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Re: Bogus ifdef guard in sys/null.h

Bernd Ernesti <> wrote:
> > POSIX says that both stddef.h and unistd.h shall provide NULL. This
>                                              ^^^^^
> shall != must
> So not a mandatory requirement.

Apart from "shall" having a slightly stronger notation in English (and
commonly used in standards or legal texts as a synonym of "must"), POSIX
explicitly defines what "shall" means:


        For an implementation that conforms to POSIX.1-2008, describes a
        feature or behavior that is mandatory. An application can rely on
        the existence of the feature or behavior.

        For an application or user, describes a behavior that is mandatory.


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