Re: new module 'tzname'

[Bruno Haible]

Hi Paul,

In tzname.texi you added:

  @item
  This variable's contents are unreliable if you use a geographical
  @env{TZ} setting like @code{TZ="America/Los_Angeles"}.

What do you mean by "unreliable"? I tested the values for this TZ
and for my local one, and tzname is reasonable — the same values on
all platforms (except native Windows, which does not support
geographical TZ values in the first place).

=================================== foo.c =============================
#include <time.h>
#include <stdio.h>
#include <stdlib.h>

int
main ()
{
  const char *tz = getenv ("TZ");
  tzset ();
  printf ("TZ=%s -> tzname[0]=\"%s\", tzname[1]=\"%s\"\n",
          tz != NULL ? tz : "(null)",
          tzname[0], tzname[1]);
  return 0;
}
=======================================================================
Results:

              TZ=Europe/Berlin ./a.out             TZ=America/Los_Angeles 
./a.out

glibc         tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
musl          tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
macOS 12      tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
FreeBSD 14.0  tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
NetBSD 10.0   tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
OpenBSD 7.5   tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
AIX 7.3       tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
Solaris 11.4  tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"
Cygwin 3.4.6  tzname[0]="CET", tzname[1]="CEST"    tzname[0]="PST", 
tzname[1]="PDT"


So, what is the actual problem?

Does the problem only appear with specific TZ values? If so, what is the
most relevant such TZ value?

And is the problem related to the unification/overloading of time zones that
caused so many discussions in summer 2021?

Bruno