note 103061 modified in function.isset by danbrown

1) Note that isset($var) doesn't distinguish the two cases when $var is undefined, or is null. Evidence is in the following code. <?php unset($undefined); $null = null; if (true === isset($undefined)){echo 'isset($undefined) === true'} else {echo 'isset($undefined) === false'); // 'isset($undefined) === false' if (true === isset($null)){echo 'isset($null) === true'} else {echo 'isset($null) === false'); // 'isset($null) === false' ?> 2) If you want to distinguish undefined variable with a defined variable with a null value, then use array_key_exist <?php unset($undefined); $null = null; if (true !== array_key_exists('undefined', get_defined_vars())) {echo '$undefined does not exist';} else {echo '$undefined exists';} // '$undefined does not exist' if (true === array_key_exists('null', get_defined_vars())) {echo '$null exists';} else {echo '$null does not exist';} // '$null exists' ?> --was-- (Please delete my previous comment, since this new one is more complete) 1) Note that isset($var) doesn't distinguish the two cases when $var is undefined, or is null. Evidence is in the following code. <?php unset($undefined); $null = null; if (true === isset($undefined)){echo 'isset($undefined) === true'} else {echo 'isset($undefined) === false'); // 'isset($undefined) === false' if (true === isset($null)){echo 'isset($null) === true'} else {echo 'isset($null) === false'); // 'isset($null) === false' ?> 2) If you want to distinguish undefined variable with a defined variable with a null value, then use array_key_exist <?php unset($undefined); $null = null; if (true !== array_key_exists('undefined', get_defined_vars())) {echo '$undefined does not exist';} else {echo '$undefined exists';} // '$undefined does not exist' if (true === array_key_exists('null', get_defined_vars())) {echo '$null exists';} else {echo '$null does not exist';} // '$null exists' ?> http://php.net/manual/en/function.isset.php