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
