[TUHS] Off topic: BSD timezone function vs. POSIX timezone variable

[arnold at skeeve.com]

Thanks to everyone who responded to my question. The answers were
helpful.

Arnold

Chet Ramey <chet.ramey at case.edu> wrote:

> On 12/14/23 10:14 AM, Leah Neukirchen wrote:
> > Aharon Robbins <arnold at skeeve.com> writes:
> > 
> >> Hi All.
> >>
> >> This is a bit off-topic, but people here are likely to know the answer.
> >>
> >> V7 had a timzone function:
> >>
> >> 	char *timezone(int zone, int dst);
> >>
> >> that returned a timezone name.  POSIX has a timezone variable which is
> >> the offset in seconds from UTC.
> >>
> >> The man pages for all of {Net,Free,Open}BSD seem to indicate that both
> >> are available on those systems.
> >>
> >> My question is, how? The declarations for both are given as being in <time.h>.
> >> But don't the symbols in libc.a conflict with each other? How does a programmer
> >> on *BSD choose which version of timezone they will get?
> > 
> > OpenBSD 7.3 only has "extern long timezone" and no timezone(3) function.
> > 
> > FreeBSD 14.0 only has the timezone(3) function (under _BSD_VISIBLE),
> > and doesn't set any variables.
>
> Darwin (macOS) conditionally defines them. If you want POSIX 2003
> compatibility, define __DARWIN_UNIX03 and get
>
> extern long timezone __DARWIN_ALIAS(timezone);
>
> If you don't define that, you get
>
> char *timezone(int, int);
>
> -- 
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
> 		 ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, UTech, CWRU    chet at case.edu    http://tiswww.cwru.edu/~chet/