Dear Monks,

I am struggling to understand the more advanced (un)pack templates, which allow me to describe my data structure.

I have this structure packed in a string $testinput:
  • byte: number of members in each of the following arrays
  • array of bytes
  • array of unsigned shorts
  • another array of unsigned shorts

    • I would like to know, if there is a single unpack template, that uses the first entry not only for sizing the following array, but instead three times for each of them.

    This is what I have tried so far, and I am not really happy with it. 
    use strict;
use warnings;

my $testinput = pack('C/a* a* a*', 
                     (pack 'C*', 1, 2), 
                     (pack 'v*', 3, 4),
                     (pack 'v*', 5, 6));

print join(',', unpack('C/C* v2 v2', $testinput)), "\n";
# gives "1,2,3,4,5,6" which is ok,
# but has the repeat factors for 'v' hardcoded

my $repeat = unpack('C', $testinput);
print join(',', unpack("C/C* v$repeat v$repeat", $testinput)), "\n";
# gives "1,2,3,4,5,6" which is ok, but uses two steps

    [download]
    Is it possible to use one call to unpack to expand this string to the values above?

    Thanks in advance, hexcoder

    In reply to pack and unpack multiple arrays with one common repeat prefix by hexcoder

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