http://www.perlmonks.org?node_id=1044463

BrowserUk has asked for the wisdom of the Perl Monks concerning the following question:

I just posted code to demonstrate a solution to Unpack an 8 bit unsigned char matrix.

Only after posting did I noticed that, despite it uses unpack template 'C*', it produces 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, rather than:

print unpack 'C*', '1234567890';;
49 50 51 52 53 54 55 56 57 48

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And without having given it a great deal of thought or experiment, I cannot for the life of me explain why. Can you?

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.

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Re: A mystery? (s/split/unpack/)
by LanX (Saint) on Jul 15, 2013 at 22:25 UTC
    I heard the theme from twilight zone while reading the title.

    spooky...

    Cheers Rolf   xD

    ( addicted to the Perl Programming Language)

    update

    I'm no big packerista, but what is split 'C*' supposed to do?

    my @matrixX10 = map[ split 'C*', $_ ], unpack '(a10)*', $buffer

    did you intend another unpack ?

      DB<105>  map [ unpack 'C*', $_] ,unpack '(a10)*', '12345678901234567
+890'
 => (
  [49, 50, 51, 52, 53, 54, 55, 56, 57, 48],
  [49, 50, 51, 52, 53, 54, 55, 56, 57, 48],
)

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      did you intend another unpack ?

      Yes. (Cliché, but LOL!)

      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.
[reply]
Re: A mystery?
by vsespb (Chaplain) on Jul 15, 2013 at 23:06 UTC
    Interesting that it dies under Linux with empty $! (unless I replace sysread with read), even if I replace CRLF with LF.
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      Interesting that it dies under Linux with empty $!

      I've no knowledge to address that.

      The only possibility that springs to mind is that *nix sysread really objects to being used on a filehandle that has previously been used in "formatted IO" mode.

      Ie. As the DATA pseudo-handle is actually the same handle used to read the source, which presumably reads it using formatted IO, trying to read it with low-level IO sysread() causes it to throw its hands up in disgust :)

      even if I replace CRLF with LF.

      sysread should be completely oblivious to CRLF/LF -- even if I was asking it to read one or more -- but I'm asking it to read 80 characters only, so there are no newlines (of any flavour) being read.

      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.
[reply]

        Works for me (Linux) if I prepend sysread() with 

         binmode( DATA );

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