PHP實現截取字符串的通用方法

/**


截取字符串
params $string 要截取的字符串
params $length: 保留長度（字符數）
params $dot: 多余部分顯示
**/
function _cutstr($string, $length, $dot = ' ...') {
if(strlen($string) <= $length) {
return $string;

}
$string = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $string);
$strcut = '';
$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('&', '"', '<', '>'), $strcut);
return $strcut.$dot;
}</pre>