Invalid sample definition for errno

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.std.c
Subject	Invalid sample definition for errno
Date	2022-11-19 18:08 -0800
Organization	None to speak of
Message-ID	<87r0xyl6nm.fsf@nosuchdomain.example.com> (permalink)

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A footnote in the section describing <errno.h> says:

    The macro errno need not be the identifier of an object. It might
    expand to a modifiable lvalue resulting from a function call (for
    example, *errno()).

Footnotes are non-normative, and this one is presumably intended to be
informal, but that's not a valid macro definition for errno, both
because it's not fully protected by parentheses and because the function
can't be named "errno".

A valid definition (and the one used by glibc) is:

    # define errno (*__errno_location ())

I suggest the footnote should be updated to use something like that
(though it needn't show the entire #define directive).

The same wording appears starting in C90 and up to and including the
latest C23 draft.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */

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Invalid sample definition for errno Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-19 18:08 -0800
  Re: Invalid sample definition for errno Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-11-20 05:26 -0800
    Re: Invalid sample definition for errno Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-20 13:58 -0800

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