in reply to Re: help needed on encoding a text file
in thread help needed on encoding a text file

Point well taken on mixing text and binmode. Doing the decode was getting pretty hairy as I had it.

I must say that I do not understand the pack("N(N/a*)" syntax. I know what N and a are but cannot find any docs on the parens; I did find docs on the slash and understand it now. (Though I have to admit that I have really TOTALLY avoided pack and unpack as they seem VERY confusing to me.)

Also why 2 N's? Seems it could be written as N/a* per the perlfunc man page.

Also, I get an error on the decoder as follows: 
/ must follow a numeric type at ./dcode2.pl line 7, <> chunk 1.

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Extrapolating this out it would seem that there is a syntax error in the decoder as it is written unpack "(N(N/a))*",$ind; and is seems it should probably be unpack "N(N/a*)",$ind; but that does not produce any output, just blank lines.

Ed

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Re: Re: Re: help needed on encoding a text file
by dakkar (Hermit) on Apr 03, 2003 at 11:17 UTC

    pack("N(N/a*)",$index{$key},$key)! meaning that the $index{$key} is written as a Number, and the $key as a length-prefixed string.

    The parenthesis are for grouping. Their meaning is half-hidden in the documentation...

    Regarding the error: I don't get it. I tested the code.

    The unpack is right as it is: it means "a series of pairs of Numbers and length-prefixed strings (in unpack you must not put the *, see the docs)

    -- 
        dakkar - Mobilis in mobile
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      Ok, so I finally understand the N/a notation but am having trouble with this code. Seems that the () notation is pretty new as it is not in my Programming Perl, 2nd Edition and my perl 5.6.1 does not support it. But, my perl 5.8.0 does support it and is documented in its perlfunc manpage.

      Here is the error that I get with the perl 5.6.1:
      Invalid type in unpack: '(' at C:\Data\test\dcode2.pl line 8, <> chunk 1.

      I am not too sure how to go about "converting" this code to work with perl 5.6.1.

      BTW, still cannot get the code to work on perl 5.8.0 without an error with the "/" as stated earlier.

      Ed
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