in reply to Mystery! Logical explanation or just Satan's work?

$packed = pack 'n/(n/a*)', 1..9;;

@array = unpack 'C*', $packed;;

print join ', ' , @array;;

[download]
Gives: 0, 9, 0, 1, 49, 0, 1, 50, 0, 1, 51, 0, 1, 52, 0, 1, 53, 0, 1, 54, 0, 1, 55, 0, 1, 56, 0, 1, 57

It looks to me like the first n/ is storing the size of your list. The (n/a*) part is then used that many times (in this case, 9).

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Re^2: Mystery! Logical explanation or just Satan's work?
by BrowserUk (Patriarch) on Aug 16, 2012 at 16:01 UTC

    You're right! I was misinterpreting the prefixed count. That's both good and bad news.

    1. Good news: It works!

      As in it packs/unpacks a list of data reliably.

    2. Bad news: Its not so good for length/data transmission protocols.

      Which want the prefix to be a count of the bytes in the packet; not the number of fields.

      That means an extra step is required:

      $p = pack 'N/a*', pack '(n/a*)*', 1..10, 'aaaa'..'aaaz';;

%h = unpack '(n/a*)*', unpack 'N/a*', $p;;

pp \%h;;
{
  1 => 2,
  3 => 4,
  5 => 6,
  7 => 8,
  9 => 10,
  aaaa => "aaab",
  aaac => "aaad",
  aaae => "aaaf",
  aaag => "aaah",
  aaai => "aaaj",
  aaak => "aaal",
  aaam => "aaan",
  aaao => "aaap",
  aaaq => "aaar",
  aaas => "aaat",
  aaau => "aaav",
  aaaw => "aaax",
  aaay => "aaaz",
}

      [download]

      That's cool, but important to know.

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

    The start of some sanity?
[reply]
[d/l]
[reply]

        Well kinda. But notes like this just confuse things. It seems to suggest the opposite of reality.

        Note that this is one of the rare cases where you cannot use the same template for pack and unpack because pack can't determine a repeat count for a () -group.
        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.

        The start of some sanity?
[reply]
[d/l]

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