PHP字符串截取

/** * * 字符截取 * @param string $string * @param int $start * @param int $length * @param string $charset * @param string $dot * * @return string */function str_cut(&$string, $start, $length, $charset = "utf-8", $dot = '...') {    if(function_exists('mb_substr')) {        if(mb_strlen($string, $charset) > $length) {            return mb_substr ($string, $start, $length, $charset) . $dot;        }        return mb_substr ($string, $start, $length, $charset);    }else if(function_exists('iconv_substr')) {        if(iconv_strlen($string, $charset) > $length) {            return iconv_substr($string, $start, $length, $charset) . $dot;        }        return iconv_substr($string, $start, $length, $charset);    }    $charset = strtolower($charset);    switch ($charset) {        case "utf-8" :            preg_match_all("/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/", $string, $ar);            if(func_num_args() >= 3) {                if (count($ar[0]) > $length) {                    return join("", array_slice($ar[0], $start, $length)) . $dot;                }                return join("", array_slice($ar[0], $start, $length));            } else {                return join("", array_slice($ar[0], $start));            }            break;        default:            $start = $start * 2;            $length   = $length * 2;            $strlen = strlen($string);            for ( $i = 0; $i < $strlen; $i++ ) {                if ( $i >= $start && $i < ( $start + $length ) ) {                    if ( ord(substr($string, $i, 1)) > 129 ) $tmpstr .= substr($string, $i, 2);                    else $tmpstr .= substr($string, $i, 1);                }                if ( ord(substr($string, $i, 1)) > 129 ) $i++;            }            if ( strlen($tmpstr) < $strlen ) $tmpstr .= $dot;            return $tmpstr;    }}