VB Forum / Win API / April 2007

That's because there is nothing to find. Think about it for a moment, there
are an infinite number of potential files but if you are using a long only a
little over 4 billion possible numbers, so it is not possible for every file
to have a unique number, nor is there any useful reason to have one. You can
generate a CRC for any file, this is a number which can be used to check the
file for corruption as it changes if the file changes but for a quantity of
large files such as media it would take too long to calculate and would
change if the files tag was edited

If you want to avoid the database losing sync with the files, put the
editing tools into the database front end and have it update the file & the
database together.

If you can read the headers of your media files and know how long the
tag/header is, you should be able to grab a K or 2 of the file which will be
the same regardless of the size of the tag or header, you can then take a
CRC of this excerpt and put that into your database then the program can
identify the file even if its name and location are changed and the tag
edited.

Best Regards
Dave O.

I think what you're looking for YisMan is the "File Index". This can be
obtained from the BY_HANDLE_FILE_INFORMATION structure, via
GetFileInformationByHandle. The file index is bigger than a long but if you
represent it in textual form then you can still use it as a unique key. For
instance...

Const INVALID_HANDLE_VALUE = -1

Const OPEN_EXISTING = 3

Private Declare Function CloseHandle Lib "kernel32" ( _
   ByVal hObject As Long) As Long

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 GetFileInformationByHandle Lib "kernel32" ( _
   ByVal hFile As Long, lpFileInformation As BY_HANDLE_FILE_INFORMATION) As
Long

Private Type FILETIME
   dwLowDateTime As Long
   dwHighDateTime As Long
End Type

Private Type BY_HANDLE_FILE_INFORMATION
   dwFileAttributes As Long
   ftCreationTime As FILETIME
   ftLastAccessTime As FILETIME
   ftLastWriteTime As FILETIME
   dwVolumeSerialNumber As Long
   nFileSizeHigh As Long
   nFileSizeLow As Long
   nNumberOfLinks As Long
   nFileIndexHigh As Long
   nFileIndexLow As Long
End Type

Private tInfo As BY_HANDLE_FILE_INFORMATION 'Current file information

Private Function sGetFileInfo(sFile As String) As String
' Fill out tInfo with file information. Returns an error string if this
fails, e.g.
' if the file doesn't exist.
Dim hFile As Long

   ' Open the file to get attributes (no I/O intended)
   hFile = CreateFile(sFile, 0, 0, 0, OPEN_EXISTING, 0, 0)
   If hFile = INVALID_HANDLE_VALUE Then
       sGetFileInfo = sGetErrMessage()
       Exit Function
   End If
   ' Read the unique file index, and the file's modifications date/time
   If GetFileInformationByHandle(hFile, tInfo) = 0 Then
       sGetFileInfo = sGetErrMessage()
   End If
   CloseHandle hFile
End Function

Private Function sFileIndex() As String
' Returns the unique file index for the current file as 16-digit hex string
(i.e. 64
' bits formatted as hex)

   sFileIndex = Right$("0000000" & Hex(tInfo.nFileIndexHigh), 8) & _
       Right$("0000000" & Hex(tInfo.nFileIndexLow), 8)
End Function

   Tony Proctor