字符串截取

//$str 待截取的字符串
//$len 截取的字符个数
//$chars 已经截取的字符数
//$res   保存的字符串
//$chars 保存已经截取的字符串个数
//$offset 截取的偏移量
//$length 字符串的字节数
//若$len>$str的字符个数，造成无谓的while循环，($offset<$length限定)
 function pub_rep($str,$len){
     $res="";
     $info="";
     $offset=0;
     $chars=0;
     $length=strlen($str);
     while($chars<$len && $offset<$length){
         $hign=decbin(ord(substr($str,$offset,1)));
         if(strlen($hign)<8){
             $count=1;
         }elseif(substr($hign,0,3)=="110"){
             $count=2;
         }elseif(substr($hign,0,4)=="1110"){
             $count=3;
         }elseif(substr($hign,0,5)=="11110"){
             $count=4;
         }elseif(substr($hign,0,6)=="111110"){
             $count=5;
         }elseif(substr($hign,0,7)=="1111110"){
             $count=6;
         }
         $res.=substr($str,$offset,$count);
         $offset+=$count;
         $chars+=1;
     }
     $rep="...";
     $res.=$rep;
     return $res;
 }