FileCopy NTFS to FAT32 changes file's modified date

I've just been bitten by an annoying quirk, experienced on 2 different WindowsXP systems.

When copying a file from an NTFS partition to a FAT32 device, the new file's modified date is sometimes changed by 1 or 2 seconds.
This became apparent in a file syncronization program I have that compares mod dates and copies newer files over the older, and in this case can never catch up since the mod date is a moving target.

Only some files do this, and they do it consistently. It seems to have something to do with the original mod date value, maybe different number systems are rounding or something??

I tried doing a drag-n-drop copy within Windows Explorer and it did the same thing.

Anyone else see this behavior?

DaveBo

Forgot to add my little code snippet

VB Code:

Private Sub Command1_Click()
    Const File1 = "C:\Junk.doc"
    Const File2 = "E:\Junk.doc"
 
    FileCopy File1, File2
    Debug.Print File1 & " "; FileDateTime(File1)
    Debug.Print File2 & " "; FileDateTime(File2)
End Sub
 
' C:\Junk.doc 2/14/2006 7:52:30 PM
' E:\Junk.doc 2/14/2006 7:52:32 PM

Hi, I don't have a FAT drive here to replicate your problem, but a possible solution could be just get the file time before copying and then change the copied file time to that time. How to do this..

In a Form..

VB Code:

Option Explicit
 
Private Type FILETIME
    dwLowDateTime As Long
    dwHighDateTime As Long
End Type
 
Private Type SYSTEMTIME
    wYear As Integer
    wMonth As Integer
    wDayOfWeek As Integer
    wDay As Integer
    wHour As Integer
    wMinute As Integer
    wSecond As Integer
    wMilliseconds As Integer
End Type
 
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, _
    ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, _
    ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, _
    ByVal hTemplateFile As Long) As Long
Private Declare Function SetFileTime Lib "kernel32" (ByVal hFile As Long, _
    lpCreationTime As FILETIME, lpLastAccessTime As FILETIME, lpLastWriteTime As FILETIME) As Long
Private Declare Function SystemTimeToFileTime Lib "kernel32" (lpSystemTime As SYSTEMTIME, _
    lpFileTime As FILETIME) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function LocalFileTimeToFileTime Lib "kernel32" (lpLocalFileTime As FILETIME, _
    lpFileTime As FILETIME) As Long
 
Private Const GENERIC_WRITE = &H40000000
Private Const OPEN_EXISTING = 3
Private Const FILE_SHARE_READ = &H1
Private Const FILE_SHARE_WRITE = &H2
 
 
Private Sub ChangeFileTime(FilePath As String, NewDateModified As Date)
Dim lngHandle       As Long
Dim udtFileTime     As FILETIME
Dim udtLocalTime    As FILETIME
Dim udtSystemTime   As SYSTEMTIME
 
    With udtSystemTime
        .wYear = Year(NewDateModified)
        .wMonth = Month(NewDateModified)
        .wDay = Day(NewDateModified)
        .wDayOfWeek = Weekday(NewDateModified) - 1
        .wHour = Hour(NewDateModified)
        .wMinute = Minute(NewDateModified)
        .wSecond = Second(NewDateModified)
        .wMilliseconds = 0
    End With
 
    ' convert system time to local time
    SystemTimeToFileTime udtSystemTime, udtLocalTime
    ' convert local time to GMT
    LocalFileTimeToFileTime udtLocalTime, udtFileTime
    ' open the file to get the filehandle
    lngHandle = CreateFile(FilePath, GENERIC_WRITE, FILE_SHARE_READ Or FILE_SHARE_WRITE, _
                           ByVal 0&, OPEN_EXISTING, 0, 0)
    ' change date/time property of the file
    SetFileTime lngHandle, udtFileTime, udtFileTime, udtFileTime
    ' close the handle
    CloseHandle lngHandle
End Sub
 
Private Sub CopyFile(FromPath As String, ToPath As String)
Dim TempDateTime As Date
 
    TempDateTime = FileDateTime(FromPath)
    FileCopy FromPath, ToPath
    ChangeFileTime ToPath, TempDateTime
End Sub

Then call it like this..

VB Code:

Private Sub Command1_Click()
    Debug.Print FileDateTime("C:\Junk.doc") 'check the file time before copying
    CopyFile "C:\Junk.doc", "E:\Junk.doc"
    Debug.Print FileDateTime("E:\Junk.doc") 'check the copied file time, should be the same
End Sub

Thanks jcis,

For now I simply put a 5-second fudge factor in the file comparison logic.
i.e. to consider a file older or newer I insist on at least a 5 sec diff.
The 5 seconds is an arbitrary number.