PHP字符串截取长度自定义方法

//截取字符串长度
function cut($Str, $Length,$more=true) {
    //$Str为截取字符串，$Length为需要截取的长度
    global $s;
    $i = 0;
    $l = 0;
    $ll = strlen($Str);
    $s = $Str;
    $f = true;
    while ($i <= $ll) {
        if (ord($Str{$i}) < 0x80) {
            $l++; $i++;
        } else if (ord($Str{$i}) < 0xe0) {
            $l++; $i += 2;
        } else if (ord($Str{$i}) < 0xf0) {
            $l += 2; $i += 3;
        } else if (ord($Str{$i}) < 0xf8) {
            $l += 1; $i += 4;
        } else if (ord($Str{$i}) < 0xfc) {
            $l += 1; $i += 5;
        } else if (ord($Str{$i}) < 0xfe) {
            $l += 1; $i += 6;
        }
         
        if (($l >= $Length - 1) && $f) {
            $s = substr($Str, 0, $i);
            $f = false;
        }
         
        if (($l > $Length) && ($i < $ll) && $more) {
            $s = $s . &#39;...&#39;; 
            break; 
            //如果进行了截取，字符串末尾加省略符号“...”
        }
    }
    return $s;
}

$str = '看看截取到哪里？';
echo cut($str,1);
echo &#39;<br>&#39;;
echo cut($str,4);
echo &#39;<br>&#39;;
echo cut($str,5);
echo &#39;<br>&#39;;
echo cut($str,5,false);
echo &#39;<br>&#39;;
 
$str = &#39;中英文混合看看hello?&#39;;
echo cut($str,18);
echo &#39;<br>&#39;;
echo cut($str,50);

看...
看看...
看看...
看看
中英文混合看看hel...
中英文混合看看hello?