PHP实现如何分辨全角和半角以避免乱码

function ChgTitle($title)
{
$length = 46;
if (strlen($title)>$length) {
$temp = 0;
for($i=0; $i<$length; $i++)
if (ord($title[$i]) > 128)
$temp++;
if ($temp%2 == 0)
$title = substr($title,0,$length)."...";
else
$title = substr($title,0,$length+1)."...";
}
return $title;
}