PHP字符中间加*星号代码，支持中英文

static function PassStart($str,$start,$end=0,$dot="*",$charset="UTF-8"){
$len = mb_strlen($str,$charset);
if($start==0||$start>$len){
$start = 1;
}
if($end!=0&&$end>$len){
$end = $len-2;
}
$endStart = $len-$end;
$top = mb_substr($str, 0,$start,$charset);
$bottom = "";
if($endStart>0){
$bottom =  mb_substr($str, $endStart,$end,$charset);
}
$len = $len-mb_strlen($top,$charset);
$len = $len-mb_strlen($bottom,$charset);
$newStr = $top;
for($i=0;$i<$len;$i++){
$newStr.=$dot;
}
$newStr.=$bottom;
return $newStr;
}