//获取汉字的首字母
function getFirstCharters($str)
{
  if (empty($str)) {
    return '';
  }
  //取出参数字符串中的首个字符
  $temp_str = substr($str,0,1);
  if(ord($temp_str) > 127){
    $str = substr($str,0,3);
  }else{
    $str = $temp_str;
    $fchar = ord($str{0});
    if ($fchar >= ord('A')  $fchar = ord('z')){
      return strtoupper($temp_str);
    }else{
      return null;
    }
  }
  $s1 = iconv('UTF-8', 'gb2312//IGNORE', $str);
  if(empty($s1)){
    return null;
  }
  $s2 = iconv('gb2312', 'UTF-8', $s1);
  if(empty($s2)){
    return null;
  }
  $s = $s2 == $str ? $s1 : $str;
  $asc = ord($s{0}) * 256 + ord($s{1}) - 65536;
  if ($asc >= -20319  $asc = -20284)
    return 'A';
  if ($asc >= -20283  $asc = -19776)
    return 'B';
  if ($asc >= -19775  $asc = -19219)
    return 'C';
  if ($asc >= -19218  $asc = -18711)
    return 'D';
  if ($asc >= -18710  $asc = -18527)
    return 'E';
  if ($asc >= -18526  $asc = -18240)
    return 'F';
  if ($asc >= -18239  $asc = -17923)
    return 'G';
  if ($asc >= -17922  $asc = -17418)
    return 'H';
  if ($asc >= -17417  $asc = -16475)
    return 'J';
  if ($asc >= -16474  $asc = -16213)
    return 'K';
  if ($asc >= -16212  $asc = -15641)
    return 'L';
  if ($asc >= -15640  $asc = -15166)
    return 'M';
  if ($asc >= -15165  $asc = -14923)
    return 'N';
  if ($asc >= -14922  $asc = -14915)
    return 'O';
  if ($asc >= -14914  $asc = -14631)
    return 'P';
  if ($asc >= -14630  $asc = -14150)
    return 'Q';
  if ($asc >= -14149  $asc = -14091)
    return 'R';
  if ($asc >= -14090  $asc = -13319)
    return 'S';
  if ($asc >= -13318  $asc = -12839)
    return 'T';
  if ($asc >= -12838  $asc = -12557)
    return 'W';
  if ($asc >= -12556  $asc = -11848)
    return 'X';
  if ($asc >= -11847  $asc = -11056)
    return 'Y';
  if ($asc >= -11055  $asc = -10247)
    return 'Z';
  return rare_words($asc);
}
//百家姓中的生僻字
function rare_words($asc=''){
  $rare_arr = array(
    -3652=>array('word'=>"窦",'first_char'=>'D'),
    -8503=>array('word'=>"奚",'first_char'=>'X'),
    -9286=>array('word'=>"酆",'first_char'=>'F'),
    -7761=>array('word'=>"岑",'first_char'=>'C'),
    -5128=>array('word'=>"滕",'first_char'=>'T'),
    -9479=>array('word'=>"邬",'first_char'=>'W'),
    -5456=>array('word'=>"臧",'first_char'=>'Z'),
    -7223=>array('word'=>"闵",'first_char'=>'M'),
    -2877=>array('word'=>"裘",'first_char'=>'Q'),
    -6191=>array('word'=>"缪",'first_char'=>'M'),
    -5414=>array('word'=>"贲",'first_char'=>'B'),
    -4102=>array('word'=>"嵇",'first_char'=>'J'),
    -8969=>array('word'=>"荀",'first_char'=>'X'),
    -4938=>array('word'=>"於",'first_char'=>'Y'),
    -9017=>array('word'=>"芮",'first_char'=>'R'),
    -2848=>array('word'=>"羿",'first_char'=>'Y'),
    -9477=>array('word'=>"邴",'first_char'=>'B'),
    -9485=>array('word'=>"隗",'first_char'=>'K'),
    -6731=>array('word'=>"宓",'first_char'=>'M'),
    -9299=>array('word'=>"郗",'first_char'=>'X'),
    -5905=>array('word'=>"栾",'first_char'=>'L'),
    -4393=>array('word'=>"钭",'first_char'=>'T'),
    -9300=>array('word'=>"郜",'first_char'=>'G'),
    -8706=>array('word'=>"蔺",'first_char'=>'L'),
    -3613=>array('word'=>"胥",'first_char'=>'X'),
    -8777=>array('word'=>"莘",'first_char'=>'S'),
    -6708=>array('word'=>"逄",'first_char'=>'P'),
    -9302=>array('word'=>"郦",'first_char'=>'L'),
    -5965=>array('word'=>"璩",'first_char'=>'Q'),
    -6745=>array('word'=>"濮",'first_char'=>'P'),
    -4888=>array('word'=>"扈",'first_char'=>'H'),
    -9309=>array('word'=>"郏",'first_char'=>'J'),
    -5428=>array('word'=>"晏",'first_char'=>'Y'),
    -2849=>array('word'=>"暨",'first_char'=>'J'),
    -7206=>array('word'=>"阙",'first_char'=>'Q'),
    -4945=>array('word'=>"殳",'first_char'=>'S'),
    -9753=>array('word'=>"夔",'first_char'=>'K'),
    -10041=>array('word'=>"厍",'first_char'=>'S'),
    -5429=>array('word'=>"晁",'first_char'=>'C'),
    -2396=>array('word'=>"訾",'first_char'=>'Z'),
    -7205=>array('word'=>"阚",'first_char'=>'K'),
    -10049=>array('word'=>"乜",'first_char'=>'N'),
    -10015=>array('word'=>"蒯",'first_char'=>'K'),
    -3133=>array('word'=>"竺",'first_char'=>'Z'),
    -6698=>array('word'=>"逯",'first_char'=>'L'),
    -9799=>array('word'=>"俟",'first_char'=>'Q'),
    -6749=>array('word'=>"澹",'first_char'=>'T'),
    -7220=>array('word'=>"闾",'first_char'=>'L'),
    -10047=>array('word'=>"亓",'first_char'=>'Q'),
    -10005=>array('word'=>"仉",'first_char'=>'Z'),
    -3417=>array('word'=>"颛",'first_char'=>'Z'),
    -6431=>array('word'=>"驷",'first_char'=>'S'),
    -7226=>array('word'=>"闫",'first_char'=>'Y'),
    -9293=>array('word'=>"鄢",'first_char'=>'Y'),
    -6205=>array('word'=>"缑",'first_char'=>'G'),
    -9764=>array('word'=>"佘",'first_char'=>'S'),
    -9818=>array('word'=>"佴",'first_char'=>'N'),
    -9509=>array('word'=>"谯",'first_char'=>'Q'),
    -3122=>array('word'=>"笪",'first_char'=>'D'),
    -9823=>array('word'=>"佟",'first_char'=>'T'),
  );
  if(array_key_exists($asc, $rare_arr)  $rare_arr[$asc]['first_char']){
    return $rare_arr[$asc]['first_char'] ;
  }else{
    return null;
  }
}
//测试：
echo getFirstCharters('窦');