Just curious, was there any response?

On Mon, 18 Jul 2022 at 18:19, Paul Eggert <eggert@cs.ucla.edu> wrote:
On 7/18/22 09:03, Paul Eggert wrote:
>
> I suppose someone should file a defect report with the C standardization
> committee.

I found what I hope is the correct email address for that (it's not
well-advertised) and submitted the following bug report:

----

Subject: strftime %z and %Z depend on more than just tm_isdst

A recent discussion in the Time Zone Database mailing list
<https://mm.icann.org/pipermail/tz/2022-July/031674.html> has prompted
me to file this bug report against the C standard.

Draft N2912, section 7.28.3.5 "The strftime function", pages 365-6,
paragraph 3 says that the %z and %Z conversion specifiers examine only
the tm_isdst members of the passed-in structure. However, this is not
how many implementations actually behave.

Some implementations (e.g., AIX, Solaris) infer %z and %Z output from
tm_year, tm_mon, tm_mday, tm_hour, tm_min, tm_sec, and tm_isdst, and
therefore sometimes guess %z or %Z output incorrectly when the clock
moves back from one standard time to another (e.g., Iran at the end of
the year 1978). These implementations typically also depend on the
current setting of the TZ environment variable.

Other implementations (e.g., FreeBSD, GNU/Linux) get the UT offset and
abbreviation from struct tm members tm_gmtoff and tm_zone that are not
specified by the C standard. These implementations do not have to guess
%z and %Z output; however, they require that the nonstandard members be
filled in correctly by localtime or equivalent.

Implementations that conform to the standard's current wording cannot
handle anything more complicated than a time zone with just one standard
time offset and abbreviation, which means they cannot handle timestamps
for locations like Iran, Portugal, etc., that have changed their
standard-time offset. The C standard should not require implementations
to be so limited that they cannot handle common timekeeping situations.

A simple fix for this issue is to require applications to initialize a
struct tm as if by localtime or equivalent, before passing the struct tm
to strftime. This is what applications need to do anyway, if they want
to be portable to real-world systems such as AIX, FreeBSD, GNU/Linux,
Solaris, etc.

Proposed fix:

1. Remove the two instances of "[tm_isdst]" in the %z and %Z entries in
Draft N2912, section 7.28.3.5 "The strftime function", pages 365-6,
paragraph 3.

2. Add the following text to that paragraph:

If the %z and %Z conversion specifiers are used, the broken-down time
structure pointed to by timeptr shall contain values generated by a
successful previous call to gmtime, gmtime_r, gmtime_s, localtime,
localtime_r, localtime_s, or mktime.