On 22/08/2015 17:38, Alexander Kapshuk wrote:
> On Sat, Aug 22, 2015 at 4:26 PM, hw <h...@gartencenter-vaehning.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.
A good way to demonstrate just how problematic floats can be is to point
out that floats are banned in the linux kernel for exactly this reason.
Integers only.
--
Alan McKinnon
alan.mckin...@gmail.com
