中英文截取字符串無亂碼

//PHP中英文截取無亂碼
header(‘Content_type=text/php;charset=UTF-8’);
$str = ‘北京beijing大學’;
//關鍵在於判斷往後截多少個字節上，這是這個函數的核心
//此函數是用客串來判斷的，效率不高
//位運算效果會更好
//110x xxxx && 1110 0000 -> 1100 0000
//1110 xxxx && 1111 0000 -> 1110 0000
//位運算時不受英文字符最高位爲0的影響，只是在轉成字符串才受到影響
function utf8sub($str,$len){
if($len<0){
     return ”;
}
$res = ”;
$offset = 0;
$chars = 0;
$count = 0;
$length = strlen($str);//待截取字符串的字節數
while($chars<$len && $offset<$length){
     $high = decbin(ord(substr(str, offset,1)));//先截取客串的一個字節，substr按字節進行截取
     //重要突破，已經能夠判斷高位字節
    if(strlen($high)<8){
         $count = 1;
    }elseif (substr($high,0,3) == ‘110’) {
        $count = 2; //取兩個字節的長度
    }elseif (substr($high,0,4) == ‘1110’) {
          $count = 3; //取三個字節的長度
    }elseif (substr($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);