How can I differentiate between 0 and whitespace in Perl?

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

I have the following piece of code in my program:

$val = chr(someFunction());

if($val == " ")
{
    #do something

}
elsif($val == 0)
{
   #do something else
}
[download]

But whenever 0 is passed to $val, the if part executes instead of the elsif which I expect to get executed. How can I fix this?

Comment on How can I differentiate between 0 and whitespace in Perl? Download Code

Replies are listed 'Best First'.
Re: How can I differentiate between 0 and whitespace in Perl? by syphilis (Archbishop) on Apr 18, 2009 at 14:04 UTC
When you use "==", both the left and right sides are evaluated in numeric context. Since, in numeric context, " " and 0 are equivalent (and are also numerically equivalent to both undef and "" btw), your 'if' and 'elsif' conditions are effectively identical. That is, if `$val == " "` is true, then so is `$val == 0`, and vice-versa Cheers, Rob	[reply] [d/l] [select]
Re: How can I differentiate between 0 and whitespace in Perl? by Anonymous Monk on Apr 18, 2009 at 13:51 UTC
Use eq to compare strings `C:\>perl -e"die int undef" 0 at -e line 1.` [download] perldoc -f int perlnumber perlop	[reply] [d/l]
Re: How can I differentiate between 0 and whitespace in Perl? by codeacrobat (Chaplain) on Apr 19, 2009 at 10:05 UTC
`use feature ":5.10"; $val=" "; given($val) { when (" ") { print "space"} when (0) { print "zero"} default { print "other" } }` [download] `print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});`	[reply] [d/l] [select]
Re^2: How can I differentiate between 0 and whitespace in Perl? by almut (Canon) on Apr 19, 2009 at 11:40 UTC
Side note: I'd `use 5.010;` instead of `use feature ":5.10";`. The net effect is the same, but the innocent/inexperienced user of an older version of Perl will probably appreciate a clear message indicating what the problem is, i.e. `$ perl -M5.010 -e1 Perl v5.10.0 required--this is only v5.8.8, stopped at ... vs. $ perl -Mfeature=:5.10 -e1 Can't locate feature.pm in @INC (@INC contains: ...` [download] with no mention of 5.10 in the latter.	[reply] [d/l] [select]
Re^3: How can I differentiate between 0 and whitespace in Perl? by codeacrobat (Chaplain) on Apr 19, 2009 at 14:40 UTC
Then this should be fixed in perlsyn, because `use feature ":5.10"` is what you find there. sigh The 5.10 vs. 5.010 syntax is nasty. `print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});`	[reply] [d/l] [select]
Re^3: How can I differentiate between 0 and whitespace in Perl? by Anonymous Monk on Apr 19, 2009 at 12:43 UTC
Then they'll comment out `#use 5.010;` and be equally confused ;)	[reply] [d/l]
Re^4: How can I differentiate between 0 and whitespace in Perl? by almut (Canon) on Apr 19, 2009 at 13:02 UTC