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Which of these correctly checks whether an array key exists, including when its value is null?

A isset($arr['key'])
B array_key_exists('key', $arr)
C empty($arr['key'])
D in_array('key', $arr)

Answer

array_key_exists('key', $arr)

isset returns false for a key whose value is null. array_key_exists distinguishes a missing key from a null value.

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