What precautions should I take when using '0' in PHP as a number?

Question

In PHP 0 is treated as boolean false. Hence, whenever I'm in a situation where a function has to return a numerical value and I have it return 0, or when I have a MySQL bool column with possible values of 0/1, and I use code such as this:

$active=(isActive()) ? 1 : 0;
$this->db->set('isActive',$active);

I get a feeling in the back of my mind that the 0 might be converted to null or an empty string e.g "".

What precautions do I need to take in order to have 0 always treated as an integar and not anything else?

Answer 1

None. 0 is 0, even if logical evaluations consider it a false value, that doesn't change its actual value.

Answer 2

If you want PHP to evaluate a statement with 'false' being the only 'false', use === instead of the usual ==

Answer 3

PHP does allow you to cast variables to a certain type.

<?php

   $value = (bool) 0; 
   $value3 = (int) 3; 

?>

If you always want 0 to be treated as a int, cast it as one.

Answer 4

Using the === comparison operator is best as it checks that the types are equal as well as their values. In php if you do:

Your best bet is to use true and false where you can, rather than setting 1 and 0 for flags. In your example, do:

$active=(isActive()) ? true : false;

or even better (assuming isActive returns a proper boolean):

$this->db->set('isActive',isActive());

rather than:

$active=(isActive()) ? 1 : 0;

Answer 5

I can't find of a single case where PHP would convert 0 to null or "". If it has to convert it to a string, it will be "0", to a boolean it will be false. There's no "null" type, so really your 0 is safe with PHP. false is converted to "" (an empty string) when cast as a string, but integers are safe.

Now it's not a guarantee that third-party code won't behave strangely when passed an integer when they expected something else, but you're mostly safe.

Answer 6

There are a few places where 0 and '0' are treated a little bit specially. This is almost always because of automatic type co-ercion. You've already noticed where 0 evaluates to false. So if PHP has a reason to convert '0' to an integer, then that will also evaluate to false. The prime one to watch out for is the empty() function. This is documented, BTW.

I rarely use empty() because of this very problem, in fact. It makes much more sense to check more narrowly, hence I use isset(), is_null() and === false or even == 0 (or != 0). There are other checks, too. I have DB handler code that not only checks using is_null() but also does is_numeric().

Other places to watch out for are where you use other developer's code who aren't completely careful with how 0 works in automatic type co-ercion. If you give a function a 0 but it ends up using a null when it should be using a 0 then you've probably found a bug in the API and should raise it with the developer. In fact, they're probably using empty() when they should be using isset() and/or is_null(). :-)

Answer 7

If you set a variable to 0, the variable remains as 0 unless you cast it to something else. The type is still integer.

You can check whether a variable is by using the is_numeric() function.

Example:

$active=(isActive()) ? 1 : 0;
if(is_numeric($active)){
     $this->db->set('isActive',$active);
}

Or You can use the comparison operator === instead of the usual ==. it'll compare the data type as well as the content of the variable.

$active=(isActive()) ? 1 : 0;
if($active === 0 || $active === 1){
     $this->db->set('isActive',$active);
}

Hope this helps!