Title: How to get an Unique Identifier for a File or Folder
Question: Everyone who creates a File/folder copy or move-function must check if a sourcefile/folder exists at the destination. But how can we proof that two files don't point to the same physical place? Windows 2000 and XP allows to mount any volume under a folder and so it's possible that the files at 'c:\data\*.*' are the same as under 'd:\*.*' for example.
Answer:
To get an unique ID from a File or Folder you can use the API-Function GetFileInformationByHandle respective the Infos got from those function. The combination of the FileIndex with the Serial-Number of the Volume identifies a File.
To check if two files points to the same physical place just compare the two UIDs got from the function below.
btw: the function also works for folders because it uses FILE_FLAG_BACKUP_SEMANTICS; But this Flag ONLY works on WinNT and higher.
{-----------------------------------------------------------------------------
Procedure: GetUFID
Arguments: Filename: String
Result: String
Comments: Generate a Unique File-Identifier based upon Fileindex and the
VolumeSerialnumber. If Filename doesn't exists result = '';
-----------------------------------------------------------------------------}
Function GetUFID(Filename: String): String;
Var
hFile : tHandle;
FileInfo : BY_HANDLE_FILE_INFORMATION;
HighOrder,
LowOrder : Int64;
Begin
// Get Filehandle ... Warning: Works only under WinNT and higher !!!
hFile := CreateFile(pChar(Filename), 0, FILE_SHARE_READ, nil, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0);
If hFile INVALID_HANDLE_VALUE then
Begin
If (GetFileInformationByHandle(hFile, FileInfo) = True) then
Begin
// Specifies the high-order word of a unique identifier associated with the file/folder
HighOrder := FileInfo.nFileIndexHigh;
// Specifies the low-order word of a unique identifier associated with the
// file. This identifier and the volume serial number uniquely identify a file/folder
LowOrder := FileInfo.nFileIndexLow;
Result := Format('[%s-%s-%s]', [IntToStr(FileInfo.dwVolumeSerialNumber), IntToStr(LowOrder), IntToStr(HighOrder)]);
End
Else Result := '';
End
else Result := '';
CloseHandle(hFile); //Release Handle
End;