GNU bug report logs - #21020
24.4; `display-time-world' tampers with TZ

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 21020 <at> debbugs.gnu.org, wgg2 <at> member.fsf.org
Subject: bug#21020: 24.4; `display-time-world' tampers with TZ
Date: Mon, 27 Jul 2015 18:09:37 -0700

Eli Zaretskii wrote:
> I'm not even sure I
> understand completely why this trick is needed (can you explain?).

On many platforms, calling 'tzset' (either directly, or indirectly via localtime 
etc.) invalidates tzname[0] and tzname[1].  For example:

   time_t t = 0;
   char *p = tzname[0];
   localtime (&t);
   puts (p ? p : "(null)");

Here 'puts' has undefined behavior if tzname[0] has been updated and its old 
value (equal to P) is no longer a valid pointer.

lib/time_rz.c attempted to work around this problem by replacing tzname[0] and 
tzname[1] with pointers to more-stable copies.  Apparently this doesn't work 
under MinGW.

> can we please do this in some less intrusive way, e.g., by
> copying the TZ names to our private storage?

OK, I did that in master commit 2856b1dd6f0ff5164eb5a54ddfadb9963f9e9237.

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