PHP unpack() Function

The PHP unpack() function unpacks data from a binary string into an array according to the given format.

The unpacked data is stored in an associative array. To accomplish this the different format codes should be named and separated by a slash /. If a repeater argument is present, then each of the array keys will have a sequence number behind the given name.

Changes were made to bring this function into line with Perl which are mentioned below:

• The "a" code now retains trailing NULL bytes.
• The "A" code now strips all trailing ASCII whitespace (spaces, tabs, newlines, carriage returns, and NULL bytes).
• The "Z" code was added for NULL-padded strings, and removes trailing NULL bytes.

Syntax

unpack(format, string, offset)

Parameters

unpack() format characters

Return Value

Returns an associative array containing unpacked elements of binary string, or false on failure.

Example: unpack() example

The example below shows the usage of unpack() function.

<?php
$binarydata = "\x04\x00\xa0\x00";
$array = unpack("cChars/nInt", $binarydata);
print_r($array);
?>

The output of the above code will be:

Array
(
    [Chars] => 4
    [Int] => 160
)

Example: unpack() example with a repeater

In the example below, the format argument contains repeater.

<?php
$binarydata = "\x04\x00\xa0\x00";
$array = unpack("c2Chars/nInt", $binarydata);
print_r($array);
?>

The output of the above code will be:

Array
(
    [Chars1] => 4
    [Chars2] => 0
    [Int] => 40960
)

Example: unpack() example with unnamed keys

If the element is not named, numeric indices starting from 1 are used as shown in the example below:

<?php
$binarydata = "\x32\x42\x00\xa0";
$array = unpack("c2/n", $binarydata);
print_r($array);
?>

The output of the above code will be:

Array
(
    [1] => 160
    [2] => 66
)