pack

(PHP 4, PHP 5)

packPack data into binary string

Description

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.

Parameters

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

Return Values

Returns a binary string containing data.

Changelog

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

Examples

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.

Notes

Caution

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.

See Also

  • unpack() - Unpack data from binary string

Коментарии

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!
2000-08-10 07:14:26
http://php5.kiev.ua/manual/ru/function.pack.html
Автор:
You will get the same effect with

<?php
function _readInt($fp)
{
   return 
unpack('V'fread($fp4));
}
?>

or unpack('N', ...) for big-endianness.
2005-10-11 13:42:30
http://php5.kiev.ua/manual/ru/function.pack.html
Автор:
/* 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];
}
2006-03-13 10:57:08
http://php5.kiev.ua/manual/ru/function.pack.html
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.
2008-05-08 10:26:17
http://php5.kiev.ua/manual/ru/function.pack.html
Автор:
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($fppack('a2'$bom)); 
fwrite($fppack("a{$len}"$text));
fwrite($fppack('a2'$bom)); 
fwrite($fppack('a2'"\n"));

fclose($fp);
?>
2010-06-21 07:53:15
http://php5.kiev.ua/manual/ru/function.pack.html
Автор:
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(215)) $foo -= pow(216);
?>
2010-10-21 00:40:15
http://php5.kiev.ua/manual/ru/function.pack.html
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
2012-02-23 23:13:28
http://php5.kiev.ua/manual/ru/function.pack.html
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.
2012-07-06 20:26:58
http://php5.kiev.ua/manual/ru/function.pack.html
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

?>
2016-05-29 06:14:51
http://php5.kiev.ua/manual/ru/function.pack.html
Автор:
pack()
h    Hex string, low nibble first (not same hex2bin())
H    Hex string, high nibble first (same hex2bin())
2017-07-11 08:45:02
http://php5.kiev.ua/manual/ru/function.pack.html

    Поддержать сайт на родительском проекте КГБ