php字符串截取 中英文混排

php字符串截取经常用到，此函数将中英文按照1比3截取，如果按照1比2截取将$noc += 3;改成$noc += 2;

从网上找的一个处理函数

function _str_cut($sourcestr,$cutlength,$suffix='...') {
        $str_length = strlen($sourcestr);
        if($str_length <= $cutlength) {
            return $sourcestr;
        }
        $returnstr='';
        $n = $i = $noc = 0;
        while($n < $str_length) {
            $t = ord($sourcestr[$n]);
            if($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
                $i = 1;
                $n++;
                $noc++;
            } elseif(194 <= $t && $t <= 223) {
                $i = 2;
                $n += 2;
                $noc += 3;
            } elseif(224 <= $t && $t <= 239) {
                $i = 3;
                $n += 3;
                $noc += 3;
            } elseif(240 <= $t && $t <= 247) {
                $i = 4;
                $n += 4;
                $noc += 3;
            } elseif(248 <= $t && $t <= 251) {
                $i = 5;
                $n += 5;
                $noc += 3;
            } elseif($t == 252 || $t == 253) {
                $i = 6;
                $n += 6;
                $noc += 3;
            } else {
                $n++;
            }
            if($noc >= $cutlength) {
                break;
            }
        }
        if($noc > $cutlength) {
            $n -= $i;
        }
        $returnstr = substr($sourcestr, 0, $n);
        if ( substr($sourcestr, $n, 6)){
          $returnstr = $returnstr . $suffix;//超过长度时在尾处加上省略号
        }
        return $returnstr;
    }