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PHP in_array Function: Check Array Values Exist

The PHP in_array() function allows you to check for the presence of a value in an array, and take an option based on this result.


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

Note That:

  • $needle can be a variable of any type (string, number, date, etc)
  • $haystack should be an array (see here, here, and here for more about arrays)
  • $strict is optional, and will ensure that the type of values is also compared when checking whether $needle is present
    • If $strict is FALSE (the default behavior), the number 1 and the string “1” will be considered the same when comparing values to check whether the value appears in $haystack
  • boolean value is returned (TRUE/FALSE), allowing you to take an action based on whether the $needle value was present in the $haystack array – see more about comparing boolean values here


As an example, we can check whether a value is present in an array containing the days of the working week:

$weekdays = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
$result = in_array("Saturday", $weekdays); // FALSE

if($result == FALSE) {
    echo "Saturday is not a weekday.";


The $strict option is not required but can be useful, especially when dealing with user input. By default in_array() will treat values of different types but the same content as being a match – 12 (a number/integer) and “12” (a string which happens to contain characters representing a number) would be treated as being a match.

Strict mode will prevent this, meaning that 12 (a number) “12” (a string which happens to contain characters representing a number) are treated as not matching due to being of different types:

$numbers = [3, 7, 11, 12];
$result = in_array("12", $numbers); // TRUE
$result = in_array("12", $numbers, TRUE); // FALSE
  • The result of the first in_array() check returns TRUE as it is not being strict about the variable type
  • The result of the second in_array() check returns FALSE as the types are different – the $needle is a string, but the value in the $haystack is a number, as it is not wrapped in quotes


Determining whether a value is present in an array can be used to do things like checking if the user has submitted a correct answer for a quiz, checking if the date of a reservation is already taken, or seeing if a user has already entered a value in a form. It’s a useful function when making sure the data is clean and well-formatted.

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To view the official documentation for the PHP in_array() function:


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I'm Brad, and I'm nearing 20 years of experience with Linux. I've worked in just about every IT role there is before taking the leap into software development. Currently, I'm building desktop and web-based solutions with NodeJS and PHP hosted on Linux infrastructure. Visit my blog or find me on Twitter to see what I'm up to.

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