Question

I was trying to understand the in_array behavior at the next scenario:

$arr = array(2 => 'Bye', 52, 77, 3 => 'Hey');
var_dump(in_array(0, $arr));

The returned value of the in_array() is boolean true. As you can see there is no value equal to 0, so if can some one please help me understand why does the function return true?

Answer 1

This is a known issue, per the comments in the documentation. Consider the following examples:

in_array(0, array(42));      // FALSE
in_array(0, array('42'));    // FALSE
in_array(0, array('Foo'));   // TRUE

To avoid this, provide the third paramter, true, placing the comparison in strict mode which will not only compare values, but types as well:

var_dump(in_array(0, $arr, true));

Other work-arounds exist that don’t necessitate every check being placed in strict-mode:

in_array($value, $my_array, empty($value) && $value !== '0');

But Why?

The reason behind all of this is likely string-to-number conversions. If we attempt to get a number from “Bye”, we are given 0, which is the value we’re asking to look-up.

echo intval("Bye"); // 0

To confirm this, we can use array_search to find the key that is associated with the matching value:

$arr = array(2 => 'Bye', 52, 77, 3 => 'Hey');
echo array_search(0, $arr);

In this, the returned key is 2, meaning 0 is being found in the conversion of Bye to an integer.