Preserve sourcefile CreationTime on backup

[John Montenigro]

This is a lot of explanation for two lines of source code, but someday you might appreciate it!

When I want to make a backup of a file, I normally think of leaving the original in place, and making a copy to a backup location. I would think to use PB's FileCopy statement to copy the original to the backup destination. However, this simple process encountered unexpected interference from the OS (XP Pro and others)...

First, the copy's CreationTime gets set to the current date and time, and the copy will NOT have the CreationTime of the original file. (Reflex reaction would be to use the SetFileTime API call, but the OS can also interfere with that...)

Second, after the copy is deleted, and another copy is made to the same location, a feature of the OS called "file tunneling" could impose the CreationTime from the DELETED file onto your new copy. I was not able to overcome this effect with any use of the SetFileTime API call.

See discussion at: http://www.powerbasic.com/support/pb...ad.php?t=39340

HOWEVER, I found that NAME actually can be used to preserve the CreationTime, IF you reverse your thinking about the backup process!!!!

Name SourceFile As DestinationFile    ' << make backup FIRST, by MOVing original
FileCopy DestinationFile, SourceFile  ' << restore original from backup copy

This way, when the OS preserves the CreationTime from the DELETED original and imposes it on the new copy, the result is precisely what was wanted -- both files are identical, right down to their CreationTime stamps!

So if it's important to you that your backup copy carry the same CreationTime stamp of the original, just follow the above two steps, and you're golden!



To add your comments, please go to the discussion thread:
http://www.powerbasic.com/support/pb...ad.php?t=39340

[John Montenigro]

I noticed that I never posted a functional routine to demonstrate how to preserve the Creation Date on a file backup... simple (simplistic?) but effective!

'FileBACKUP_test.bas
#Dim All

Function BackupFile(ByVal SourceFile As String, ByVal DestinationFile As String) As Long

   'this works, and is the ONLY way I've found to have the "backed up" file retain the original CreationTime stamp!
   Name SourceFile As DestinationFile     'the order of these two statements is counter-intuitive, BUT...
   FileCopy DestinationFile, SourceFile   '...they accomplish the desired end result with ease!
   'the logical alternatives involving API calls DO NOT work due to "file tunneling" as discussed in:
   'http://www.powerbasic.com/support/pbforums/showthread.php?t=39340 '...teaser thread
   'http://www.powerbasic.com/support/pbforums/showthread.php?t=39419 '...concise explanation (above)

   If Err Then
      MsgBox Str$(Err),,"Error during FileCopy"
      Function = 0   'failure
   Else
      Function = 1   'success
   End If
End Function

'simple driver
Function PBMain () As Long
   Local SourceFile, DestinationFile As String, RetVal As Long

   SourceFile = "c:\bat\MOVEME.txt"
   DestinationFile = "c:\copiedMOVEME2.txt"

   RetVal = BackupFile (SourceFile, DestinationFile)
   If RetVal Then
      MsgBox SourceFile & " ==> " & DestinationFile,,"File backup succeeded!"
   Else
      MsgBox SourceFile & " ==> " & DestinationFile,,"File backup failed!"
   End If
   'compare the source and destination files' Creation Dates - they're the same! I don't know of any other way to do that! 
End Function