How to change a file without affecting the "last write time"

Question

I would like to write some stuff to file, like

using( var fs = File.OpenWrite( file ) )
{
  fs.Write( bytes, 0, bytes.Length );
}

However, this changes the "last write time". I can reset it later, by using

File.SetLastWriteTime( file, <old last write time> );

But in the meantime, a FileSystemWatcher already triggers.

Now my question: Is is possible to write a file without altering the "last write time"?

Do you really really really really want that? You do actually write to the file.. Instead you could just pause the FileSystemWatcher (which is already unreliable), so you don't have to mess with fake write times. — JustAnotherUserYouMayKnow, Apr 09 '13 at 14:04
I don't think so! unless you replace the underlying driver :P :) ! — Parimal Raj, Apr 09 '13 at 14:05
@JustAnotherUserYouMayKnow: the `FileSystemWatcher` is not necessarily under my control:/ — tanascius, Apr 09 '13 at 14:20

John Willemse · Answer 1 · 2013-04-09T14:21:12.417

You can achieve it by using P/Invoke calls in Kernel32.dll.

This Powershell script from MS TechNet achieves it, and explicitly states that a FileSystemWatcher's events are not triggered.

I have briefly looked into the script and the code is pretty straightforward and can easily be copied to your C# project.

Declaration:

[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool SetFileTime(IntPtr hFile, ref long lpCreationTime, ref long lpLastAccessTime, ref long lpLastWriteTime);

The script uses SetFileTime to lock the file times before writing.

private const int64 fileTimeUnchanged = 0xFFFFFFFF;

This constant is passed as reference to the method for lpCreationTime, lpLastAccessTime and lpLastWriteTime:

// assuming fileStreamHandle is an IntPtr with the handle of the opened filestream
SetFileTime(fileStreamHandle, ref fileTimeUnchanged, ref fileTimeUnchanged, ref fileTimeUnchanged);
// Write to the file and close the stream

Thanks for your suggestion. It seems like a possible solution, unfortunately until now, I couldn't make it work. As soon as I know more, I'll provide some feedback. — tanascius, Apr 11 '13 at 09:59

score 2 · Answer 2 · edited May 23 '17 at 11:56

2

Don't think it's possible,nor that I'm aware of.

Also consider that "last write time" Is Not Always Updated, which leads to some wired results if you're going to pick (say) some files from the folder based on that parameter or rely on that property in some way. So it's not a parameter you can rely on in your development, it's just not reliable by architecture of OS.

Simply create a flag: boolean, if this you write and watch into the same application, or a flag, like some specific named file, if you write form one and watch from another application.

edited May 23 '17 at 11:56

Community

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answered Apr 09 '13 at 14:10

Tigran

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Thanks for the answer. I am not able to work with flags or files, because the application with the FileSystemWatcher is not under my control. – tanascius Apr 11 '13 at 10:00

How to change a file without affecting the "last write time"

2 Answers2