array_key_exists

(PHP 4 >= 4.0.7, PHP 5, PHP 7)

Checks if the given key or index exists in the array

bool array_key_exists ( mixed $key, array $array )

array_key_exists() returns TRUE if the given key is set in the array. key can be any value possible for an array index.

Parameters:

key

Value to check.

array

An array with keys to check.

Returns:

Returns TRUE on success or FALSE on failure.

Notes:

For backward compatibility reasons, array_key_exists() will also return TRUE if key is a property defined within an object given as array. This behaviour should not be relied upon, and care should be taken to ensure that array is an array.

To check whether a property exists in an object, use property_exists().

Examples:

array_key_exists() example

<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>

array_key_exists() vs isset()

isset() does not return TRUE for array keys that correspond to a NULL value, while array_key_exists() does.

<?php
$search_array = array('first' => null, 'second' => 4);
 
// returns false
isset($search_array['first']);
 
// returns true
array_key_exists('first', $search_array);
?>