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File.SetLastWriteTime Not working as planned

Posted on 2014-01-28
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Last Modified: 2014-02-21
Hi All,
I am trying to set the File.SetLastWriteTime with that of a file that it was copied from.
It kinda works.  Problem is that when getting the new GetLastWriteTime it is one or two seconds greater than the date/time provided.

For instance if the Source file is 01/28/2014 1:18 PM, the Destination file, that is being altered, shows a value of 01/28/2014 1:20 PM. It's as if the SetLastWriteTime is working but taking a couple seconds, so that a new value is set.

example: (TDest$ and TSource$ are files, including paths)
File.SetLastWriteTime(TDest$, File.GetLastWriteTime(TSource$))

Any ideas?
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Question by:Thunder724
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Expert Comment

by:CodeCruiser
ID: 39816487
That is actually 2 minutes not seconds. Is there any other code between the setting the time and closing the file?
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Author Comment

by:Thunder724
ID: 39816535
Oh, sorry.... My fault in the example. it is actually seconds not minutes; I forgot to add the minute part.  No there is nothing between the code at all, that's why its driving me insane.
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Expert Comment

by:CodeCruiser
ID: 39816542
Can you show your code?
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LVL 4

Author Comment

by:Thunder724
ID: 39816551
sure, I put it in the original message.
But before that I am copying these files first.  
I even tried changing the SetLastWriteTime after the function that runs and contains the CopyFile function.

My.Computer.FileSystem.CopyFile(TSource$, TDest$, FileIO.UIOption.AllDialogs, FileIO.UICancelOption.ThrowException)

File.SetLastWriteTime(TDest$, File.GetLastWriteTime(TSource$))
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Expert Comment

by:CodeCruiser
ID: 39817332
If you do a

msgbox File.GetLastWriteTime(TSource$)

do you get the same datatime stamp as you see in explorer?
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Author Comment

by:Thunder724
ID: 39818185
I can't explain it; but it looks to be working correctly now. I really didn't do anything either.
I will get back to you tomorrow to close this if everything is still testing out correctly.  
Thanks very much for you help.
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Expert Comment

by:Ark
ID: 39820141
Which file system was on TDest$?
According to http://www.xxcopy.com/xxcopy15.htm
For the compatibility's sake, even WinNT/2K
  uses the same 2-second granularity for the "Last-modified" time for
  FAT-based file system (does not apply for NTFS files).
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Author Comment

by:Thunder724
ID: 39825273
NTFS.
it seems to be a specific issue only when syncing to/from a usb stick.
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Accepted Solution

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Ark earned 500 total points
ID: 39825782
There is another issue with NTFS - it does store time stamps with 100 ns granularity but it UPDATES values only after 1 hour
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