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unpack

(PHP 4, PHP 5)

unpackUnpack data from binary string

Description

array unpack ( string $format , string $data )

Unpacks from a binary string into an array according to the given format.

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

Parameters

format

See pack() for an explanation of the format codes.

data

The packed data.

Return Values

Returns an associative array containing unpacked elements of binary string.

Changelog

Version Description
5.5.0

Changes were made to bring this function into line with Perl:

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.

Examples

Example #1 unpack() example

<?php
$binarydata 
"\x04\x00\xa0\x00";
$array unpack("cchars/nint"$binarydata);
?>

The resulting array will contain the entries "chars" with value 4 and "int" with 160.

Example #2 unpack() example with a repeater

<?php
$binarydata 
"\x04\x00\xa0\x00";
$array unpack("c2chars/nint"$binarydata);
?>

The resulting array will contain the entries "chars1", "chars2" and "int".

Notes

Caution

Note that PHP internally stores integral values as signed. If you unpack a large unsigned long and it is of the same size as PHP internally stored values the result will be a negative number even though unsigned unpacking was specified.

Caution

Be aware that if you do not name an element, an empty string is used. If you do not name more than one element, this means that some data is overwritten as the keys are the same such as in:

Example #3 unpack() example with unnamed keys

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

The resulting array will contain the entries "1" with value 160 and "2" with 66. The first value from the c specifier is overwritten by the first value from the n specifier.

See Also

  • pack() - Pack data into binary string

PHP Manual