FAQ: How do I check whether a file is in use?

Question

How do I check whether a file is in use?

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Answer 1

The common managed way to check whether a file is in use is to open the file in a try block. If the file is in use, it will throw an IOException.

    public bool IsFileLocked(string filename)
        {
            bool Locked = false;
            try
            {
                FileStream fs =
                    File.Open(filename, FileMode. OpenOrCreate,
                    FileAccess.ReadWrite, FileShare.None);
                fs.Close();
            }
            catch (IOException ex)
            {
                Locked = true;
            }
            return Locked;
        }

 

Another way to check whether a file is in use is to call the CreateFile API. If a file is in use, the handle return is invalid.

    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern SafeFileHandle CreateFile(string lpFileName,
    FileSystemRights dwDesiredAccess, FileShare dwShareMode, IntPtr
    securityAttrs, FileMode dwCreationDisposition, FileOptions
    dwFlagsAndAttributes, IntPtr hTemplateFile);

        const int ERROR_SHARING_VIOLATION = 32;

        private bool IsFileInUse(string fileName)
        {
            bool inUse = false;

            SafeFileHandle fileHandle = 
            CreateFile(fileName, FileSystemRights.Modify, 
                  FileShare.Write, IntPtr.Zero,                  
                  FileMode.OpenOrCreate, FileOptions.None, IntPtr.Zero);

            if (fileHandle.IsInvalid)
            {
               if (Marshal.GetLastWin32Error() == 
                   ERROR_SHARING_VIOLATION)
               {
     			   inUse = true;
               }           
            }
            fileHandle.Close();
            return inUse;
        }

 

Related threads:

 

The process cannot access the file because it is being used by another process

http://social.msdn.microsoft.com/Forums/en/netfxbcl/thread/e99a7cea-43d3-49b1-82bc-5669e0b9d052

 

How to check if a .txt file is already open

http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/76d63016-3864-4020-849a-01a82276493d/

 

How to check file is open or not

http://social.msdn.microsoft.com/forums/fr-FR/netfxbcl/thread/a539cbdc-5f42-4f09-9e04-860845aa049d/

 

How to know when a file is locked by another process?

http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/4e3a6014-4cd7-4d38-ba87-ccf9ce28b3c5/

 

File Locked Or In Use

http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/f225e48c-0321-49a3-9134-53f409dee5d9/

  

For more FAQ about Base Class Library, please see Base Class Library FAQ

 

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Please remember to mark the replies as answers if they help and unmark them if they provide no help.
Welcome to the All-In-One Code Framework! If you have any feedback, please tell us.

Answer 2

This is just an FYI...

The isFileLocked function didn't work in my case.  It did not operate the way I expected.  For example, if I opened the file from Windows Explorer and ran the code, it reported the file WAS NOT in use - although it was open.  If I set a breakpoint on fs.close and open the file from Windows Explorer, I would receive the following error:

"The process cannot access the file because it is being used by another process."


Of course, I expected to receive an IOException when the file.open method was called while it was open in Windows Explorer.

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Orlanzo

Answer 3

Look at below url :-

 

http://dotnet-magic.blogspot.com/2012/01/how-to-check-for-file-lock-file-in-use.html

 

I have used same in my Application. It is wokring.