FileSystemInfo.LastWriteTime and 12/31/1600

I’ve been working on an application tracking the age of files and if they reaches a certain threshold an error gets trigged.

FileInfo f = new FileInfo(new SystemPath(m.FolderName).Combine(m.FileName).ToString());
double totalminutes = DateTime.Now.Subtract(f.LastWriteTime).TotalMinutes;
if (totalminutes >= ErrorIntervalInMinutes)

I setup an error message to display information about the files when the error occurs and got something like this:

Error: File (d:\outbound\997_42772_06182010_1504_91.txt) File Time: 12/31/1600 4:00:00 PM Current Time: 6/18/2010 3:06:10 PM has failed to upload via FTP for 215356266.168919 minutes.

Whoa, over 400 years! That’s a lot of minutes not to mention 12/31/1600 looks a bit suspicious. A peek at the documentation for FileInfo.LastWriteTime reveals:

If the file described in the FileSystemInfo object does not exist, this property will return 12:00 midnight, January 1, 1601 A.D. (C.E.) Coordinated Universal Time (UTC), adjusted to local time. 

Ah ha! The list of files being processed in this case is static and files are getting uploaded to an FTP server so clearly the file causing the error is no longer on disk thus the error. Adding an if(!f.Exists) continue; should do the trick.

Now, I didn’t investigate UTC once converted to local time resulting in 12/31/1600 vs. 1/1/1601 but I found my answer and after adding a simple check I was on my way.

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2 thoughts on “FileSystemInfo.LastWriteTime and 12/31/1600”

  1. Of course, this introduces a race – a file may exist for File.Exists, but be deleted when you get its modification time. How likely that is to be a concern depends on your situation.

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