On Sun, 18 Aug 2019 15:08:25 +0800, David Crayford wrote:
>I once wrote some C code that sets the TZ, _TZ variables from the time
>zone offset, leap second offset values in the CVT.
> ...
> // set the time zone offset and apply the leap second offset
> int64_t ldto = cvt->cvtext2->cvtldto - cvt->cvtext2->cvtlso + adjust;
>
Is this intended to be used with localtime() and strftime()? Localtime()
expects time() to have accounted for leap seconds, so they should not
appear in TZ. An example on Linux (TZ value simulated by hand):
510 $ TZ=Asia/Calcutta date; TZ=GMT-5:29:33 date
Sun Aug 18 21:45:02 IST 2019
Sun Aug 18 21:44:35 GMT 2019
... I claim the former is correct. Also, the zone name, GMT, is wrong.
Correct is IST.
> ...
> // if minutes have been specified then calculate them
> uint64_t mins = ldto % STCK_UNIT_HOUR;
>
( My C skill fails me. What kind of statement is that? An assignment?
I'd not expect two tokens left of "=". A cast? I'd expect "( ... )", and
a cast has no L-value. A declaration with initialization? It would be out
of place. )
What happens if a DST transition, or even a leap second, occurs between
such a setting of TZ and your program's formatting of current time?
> ...
> setenv("TZ", tzone, 1); // for POSIX
> setenv("_TZ", tzone, 1); // for non-POSIX
>
Why do those names need to be different? Conway's law?
A Modest Proposal: Isn't the HMC a PC running Linux? Shouldn't
it have zoneinfo installed. Then the last line of each zoneinfo
entry is the POSIX-formatted TZ string. Examples from my
desktop Linux guest:
505 $ cd /usr/share/zoneinfo
506 $ tail -1 America/New_York
EST5EDT,M3.2.0,M11.1.0
507 $ tail -1 Australia/Canberra
AEST-10AEDT,M10.1.0,M4.1.0/3
512 $ tail -1 Asia/Calcutta
IST-5:30
508 $ ls -l /etc/localtime
lrwxrwxrwx 1 root root 34 Aug 15 17:46 /etc/localtime ->
/usr/share/zoneinfo/America/Denver
509 $ tail -1 /etc/localtime
MST7MDT,M3.2.0,M11.1.0
Wouldn't it be great if HMC passed such a string to z/OS UNIX
at startup, to be used in formatting times elsewhere? The
syntax is such that it could easily be parsed as a source for
CVTLDTO, etc., so everything could be set once, consistently,
in a human-friendly format, on the HMC.
-- gil
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