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On 22/08/2015 17:38, Alexander Kapshuk wrote: |
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> On Sat, Aug 22, 2015 at 4:26 PM, hw <hw@×××××××××××××××××××××.de> wrote: |
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>> |
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>> Hi, |
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>> |
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>> I have the following in a perl script: |
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>> |
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>> |
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>> if ($a != $b) { |
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>> print "e: '$a', t: '$b'\n"; |
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>> } |
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>> |
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>> |
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>> That will print: |
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>> |
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>> e: '69.99', t: '69.99' |
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>> |
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>> |
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>> When I replace != with ne (if ($a ne $a) {), it doesn't print. |
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>> |
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>> |
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>> Is that a bug or a feature? And if it's a feature, what's the explanation? |
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>> |
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>> And how do you deal with comparisions of variables when you get randomly |
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>> either correct results or wrong ones? It's randomly because this statement |
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>> checks multiple values in the script, and 69.99 is the only number showing |
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>> up yet which isn't numerically equal to itself (but equal to itself when |
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>> compared as strings). |
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>> |
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> |
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> Perl Cookbook, 2nd edition, suggests these two approaches to comparing |
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> floats for equality. |
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> (1). Use sprintf to format the numbers to a certain number of decimal |
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> places, then compare the resulting strings. |
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> (2). Alternatively, store the numbers as integers by assuming the decimal place. |
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A good way to demonstrate just how problematic floats can be is to point |
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out that floats are banned in the linux kernel for exactly this reason. |
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Integers only. |
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-- |
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Alan McKinnon |
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alan.mckinnon@×××××.com |
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