[PHP] - 按长度截取字符串(针对UTF-8)

/*********************************************************************
*
* Func Name : SubStrEx
*
* Description :
*     按长度截取字符串
*
*
* Parameters :
*     $sString[string] : 字符串
*     $nLength[int] : 要取长度
*     $sDot[string="..."] : 截断符
*     $sCharset[string="UTF-8"] : 编码
*
* Returns : [bool]保存结果
*
*********************************************************************/
function SubStrEx ($sString, $nLength, $sDot = "...", $sCharset = "UTF-8") {
if (strlen($sString) <= $nLength) {
return $sString;
}

$sString = str_replace(array("&", "\"", "<", ">"), array("&", "\"", "<", ">"), $sString);

$sStrcut = "";
if (strtoupper($sCharset) == "UTF-8") {

$nPos = 0;
$nWordLen = 0;
$noc = 0;  // 单字节字符+1,多字节+2(将非单字节字符的长度当做是2[应该是视觉感觉吧])
while ($nPos < strlen($sString)) {

$t = ord($sString[$nPos]);
if ($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
$nWordLen = 1;
$noc++;
} elseif (194 <= $t && $t <= 223) {
$nWordLen = 2;
$noc += 2;
} elseif (224 <= $t && $t <= 239) {
$nWordLen = 3;
$noc += 2;
} elseif (240 <= $t && $t <= 247) {
$nWordLen = 4;
$noc += 2;
} elseif (248 <= $t && $t <= 251) {
$nWordLen = 5;
$noc += 2;
} elseif ($t == 252 || $t == 253) {
$nWordLen = 6;
$noc += 2;
} else {
$nWordLen = 0;
}

$nPos += ($nWordLen > 0) ? $nWordLen : 1;

if ($noc >= $nLength) {
break;
}
}
if ($noc > $nLength) {
$nPos -= $nWordLen;
}
$sStrcut = substr($sString, 0, $nPos);

} else {
for ($i = 0; $i < $nLength; $i++) {
$sStrcut .= ord($sString[$i]) > 127 ? $sString[$i] . $sString[++ $i] : $sString[$i];
}
}

$sStrcut = str_replace(array("&", "\"", "<", ">"), array("&", "\"", "<", ">"), $sStrcut);

return $sStrcut . $sDot;
}