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Date: Fri, 02 May 2008 19:24:43 +0200
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To: Jonathan Bond-Caron <jbondc@openmv.com>
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Subject: Re: [PHP-DEV] Float comparison
From: andrey@mysql.com (Andrey Hristov)

  Hi,
Jonathan Bond-Caron wrote:
> Hi,
> 
>  
> 
> I'm new to the PHP internals list and I'm posting an issue I'm sure has been
> mentioned before -- float comparison
> 
>  
> 
> I'd like to know if there are reasons not to change the default behavior
> when comparing floats.
> 
>  
> 
> i.e. This would seem logical to me:
> 
>  
> 
>                 $test = 19.6*100;
> 
>                 if((float)(string)$test == (double)1960)
> 
>                                 echo "GOOD BEHAVIOR";
> 
>                 
> 
>                 // Implicitely convert the float to string then float (en_US
> locale)
> 
>                 if($test == (double)1960)
> 
>                                 echo "THIS SHOULD PASS by casting
> (float)(string)$test internally...";
> 
>                 else
> 
>                                 echo "NOT GOOD BEHAVIOR";
> 
>  
> 
>                 // Exact comparison would still fail
> 
>                 if($test !== (double)1960)
> 
>                                 echo "GOOD BEHAVIOR";
> 
>  
> 
> Any reason why $test == (double)1960 should fail? I realized we are
> comparing two floats, but couldn't php internally convert to string then
> float - for the non strict (===) case  
> 
>  
> 
> Thanks
> 

Never compare directly floats but subtract one from the other and check 
whether the difference is bigger or smaller than a small predefined number.

Regards,
Andrey



-- 
Andrey Hristov, Connectors Software Developer
Sun Microsystems GmbH, Sonnenallee 1, 85551 Kirchheim-Heimstetten
Amtsgericht Muenchen: HRB161028
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