PHP pack with multiple values with different lengths

Question

I'd like to pack a string consisting of a 64 bits, 32 bits and 32 bits ints. I don't have much experience with the pack function (or bits altogether) so I'm trying to do something like this:

pack('JNN', 1, 2, 3);
// and
unpack('JNN');

But that does not yield the result I'm after.

The problem is that when I run that code I receive the following:

array [
  "NN" => 1
]

But I expected this:

array [
  1,
  2,
  3
]

Any idea how to approach this?

Thanks in advance,

Answer 1

pack creates a 16-character string.

$str = pack('JNN', 1, 2, 3);
//string(16) "\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x02\x00\x00\x00\x03"

unpack requires keys for the format elements. Example:

$arr = unpack('Jint64/N2int32_',$str);
/*
array (
  'int64' => 1,
  'int32_1' => 2,
  'int32_2' => 3,
)
*/

For more examples, see Unpack in the PHP manual.

If purely numeric keys are required, the array_values function can be used.