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Re: check if its a number
by snoopy (Curate) on Apr 12, 2008 at 00:33 UTC
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> Scalar::Util's looks_like_number method will do what you want.
Scalar::Util uses a regex to get the answer. I'm not sure why snoopy's request has that requirement, but...
ben@Tyr:~$ perl -wne'print if /sub looks_like_number/../}/' `perldoc -
+l Scalar::Util`
sub looks_like_number {
local $_ = shift;
# checks from perlfaq4
return 0 if !defined($_) or ref($_);
return 1 if (/^[+-]?\d+$/); # is a +/- integer
return 1 if (/^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/); #
+a C float
return 1 if ($] >= 5.008 and /^(Inf(inity)?|NaN)$/i) or ($] >= 5.006
+001 and /^Inf$/i);
0;
}
--
Human history becomes more and more a race between education and catastrophe. -- HG Wells
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[d/l] |
Re: check if its a number
by dragonchild (Archbishop) on Apr 12, 2008 at 00:34 UTC
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Why is a regular expression bad? They're extremely efficient and simple to understand and the right tool for the job.
if ( defined($x) && length($x) && $x !~ /\D/ && 0 <= $x && $x <= 10 )
+{
# It matches
}
Of course, if this is homework, be prepared to explain why each of those is important. :-)
My criteria for good software:
- Does it work?
- Can someone else come in, make a change, and be reasonably certain no bugs were introduced?
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[d/l] |
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I think I will go with the regexp as several people suggested. Originally I didn't want to do that because I remembered a while back I did some benches on using regexp vs substr+index and the regexp was always slower. This code is to run in a mod_perl handler which handles a ton of requests and I was worried about it slowing everything down.
thanks
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Re: check if its a number
by ysth (Canon) on Apr 12, 2008 at 01:15 UTC
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What do you mean by "is a number"? Between inclusively or exclusively?
Is "01" ok? What about "000000000000000000000001"?
Here's one bad way:
$isanum = !($x !~ y/.//) + $x =~ y/0-9// == $x =~ y/0-9.//c + $x !~ y/
+0-9// + length($x) && $x <= 10;
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[d/l] |
Re: check if its a number
by AV-2 (Novice) on Apr 12, 2008 at 02:13 UTC
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I was going to post something else, but in the process I tried this:
my $foo = 'name';
print $foo + 1;
Perl warns me "Argument "name" isn't numeric in addition (+)"
How does Perl know it isn't a number? Is the method available through a function? | [reply]
[d/l] |
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Yes you can write a function that tells you if a given string triggers the warning.
sub perl_thinks_it_is_number {
eval {
use warnings FATAL => 'numeric';
no warnings 'void';
0+shift;
1;
}
}
print "'foo' isn't a number\n"
unless perl_thinks_it_is_number 'foo';
print "'17' is a number\n"
if perl_thinks_it_is_number '17';
Note that this will consider '00' and some other oddities to be a number. You are probably better sticking with other answers elsewhere in this thread. | [reply]
[d/l] |
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... warning comes up only when using, well, warnings pragma (otherwise string is used as a zero).
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[d/l] |
Re: check if its a number
by pc88mxer (Vicar) on Apr 12, 2008 at 00:35 UTC
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Why don't you want to use regular expressions?
Here's an extensive discussion on checking whether a string represents a number: link removed due to copyright concerns. | [reply] |
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Is this link legitimate? Looks like they make a lot of ebooks by many different publishers available on their website, including some texts written by some of the users of this site.
Martin
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