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Date: Sun, 23 Oct 2016 21:18:28 +0200
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Subject: Re: [PHP-DEV] strtod and NaN vs. zero
From: dev@mabe.berlin (Marc Bennewitz)



Am 23.10.2016 um 21:13 schrieb Marc Bennewitz:
>
>
> Am 23.10.2016 um 13:49 schrieb Niklas Keller:
>> 2016-10-23 12:55 GMT+02:00 Marc Bennewitz <dev@mabe.berlin
>> <mailto:dev@mabe.berlin>>:
>>
>>     Hi internals,
>>
>>     On casting a non numeric value to a float in PHP the result will be
>>     float(0).
>>
>>     In PHP-7.0 an exception was introduced that on casting a string
>>     "/\s*NaN\s*/i" will result in float(NaN).
>>
>>     https://3v4l.org/2Xakm
>>
>>     Wouldn't it be more logical and expected to return NaN in all cases
>>     of casting a non numeric string to a floating point number?
>>
>>     Thanks
>>     Marc
>>
>>     --
>>     PHP Internals - PHP Runtime Development Mailing List
>>     To unsubscribe, visit: http://www.php.net/unsub.php
>>
>>
>> +1
>
> I just noticed that the behavior change in PHP-7 has been "fixed"
> already by https://bugs.php.net/bug.php?id=73329.
>
> So the old behavior will be presented soon.
>
> But I'm still curious why casting any non numeric string results in the
> valid number float(0) where there is a special value in floating point
> numbers declared to represent not a number values.
>
> I also did a small research on other languages and found the following:
>
> C strtod returns float(0)
>   -> but supports converting the strings "INFINITY" or "NAN"
> (case-insensitive)
>
> JavaScript returns NaN

I forgot to mention that in JavaScript (parseFloat) it is nearly the 
behavior I would expect. The only difference is that it allows the 
string +/- "Infinity" to be casted to Infinity.

>
> Python throws ValueError: could not convert string to float
>   -> but supports the string +/- "NaN", "Inf", "Infinity"
> (case-insensitive)
>
> Perl returns float(0)
>   -> but supports the string +/- "NaN", "Inf", "Infinity"
> (case-insensitive)
>
> So there is a nice mix of how other languages will handle this problem.
>
>
> In my opinion it still makes much more sense to return NaN in any case a
> not numeric string will be casted to float incl. "Inf" and "Infinity".
> (If spaces should be ignored or suffixes allowed is another question)
>
> = The beginning of a string must contain at least one number by ignoring
> spaces to be casted to a valid floating point number. In any other
> situations NaN must be returned because this represents what it is = Not
> a Number.
>
> So for me the following example table makes sense:
>
> In -> Out
> "" -> NaN
> " " -> NaN
> "+" -> NaN
> "-" -> NaN
> "." -> NaN
> ".5" -> 0.5
> "0.5" -> 0.5
> " 0.5" -> 0.5
> "0" -> 0
> " 0" -> 0
> "Nan" -> NaN
> "Inf" -> NaN
> "Info" -> NaN
> "foo" -> NaN
> ".foo" -> NaN
> ".2foo" -> 0.2
> " .2foo" -> 0.2
> "foo1" -> NaN
> "foo." -> NaN
> "foo0.1" -> NaN
>
>
> Thoughts
> Marc
>
>>
>> Regards, Niklas
>