Re: [gentoo-user] 69.99 != 69.99

[Alexander Kapshuk]

On Sat, Aug 22, 2015 at 4:26 PM, hw <hw@×××××××××××××××××××××.de> wrote:
>
> Hi,
>
> I have the following in a perl script:
>
>
>       if ($a != $b) {
>         print "e: '$a', t: '$b'\n";
>       }
>
>
> That will print:
>
> e: '69.99', t: '69.99'
>
>
> When I replace != with ne (if ($a ne $a) {), it doesn't print.
>
>
> Is that a bug or a feature?  And if it's a feature, what's the explanation?
>
> And how do you deal with comparisions of variables when you get randomly
> either correct results or wrong ones?  It's randomly because this statement
> checks multiple values in the script, and 69.99 is the only number showing
> up yet which isn't numerically equal to itself (but equal to itself when
> compared as strings).
>

Perl Cookbook, 2nd edition, suggests these two approaches to comparing
floats for equality.
(1). Use sprintf to format the numbers to a certain number of decimal
places, then compare the resulting strings.
(2). Alternatively, store the numbers as integers by assuming the decimal place.