Processing Binary Files In PHP

This little tip might be usefull for people who have recently started learning PHP and have some experience in other languages (like me).

Recently I needed to write a PHP script that would process a binary file I had created in my Delphi program. However, it turned out that fread() doesn’t work as expected – it always returns a string. So if you want to read a 32-bit integer from a binary file, doing $an_integer=fread($f, 4) won’t get the desired result – $an_integer will be a string containing some weird characters.

To correctly read/write binary data in PHP you need to use the pack() and unpack() functions.

For example, to read two cardinals (unsigned 32-bit integer) from a file:

$fp=fopen(”file.bin”,”rb”);
$bin=fread($fp,8);
$data=unpack(”V1x/V1y”,$bin);
fclose($fp)

$data["x"] and $data["y"] would contain the two numbers. The first argument to unpack() defines the structure of data to be read. See the documentation for a description of the format string.

Another thing to note is that Delphi (at least the latest versions) will save fixed-length strings as null-padded (format code “a”). Also, if you write record structures to a file you intend to process with PHP or another non-Delphi program, it is advisable to use the packed keyword to make the actual structure of binary data more predictable.

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This entry was posted on Tuesday, October 17th, 2006 at 21:22 and is filed under Programming, Tutorials. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

6 Responses to “Processing Binary Files In PHP”

  1. 1
    kuldeep says:
    June 13, 2007 at 12:12

    can u help me about getting data form binary file
    that extension is .cgh

  2. 2
    White Shadow says:
    June 13, 2007 at 14:42

    Sorry, I don’t know what type of data .cgh files contain and I couldn’t find this extension at http://filext.com/file-extension/chg … I’m afraid I can’t help you in this case.

  3. 3
    Andy H. says:
    January 17, 2008 at 16:29

    That is great! Thank you very much for posting this as it is exactly what I was looking for. Nowhere else, including _PHP in a Nutshell_, does anyone mention this critical fact when working with binary data.

  4. 4
    White Shadow says:
    January 17, 2008 at 16:35

    You’re welcome :)

  5. 5
    Chris says:
    April 23, 2009 at 19:26

    Another very useful tool is bin2hex() if you’re looking to get hex data from the binary file.

  6. 6
    dayg says:
    April 29, 2009 at 05:47

    Coming from the Java land, I have been searching for a method similar to DataOutputStream.writeUTF() for the last couple of days.

    Your tip on the PHP pack() method solved my problem.

    Thanks!

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