php摘要生成函数(无乱码)

function cutstr($string, $length,$charset,$dot) {//字符，截取长度，字符集，结尾符
if(strlen($string) <= $length) {
return $string;
}
$pre = chr(1);
$end = chr(1);
//保护特殊字符串
$string = str_replace(array('&amp;', '&quot;', '&lt;', '&gt;'), array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), $string);
$strcut = '';
if(strtolower($charset) == 'utf-8') {
$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, $n);
} else {
for($i = 0; $i < $length; $i++) {
$strcut .= ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i];
}
}
//还原特殊字符串
$strcut = str_replace(array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), array('&amp;', '&quot;', '&lt;', '&gt;'), $strcut);
//修复出现特殊字符串截段的问题
$pos = strrpos($s, chr(1));
if($pos !== false) {
$strcut = substr($s,0,$pos);
}
return $strcut.$dot;
}