PHP字符串截取，计算字符串长度

/**
 * 字符串截取，支持中文和其他编码
 * @param  [string]  $str     [字符串]
 * @param  integer $start   [起始位置]
 * @param  integer $length  [截取长度]
 * @param  string  $charset [字符串编码]
 * @param  boolean $suffix  [是否有省略号]
 * @return [type]           [description]
 */
function msubstr($str, $start=0, $length=15, $charset="utf-8", $suffix=true) {
    if(function_exists("mb_substr")) {
        return mb_substr($str, $start, $length, $charset);
    } elseif(function_exists('iconv_substr')) {
        return iconv_substr($str,$start,$length,$charset);
    }
    $re['utf-8']   = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/";
    $re['gb2312'] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/";
    $re['gbk']    = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/";
    $re['big5']   = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/";
    preg_match_all($re[$charset], $str, $match);
    $slice = join("",array_slice($match[0], $start, $length));
    if($suffix) {
        return $slice."…";
    }
    return $slice;
}
/**
 * @计算中文字符串长度，只支持UTF8编码
 */
function utf8_strlen($string = null) {
       preg_match_all(“/./us”, $string, $match);
       return count($match[0]);
}