unpack

(PHP 4, PHP 5, PHP 7, PHP 8)

unpack — Déconditionne des données depuis une chaîne binaire

Description

unpack(string $format, string $string, int $offset = 0): array|false

Déconditionne les données data depuis une chaîne binaire avec le format format.

Les données déconditionnées sont stockées dans un tableau. Pour cela, il faut donner un nom à chaque format utilisé et les séparer par des slash (/). Si un argument de répétition est présent, alors chacune des clés du tableau aura un numéro de séquence derrière le nom fourni.

Des modifications ont été effectuées pour aligner le comportement de cette fonction avec Perl :

Le code "a" ne supprime plus les octets NULL finaux.
Le code "A" supprime maintenant tous les espaces blancs ASCII finaux (espace, tabulation, nouvelles lignes, retour à la ligne, et octets NULL).
Le code "Z" a été ajouté pour les chaînes complétées par des caractères NULL, et supprime les octets NULL finaux.

Liste de paramètres

format: Voir la fonction pack() pour une explication des codes de format.
string: Les données conditionnées.
offset: La position où débuter le déconditionnement.

Valeurs de retour

Retourne un tableau associatif contenant les éléments déconditionnés d'une chaîne binaire, ou false si une erreur survient.

Historique

Version	Description
7.2.0	Les types float et double supporte à la fois l'orientation Big Endian et Little Endian.
7.1.0	La position `offset` optionnelle à été ajouté.

Exemples

Exemple #1 Exemple avec unpack()

<?php
$binarydata = "\x04\x00\xa0\x00";
$array = unpack("cchars/nint", $binarydata);
print_r($array);
?>

L'exemple ci-dessus va afficher :

Array
(
    [chars] => 4
    [int] => 160
)

Exemple #2 Exemple avec unpack() et un argument de répétition

<?php
$binarydata = "\x04\x00\xa0\x00";
$array = unpack("c2chars/nint", $binarydata);
print_r($array);
?>

L'exemple ci-dessus va afficher :

Array
(
    [chars1] => 4
    [chars2] => 0
    [int] => 40960
)

Notes

Attention

Il faut noter que PHP gère les valeurs en interne sous forme signée. Si vous déconditionnez une valeur qui est aussi grande que la taille utilisée en interne par PHP, le résultat se trouvera être un nombre négatif, même s'il a été déconditionné avec l'option " non signé ".

Attention

Si vous ne nommez pas un élément, les index numériques à partir de 1 sont utilisés. Sachez que si vous avez plus d'un élément sans nom, certaines données sont écrasées parce que la numérotation redémarre à partir de 1 pour chaque élément.

Exemple #3 Exemple avec unpack() avec des clés non nommées

<?php
$binarydata = "\x32\x42\x00\xa0";
$array = unpack("c2/n", $binarydata);
var_dump($array);
?>

L'exemple ci-dessus va afficher :

array(2) {
  [1]=>
  int(160)
  [2]=>
  int(66)
}

Notez que la première valeur depuis le spécificateur c est écrasé par la première valeur depuis le spécificateur n.

Voir aussi

pack() - Compacte des données dans une chaîne binaire

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User Contributed Notes 14 notes

down

stanislav dot eckert at vizson dot de ¶

8 years ago

A helper class to convert integer to binary strings and vice versa. Useful for writing and reading integers to / from files or sockets.

<?php

    class int_helper
    {
        public static function int8($i) {
            return is_int($i) ? pack("c", $i) : unpack("c", $i)[1];
        }

        public static function uInt8($i) {
            return is_int($i) ? pack("C", $i) : unpack("C", $i)[1];
        }

        public static function int16($i) {
            return is_int($i) ? pack("s", $i) : unpack("s", $i)[1];
        }

        public static function uInt16($i, $endianness=false) {
            $f = is_int($i) ? "pack" : "unpack";

            if ($endianness === true) {  // big-endian
                $i = $f("n", $i);
            }
            else if ($endianness === false) {  // little-endian
                $i = $f("v", $i);
            }
            else if ($endianness === null) {  // machine byte order
                $i = $f("S", $i);
            }

            return is_array($i) ? $i[1] : $i;
        }

        public static function int32($i) {
            return is_int($i) ? pack("l", $i) : unpack("l", $i)[1];
        }

        public static function uInt32($i, $endianness=false) {
            $f = is_int($i) ? "pack" : "unpack";

            if ($endianness === true) {  // big-endian
                $i = $f("N", $i);
            }
            else if ($endianness === false) {  // little-endian
                $i = $f("V", $i);
            }
            else if ($endianness === null) {  // machine byte order
                $i = $f("L", $i);
            }

            return is_array($i) ? $i[1] : $i;
        }

        public static function int64($i) {
            return is_int($i) ? pack("q", $i) : unpack("q", $i)[1];
        }

        public static function uInt64($i, $endianness=false) {
            $f = is_int($i) ? "pack" : "unpack";

            if ($endianness === true) {  // big-endian
                $i = $f("J", $i);
            }
            else if ($endianness === false) {  // little-endian
                $i = $f("P", $i);
            }
            else if ($endianness === null) {  // machine byte order
                $i = $f("Q", $i);
            }

            return is_array($i) ? $i[1] : $i;
        }
    }
?>

Usage example:
<?php
    Header("Content-Type: text/plain");
    include("int_helper.php");

    echo int_helper::uInt8(0x6b) . PHP_EOL;  // k
    echo int_helper::uInt8(107) . PHP_EOL;  // k
    echo int_helper::uInt8("\x6b") . PHP_EOL . PHP_EOL;  // 107

    echo int_helper::uInt16(4101) . PHP_EOL;  // \x05\x10
    echo int_helper::uInt16("\x05\x10") . PHP_EOL;  // 4101
    echo int_helper::uInt16("\x05\x10", true) . PHP_EOL . PHP_EOL;  // 1296

    echo int_helper::uInt32(2147483647) . PHP_EOL;  // \xff\xff\xff\x7f
    echo int_helper::uInt32("\xff\xff\xff\x7f") . PHP_EOL . PHP_EOL;  // 2147483647

    // Note: Test this with 64-bit build of PHP
    echo int_helper::uInt64(9223372036854775807) . PHP_EOL;  // \xff\xff\xff\xff\xff\xff\xff\x7f
    echo int_helper::uInt64("\xff\xff\xff\xff\xff\xff\xff\x7f") . PHP_EOL . PHP_EOL;  // 9223372036854775807

?>

down

Sergio Santana: ssantana at tlaloc dot imta dot mx ¶

20 years ago

This is about the last example of my previous post. For the sake of clarity, I'm including again here the example, which expands the one given in the formal documentation:

<?
  $binarydata = "AA\0A";
  $array = unpack("c2chars/nint", $binarydata);
  foreach ($array as $key => $value)
     echo "\$array[$key] = $value <br>\n";
?>

This outputs:

$array[chars1] = 65 
$array[chars2] = 65 
$array[int] = 65 

Here, we assume that the ascii code for character 'A' is decimal 65.

Remebering that the format string structure is:
<format-code> [<count>] [<array-key>] [/ ...],
in this example, the format string instructs the function to
  1. ("c2...") Read two chars from the second argument ("AA ...), 
  2. (...chars...) Use the array-keys "chars1", and "chars2" for 
      these two chars read,
  3. (.../n...) Read a short int from the second argument (...\0A"),
  4. (...int") Use the word "int" as the array key for the just read
      short.

I hope this is clearer now,

Sergio.

down

jjfoerch at earthlink dot net ¶

20 years ago

I had a situation where I had to unpack a file filled with little-endian order double-floats in a way that would work on either little-endian or big-endian machines.  PHP doesn't have a formatting code that will change the byte order of doubles, so I wrote this workaround.

<?php
/*The following code is a workaround for php's unpack function
which does not have the capability of unpacking double precision
floats that were packed in the opposite byte order of the current
machine.
*/
function big_endian_unpack ($format, $data) {
    $ar = unpack ($format, $data);
    $vals = array_values ($ar);
    $f = explode ('/', $format);
    $i = 0;
    foreach ($f as $f_k => $f_v) {
    $repeater = intval (substr ($f_v, 1));
    if ($repeater == 0) $repeater = 1;
    if ($f_v{1} == '*')
    {
        $repeater = count ($ar) - $i;
    }
    if ($f_v{0} != 'd') { $i += $repeater; continue; }
    $j = $i + $repeater;
    for ($a = $i; $a < $j; ++$a)
    {
        $p = pack ('d',$vals[$i]);
        $p = strrev ($p);
        list ($vals[$i]) = array_values (unpack ('d1d', $p));
        ++$i;
    }
    }
    $a = 0;
    foreach ($ar as $ar_k => $ar_v) {
    $ar[$ar_k] = $vals[$a];
    ++$a;
    }
    return $ar;
}

list ($endiantest) = array_values (unpack ('L1L', pack ('V',1)));
if ($endiantest != 1) define ('BIG_ENDIAN_MACHINE',1);
if (defined ('BIG_ENDIAN_MACHINE')) $unpack_workaround = 'big_endian_unpack';
else $unpack_workaround = 'unpack';
?>

This workaround is used like this:

<?php

function foo() {
        global $unpack_workaround;
    $bar = $unpack_workaround('N7N/V2V/d8d',$my_data);
//...
}

?>

On a little endian machine, $unpack_workaround will simply point to the function unpack.  On a big endian machine, it will call the workaround function.

Note, this solution only works for doubles.  In my project I had no need to check for single precision floats.

down

kennwhite dot nospam at hotmail dot com ¶

20 years ago

If having a zero-based index is useful/necessary, then instead of:

$int_list = unpack("s*", $some_binary_data);

 try:

$int_list = array_merge(unpack("s*", $some_binary_data));

This will return a 0-based array:

$int_list[0] = x
$int_list[1] = y
$int_list[2] = z
...

rather than the default 1-based array returned from unpack when no key is supplied:

$int_list[1] = x
$int_list[2] = y
$int_list[3] = z
...

It's not used often, but array_merge() with only one parameter will compress a sequentially-ordered numeric-index, starting with an index of [0].

down

Anonymous ¶

15 years ago

Functions I found useful when dealing with fixed width file processing, related to unpack/pack functions.
<?php
/**
* funpack
* format: array of key, length pairs
* data: string to unpack
*/
function funpack($format, $data){
    foreach ($format as $key => $len) {
        $result[$key] = trim(substr($data, $pos, $len));
        $pos+= $len;
    }
    return $result;
}

/**
* fpack
* format: array of key, length pairs
* data: array of key, value pairs to pack
* pad: padding direction
*/
function fpack($format, $data, $pad = STR_PAD_RIGHT){
    foreach ($format as $key => $len){
        $result .= substr(str_pad($data[$key], $len, $pad), 0, $len);
    }
    return $result;
}
?>

down

Sergio Santana: ssantana at tlaloc dot imta dot mx ¶

20 years ago

Suppose we need to get some kind of internal representation of an integer, say 65, as a four-byte long. Then we use, something like:

<?
  $i = 65;
  $s = pack("l", $i); // long 32 bit, machine byte order
  echo strlen($s) . "<br>\n";
  echo "***$s***<br>\n";
?>

The output is:

X-Powered-By: PHP/4.1.2
Content-type: text/html

4
***A*** 

(That is the string "A\0\0\0")

Now we want to go back from string "A\0\0\0" to number 65. In this case we can use:

<?
  $s = "A\0\0\0"; // This string is the bytes representation of number 65
  $arr = unpack("l", $s);
  foreach ($arr as $key => $value)
     echo "\$arr[$key] = $value<br>\n";
?>

And this outpus:
X-Powered-By: PHP/4.1.2
Content-type: text/html

$arr[] = 65

Let's give the array key a name, say "mykey". In this case, we can use: 

<?
  $s = "A\0\0\0"; // This string is the bytes representation of number  65
  $arr = unpack("lmykey", $s);
  foreach ($arr as $key => $value)
     echo "\$arr[$key] = $value\n";
?>

An this outpus:
X-Powered-By: PHP/4.1.2
Content-type: text/html

$arr[mykey] = 65

The "unpack" documentation is a little bit confusing. I think a more complete example could be:

<?
  $binarydata = "AA\0A";
  $array = unpack("c2chars/nint", $binarydata);
  foreach ($array as $key => $value)
    echo "\$array[$key] = $value <br>\n";
?>

whose output is:

X-Powered-By: PHP/4.1.2
Content-type: text/html

$array[chars1] = 65 <br>
$array[chars2] = 65 <br>
$array[int] = 65 <br>

Note that the format string is something like
<format-code> [<count>] [<array-key>] [/ ...]

I hope this clarifies something

Sergio

down

ludwig at kni-online dot de ¶

4 years ago

Don't forget to decode user-defined-pseudo-byte-sequences before unpacking...
<?php
  $byte_code_string =  '00004040';
  var_dump ( unpack ( 'f', $byte_code_string ) );
?>
Result:
  array(1) {
    [1]=>
    float(6.4096905560973E-10)
  }

whereas
<?php
   $byte_code_string =  '00004040';
   var_dump ( unpack ( 'f', hex2bin ( $byte_code_string ) ) );
?>
Result:
  array(1) {
    [1]=>
    float(3)
  }

down

Aaron Wells ¶

14 years ago

Another option for converting binary data into PHP data types, is to use the Zend Framework's Zend_Io_Reader class:
http://bit.ly/9zAhgz

There's also a Zend_Io_Writer class that does the reverse.

down

-1

Anonymous Coward ¶

16 years ago

Warning: This unpack function makes the array with keys starting at 1 instead of starting at 0.

For example:
<?php
 function read_field($h) {
  $a=unpack("V",fread($h,4));
  return fread($h,$a[1]);
 }
?>

down

-3

rogier ¶

13 years ago

be aware of the behavior of your system that PHP resides on.



On x86, unpack MAY not yield the result you expect for UInt32



This is due to the internal nature of PHP, being that integers are internally stored as SIGNED!



For x86 systems, unpack('N', "\xff\xff\xff\xff") results in -1

For (most?) x64 systems, unpack('N', "\xff\xff\xff\xff") results in 4294967295.



This can be verified by checking the value of PHP_INT_SIZE.

If this value is 4, you have a PHP that internally stores 32-bit.

A value of 8 internally stores 64-bit.



To work around this 'problem', you can use the following code to avoid problems with unpack.

The code is for big endian order but can easily be adjusted for little endian order (also, similar code works for 64-bit integers):



<?php

function _uint32be($bin)

{

    // $bin is the binary 32-bit BE string that represents the integer

    if (PHP_INT_SIZE <= 4){

        list(,$h,$l) = unpack('n*', $bin);

        return ($l + ($h*0x010000));

    }

    else{

        list(,$int) = unpack('N', $bin);

        return $int;

    }

}

?>



Do note that you *could* also use sprintf('%u', $x) to show the unsigned real value.

Also note that (at least when PHP_INT_SIZE = 4) the result WILL be a float value when the input is larger then 0x7fffffff (just check with gettype);



Hope this helps people.

down

-2

norwood at computer dot org ¶

14 years ago

Reading a text cell from an Excel spreadsheet returned a string with low-order embedded nulls: 0x4100 0x4200 etc. To remove the nulls, used



<?php

$strWithoutNulls = implode( '', explode( "\0", $strWithNulls ) );

?>



(unpack() didn't seem to help much here; needed chars back to re-constitute the string, not integers.)

down

-4

googlybash24 at aol dot com ¶

12 years ago

To convert big endian to little endian or to convert little endian to big endian, use the following approach as an example:

<?php
// file_get_contents() returns a binary value, unpack("V*", _ ) returns an unsigned long 32-bit little endian decimal value, but bin2hex() after that would just give the hex data in the file if alone, so instead we use:
// file_get_contents(), unpack("V*", _ ), then dechex(), in that order, to get the byte-swapping effect.
?>

With the logic of the approach in this example, you can discover how to swap the endian byte order as you need.

down

-3

sica at wnet com br ¶

15 years ago

The script following is a example how to save more than one values on file separating its with "\r\n" and how to recovering its values.

<?php
// Save two integer values in a binary file
$nomearq = "./teste.bin";
$valor = 123;
$ptrarq = fopen($nomearq, "wb");
$valorBin = pack("L",$valor);
echo "First value ($valor) packed with ";
echo fwrite($ptrarq, $valorBin)." bytes<br>";
echo "Separator \\r\\n with ";
echo fwrite($ptrarq, "\r\n")." bytes<br>";
$valor = 456;
$valorBin = pack("L",$valor);
echo "Second value ($valor) packed with ";
echo fwrite($ptrarq, $valorBin)." bytes<br>";
fclose($ptrarq);

// Recover the saved values
$ptrarq = fopen($nomearq, "rb");
$valorBin = file($nomearq,filesize($nomearq));
echo "<br>The reading values is:<br>";
foreach($valorBin as $valor){
  $valor = unpack("L",$valor);
  print_r($valor);
  echo "<br>";
}
fclose($ptrarq);
?>

Results:
First value (123) packed with 4 bytes
Separator \r\n with 2 bytes
Second value (456) packed with 4 bytes

The reading values is:
Array ( [1] => 123 ) 
Array ( [1] => 456 )

down

-3

iredden at redden dot on dot ca ¶

24 years ago

<?php



function parse_pascalstr($bytes_parsed, $parse_str) { 

    $parse_info = unpack("x$bytes_parsed/cstr_len", $parse_str);

    $str_len = $parse_info["str_len"]; 

    $bytes_parsed = $bytes_parsed + 1; 

    $parse_info = unpack("x$bytes_parsed/A".$str_len."str", $parse_str); 

    $str = $parse_info["str"]; 

    $bytes_parsed = $bytes_parsed + strlen($str); 



    return array($str, $bytes_parsed); 

}



?>

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