How do get around 0 being treated as a null value?

[toe_head2001]

I have a form input in which I would like to submit the the value of 0, but it being treated as a null value. I don't want to have to use 00.

I'm using this code, what changes do I need to make?

if (!$_POST['description'] | !$_POST['id']) {
die('You did not complete all of the required fields');
} 

[Schmoopy]

if (!$_POST['description'] || !$_POST['id']  && $_POST['id'] != '0') {
die('You did not complete all of the required fields');
} 

Treats 0 as a literal string, there may be other ways of doing it but this seems to work.

[Twey]

The string '0' is falsy in PHP: that is to say, '0' == false. Nobody knows quite why; it's counterintuitive and frankly stupid, but hey, it's PHP: we're used to it.

Anyway, the proper way around it, in this case, is to use the empty() function:

if (empty($_POST['description']) || empty($_POST['id']))
  die('You did not complete all the required fields.');

Generally, if you need to check two values, use ===, the equality operator, rather than ==, the type-converting equality operator. Use == only if you've carefully considered all the possible types of both sides and explicitly want to allow them all.

Something else to watch out for is that || (logical OR) is not the same as | (bitwise OR). In many situations, via several type coercions, bitwise operators will act in a similar manner to their logical counterparts, but bitwise operators do not short-circuit, so they will often exhibit worse performance, and additionally in some cases they may exhibit vastly different behaviour: '8' & '4' is falsy, even though '8' && '4' is true.

[Schmoopy]

I can't believe I'm saying this, but for once I think you're wrong

I've used empty() before and have known it to take "0" as a null string, as it says in the php manual:

The following things are considered to be empty:

"" (an empty string)
0 (0 as an integer)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
var $var; (a variable declared, but without a value in a class)

I also tested the code and as I expected, inputting 0 in a field returned "You did not complete all the required fields".

I'm pretty sure the way I've done it isn't the most efficient either, but the way you have proposed doesn't seem to work at all. Am I missing something?

[Twey]

Ah, it seems you're right — that was added in PHP4. I should have read the fine manual before commenting

The other option here, then, would be:

if (@$_POST['description'] === NULL || @$_POST['id'] === NULL)

Something peculiar happened when I was trying to test out empty():

php > print empty("");
php > print empty("0") ? "Yes" : "No";
php > print (empty("0") ? "Yes" : "No");
php > print "huh?";
huh?
php > print true ? "yes" : "no";
yes
php > print empty("0") ? "Yes" : "No";
php > error_reporting(E_ALL);
php > print empty("0") ? "Yes" : "No";
php > echo("Hi");
Hi
php > echo(true ? "Yes" : "No");
Yes
php > echo(empty(0) ? "Yes" : "No");
php >

It seems I can't print the value of an expression containing empty(). Maybe I'm missing something here.

[CrazyChop]

Ah, it seems you're right — that was added in PHP4. I should have read the fine manual before commenting

It seems I can't print the value of an expression containing empty(). Maybe I'm missing something here.

there is also the is_number() if you wish to check whether it is NULL or what, but === is the way to go.

Re: empty() -- maybe it only works on variables and not expression?

[Schmoopy]

I don't think $variable === null works either, I just tried it and it didn't stop anything, if I put in a 0 it didn't pick up on it, if I left it blank it did the same thing. There must be a better way to do this, but the null way doesn't seem to work at all.

Edit:

if ($_POST['description'] === '' || $_POST['id'] === '') 

This seems to work too, allows 0.

[Twey]

Er, yes, of course — I was thinking they'd be undefined, but of course they're only actually likely to be empty strings. That's what you want.

[CrazyChop]

I don't think $variable === null works either, I just tried it and it didn't stop anything, if I put in a 0 it didn't pick up on it, if I left it blank it did the same thing. There must be a better way to do this, but the null way doesn't seem to work at all.

Edit:

if ($_POST['description'] === '' || $_POST['id'] === '') 

This seems to work too, allows 0.

if (isset($_POST['id'] && $_POST['id'] === null) 

For cases when id is not set (hey, that may happen...what if the user types in the URL directly?)

Anothing to try may be

$_POST['id'] = intval($_POST['id']);

// If isset code here 

Typically, it's better to leave a variable undefined then to have it points to empty for query string, IMHO.

[Nile]

It seems I can't print the value of an expression containing empty(). Maybe I'm missing something here.

From what I understand, it appears empty() cant take direct input. Even though it should be a mixed var. Hmm... Maybe its being fixed for PHP 6.