Not a Number

batt0usai has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Not a Number by rasta (Hermit) on Oct 18, 2002 at 07:24 UTC
Look at strtod() in POSIX package. -- yuriy	[reply]
Re: Not a Number by robartes (Priest) on Oct 18, 2002 at 07:22 UTC
You use regexes to check whether something is a valid number. The advantage of this is that you can easily adapt the regexes to whatever your interpretation of a number is. Here's an example out of the Cookbook: `use strict; my $number="3.141529"; print "$number is a C float!\n" if $number=~/^([+-]?)(?=\d\|\.\d)\d(\. +\d)?([Ee]([+-]?\d+))?$/;` [download] Chapter 2 of the Perl Cookbook provides numerous recipes for dealing with numbers in Perl. It comes highly recommended. CU Robartes-	[reply] [d/l]
Re: Re: Not a Number by rasta (Hermit) on Oct 18, 2002 at 07:45 UTC
NaN is an IEEE standard constant which stands for Not a Number. It is returned if an invalid operation exception occurs within an operation. For example, sqrt(-1) will return a number with a bit configuration that is recognized as NaN because this operation would result in an imaginary number. Therefore regexps don't help us in that issue. -- yuriy	[reply]
Re: Re: Re: Not a Number by physgreg (Scribe) on Oct 18, 2002 at 13:42 UTC
When I tried the sqrt(-1) example, I got the message `Can't take sqrt of -1 at -e line 1.` [download] so it would seem that NaN is not used.	[reply] [d/l]
Re: Not a Number by George_Sherston (Vicar) on Oct 18, 2002 at 10:48 UTC
This question seems to come round with the fall of the leaf. When I asked it last year I didn't realise that it was so interesting and complex. Now I know, though I admit part of me just wants to say, like Sir Roger de Coverley would if he'd had a Babbage Engine, "well come on, I mean to say dash it all, a thing's either a number or it's not, don't you know?" § George Sherston	[reply]
Re: Re: Not a Number by broquaint (Abbot) on Oct 18, 2002 at 11:17 UTC
It may be a little late now but here's a funky little subroutine from merlyn that distinguishes between numbers and strings `sub is_numeric { ($_[0] & ~ $_[0]) eq "0"; }` [download] The original post can be found here. HTH `_________ broquaint`	[reply] [d/l]
Re: Re: Re: Not a Number by rasta (Hermit) on Oct 18, 2002 at 15:24 UTC
OK, what will your subroutine return for '1e+2'?.. perltod() works fine.	[reply]


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