Question

I have found some odd behaviour while I was using the PHP function in_array(). I have an array like this:

$arr = [TRUE, "some string", "something else"];

Now if I want to check if "test" is in the array it is clearly not, but in_array() still returns TRUE, why is that?

$result = in_array("test", $arr);
var_dump($result);  //Output: bool(true)

The same thing happens when using array_search():

$result = array_search("test", $arr);
var_dump($result);  //Output: int(0)

I thought maybe that the value TRUE in the array was automatically causing the function to return TRUE for every result without checking the rest of the array, but I couldn’t find any documentation that would suggest that very odd functionality.

Answer 1

This behaviour of the function in_array() and array_search() is not a bug, but instead well documented behaviour.

Both functions have a 3rd optional parameter called $strict which by default is FALSE:

bool in_array ( mixed $needle , array $haystack [, bool $strict = FALSE ] )

mixed array_search ( mixed $needle , array $haystack [, bool $strict = false ] )

Now what that means is that by default both functions use loosely(==) comparison to compare the values. So they only check if the values are the same after PHP type juggling and without checking the type. Because of that in your example TRUE == "any none emtpy string" evaluates to TRUE.

So by setting the 3rd parameter to TRUE while calling the function you say that PHP should use strict(===) comparison and it should check value AND type of the values while comparing.

See this as a reference: How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?