不能修改常量的值？
define('SESS_ID', $sess->get_session_id());

PHP code

if(empty(SESS_ID)){ SESS_ID = 'xxwe';}

PHP code

define('SESS_ID', $sess->get_session_id());#==============================if ( !defined('SESS_ID') ) {    echo "木有定义哦~";    define('SESS_ID', 'xxwe');}