PHP 下载文件时自动添加bom头的方法，

    // 文件名
  $filename = "www.111cn.net .csv";
  
  header('Expires: ' . gmdate('D, d M Y H:i:s', $_SERVER['REQUEST_TIME'] + 10) . ' GMT');
  header('Cache-Control: max-age=10');
  //header('Content-Type: application/vnd.ms-excel; charset=utf-8');
  header('Content-Type: text/csv; charset=utf-8');
  header("Content-Disposition: attachment; filename={$filename}");
  
  // 如果结果中有提示信息，则把第一行输出改为提示信息文字
  $out = "xEFxBBxBF";// 加上bom头，系统自动默认为UTF-8编码
  if (!empty($extra['notice'])) {
   $out .= "{$extra['notice']}rn";
  }
 
  // 输出
  foreach ($table as $row) {
   $out .= implode(",", $row) . "rn";
  }
  
  /* if (mb_detect_encoding()($out) == 'UTF-8') {
   $out = iconv("UTF-8//IGNORE", "GBK", $out);
  } */
  echo $out;