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PHP : Function Reference : Miscellaneous Functions : pack


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

Example 1360. pack() example

= 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.

Related Examples ( Source code ) » pack

Code Examples / Notes » pack


^-^ 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;

patrik fimml

You will get the same effect with
function _readInt($fp)
  return unpack('V', fread($fp, 4));
or unpack('N', ...) for big-endianness.


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*',

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

chr dot eichert
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">
$rh = fopen ($_FILES['thefile']['tmp_name'], "r");
$pb = fread($rh, 8192);
$pc = bin2hex($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 ...
$data = pack("H" . strlen($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!


This is how I used pack to convert base2 to base64 since base_convert doesn't support base64
The base conversions don't work for long strings, which is why I convert 1 byte at a time
Hope this helps someone
function base2to64($base2) {
if ($remainbits = strlen($base2)%8) $base2 .= str_repeat('0',8-$remainbits);
$base64 = NULL;
for ($i=0;$i<strlen($base2);$i+=8) $base16 .= sprintf('%02x',bindec(sprintf('%08d',substr($base2,$i,8))));
return base64_encode(pack('H*',$base16));
function base64to2($base64) {
list($base16) = unpack('H*0',base64_decode($base64));
$base2 = NULL;
for ($i=0;$i<strlen($base16);$i++) $base2 .= sprintf('%04d',base_convert(substr($base16,$i,1),16,2));
return $base2;

jurgen braam

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...


Note that the the upper command in perl looks like this:
$binarydata = pack ("n v c*", 0x1234, 0x5678, 65, 66);
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!


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.

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;

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;

Im not sure these are the most efficient functions, but surely alot faster than loading up a perl interpreter for every binary conversion =)

19-feb-2005 07:09

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.


a cool function to converrt numbers to Persian numbers(utf-8)
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);
               $ret .= $c;
 return $ret;


/* 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];

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