Re: __func__ is not a keyword

Kaz Kylheku <643-408-1753@kylheku.com> writes:

On 2025-03-16, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:

Are you suggesting that a conforming compiler must accept the above
code (defining __func__ in an inner scope)?  If so, I disagree.

>
I was initially divided on this one.
>
On the one hand, inside a function, __func__ is not reserved (for future
use); it is described as being bound as a variable name, and that makes
it compatible with lexical shadowing.

That's where I disagree, though I'm not 100% certain.

Identifiers starting with __ are not conditionally reserved, and
they're not reserved "for future use".  They're simply "reserved
for any use".

"If the program declares or defines an identifier in a context in
which it is reserved (other than as allowed by 7.1.4), the behavior
is undefined."

The fact that the language defines its own use for __func__ IMHO
doesn't unreserve it.  Referring to __func__ within a function
definition is of course allowed, but declaring or defining it still
has undefined behavior.

I'm using the N3096 draft at the moment; other drafts should have
similar or identical wording.  6.4.2.1 discusses identifiers,
and says that certain identifiers are "reserved for any use".
6.4.2.2 discusses predefined identifiers, specifically __func__
(which is the only predefined identifier).  I think you're assuming
that 6.4.2.2 describes an exception to the rules in 6.4.2.1.  I think
it doesn't; __func__ is specified in a way that's consistent with
it continuing to be reserved for any use.

And James Kuyper has pointed out the footnote in 6.4.2.2:

    Since the name __func__ is reserved for any use by the
    implementation (7.1.3), if any other identifier is explicitly
    declared using the name __func__, the behavior is undefined.

[...]

Of course, from a portable programming point of view, we must regard
__func__ as off-limits. In light of the above possibilities, though, it
seems that it would be best to formally interpret it that way, too.

Agreed.

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */