the rest.)
Suggestions?

[Edit: So it appears that it is not a good idea to even try. Which may be why there's no easy way to do it. The best I could find is getting the HRESULT of the exception in the reference from Richard Bishop's solution. At least I can give simplified error messages for the detectable conditions.]

Posted 14-Nov-13 9:24am

Matt T Heffron

Updated 14-Nov-13 11:26am

v2

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BillWoodruff 14-Nov-13 17:03pm

I think you will benefit from the excellent analysis here of issues in determining File availability:

http://stackoverflow.com/a/265958/133321

2 solutions

Solution 2

I would create a function something like this:

C#

public static bool TryOpenRead(this System.IO.FileInfo file, out System.IO.FileStream fileStream)
{
    fileStream = null;

    try
    {
        fileStream = file.OpenRead();

        return true;
    }
    catch (System.IO.IOException ioException)
    {

    }

    return false;
}

Which, of course, is an extension method for FileInfo[^].

Thats at least the only reliable way to both see if the file is available for reading AND get the file at the same time.

Posted 14-Nov-13 9:58am

Ron Beyer

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Richard C Bishop · Accepted Answer · 2013-11-14T09:54:00

Solution 1

I found this article:

Check if file is being used by another process[^]

Posted 14-Nov-13 9:54am

Richard C Bishop