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pack

Pack data into binary string (PHP 4, PHP 5)
string pack ( string format [, mixed args [, mixed ...]] )

Pack given arguments into binary string according to format.

The idea to this function was taken from Perl and all formatting codes work the same as there, however, there are some formatting codes that are missing such as Perl's "u" format code.

Note that the distinction between signed and unsigned values only affects the function unpack(), where as function pack() gives the same result for signed and unsigned format codes.

Also note that PHP internally stores integer values as signed values of a machine dependent size. If you give it an unsigned integer value too large to be stored that way it is converted to a float which often yields an undesired result.

Parameters

format

The format string consists of format codes followed by an optional repeater argument. The repeater argument can be either an integer value or * for repeating to the end of the input data. For a, A, h, H the repeat count specifies how many characters of one data argument are taken, for @ it is the absolute position where to put the next data, for everything else the repeat count specifies how many data arguments are consumed and packed into the resulting binary string.

Currently implemented formats are:

Table 174. pack() format characters

CodeDescription
aNUL-padded string
ASPACE-padded string
hHex string, low nibble first
HHex string, high nibble first
csigned char
Cunsigned char
ssigned short (always 16 bit, machine byte order)
Sunsigned short (always 16 bit, machine byte order)
nunsigned short (always 16 bit, big endian byte order)
vunsigned short (always 16 bit, little endian byte order)
isigned integer (machine dependent size and byte order)
Iunsigned integer (machine dependent size and byte order)
lsigned long (always 32 bit, machine byte order)
Lunsigned long (always 32 bit, machine byte order)
Nunsigned long (always 32 bit, big endian byte order)
Vunsigned long (always 32 bit, little endian byte order)
ffloat (machine dependent size and representation)
ddouble (machine dependent size and representation)
xNUL byte
XBack up one byte
@NUL-fill to absolute position


args

Return Values

Returns a binary string containing data.

Examples

Example 1360. pack() example

<?php
$binarydata
= pack("nvc*", 0x1234, 0x5678, 65, 66);
?>

The resulting binary string will be 6 bytes long and contain the byte sequence 0x12, 0x34, 0x78, 0x56, 0x41, 0x42.


See Also
unpack()