Re: get_date returning false

[Ian Abbott]

On 08/04/2005 16:05, Derek Price wrote:
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> Ian Abbott wrote:
>
> | If you want to try and reproduce it, you'll probably need to set
> | the TZ environment variable. Mine is set to "Europe/London", but if
> |  your libc doesn't understand that format, you can try
> | "GMT0BST,M3.5.0,M10.5.0" or "GMT0BST" instead.
>
> Is one of these formats likely to be portable?  I could add this to
> the test suite, then...

The TZ environment variable has evolved over the years.  Old Unix 
systems only supported the STD<offset>[DST[<offset>]] format like my 
"GMT0BST" above, so that format is the most portable, but the daylight 
savings rules are incorrect, except in the US (and Canada?).  The 
"daylight savings rules" part of the TZ variable were added in later 
Unix versions (I first encountered it in IBM AIX).  If the daylight 
savings rules section was left off, the system defaulted to US daylight 
savings rules.  The full format is described in the tzset(3) manpage or 
the environ(5) manpage (for the TZ variable).

The modern "Europe/London" format uses a database of timezone rules over 
history for each geographic and/or political region.  This is known as 
the "tz" or "zoneinfo" database and is used in most modern Unix systems. 
 Read more about it here: <http://www.twinsun.com/tz/tz-link.htm>.

--
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk>        )=-
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