pack

(PHP 4, PHP 5, PHP 7)

pack — Pack data into binary string

Descrierea

pack ( string $format , mixed ...$values ) : string

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.

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
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)
q	signed long long (always 64 bit, machine byte order)
Q	unsigned long long (always 64 bit, machine byte order)
J	unsigned long long (always 64 bit, big endian byte order)
P	unsigned long long (always 64 bit, little endian byte order)
f	float (machine dependent size and representation)
g	float (machine dependent size, little endian byte order)
G	float (machine dependent size, big endian byte order)
d	double (machine dependent size and representation)
e	double (machine dependent size, little endian byte order)
E	double (machine dependent size, big endian byte order)
x	NUL byte
X	Back up one byte
Z	NUL-padded string (new in PHP 5.5)
@	NUL-fill to absolute position

values

Valorile întoarse

Returns a binary string containing data, sau false în cazul eșecului.

Istoricul schimbărilor

Versiune	Descriere
8.0.0	This function no longer returns `false` on failure.
7.2.0	float and double types supports both Big Endian and Little Endian.
7.0.15,7.1.1	The "e", "E", "g" and "G" codes were added to enable byte order support for float and double.
5.6.3	The "q", "Q", "J" and "P" codes were added to enable working with 64-bit numbers.
5.5.0	The "Z" code was added with equivalent functionality to "a" for Perl compatibility.

Exemple

Example #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

Precauţie

Note that PHP internally stores int values as signed values of a machine-dependent size (C type long). Integer literals and operations that yield numbers outside the bounds of the int 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 int type if it were unsigned. In systems where the int type has a 32-bit size, the cast usually results in the same byte pattern as if the int were unsigned (although this relies on implementation-defined unsigned to signed conversions, as per the C standard). In systems where the int 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 int negative values with the same byte representation as the desired unsigned value.

A se vedea și

unpack() - Unpack data from binary string

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User Contributed Notes 10 notes

down

chadm at codeangel dot org ¶

12 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

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

plutus at gmx dot de ¶

24 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!

down

FrozenFire ¶

14 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);

?>

down

j.s.hoekstra ¶

18 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];
}

down

php at nagler-ihlein dot de ¶

16 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.

down

petepostma at gmail dot spam dot com ¶

12 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.

down

Patrik Fimml ¶

19 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.

down

Ammar Hameed ¶

14 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);
?>

down

ru ¶

7 years ago


pack()
h    Hex string, low nibble first (not same hex2bin())
H    Hex string, high nibble first (same hex2bin())

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