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.T...@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */