php 截取两个字符间的字符串

    /**     * 截取两个字符间的字符串     * @param     * @param     */    function substr_between($string, $start, $end=null) {        if(($start_pos = strpos($string, $start)) !== false) {            if($end) {                if(($end_pos = strpos($string, $end, $start_pos + strlen($start))) !== false) {                    return substr($string, $start_pos + strlen($start), $end_pos - ($start_pos + strlen($start)));                }            } else {                return substr($string, $start_pos);            }        }        return false;    }