Re: strftime(3) oddities with %s, %z

[Valery Ushakov <uwe%stderr.spb.ru@localhost>]

On Tue, Nov 01, 2022 at 05:20:17 +0700, Robert Elz wrote:

> How are you proposing that a portable implementation of strftime()
> done today, before the next posix standard is released (maybe next
> year, but perhaps not until 2024) would achieve what you're requesting?

I think this is the point of confusion.  It's not useful to pretend
that struct tm and strftime are the proverbial spherical horses in
vacuum and argue for "a portable implementation" of strftime, and then
from that argument infer properties for all potential implementations
of strftime including those that are privy to the implementation
details of its own struct tm - which all "real" strftime
implementations do.  The problematic bit in your argument is
specifically that inference step.

POSIX doesn't specify the private parts of struct tm.  Yes, public
parts of struct tm are not enough to construct tm that is another
timezone, but the implementation provides a group of functions that
operate on its own private tm that usually does have that information.
What initially surprised me, and what I think dh@ is also pointing
out, is that %s behaves as if it is indeed "a portable implementation"
that doesn't have access to the full tm, including private tz-related
parts.  I think we both tried to convey that point of view in various
ways, apparently without much success.


> How do you tell what produced a struct tm?   Magic?

In other words, class tm doesn't have a public constructor that
provides a way to specify TZ info.  There are other factory methods
that allow one to obtain an instance of tm that has the TZ info (in
its private parts). ...

But I don't have time or energy to elaborate this argument further
because you seem to disagree with the basic premise of it - that for a
class method (strftime) to be aware and to use the private data of the
class (struct tm as fully defined by the implementation, not just the
public "at least the memebers tm_foo, tm_bar" as specified in the
standard) is actually a reasonable thing to do.

-uwe