Re: [Mingw-users] Setting the time zone

[Ilana L. <il...@is...>]

Hi,

I have been looking at the timezone code again, focussing on the=20
example=A0supplied by Tor Lillqvist. =A0I was a bit in the dark about time =
zones=20
but now have a better understanding (and more questions :-).

In Linux, the tzselect program is used to set the TZ variable by selecting =
a =20
specific time zone e.g. =A0Africa/Johannesburg.

This then actually points to a time zone file=20
e.g. /usr/share/zoneinfo/Africa/Johannesburg (the file specification is=20
relative to the system timezone directory). =A0This file has to be in=20
a=A0specific format namely the tzfile format. =A0When tzset() is called, th=
is=20
file is read and interpreted.

Local time functions will then use these values when converting GMT to loca=
l=20
time.

As an example, the following code will use the Johannesburg time zone=20
variables:

putenv("TZ=3D:/usr/share/zoneinfo/Africa/Johannesburg");
tzset();

Tor stated that setting TZ=3DAfrica/Johannesburg is illegal. =A0I have trie=
d to=20
do the same on Windows (mingw) anyway, but it seems as if it does not=20
have this functionality presently.

In addition, the time zone file contains information about daylight savings=
 =20
time as well as changes to conversion rules. =A0This enables one to read=20
historic GMT time data and convert it correctly to local time.

=46rom the time zone code documentation I found the following:

=2D->
In SVR2, the TZ variable had to be a three-letter time zone, followed by a=
=20
number representing the difference between local time and Greenwich Mean Ti=
me=20
in hours, followed by an optional three-letter name for a daylight time=20
zone;" when the optional daylight time zone is present, "standard U.S.A.
Daylight Savings Time conversion is applied." This means that SVR2 cannot=20
handle other (for example, Australian) daylight savings time rules, or=20
situations where more than two time zone abbreviations are used in an area.

This have been improved and The "TZ" environment variable is used in=20
generating the name of a file from which time zone information is read (or =
is=20
interpreted a la POSIX); "TZ" is no longer constrained to be a three-letter=
=20
time zone name followed by a number of hours and an optional three-letter=20
daylight time zone name. =A0The daylight saving time rules to be used for a=
=20
particular time zone are encoded in the time zone file; the format of the=20
file allows U.S., Australian, and other rules to be encoded, and allows for=
=20
situations where more than two time zone abbreviations are used.
<--

I am uncertain as to how mingw libraries work (whether it is e.g. a layer o=
n=20
top of the microsoft libraries), but it appears as if only the old method=20
(three-letter time zone) of setting TZ is supported. =A0Does anyone know of=
 a=20
workaround for this problem?  Is there perhaps a way to override the curren=
t=20
date functions?

Regards,
Ilana

=2D-=20
Ilana Loubser
ISS International Limited, Technology Division, Software Engineering=20
P O Box 12063, DIE BOORD 7613, South Africa
Tel: +27 (0)21 809-2091 Fax: +27 (0)21 809-2061
Email: il...@is... Web Page: http://www.issi.co.za

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