PHP - 8 decimals don't work

Question

Here is a very simple code.

$a = 2000000.00000000;
$b = 0.00000001;

echo $a-$b; //output 2000000

I was expecting 1999999.99999999. 

Can someone explain how to make it work ? It would be very appreciate.

Answer 1

You can set the precision used when formatting floats as strings using the precision ini setting, the default being 14:

ini_set('precision', 16);
echo $a - $b; // 1999999.99999999

Also, read this article for a more generic breakdown on the subject.