mb_substr( $str, $start, $length, $encoding ) $str，需要截断的字符串 $start，截断开始处，起始处为0 $length，要截取的字数 $encoding，网页编码，如utf-8,GB2312,GBK ================================== mb_strlen( $str, $encoding ) $str，要计算长度的字符串 $encoding，网页编码，如utf-8,GB2312,GBK