字符截取 支持UTF8/GBK

/**
 * 字符截取 支持UTF8/GBK
 * @param $string
 * @param $length
 * @param $dot
 */
function str_cut($string, $length, $dot = '...') {
    $strlen = strlen($string);
    if($strlen <= $length) return $string;
    $string = str_replace(array(' ','&nbsp;', '&amp;', '&quot;', ''', '&ldquo;', '&rdquo;', '&mdash;', '&lt;', '&gt;', '&middot;', '&hellip;'), array('∵',' ', '&', '"', "'", '“', '”', '—', '<', '>', '·', '…'), $string);
    $strcut = '';
    if(strtolower(CHARSET) == 'utf-8') {
        $length = intval($length-strlen($dot)-$length/3);
        $n = $tn = $noc = 0;
        while($n < strlen($string)) {
            $t = ord($string[$n]);
            if($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
                $tn = 1; $n++; $noc++;
            } elseif(194 <= $t && $t <= 223) {
                $tn = 2; $n += 2; $noc += 2;
            } elseif(224 <= $t && $t <= 239) {
                $tn = 3; $n += 3; $noc += 2;
            } elseif(240 <= $t && $t <= 247) {
                $tn = 4; $n += 4; $noc += 2;
            } elseif(248 <= $t && $t <= 251) {
                $tn = 5; $n += 5; $noc += 2;
            } elseif($t == 252 || $t == 253) {
                $tn = 6; $n += 6; $noc += 2;
            } else {
                $n++;
            }
            if($noc >= $length) {
                break;
            }
        }
        if($noc > $length) {
            $n -= $tn;
        }
        $strcut = substr($string, 0, $n);
        $strcut = str_replace(array('∵', '&', '"', "'", '“', '”', '—', '<', '>', '·', '…'), array(' ', '&amp;', '&quot;', ''', '&ldquo;', '&rdquo;', '&mdash;', '&lt;', '&gt;', '&middot;', '&hellip;'), $strcut);
    } else {
        $dotlen = strlen($dot);
        $maxi = $length - $dotlen - 1;
        $current_str = '';
        $search_arr = array('&',' ', '"', "'", '“', '”', '—', '<', '>', '·', '…','∵');
        $replace_arr = array('&amp;','&nbsp;', '&quot;', ''', '&ldquo;', '&rdquo;', '&mdash;', '&lt;', '&gt;', '&middot;', '&hellip;',' ');
        $search_flip = array_flip($search_arr);
        for ($i = 0; $i < $maxi; $i++) {
            $current_str = ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i];
            if (in_array($current_str, $search_arr)) {
                $key = $search_flip[$current_str];
                $current_str = str_replace($search_arr[$key], $replace_arr[$key], $current_str);
            }
            $strcut .= $current_str;
        }
    }
    return $strcut.$dot;
}