Problem with Floats! (in PHP)

Question

What's wrong with php floats?

$v = 5.2 * 3; if($v==15.6) { echo 'Everything is fine =)'; } else { echo 'Okay something is wrong :S'; var_dump($v); // float 15.6 }

Check this out too:

$v = 5.2 * 3; if($v>15.6 AND $v<15.60000000001) { echo 'We are doomed :S'; var_dump($v); // float 15.6 } else { echo 'Everything is fine =)'; }

I guess it has something to do with the internal representation or some obscure low level stuff? If that's the case, how do I get around this issue? Anything else I should know before using this to calculate real money transactions?

This should be helpful: docs.sun.com/source/806-3568/ncg_goldberg.html — Piskvor left the building
– Piskvor left the building, Commented Nov 25, 2010 at 11:36

Gordon · Accepted Answer · 2010-11-25 11:39:52Z

I am sure this is a duplicate, so I'm making this a CW

$v = 5.2 * 3; if (bccomp($v, 15.6) === 0) { echo 'Everything is fine =)'; } else { echo 'Okay something is wrong :S'; var_dump($v); // float 15.6 }

will give 'Everything is fine =)'

Lucas Moeskops · Accepted Answer · 2010-11-25 11:33:06Z

It has to do with the internal representation indeed :). Never compare float values. I think there will exists php classes/modules that work around this problem, but you can also store your money values as integers and multiply them by 100. Before display you can divide them again :)

Sebastian Hoitz · Accepted Answer · 2010-11-25 11:33:13Z

This has to do with floats in general and is not limited to PHP.

When using floats you should check for intervals with a specific precision, just as you did in your last example:

if(abs($v - 15.6) < 0.0001) { // Yey :) }

You can run into a lot of problems when using exact values.

Community · Accepted Answer · 2017-05-23 12:00:40Z

the value you are getting is 15.600000000000001 and it is diferent to 15.6, this topic has been widely discussed, you can take a look to this threads:

HTH, Regards

crdx · Accepted Answer · 2010-11-25 11:36:09Z

The PHP page on floats has a warning against comparing for equality and also links to this page which links to bccomp.

Ray · Accepted Answer · 2010-11-25 11:37:10Z

If you really need to compare floats check for being in bounds of an allowed deviation instead of an exact match, like

$DEVIATION = 0.0001; if(abs($v-15.6)<$DEVIATION) ...

JimBeeUK · Accepted Answer · 2010-11-25 11:44:35Z

$v = 5.2 * 3; if((string)$v == "15.6") { print "yes"; }

It's always good to check PHP website as most developers have come across problems before PHP.net Floating Point Number this comment shows a function for comparing floats.

<?php function IsFloatEqual($x,$y,$precision=0.0000001) { return ($x+$precision >= $y) && ($x-$precision <= $y); } ?>

Gekkie · Accepted Answer · 2010-11-25 12:07:58Z

Just a minor addition for anywone looking:

the BC* functions are the only true way to work with floats in PHP!

CleverSkull · Accepted Answer · 2025-04-16 18:36:42Z

You can use serialize_precision setting.

ini_set('serialize_precision',-1);

which uses enhanced rounding.

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