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CGI parameter of 0 behaving strangely

by Ming (Acolyte)
on Jun 12, 2003 at 15:41 UTC ( [id://265392]=perlquestion: print w/replies, xml ) Need Help??

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

This code doesn't delete the first line when passed a parameter of delete=0. It works for all other values. How come? 
use CGI qw(:standard);

if(param('delete'))
{
   $lineNum = param('delete');

   open(FILE, "$filename");
   @lines = <FILE>;
   close(FILE);

   splice(@lines, $lineNum, 1);

   open(FILE, ">$filename");
   print FILE (@lines);
   close(FILE);
}

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Replies are listed 'Best First'.
Re: CGI parameter of 0 behaving strangely
by hardburn (Abbot) on Jun 12, 2003 at 15:48 UTC

    Because when delete=0, then param('delete') returns 0. When evaluated in boolean context (which is what if does), 0 is false and all other values are true.

    I think what you want is if(defined param('delete')) { . . . }. defined() returns true if the value given is actually defined, but doesn't care what it was defined as.

    ----
    I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
    -- Schemer

    Note: All code is untested, unless otherwise stated

[reply]
[d/l]
[select]
      I see... thank you.
[reply]
Re: CGI parameter of 0 behaving strangely
by edan (Curate) on Jun 12, 2003 at 15:48 UTC

    Because in perl, zero ('0') is false, so the 'if' test fails.

    --
    3dan
[reply]

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