== in php causing false positives when variable is zero

Question

I have the strangest php behavior I've never noticed before:

$array =array(0,1,2, 'parent');
   foreach ($array as $value)
{
    if ($value=='parent')
    {
        echo $value;
        echo '<br>';
        continue; 
    }

}
exit;

Will return

0
parent

I was wondering if anyone could explain to me why it matches the 0 to the string 'parent'?

Read the relevant section of the PHP documents on [loose comparisons and typecasting](http://www.php.net/manual/en/types.comparisons.php) — Mark Baker, Jan 25 '14 at 01:36
try to var_dump($value);instead of echo. You will get clearer picture. As @Ignacio Vazquez-Abrams "Because that's how PHP rolls: Like a square wheel." — pregmatch, Jan 25 '14 at 01:43

score 1 · Accepted Answer · answered Jan 25 '14 at 01:38

1

what Mark said but to expound, 0 is a number so the == operator casts the 'parent' string to a number, which gives 0. The == operator does not care about type. So they match.

answered Jan 25 '14 at 01:38

troseman

1,842
20
19

crazy. all these years I never ran into. – atwellpub Jan 25 '14 at 01:52
yeah, that's why you see === used a lot, so you don't get caught by a type mistake. you can always cast to string/number. – troseman Jan 25 '14 at 02:15

score 1 · Answer 2 · answered Jan 25 '14 at 01:46

The "==" operator in php does not compare the type of the objects, it converts the objects to another type. So in your case you are comparing a numerical object with a string object. So it changes the type of your string 'parent'. Since that string does not contain any numerical value it probably changes it to 0. See http://il.php.net/manual/en/language.operators.comparison.php and http://il.php.net/manual/en/language.types.string.php#language.types.string.conversion for more explanations

== in php causing false positives when variable is zero

2 Answers2