srodriguez srodriguez - 6 months ago 117
C# Question

System.IO.IOException: file used by another process

Dear all,
I've been working in this small piece of code that seems trivial but still i cannot really see where is the problem. My functions does 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);


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

result = true;
catch (Exception 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,


Sounds like an external process (AV?) is locking it, but can't you avoid the problem in the first place?

private static bool modifyFile(FileInfo file, string extractedMethod, string modifiedMethod)
        string contents = File.ReadAllText(file.FullName);
        Console.WriteLine("input : {0}", contents);
        contents = contents.Replace(extractedMethod, modifiedMethod);
        Console.WriteLine("replaced String {0}", contents);
        File.WriteAllText(file.FullName, contents);
        return true;
    catch (Exception ex)
        return false;