How to know if a PHP variable exists, even if its value is NULL? -

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$a = null; $c = 1; var_dump(isset($a)); // bool(false) var_dump(isset($b)); // bool(false) var_dump(isset($c)); // bool(true)

how can distinguish $a, exists has value of null, “really non-existent” $b?

use following:

$a = null; var_dump(true === array_key_exists('a', get_defined_vars()));

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