What is wrong with the PHP function in_array(...)? [duplicate]

Question

The PHP function in_array(...) "checks if a value exists in an array".

But I'm observing a very strange behavior on handling strings (PHP v7.0.3). This code

$needle = 'a';
$haystacks = [['a'], ['b'], [123], [0]];
foreach ($haystacks as $haystack) {
    $needleIsInHaystack = in_array($needle, $haystack);
    var_dump($needleIsInHaystack);
}

generates following output:

bool(true)
bool(false)
bool(false)
bool(true) <- WHAT?

The function returns true for every string $needle, if the $haystack contains an element with the value 0!

Is it really by design? Or is it a bug and should be reported?

Matteo Tassinari · Accepted Answer · 2016-07-28 16:39:41Z

13

If you do not set the third parameter of in_array to true, comparison is done using type coercion.

If the third parameter strict is set to TRUE then the in_array() function will also check the types of the needle in the haystack.

Under loose comparison rules, effectively 'a' is equal to 0 since (int)'a' == 0.

edited Jul 28, 2016 at 16:39

answered Jul 28, 2016 at 9:35

Matteo Tassinari

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3 Comments

automatix Over a year ago

Thank you for your answer! Yes, I didn't consider, that 'a' == 0 is true.

automatix Over a year ago

And it's even more crazy: While 'a' == 0 is true, '1' == 0 IS false (because (int) '1' IS 1 and 1 IS NOT 0).

automatix Over a year ago

'a' == 0 IS TRUE, 0 == null IS TRUE, null == 'a' IS FALSE. If we replace the concrete values by variables, we'll see, that this behavior is illogical: a = b, b = c, c <> a.

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