Re: Working with floats

Thanks for the reply. I know of the fact that converting the key to a string would be the 'correct' way of using it, i was more curious as to the difference in the var_dump-s... But the precision setting is new to me, i'll have a look into that... That would indeed make the differences in the resulting $i visible and thus explainable to others. Regards, Robin Speekenbrink Op dinsdag 24 juli 2012 10:42:45, Galen Wright-Watson schreef:

On Tue, Jul 24, 2012 at 1:01 AM, Kingsquare.nl - Robin Speekenbrink <robin@kingsquare.nl <mailto:robin@kingsquare.nl>> wrote:

    Hi all,
    [...]

    Why does the last of the following examples lower my key to 18 BUT
    does the var dump of the float clearly state 'float(19)' as the
    actual value:

        <?php
        [...]
        $i =(float) 1.19;
        $i -= 1;
        $i *= 100;
        var_dump($i);
        $arr = array($i=>1);
        var_dump($arr);
        ?>

When displaying floating point numbers, PHP uses the precision config option (http://php.net/precision) so as to shorten output (and to hide rounding errors in some circumstances). If you increase precision to 17 digits or so (64-bit IEEE floating point numbers have a decimal precision of around 15 to 17 digits), the var_dump will reveal that $i is actually 18.999999999999993.... When you use it as an array index, it ends up converted to an integer, which is done by truncation. If instead you were to convert $i to a string when using it as an index:

    array("$i" => 1);
    array((string)$i => 1);

you'd get a result more along the lines that you expect.

    I do know this is not really an internals thing, but after
    fiddling with this for some time, i gave up (bug 32671 might
    relate to this)

It's central to what you see, but note that it was decided that the behavior was correct; the bug was in the documentation.

    Again, if i'm to be regarded as a traditional n00b, i understand
    as i've seen float / casting discussions before.

I think those were more of the "how should PHP handle this" rather than the "why does it do this" variety. There is probably a more suitable venue for your question than the internals list; perhaps the general usage list. I can be a bit grumpy about these things, but from what I've seen, the PHP community likes to be inclusive, so I doubt it's a big deal.