中英文截取字符串无乱码

//PHP中英文截取无乱码
header(‘Content_type=text/php;charset=UTF-8’);
$str = ‘北京beijing大学’;
//关键在于判断往后截多少个字节上，这是这个函数的核心
//此函数是用客串来判断的，效率不高
//位运算效果会更好
//110x xxxx && 1110 0000 -> 1100 0000
//1110 xxxx && 1111 0000 -> 1110 0000
//位运算时不受英文字符最高位为0的影响，只是在转成字符串才受到影响
function utf8sub($str,$len){
if($len<0){
     return ”;
}
$res = ”;
$offset = 0;
$chars = 0;
$count = 0;
$length = strlen($str);//待截取字符串的字节数
while($chars<$len && $offset<$length){
     $high = decbin(ord(substr(str,offset,1)));//先截取客串的一个字节，substr按字节进行截取
     //重要突破，已经能够判断高位字节
    if(strlen($high)<8){
         $count = 1;
    }elseif (substr($high,0,3) == ‘110’) {
        $count = 2; //取两个字节的长度
    }elseif (substr($high,0,4) == ‘1110’) {
          $count = 3; //取三个字节的长度
    }elseif (substr($high,0,5) == ‘11110’) {
          $count = 4;
    }elseif (substr($high,0,6) == ‘111110’) {
         $count = 5;
    }elseif(substr($high,0,7)==’1111110’){
         $count = 6;
    }
    $res .= substr($str,$offset,$count);
    $chars +=1;
    $offset += $count;
     }
    return $res;
}
echo utf8sub($str,5);
echo utf8sub($str,10);