PHP Australia Conference 2015

pack

(PHP 4, PHP 5)

packPack data into binary string

Descrizione

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

Pack given arguments into a binary string according to format.

The idea for this function was taken from Perl and all formatting codes work the same as in Perl. 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.

Elenco dei parametri

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:

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
csigned 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
Z NUL-padded string (new in PHP 5.5)
@ NUL-fill to absolute position

args

Valori restituiti

Returns a binary string containing data.

Log delle modifiche

Versione Descrizione
5.5.0 The "Z" code was added with equivalent functionality to "a" for Perl compatibility.

Esempi

Example #1 pack() example

<?php
$binarydata 
pack("nvc*"0x12340x56786566);
?>

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

Note

Attenzione

Note that PHP internally stores integer values as signed values of a machine-dependent size (C type long). Integer literals and operations that yield numbers outside the bounds of the integer type will be stored as float. When packing these floats as integers, they are first cast into the integer type. This may or may not result in the desired byte pattern.

The most relevant case is when packing unsigned numbers that would be representable with the integer type if it were unsigned. In systems where the integer type has a 32-bit size, the cast usually results in the same byte pattern as if the integer were unsigned (although this relies on implementation-defined unsigned to signed conversions, as per the C standard). In systems where the integer type has 64-bit size, the float most likely does not have a mantissa large enough to hold the value without loss of precision. If those systems also have a native 64-bit C int type (most UNIX-like systems don't), the only way to use the I pack format in the upper range is to create integer negative values with the same byte representation as the desired unsigned value.

Vedere anche:

  • unpack() - Unpack data from binary string

add a note add a note

User Contributed Notes 18 notes

up
10
chadm at codeangel dot org
2 years ago
If you'd like to understand pack/unpack. There is a tutorial here in perl, that works equally well in understanding it for php:

http://perldoc.perl.org/perlpacktut.html
up
6
FrozenFire
3 years ago
If you need to unpack a signed short from big-endian or little-endian specifically, instead of machine-byte-order, you need only unpack it as the unsigned form, and then if the result is >= 2^15, subtract 2^16 from it.

And example would be:

<?php
$foo
= unpack("n", $signedbigendianshort);
$foo = $foo[1];
if(
$foo >= pow(2, 15)) $foo -= pow(2, 16);
?>
up
2
petepostma at gmail dot spam dot com
2 years ago
Even though in a 64-bit architecure intval(6123456789) = 6123456789, and sprintf('%b', 5000000000) = 100101010000001011111001000000000
pack will not treat anything passed to it as 64-bit.  If you want to pack a 64-bit integer:

<?php
$big
= 5000000000;

$left = 0xffffffff00000000;
$right = 0x00000000ffffffff;

$l = ($big & $left) >>32;
$r = $big & $right;

$good = pack('NN', $l, $r);

$urlsafe = str_replace(array('+','/'), array('-','_'), base64_encode($good));

//done!

//rebuild:
$unurl str_replace(array('-','_'), array('+','/'), $urlsafe);
$binary = base64_decode($unurl);

$set = unpack('N2', $tmp);
print_r($set);

$original = $set[1] << 32 | $set[2];
echo
$original, "\\r\\n";
?>

results in:
Array
(
    [1] => 1
    [2] => 705032704
)
5000000000

but ONLY on a 64-bit enabled machine and PHP distro.
up
2
Coder
5 years ago
These two functions allow conversion between binary string and signed integer with possibility to give the bit length.

Usage:
<?php
echo si2bin(-10, 32);
11111111111111111111111111110110
echo si2bin(10, 32);
00000000000000000000000000001010
echo bin2si("11111111111111111111111111110110", 32);
-
10
echo bin2si("00000000000000000000000000001010", 32);
10

// signed integer to binary
function si2bin($si, $bits=32)
{
    if (
$si >= -pow(2,$bits-1) and $si <= pow(2,$bits-1) )
    {
        if (
$si >= 0) // positive or zero
       
{
           
$bin = base_convert($si,10,2);
           
// pad to $bits bit
           
$bin_length = strlen($bin);
            if (
$bin_length < $bits) $bin = str_repeat ( "0", $bits-$bin_length).$bin;
        }
        else
// negative
       
{
           
$si = -$si-pow(2,$bits);
           
$bin = base_convert($si,10,2);
           
$bin_length = strlen($bin);
            if (
$bin_length > $bits) $bin = str_repeat ( "1", $bits-$bin_length).$bin;
        }
        return
$bin;
    }
}

// binary to signed integer
function bin2si($bin,$bits=32)
{
    if (
strlen($bin)==$bits)
    {
        if (
substr($bin,0,1) == 0) // positive or zero
       
{
           
$si = base_convert($bin,2,10);
        }
        else
// negative
       
{
           
$si = base_convert($bin,2,10);
           
$si = -(pow(2,$bits)-$si);
        }
        return
$si;
    }
}
?>
up
1
Quis AT spam.to.my.devnull.quis.cx
6 years ago
<?PHP
function ntohs($port) {
 
$b=pack("N", $port);
  return
substr($b,2,2);
}
?>

I've spent a number of hours (n>=2) finding how to do this,
it works like the c function 'ntohs', used for eg the socks5 proxy protocol.
up
1
Newdawn.dk
8 years ago
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
up
2
Gerjoo at gmail dot com
3 years ago
You can use pack to strip the byte order mark (BOM) from a file.

For example, strip the UTF-8 BOM:

<?php

// Strips the UTF-8 mark: (hex value: EF BB BF)
function trimUTF8BOM($data){
    if(
substr($data, 0, 3) == pack('CCC', 239, 187, 191)) {
        return
substr($data, 3);
    }
    return
$data;
}

?>

This function could be easily adjusted to match any byte order mark. Have a look at wikipedia for a full list of hex codes for each specific encoding.

- Gerard
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1
Anonymous
5 years ago
Coder's example is basically an explanation of bindec() and decbin(), not pack() and unpack().

Here's some code to convert a string binary expression into its binary-string equivalent and vice versa.

(Would be even simpler if pack/unpack offered a 'b' format code....)

<?php
function bin2bstr($input)
// Convert a binary expression (e.g., "100111") into a binary-string
{
  if (!
is_string($input)) return null; // Sanity check

  // Pack into a string
 
return pack('H*', base_convert($input, 2, 16));
}

function
bstr2bin($input)
// Binary representation of a binary-string
{
  if (!
is_string($input)) return null; // Sanity check

  // Unpack as a hexadecimal string
 
$value = unpack('H*', $input);
 
 
// Output binary representation
 
return base_convert($value[1], 16, 2);
}

// Returns string(3) "ABC"
var_dump(bin2bstr('01000001 01000010 01000011'));

// Returns string(24) "010000010100001001000011"
var_dump(bstr2bin('ABC'));
?>
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1
Anonymous
6 years ago
Array pack:
<?php
function pack_array($v,$a) {
return
call_user_func_array(pack,array_merge(array($v),(array)$a));
}
?>
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1
php at nagler-ihlein dot de
6 years ago
Be aware of format code H always padding the 0 for byte-alignment to the right (for odd count of nibbles).

So pack("H", "7") results in 0x70 (ASCII character 'p') and not in 0x07 (BELL character)
as well as pack("H*", "347") results in 0x34 ('4') and 0x70 ('p') and not 0x03 and 0x47.
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1
dylan at pow7 dot com
7 years ago
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;
}
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1
j.s.hoekstra
8 years ago
/* 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];
}
up
1
plutus at gmx dot de
14 years ago
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!
up
2
Patrik Fimml
8 years ago
You will get the same effect with

<?php
function _readInt($fp)
{
   return
unpack('V', fread($fp, 4));
}
?>

or unpack('N', ...) for big-endianness.
up
1
zilinex at yahoo dot com
10 years ago
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;
}
up
0
jrm456 at speed dot 1s dot fr
7 months ago
How to convert an integer to raw data, specifying the amount of bytes to convert to (will be padded with 0's):

    public function toRaw($int, $bytes = 4)
    {
        $hex = dechex($int);
       
        if (strlen($hex) % 2 != 0)
            $hex = '0'. $hex;

        $arr = str_split($hex, 2);

        while (count($arr) < $bytes)
            array_unshift($arr, 0);
       
        $arr = array_map('hexdec', $arr);
        $arr = array_map('chr', $arr);

        return join('', array_reverse($arr));
    }
up
0
Ammar Hameed
4 years ago
Using pack to write Arabic char(s) to a file.

<?php
$text
= "&#13574;&#13830;&#13830;";

$text = mb_convert_encoding($text, "UCS-2BE", "HTML-ENTITIES");

$len mb_strlen($text);

$bom = mb_convert_encoding("&#65534;", "unicode", "HTML-ENTITIES");

$fp = fopen('text.txt', 'w');

fwrite($fp, pack('a2', $bom)); 
fwrite($fp, pack("a{$len}", $text));
fwrite($fp, pack('a2', $bom));
fwrite($fp, pack('a2', "\n"));

fclose($fp);
?>
up
0
SixThreeOh
4 years ago
If you're bugged by http://bugs.php.net/bug.php?id=5889 then you can try this:

Use igbinary-serialize if you don't mind a little overhead.

Or intarray (by the same person) if you don't mind using a slightly experimental package which may have problems sharing data between differently byte/bit ordered architectures.

I don't believe it would be too difficult to shove a serialize function and unserialize function in there if you rip out the code from igbinary for storing numeric arrays with the correct endianess. Looking at `igbinary_serialize32` and `igbinary_unserialize32` in igbinary.c it should be very easy to copy that functionality to intarray.c.

Take away the "<<0" though, that's just stupid :P

Ref: http://opensource.dynamoid.com/
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