mixed array_search ( mixed $needle , array $haystack [, bool $strict ] )
If the third parameter strict is set to TRUE then the array_search() function will also check the types of the needle in the haystack .
I don't see what it means,maybe an example can help?
If the last argument is true, it will use strict (also known as identity) comparison (===) when searching the array.
The equality comparison (==) compares the value where as the identity comparison (===) compares the value and the type.
'0' == 0 ; //true, the string is converted to an integer and then the are compared.
'0' === 0; //false, a string is not equal to a integer
You will find more information in this question How do the equality (== double equals) and identity (=== triple equals) comparison operators differ?
This means that if you had an array of numbers
$a = array(0,1,2,3,4);
Using a strict comparison for the string value '2' will return false (not find a match) as there are no strings with the value '2'.
array_search('2', $a, true); //returns false
However if you don't do a strict search, the string is implicitly converted into an integer (or the other way around) and it returns the index of 2, as 2 == '2'
array_search('2', $a, false); //returns 2
The third parameter tells the function to check also the types of needle and the haystack elements (i.e. to use a strict comparison ===).
<?php
$needle = "2"; //a string
$haystack = array (1,2,"2","test");
$search = array_search ($needle ,$haystack, false);
// Will output 1, as it is the key for the second element of the array (an integer)
print_r($search);
$search = array_search ($needle ,$haystack, true);
//Will output 2, as it is the key for the third element of the array (a string)
print_r($search);
?>
In array_search third argument is used for strict type checking.
For example if third argument is false , 123 is equal to "123" ==> true
if third argument is true , 123 is not equal to "123" ==> since both had different types .