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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.std.c
Subject: Re: C23: asctime is obsolescent
Date: Thu, 20 Jul 2023 15:20:38 -0700
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Kaz Kylheku <864-117-4973@kylheku.com> writes:
> On 2022-11-24, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>> In the latest C23 draft:
>>     https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3047.pdf
>> the descriptions of the __DATE__ and __TIME__ macros refer to the
>> asctime() function.
>>
>> That's not new.  What's new is that asctime() is deprecated.
>>
>> Referring to a deprecated function isn't really a problem, but if
>> asctime() is actually removed in a future standard the descriptions of
>> __DATE__ and __TIME__ will need to be updated.
>
> This seems like a minor oversight. __DATE__ and __TIME__ do not
> depened on the semantics of asctime in any deep way; just that
> __DATE__ produces a "Mmm dd yyyy" time in the same way that
> asciitime would generate those fields, and similarly for __TIME__'s
> "hh:mm:ss".
>
> The documentation could refer to specific conversion specifiers of
> strftime. __DATE__'s "Mmm dd yyyy" corresponds to "%b %d %Y".

I like it.

> The minor oversight points at a possible process problem though; it
> seems that someone carelessly deprecated a function without searching
> the document for occurrences of that name, and doing something about it,
> resulting in requirements of a non-obsolescent feature being described
> with the help of an obsolescent feature.

Sounds about right.

It's the same in the last public C23 draft, N3096, dated April 1, 2023.
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf

>> It would also be nice to have a new macro that expands to the current
>> date in the form "YYYY-MM-DD".  I do not suggest changing the behavior
>> of __DATE__, but perhaps something like __ISODATE__ could be added.
>
> How about:
>
>   __DATEF("%Y-%M-%d")

You'd need some special-case rules; it wouldn't quite act like a normal
macro.  I presume the argument would have to be a string literal (or
something that expands to a string literal, or two or more string
literals like `__DATEF("%Y-%M" "%d")`).  The form implies that something
like `__DATEF("%Y")` should also work; I'm not convinced that level of
flexibility is necessary.

> Let's nuke trailing underscores Two leading underscores give us the
> needed namespace privacy. Or just _DATEF, for that matter.

I see what you mean, but all the other mandatory macros are of the form
__FOO__.  I don't think it would be good for _DATEF to stand out from
the others.

>> Question: If this is done, should __DATE__ be deprecated?
>
> Deprecating safe features used in countless code bases doesn't seem very
> productive; it's just disruptive.

I agree.  The same argument could be made about deprecating asctime(),
but I don't think it's used as widely.

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