How to convert Short to Long filenames

uses
  Shellapi;

function GetLongFileName(const FileName: string): string;
var
  SHFileInfo: TSHFileInfo;
begin
  if SHGetFileInfo(PChar(FileName),
                   0,
                   SHFileInfo,
                   SizeOf(SHFileInfo),
                   SHGFI_DISPLAYNAME) <> 0 then
    Result := string(SHFileInfo.szDisplayName)
  else
    Result := FileName;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Caption := GetLongFileName('C:\Program Files\Delphi6\Lib\BK_STR~1.DPK');
  // --> BK_StringGrid.dpk
end;