CODEWITHSUNDEEP
c#
amccormack
amccormack

Reputation: 13927

Open a file that has just been closed

I'm writing an application that manipulates a text file. The first half of my function reads the textfile, while the second half writes to (optionally) the same file. Although I call .close() on the StreamReader object before opening the StreamWriter object, I still get a IOException: The process cannot access the file "file.txt" because it is being used by another process.

How do I force my program to release the file before continuing?

public static void manipulateFile(String fileIn, String fileOut,String obj)
    {
        StreamReader sr = new StreamReader(fileIn);
        String line;
        while ((line = sr.ReadLine()) != null)
        {
            //code to split up file into part1, part2, and part3[]
        }
        sr.Close();

        //Write the file
        if (fileOut != null)
        {
            StreamWriter sw = new StreamWriter(fileOut);
            sw.Write(part1 + part2);
            foreach (String s in part3)
            {
                sw.WriteLine(s);
            }
            sw.Close();
        }

    }

Upvotes: 1

Views: 196

Answers (3)

Hans Passant
Hans Passant

Reputation: 941317

Getting read access to a file that's already opened elsewhere isn't usually difficult. Most code would open a file for reading with FileShare.Read, allowing somebody else to read the file as well. StreamReader does so for example.

Getting write access is an entirely different ball of wax. That same FileShare.Read does not include FileShare.Write, allowing you to write the file while somebody else is reading it. That's very troublesome, you're jerking the mat out from under that somebody else, suddenly providing entirely different data.

All you have to do is find out who that 'somebody else' might be. SysInternals' Handles utility can tell you. Hopefully it is your own program, you could do something about that.

Upvotes: 1

user348905
user348905

Reputation:

May sound like a stupid question, but are you sure you didn't edit the file with another application, which didn't release the file? I've had this situation before, mostly with Excel files where Excel didn't completely unloading from memory (or me just being dumb enough not to close the other application sometimes). Might happen with whatever application you use for .txt files, if any. Just a suggestion.

Upvotes: 0

Mark Byers
Mark Byers

Reputation: 838076

Your code as posted runs fine - I don't see the exception.

However calling Close() manually like that is a bad idea - if an exception is thrown your call to Close() might never be made. You should use a finally block, or better yet : a using statement.

using (StreamReader sr = new StreamReader(fileIn))
{
    // ...
}

But the actual problem you are experiencing might not be specifically with this method, but a general problem with forgetting to close files properly in using blocks. I suggest you go through all your code base and look for all the places in your code where you use IDisposable objects and check that you dispose them correctly even when there could be exceptions.

Upvotes: 4

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