phpfloating-point

Compare floats in php

I want to compare two floats in PHP, like in this sample code:

$a = 0.17;
$b = 1 - 0.83; //0.17
if($a == $b ){
 echo 'a and b are same';
}
else {
 echo 'a and b are not same';
}

In this code it returns the result of the else condition instead of the if condition, even though $a and $b are same. Is there any special way to handle/compare floats in PHP?

If yes then please help me to solve this issue.

Or is there a problem with my server config?

Solution

  • If you do it like this they should be the same. But note that a characteristic of floating-point values is that calculations which seem to result in the same value do not need to actually be identical. So if $a is a literal .17 and $b arrives there through a calculation it can well be that they are different, albeit both display the same value.

    Usually you never compare floating-point values for equality like this, you need to use a smallest acceptable difference:

    if (abs(($a-$b)/$b) < 0.00001) {
  echo "same";
}

    Something like that.