[ComImport(),
    Guid("00021500-0000-0000-C000-000000000046"),
    InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IQueryInfo
    {

        [PreserveSig]
        int GetInfoTip(
            int dwFlags,
            out IntPtr ppwszTip );

        [PreserveSig]
        int GetInfoFlags( out int pdwFlags );
    }

    // free ppwszTip by CoTaskMemFree()
    //
    //     IntPtr p;
    //     if( 0 == qi.GetInfoTip( dwFlags, out p ) )
    //    {
    //        string strTip = Marshal.PtrToStringUni( p );
    //        Marshal.FreeCoTaskMem( p );
    //        ...
    //    }