在使用php的include/require/include_once/require_once时有时会碰到路径困扰，尤其是重复包含或嵌套包含时，一个有效的办法是定义文件“根”，如：
if (!defined('KEIYICLASS_ROOT')) {define('KEIYICLASS_ROOT', dirname(__FILE__) . '/');}// core classesinclude_once(KEIYICLASS_ROOT."core/date.php");include_once(KEIYICLASS_ROOT."core/db.php");include_once(KEIYICLASS_ROOT."core/init.php");include_once(KEIYICLASS_ROOT."core/sys.php");