You mandate it like you mandate anything else in C. You don't.
You pick C because you want a language that doesn't require a variable to be initialised before mutably referencing it, and you write your defer statements or "destructors" defensively, expecting that a variable could be in any state when it comes time to dispose of it.
Or if you find that unacceptable, you accept that C isn't the language you want. There's many other choices available.
