php里的unpack函数判断上传文件的类型

$filename = "F:\msn.rar";
$file    = fopen($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:
        $fileType = "png";
        break;
    default:
        echo "unknown";
}
echo "this is a(an) ".$fileType." file:".$typeCode;
exit;