php man page for array_key_exists

ARRAY_KEY_EXISTS(3)							 1						       ARRAY_KEY_EXISTS(3)

array_key_exists - Checks if the given key or index exists in the array

SYNOPSIS
       bool array_key_exists (mixed  $key, array  $array)

DESCRIPTION
       array_key_exists(3) returns TRUE if the given $key is set in the array. $key can be any value possible for an array index.

PARAMETERS
	      o $key
		- Value to check.

	      o $array
		- An array with keys to check.

RETURN VALUES
	Returns TRUE on success or FALSE on failure.

EXAMPLES
       Example #1

	      array_key_exists(3) example

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

       Example #2

	      array_key_exists(3) vs isset(3)

	      isset(3) does not return TRUE for array keys that correspond to a NULL value, while array_key_exists(3) does.

	      <?php
	      $search_array = array('first' => null, 'second' => 4);

	      // returns false
	      isset($search_array['first']);

	      // returns true
	      array_key_exists('first', $search_array);
	      ?>

NOTES
       Note

	       For backward compatibility, the following deprecated alias may be used: key_exists(3)

       Note

	       For  backward compatibility reasons, array_key_exists(3) 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(3).

SEE ALSO
       isset(3), array_keys(3), in_array(3), property_exists(3).

PHP Documentation Group 												       ARRAY_KEY_EXISTS(3)