PHP判断上传文件类型的解决办法

/** 
* 读取文件前几个字节 判断文件类型 
* @return string 
*/ 
function checktitle($filename){ 
  $file=fopen($filename, "rb"); 
  $bin=fread($file, 2); //只读2字节 
  fclose($file); 
  $strinfo =@unpack("c2chars", $bin); 
  $typecode=intval($strinfo['chars1'].$strinfo['chars2']); 
  $filetype=''; 
  switch($typecode){ 
    case 7790: 
      $filetype='exe'; 
    break; 
    case 7784: 
      $filetype='midi'; 
    break; 
    case 8297: 
      $filetype='rar'; 
    break; 
    case 255216: 
      $filetype='jpg'; 
    break; 
    case 7173: 
      $filetype='gif'; 
    break; 
    case 6677: 
      $filetype='bmp'; 
    break; 
    case 13780: 
      $filetype='png'; 
    break; 
    default: 
      $filetype='unknown'.$typecode; 
    break; 
  } 
  //fix 
  if($strinfo['chars1']=='-1' && $strinfo['chars2']=='-40'){ 
    return 'jpg'; 
  } 
  if($strinfo['chars1']=='-119' && $strinfo['chars2']=='80'){ 
    return 'png'; 
  } 
  return $filetype; 
}