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Last updated: Sat, 27 Jan 2007

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# pack

(PHP 3, PHP 4, PHP 5)

pack -- Pack data into binary string

## Description

string pack ( string format [, mixed args [, mixed ...]] )

Pack given arguments into binary string according to `format`. Returns binary string containing data.

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. 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 are

Таблица 1. pack() format characters

Code | Description
--- | ---
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

Пример 1. 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.

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.

See also unpack().

add a note User Contributed Notes
pack
Chr dot Eichert<moga at mx dot homelinux dot org>
15-Feb-2007 04:21
`This is how you can produce a code that is in fact a picture.
(This code is a complete tool, copy it to a file, call it 'somehow.php' and produce your pictures as hexcode).
<!--// ***Begin of File*** //-->
<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>" enctype="multipart/form-data">
<input type="file" name="thefile"><input type="submit">
</form>
<?php
$rh = fopen ($_FILES['thefile']['tmp_name'], "r");
$pb = fread($rh, 8192);
fclose($rh);
$pc = bin2hex($pb);
$pd = wordwrap($pc, 76, "\".<br /> \n \"", 1);
echo "<TT>\$hexpic=\""."$pd"."\"\n</TT>;";
?>
<!--// ***End of File*** //-->
Copy the result in your site code somewhere. For to show the code as a picture you can use something like what dirk (at) camindo de wrote ...
<?php
$hexpic=".......................
.....................";
$data = pack("H" . strlen($hexpic), $hexpic);
header("Content-Type: image/png");
// maybe your is jpeg / gif / png
header("Last-Modified: " . date("r", filectime($_SERVER['SCRIPT_FILENAME'])));
header("Content-Length: " . strlen($data));
echo $data;
?>
have fun!`
dirk (at) camindo de
19-Jan-2007 03:22
`Work around newsletter tracking:
include a transparent gif (1x1 pixel) with url = track.php and parameters.
track.php has to write the parameters e.g. into a database and provides the gif - using following code:
header("Content-Type: image/gif");
header("Content-Length: 49");
echo pack('H*',
'47494638396101000100910000000000ffffffff'
.'ffff00000021f90405140002002c000000000100'
.'01000002025401003b'
);`
Newdawn.dk
22-Mar-2006 04:25
`When trying to create a ZIP file using the pack function - I experienced trouble with the "a" code - It converted all chars correct from the std. ASCII charset but not more language specific like ÆøÅ.
It seems that ZIP files do not use the same HEX for these as everything else does.
The fix was a quick workaround but you'll probably get the picture:
function UniHex($str) {
// æ ø å Æ Ø Å
//These are simply one HEX code being replaced by another to correct the issue
$except = array("E6"=>"91","F8"=>"9B","E5"=>"86","C6"=>"92","D8"=>"9D", "C5"=>"8F");
for($i = 0; $i < strlen($str); $i++) {
$hex = bin2hex(substr($str, $i, 1));
if ($except[strtoupper($hex)])
$hex = $except[strtoupper($hex)];
$return .= $hex;
}
return $return;
}
And then i replaced an "a100" code with "H".strlen(uniHex($mystring))
This is like i said a quick workaround, but if you find the real reason for this i'd be happy to see it`
j.s.hoekstra
13-Mar-2006 08:57
`/* Convert float from HostOrder to Network Order */
function FToN( $val )
{
$a = unpack("I",pack( "f",$val ));
return pack("N",$a[1] );
}
/* Convert float from Network Order to HostOrder */
function NToF($val )
{
$a = unpack("N",$val);
$b = unpack("f",pack( "I",$a[1]));
return $b[1];
}`
Patrik Fimml
11-Oct-2005 10:42
`You will get the same effect with
<?php
function _readInt($fp)
{
return unpack('V', fread($fp, 4));
}
?>
or unpack('N', ...) for big-endianness.`
19-Feb-2005 11:09
`I needed to convert binary values from a file to integers.
Maybe there is something simpler, but the snippets i saw above seemed a little convoluted:
function bin2asc ($binary)
{
$val = 0;
for ($i = strlen($binary) - 1; $i >= 0; $i--) {
$ch = substr($binary, $i, 1);
$val = ($val << 8) | ord($ch);
}
return $val;
}
This was called like the following from a binary file:
function _readInt($fp)
{
return bin2asc(fread($fp, 4));
}
Note that the for loop should be reversed for network byte order instead of intel byte order. Also the conversion will work with any number of bytes, but will happily overflow.`
zilinex at yahoo dot com
01-Sep-2004 11:12
`a cool function to converrt numbers to Persian numbers(utf-8)
origin: http://www.farsiweb.info/jalali/jalali.phps
function farsinum($str)
{
$ret = "";
for ($i = 0; $i < strlen($str); ++$i) {
$c = $str[$i];
if( $c >= '0' && $c <= '9' )
$out .= pack("C*", 0xDB, 0xB0 + $c);
else
$ret .= $c;
}
return $ret;
}`
Jurgen Braam
02-Oct-2003 11:39
`take note: if you produce binary files using PHP on multiple platforms, that you use one of the machine-independent pack options.
This means 's' 'S' 'i' 'I' 'd' and 'f' are _EVIL_ :) Took me some time to figure out what my Excel-generator what futzing about :) Turned out the production machine was a Sun Sparc. I develop on my own x86 Linux server.
Hope this helps anyone...
c-ya,
Jurgen`
master at dreamphp dot com
02-Sep-2001 04:48
`^-^ Simple version.
function bin2asc ($temp) {
$len = strlen($temp);
for ($i=0;$i<$len;$i+=8) $data.=chr(bindec(substr($temp,$i,8)));
return $data;
}
function asc2bin ($temp) {
$len = strlen($temp);
for ($i=0; $i<$len; $i++) $data.=sprintf("%08b",ord(substr($temp,$i,1)));
return $data;
}`
mfisch[at]kaz[dot]com
10-Jul-2001 09:53
`If you are trying to do ascii <--> binary conversions like me;
you probably found that unlike the perl pack functions, these wont help too much. Attached are two functions I wrote to accomplish this task.
<br>
function bin2asc ($binary)
{
$i = 0;
while ( strlen($binary) > 3 )
{
$byte[$i] = substr($binary, 0, 8);
$byte[$i] = base_convert($byte[$i], 2, 10);
$byte[$i] = chr($byte[$i]);
$binary = substr($binary, 8);
$ascii = "$ascii$byte[$i]";
}
return $ascii;
}
<br>
function asc2bin ($ascii)
{
while ( strlen($ascii) > 0 )
{
$byte = ""; $i = 0;
$byte = substr($ascii, 0, 1);
while ( $byte != chr($i) ) { $i++; }
$byte = base_convert($i, 10, 2);
$byte = str_repeat("0", (8 - strlen($byte)) ) . $byte; # This is an endian (architexture) specific line, you may need to alter it.
$ascii = substr($ascii, 1);
$binary = "$binary$byte";
}
return $binary;
}
<br>
Im not sure these are the most efficient functions, but surely alot faster than loading up a perl interpreter for every binary conversion =)`
plutus at gmx dot de
10-Aug-2000 04:14
`Note that the the upper command in perl looks like this:<br>
$binarydata = pack ("n v c*", 0x1234, 0x5678, 65, 66);<br>
In PHP it seems that no whitespaces are allowed in the first parameter. So if you want to convert your pack command from perl -> PHP, don't forget to remove the whitespaces!`
add a note
php_check_syntax ignore_user_abort

Last updated: Sat, 27 Jan 2007
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