System.IO.IOException: file used by another proces

Question

I've been working on this small piece of code that seems trivial but still, i cannot really see where is the problem. My functions do a pretty simple thing. Opens a file, copy its contents, replace a string inside and copy it back to the original file (a simple search and replace inside a text file then). I didn't really know how to do that as I'm adding lines to the original file, so I just create a copy of the file, (file.temp) copy also a backup (file.temp) then delete the original file(file) and copy the file.temp to file. I get an exception while doing the delete of the file. Here is the sample code:

private static bool modifyFile(FileInfo file, string extractedMethod, string modifiedMethod)
    {
        Boolean result = false;
        FileStream fs = new FileStream(file.FullName + ".tmp", FileMode.Create, FileAccess.Write);
        StreamWriter sw = new StreamWriter(fs);

        StreamReader streamreader = file.OpenText();
        String originalPath = file.FullName;
        string input = streamreader.ReadToEnd();
        Console.WriteLine("input : {0}", input);

        String tempString = input.Replace(extractedMethod, modifiedMethod);
        Console.WriteLine("replaced String {0}", tempString);

        try
        {
            sw.Write(tempString);
            sw.Flush();
            sw.Close();
            sw.Dispose();
            fs.Close();
            fs.Dispose();
            streamreader.Close();
            streamreader.Dispose();

            File.Copy(originalPath, originalPath + ".old", true);
            FileInfo newFile = new FileInfo(originalPath + ".tmp");
            File.Delete(originalPath);
            File.Copy(fs., originalPath, true);

            result = true;
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
        }

        return result;
    }`

And the related exception

System.IO.IOException: The process cannot access the file 'E:\mypath\myFile.cs' because it is being used by another process.
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.File.Delete(String path)
   at callingMethod.modifyFile(FileInfo file, String extractedMethod, String modifiedMethod)

Normally these errors come from unclosed file streams, but I've taken care of that. I guess I've forgotten an important step but cannot figure out where. Thank you very much for your help,

Answer 1

I realize that I is kinda late, but still better late than never. I was having similar problem recently. I used XMLWriter to subsequently update XML file and was receiving the same errors. I found the clean solution for this:

The XMLWriter uses underlying FileStream to access the modified file. Problem is that when you call XMLWriter.Close() method, the underlying stream doesn't get closed and is locking the file. What you need to do is to instantiate your XMLWriter with settings and specify that you need that underlying stream closed.

Example:

XMLWriterSettings settings = new Settings();
settings.CloseOutput = true;
XMLWriter writer = new XMLWriter(filepath, settings);

Hope it helps.

Answer 2

After coming across this error and not finding anything on the web that set me right, I thought I'd add another reason for getting this Exception - namely that the source and destination paths in the File Copy command are the same. It took me a while to figure it out, but it may help to add code somewhere to throw an exception if source and destination paths are pointing to the same file.

Good luck!

Answer 3

Are you running a real-time antivirus scanner by any chance ? If so, you could try (temporarily) disabling it to see if that is what is accessing the file you are trying to delete. (Chris' suggestion to use Sysinternals process explorer is a good one).