Handling both string and numeric comparisons

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

Hi,

I overcame a problem which displays warnings while executing perl program, the situation is

sub compare{
  $param=shift;
  print "String" if($param eq "5");
}
[download]

In the above case the $param may be a string or integer and in case if it is a integer then, we will usually get a warning saying cannot do a string comparison for the integer value .

so can this be avoided ,is there a way to check if $param is integer of string and based on that do a string or integer comparison? Like we do a check for Ref("ARRRAY")?

Regards

CODE tags added by Arunbear

Comment on Handling both string and numeric comparisons Download Code

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Re: Handling both string and numeric comparisons by holli (Abbot) on May 12, 2005 at 13:00 UTC
In this code the warning occurs, only at the numeric comparison (==) not the at string (eq). Can you post an example to demonstrate your problem? `use strict; use warnings; my ($number, $string) = (5, "hello"); print 1 if $number eq $string; #ok print 2 if $number == $string; #Argument "hello" isn't numeric in nume +ric eq (==) at C:\w.pl line 6.` [download] holli, /regexed monk/	[reply] [d/l]
Re: Handling both string and numeric comparisons by rob_au (Abbot) on May 12, 2005 at 11:31 UTC
You can force the numeric context for your string in the following fashion: `if (0 + $param == 5) { ... }` [download] This will execute and provide the comparison operation that you desire without error or warning. Where `$param` is a string, the result of the inner operation is zero. `perl -le "print unpack'N', pack'B32', '00000000000000000000001000000000'"`	[reply] [d/l] [select]
Re^2: Handling both string and numeric comparisons by Roy Johnson (Monsignor) on May 12, 2005 at 12:01 UTC
If you `use warnings;`, you will get a warning: `Argument "five" isn't numeric in addition (+) at try.pl line 6.` [download] You will not get a warning for doing string comparison on a number, though. Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re: Handling both string and numeric comparisons by thcsoft (Monk) on May 12, 2005 at 11:34 UTC
i never read the error message you're reporting. but if it really occours, try to avoid it with a small regex: `my $isnum = 1 if ($param =~ /^\d+$/);` [download] another way might work with sprintf(). however, perl doesn't care for the difference between strings an numbers, as long as you don't try execute inappropriate operations on them. language is a virus from outer space.	[reply] [d/l]
Re^2: Handling both string and numeric comparisons by chromatic (Archbishop) on May 12, 2005 at 14:58 UTC
Be careful with that construct. What will `$isnum` be if the regex is false?	[reply] [d/l]
Re: Handling both string and numeric comparisons by Aragorn (Curate) on May 12, 2005 at 14:44 UTC
In the standard module Scalar::Util, there is a function `looks_like_number EXPR` with which you can check this. It'll return true if Perl thinks EXPR is a number. Arjen	[reply] [d/l]
Re: Handling both string and numeric comparisons by starbolin (Hermit) on May 12, 2005 at 17:45 UTC
I have to agree with holli. Can you show a piece of code where ( $param eq '5' ) fails? Perl will convert integers to string automatically. The only time I have problems is when I need to force an integer. perl_devel writes: "is there a way to check if $param is integer of string and based on that do a string or integer comparison?" I don't see the purpose. Perl does the integer to string conversion automatically depending on what it thinks it needs. To check for both would require explicitly casting a string to an integer. So, if you are casting it to one or the other, what's the point?? s//----->\t/;$~="JAPH";s//\r<$~~/;{s\|~$~-\|-~$~\|\|\|s \|-$~~\|$~~-\|\|\|s,<$~~,<~$~,,s,~$~>,$~~>,, $\|=1,select$,,$,,$,,1e-1;print;redo}	[reply]