Re: distinguish between null variable and unset variable

2009/1/21 Daniel Brown <danbrown@php.net>: > On Wed, Jan 21, 2009 at 20:27, Jack Bates <ms419@freezone.co.uk> wrote: >> How can I tell the difference between a variable whose value is null and >> a variable which is not set? > > Unfortunately, in PHP - like other languages - you can't. > > A variable is considered to be null if: > * it has been assigned the constant NULL. > * it has not been set to any value yet. > * it has been unset(). Actually, you can, but it's not terribly pretty. Check for the variable name as a key in the array returned from get_defined_vars(): <?php $foo = 0; $bar = null; $variables = get_defined_vars(); // Check for $foo, $bar, and $baz: foreach (array('foo', 'bar', 'baz') as $var) { if (!array_key_exists($var, $variables)) { echo "\$$var does not exist in the current scope.\n"; continue; } if (is_null($$var)) { echo "\$$var exists and is null in the current scope.\n"; continue; } echo "\$$var exists and is not null in the current scope.\n"; } ?> Again, not that pretty, and it only checks the local scope, but it can be done. Regards, Torben