ternary operator

kevind0718 has asked for the wisdom of the Perl Monks concerning the following question:

Hello kind and Wise Monks:

I have a bit of simple code and do not understand why it does not behave as I expect.

         $col->[26] = (($col[26] eq  '0') ? ''  :  $col->[26] );
         print '  $col->[26]:'  .  $col->[26]  .  ":\n"  ;
[download]

$col->26 is expected to contain a string which is a date. I.e. '20090711'
If it does not contain a date it contains a zero. I.e. 0
Not what I would like, but I have to deal with it.

If $col->26 contains '20090711' I get $col->26:20090711: from the above code.

If $col->26 contains '0' I get $col->26:0: from the above code.

Not what I expected. I want to get an empty string as in ''.

So the question is, what am I doing wrong?
Thanks for your assistance.

KD

Comment on ternary operator Download Code

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Re: ternary operator by ikegami (Patriarch) on Dec 16, 2008 at 23:18 UTC
Use `use strict;`! Use `use warnings;`! Both would have caught the error independently. `$col->[26] = (($col[26] eq '0') ? '' : $col->[26] );` [download] should be `$col->[26] = (($col->[26] eq '0') ? '' : $col->[26] );` [download]	[reply] [d/l] [select]
Re^2: ternary operator by kevind0718 (Scribe) on Dec 16, 2008 at 23:28 UTC
yes that is much better. Been a long day. thanks kd	[reply]
Re: ternary operator by Tanktalus (Canon) on Dec 16, 2008 at 23:19 UTC
Probably, you're not using strict and warnings. Either that, or you have both a scalar $col and an array @col in the same scope, which is just asking for confusion. Or, I suppose, both, but we'll assume just one at a time for now ;-) `$col->[26] = $col->[26] eq '0" ? '' : $col->[26]; # note the extra -> +in there that was missing from your code. # or, more succinctly: $col->[26] = '' if $col->[26] eq '0'; # or, probably better yet: $col->[26] \|\|= '';` [download]	[reply] [d/l]
Re: ternary operator by moritz (Cardinal) on Dec 16, 2008 at 23:20 UTC
`$col->[26] = (($col[26] eq '0') ? '' : $col->[26] ); ^^^` [download] You're missing an arrow here. Start all your scripts with `use strict; use warnings;` [download] and declare your variables, that would have helped to catch this error.	[reply] [d/l] [select]
Re: ternary operator by graff (Chancellor) on Dec 17, 2008 at 01:58 UTC
This logic (corrected as per previous replies): `$col->[26] = (($col->[26] eq '0') ? '' : $col->[26] );` [download] could also be expressed as: `$col->[26] \|\|= '';` [download] If the array element in question contains "0", that will evaluate to false, and the value will be set to the empty string; the assignment will also happen if the array element is undef (which might be a good thing to handle), and if it is already an empty string (which causes an insignificant redundancy). But if I were expecting a field to contain an 8-digit date, I'd be tempted to be at least a little more explicit about that: `$col->[26] = '' unless ( $col->[26] =~ /^\d{8}$/ );` [download] That still allows dates like "00000000" (which would have been caught by the "\|\|=" operator) or "99999999" (which would probably be easy to catch by using one of the Date::... modules to validate the value). Deciding how careful you want to be is a question of trade-offs -- striking the right balance between flagrant carelessness and compulsive precision -- and how well you know your input data.	[reply] [d/l] [select]