On Fri, 13 Jul 2007, Roland Mainz wrote:
> Frank Hofmann wrote:
>> On Wed, 4 Jul 2007, Frank Hofmann wrote:
>>> I wonder what is the simplest way to validate, from a C program, whether a
>>> given string can be successfully parsed as TZ (timezone) environment
>>> variable.
[ ... ]
> What about checking whether the TZ value has a subdir in
> /usr/share/lib/zoneinfo/ ?
That doesn't allow to test for "direct" specifications according to
environ(5),
TZ
Timezone information. The contents of this environment
variable are used by the functions ctime(3C),
localtime(3C), strftime(3C), and mktime(3C) to override
the default timezone. The value of TZ has one of the two
formats (spaces inserted for clarity):
:characters
or
std offset dst offset, rule
If TZ is of the first format (that is, if the first
character is a colon (:)), or if TZ is not of the second
format, then TZ designates a path to a timezone database
file relative to /usr/share/lib/zoneinfo/, ignoring a
leading colon if one exists.
Otherwise, TZ is of the second form, which when expanded
is as follows:
stdoffset[dst[offset][,start[/time],end[/time]]]
[ ... blah blubb very very gory details follow ... ]
I.e. you can say something like:
GMT1GMT2,90/02:00:00,304/02:00:00
to get central european time (not sure if I get start/end correct there).
Not that anyone really uses this ... not that I've seen anyway. Maybe
that's why noone bothers about being able to verify such a setting.
Olson's files are bliss :)
FrankH.
>
> ----
>
> Bye,
> Roland
>
> P.S.: Is there any (POSIX) API to list all supported timezones ?
Given that the above 'handcrafted' syntax allows you to specify anything
(like, time changing from GMT+5 to GMT-10 on January, 17th, 04:55:23, and
changing back on January, 29th, 23:01:03) for the rules, I don't think
there actually can be such an API. Even for the "named" TZs, it's a
problem as politicians change these at whim, see last year's flurry of
timezone patches ...
FrankH.
>
> --
> __ . . __
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