function substring($str, $start, $length){ //比较好用字符串截取函数
  $len = $length;
  if($length < 0){
  $str = strrev($str);
  $len = -$length;
  }
  $len= ($len < strlen($str)) "";
  for ($i= $start; $i < $len; $i ++)
  {
      if (ord(substr($str, $i, 1)) > 0xa0)
      {
       $tmpstr .= substr($str, $i, 2);
       $i++;
      } else {
       $tmpstr .= substr($str, $i, 1);
      }
  }
  if($length < 0) $tmpstr = strrev($tmpstr);
  return $tmpstr;
}

$str1 = '我是一串比较长的中文不带英文';
$str2 = '我是一串比较长的中文带yingwen';


$len = strlen($str1);
echo '<br />'.$len; //return 28

$len = strlen($str2);
echo '<br />'.$len; //return 29

echo '<br />';  
echo substring($str1, 0, 11);  
echo '<br />';
echo substring($str2, 0, 11);    
echo '<br />';
echo substring($str1, 16, 28);  
echo '<br />';
echo substring($str2, 16, 29);  

function formatName($str, $size){
  $len = strlen($str);
  if(strlen($str) > $size) {
    $part1 = substring($str, 0, $size / 2);
    $part2 = substring($str, $len - ($size/2), $len);
    return $part1 . "..." . $part2;
  } else {
    return $str;
  }
}

function strlen_UTF8($str)
{
  $len = strlen($str);
  $n = 0;
  for($i = 0; $i < $len; $i++) {
    $x = substr($str, $i, 1);
    $a = base_convert(ord($x), 10, 2);
    $a = substr('00000000'.$a, -8);
    if (substr($a, 0, 1) == 0) {
    }elseif (substr($a, 0, 3) == 110) {
      $i += 1;
    }elseif (substr($a, 0, 4) == 1110) {
      $i += 2;
    }
    $n++;
  }
  return $n;
} // End strlen_UTF8;

function subString_UTF8($str, $start, $lenth)
  {
    $len = strlen($str);
    $r = array();
    $n = 0;
    $m = 0;
    for($i = 0; $i < $len; $i++) {
      $x = substr($str, $i, 1);
      $a = base_convert(ord($x), 10, 2);
      $a = substr('00000000'.$a, -8);
      if ($n < $start){
        if (substr($a, 0, 1) == 0) {
        }elseif (substr($a, 0, 3) == 110) {
          $i += 1;
        }elseif (substr($a, 0, 4) == 1110) {
          $i += 2;
        }
        $n++;
      }else{
        if (substr($a, 0, 1) == 0) {
          $r[ ] = substr($str, $i, 1);
        }elseif (substr($a, 0, 3) == 110) {
          $r[ ] = substr($str, $i, 2);
          $i += 1;
        }elseif (substr($a, 0, 4) == 1110) {
          $r[ ] = substr($str, $i, 3);
          $i += 2;
        }else{
          $r[ ] = '';
        }
        if (++$m >= $lenth){
          break;
        }
      }
    }
    return join($r);
  } // End subString_UTF8;

function formatName($str, $size){
 $len = strlen_UTF8($str);
 $one_len = strlen($str);
 $size = $size * 1.5 * $len / ($one_len);
 if(strlen_UTF8($str) > $size) {
  $part1 = subString_UTF8($str, 0, $size / 2);
  $part2 = subString_UTF8($str, $len - ($size/2), $len);
  return $part1 . "..." . $part2;
 } else {
  return $str;
 }
}