PHP unpack() function

PHP Miscellaneous Functions

Definition and Usage

The unpack() function unpacks data from a binary string.

Syntax

unpack(format,data)
Parameter Description
format Required. Specifies the format used when unpacking data.
data Optional. Specifies the unpacked binary data.

format parameter's possible values:

  • a - NUL-padded string
  • A - SPACE-padded string
  • h - Hex string, low nibble first
  • H - Hex string, high nibble first
  • c - signed char
  • C - unsigned char
  • s - signed short (always 16 bit, machine byte order)
  • S - unsigned short (always 16 bit, machine byte order)
  • n - unsigned short (always 16 bit, big endian byte order)
  • v - unsigned short (always 16 bit, little endian byte order)
  • i - signed integer (machine dependent size and byte order)
  • I - unsigned integer (machine dependent size and byte order)
  • l - signed long (always 32 bit, machine byte order)
  • L - unsigned long (always 32 bit, machine byte order)
  • N - unsigned long (always 32 bit, big endian byte order)
  • V - unsigned long (always 32 bit, little endian byte order)
  • f - float (machine dependent size and representation)
  • d - double (machine dependent size and representation)
  • x - NUL byte
  • X - Back up one byte
  • @ - NUL-fill to absolute position

Instance

Example 1

<?php
$data = "PHP";
print_r(unpack("C*",$data));
?>

Output:

Array
(
[1] => 80
[2] => 72
[3] => 80
)

Example 2

<?php
$data = "PHP";
print_r(unpack("C*myint",$data));
?>

Output:

Array
(
[myint1] => 80
[myint2] => 72
[myint3] => 80
)

Example 3

<?php
$bin = pack("c2n2",0x1234,0x5678,65,66);
print_r(unpack("c2chars/n2int",$bin));
?>

Output:

Array
(
[chars1] => 52
[chars2] => 120
[int1] => 65
[int2] => 66
)

PHP Miscellaneous Functions