On Tue, Jul 24, 2012 at 1:01 AM, Kingsquare.nl - Robin Speekenbrink
<
[email protected] <
mailto:[email protected]>> 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.