(PHP 4 >= 4.0.7, PHP 5)
array_key_exists — Checks if the given key or index exists in the 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. array_key_exists() also works on objects.
Value to check.
An array with keys to check.
Returns TRUE on success or FALSE on failure.
Example#1 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";
}
?>
Note: The name of this function is key_exists() in PHP 4.0.6.
Example#2 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);
?>