unpack

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

unpack — Desempacota dados de uma string binária

Descrição

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

Desempacota uma srting binária em um array de acordo com o formato especificado em format.

Os dados desempacotados são armazenados em um array associativo. Para que isto seja feito, os diferentes códigos de formato devem ser nomeados e separados por uma barra /. Se um argumento repetidor estiver presente, cada chave do array terá um número de sequência atrás do nome fornecido.

Form feitas alterações para que esta função ficasse alinhada com a linguagem Perl:

O código "a" agora retém os bytes NULL ao final da string.
O código "A" agora remove todos os tipos de espaço ASCII do final da string (espaços, tabulações, novas linhas, retorno de carro e bytes NULL).
O código "Z" foi adicionado para strings com bytes NULL à esquerda, e remove bytes NULL à direita.

Parâmetros

format: Consulte a página da função pack() para uma explicação sobre os códigos de formatos.
string: Os dados empacotados.
offset: O deslocamento na string a partir de onde os dados serão desempacotados.

Valor Retornado

Retorna um array associativo contendo elementos desempacotados da string binária, ou false em caso de falha.

Registro de Alterações

Versão	Descrição
7.2.0	Tipos float e double suportam Big Endian e Little Endian.
7.1.0	O parâmetro opcional `offset` foi adicionado.

Exemplos

Exemplo #1 Exemplo de unpack()

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

O exemplo acima produzirá:

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

Exemplo #2 Exemplo de unpack() com um repetidor

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

O exemplo acima produzirá:

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

Notas

Cuidado

Observe que internamente o PHP armazena com sinal os valores inteiros. Se um inteiro grande longo sem sinal for desempacotado, e for do mesmo tamanho que os valores armazenados internamente pelo PHP, o resultado será um número negativo mesmo que tenha sido especificado um desempacotamento sem sinal.

Cuidado

Se um elemento não for nomeado, seão usados índices numéricos iniciando em 1. Fique ciente que se houver mais de um elemento sem nome, alguns dados serão sobrescritos porque a numeração reiniciará a partir de 1 para cada elemento.

Exemplo #3 Exemplo de unpack() com chaves sem nome

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

O exemplo acima produzirá:

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

Observe que o primeiro valor especificado por c foi sobrescrito pelo primeiro valor de n especificado.

Veja Também

pack() - Empacota dados em uma string binária

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Notas de Usuários 14 notes

down

stanislav dot eckert at vizson dot de ¶

9 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

jjfoerch at earthlink dot net ¶

21 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

Sergio Santana: ssantana at tlaloc dot imta dot mx ¶

21 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

kennwhite dot nospam at hotmail dot com ¶

21 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

Sergio Santana: ssantana at tlaloc dot imta dot mx ¶

21 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

Anonymous ¶

16 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

ludwig at kni-online dot de ¶

5 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

Anonymous Coward ¶

17 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

-1

Aaron Wells ¶

15 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

-2

norwood at computer dot org ¶

15 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

-3

googlybash24 at aol dot com ¶

13 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

-4

rogier ¶

14 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

-4

sica at wnet com br ¶

16 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

-4

iredden at redden dot on dot ca ¶

25 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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