array_key_exists Checks if the given key or index exists in the array &reftitle.description; boolarray_key_exists mixedkey arrayarray array_key_exists returns &true; if the given key is set in the array. key can be any value possible for an array index. &reftitle.parameters; key Value to check. array An array with keys to check. &reftitle.returnvalues; &return.success; array_key_exists will search for the keys in the first dimension only. Nested keys in multidimensional arrays will not be found. &reftitle.examples; 1, 'second' => 4); if (array_key_exists('first', $search_array)) { echo "The 'first' element is in the array"; } ?> ]]> isset does not return &true; for array keys that correspond to a &null; value, while array_key_exists does. null, 'second' => 4); // returns false isset($search_array['first']); // returns true array_key_exists('first', $search_array); ?> ]]> &reftitle.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. &reftitle.seealso; isset array_keys in_array property_exists