CGI parameter of 0 behaving strangely

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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Comment on CGI parameter of 0 behaving strangely Download Code

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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]
Re: Re: CGI parameter of 0 behaving strangely by Ming (Acolyte) on Jun 12, 2003 at 16:15 UTC
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]