What is the difference between the isset() and empty() functions in PHP?

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Accepted Answer

isset() checks if a variable is set and not null, while empty() checks if a variable is empty or not.

isset() returns true if the variable exists and is not null. Example: isset($var) returns true if $var is defined.
empty() returns true if the variable is empty. This includes '', 0, '0', null, false, and an empty array. Example: empty($var) returns true if $var is '' or 0.
isset() does not generate a warning if the variable is not defined, while empty() can be used on undefined variables without warnings.
Using isset() on an empty variable will return false, while empty() will return true. Example: $var = ''; isset($var) is false, empty($var) is true.

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