On Fri, May 02, 2008 at 14:46 +0300, Asko Kauppi wrote:
This cannot be done in Lua 5.1 since 'os.time()' only
calls for
'mktime()', never 'timegm'. These two are a pair, and
described
together on the man pages (man mktime). mktime is for
creating epoch
ticks out of local time; timegm is for doing the same
from UTC time.
Is there a reason for the omission, and could
'os.time()' support UTC
input in the future?
I don't know about the system you refer to (Darwin?),
but 'man mktime'
on the system I'm currently at opens the ctime(3)
manpage which only
lists mktime() in the synopsis and has a timegm(3) xref
in the SEE ALSO
section. The (separate) timegm(3) manpage states:
| ...
|
| CONFORMING TO
|
| These functions are non-standard GNU extensions that
are also
| present on the BSDs. Avoid their use; see NOTES.
|
| NOTES
|
| ...
|
| For a portable version of timegm(), set the TZ
environment
| variable to UTC, call mktime(3) and restore the
value of
| TZ. Something like
|
| ...
Looking up the www.freebsd.org -> documentation ->
manpages -> "timegm"
search text brings up the ctime(3) manpage, where the
STANDARDS section
states:
| The timegm() function is not specified by any
standard; its function
| cannot be completely emulated using the standard
functions described
| above.
This is what Klaus cited, too, IIUC.
So it seems the timegm(3) function may or may not be
present, and since
it's not ANSI it certainly won't be used in stock Lua.
If support for
your request would be introduced, it either had to use
the workaround
mentioned in the Linux manpage (modify TZ and restore it
after calling
mktime(), which seems ugly and might introduce new
problems depending on
how environment variables and e.g. OS threads interact)
or be an option
which is off by default (to get enabled by the user on
systems where
timegm() is known to exist and work correctly).
Would an alternative approach be to determine the
difference between the
local and the UTC coordinates and apply that offset to
the ticks value
before calling the actual conversion or breaking down?
Could that solve
your problem as well, and do so faster?
virtually yours
Gerhard Sittig
--
If you don't understand or are scared by any of the
above
ask your parents or an adult to help you.
