How do I pass undefined vars to functions without E_NOTICE errors?

Question

Pretty simple question really, how do I pass undefined vars to functions without E_NOTICE errors?

When passing undefined variables to functions such as isset(), no e

Answer 1

isset is a bit special as it is actually a PHP language construct rather than a function [1].

If a variable is undefined, you can't really pass it because it isn't defined (hence the warning).

As stated in comments, you can suppress the warnings by prepending an @ to the variable which will prevent a warning from being emitted if it is not set. Then within the function you can check to see if the value is null or try using isset to see if it is registered.