PHP | pack() Function

The pack() function is an inbuilt function in PHP which is used to pack the given parameter into a binary string in a given format.

Syntax:

pack( $format, $arguments )

Parameters: This function accepts two parameters as mentioned above and described below:

• $format: It is required parameter. It specifies the format to be used while packing the data. The possible values of format are:
  • a – string which is NUL-padded
  • A – string which is SPACE-padded
  • h – low nibble first Hex string
  • H – high nibble first Hex string
  • c – signed character
  • C – unsigned character
  • s – signed short (16 bit, machine byte order)
  • S – unsigned short ( 16 bit, machine byte order)
  • n – unsigned short ( 16 bit, big endian byte order)
  • v – unsigned short ( 16 bit, little endian byte order)
  • i – signed integer (machine dependent byte order and size)
  • I – unsigned integer (machine dependent byte order and size)
  • l – signed long ( 32 bit, machine byte order)
  • L – unsigned long ( 32 bit, machine byte order)
  • N – unsigned long ( 32 bit, big endian byte order)
  • V – unsigned long ( 32 bit, little endian byte order)
  • f – float (machine dependent representation and size)
  • d – double (machine dependent representation and size)
  • x – NUL byte
  • X – Back up one byte
  • Z – string which is NUL-padded
  • @ – NUL-fill to absolute position
• $arguments: It is Optional parameter. It specifies one or more arguments to be packed.

Return Value: It returns a binary string containing data.

Note: This function is available on PHP 4.0.0 and newer version.

Program 1: This program uses C format to format the input parameter.

<?php
echo pack("C13", 71, 69, 69, 75, 83, 70, 79, 82, 71, 69, 69, 75, 83);
?>

Output:

GEEKSFORGEEKS

Program 2: This program uses A format to format the input parameter.

<?php
echo pack("A3", 71898);
?>

Output:

718

Program 3: This program uses i format to format the input parameter.

<?php
echo pack("i3", 56, 49, 54);
?>

Output:

816

Reference: https://www.php.net/manual/en/function.pack.php