PHP array_key_exists function

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array_key_exists

(PHP 4 >= 4.1.0, PHP 5)

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.

Example 1. array_key_exists() example

$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.

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

See also isset(),
array_keys(), and
in_array().