Re: slickest way to find out local time zone offset in pure lua?

[Geoff Leyland <geoff_leyland@...>]

On 5/03/2008, at 7:49 AM, Norman Ramsey wrote:
> I'm sure this question has come up many times, but the way I'm doing
> it seems clunky, and I hope someone here has a solution that looks  
> sweet:
> using pure Lua, how can I compute the time difference between local  
> time
> and UCT (sometimes known as universal time or Greenwich Mean Time)?
>
>
> Norman

This isn't what you want, and it's also a bit clunky, but here's how  
I handle date/times in UTC (Lua interprets them as local time, so you  
have to offset them by the time zone, handling DST as you go).  There  
might be something in there helpful though?

Cheers,
Geoff


-- Takes a time struct with a date and time in UTC and converts it into
-- seconds since Unix epoch (0:00 1 Jan 1970 UTC).
-- Trickier than you'd think because os.time assumes the struct is in  
local time.
function time(t)
  local t_secs = os.time(t)             -- get seconds if t was in  
local time.
  t = os.date("*t", t_secs)             -- find out if daylight  
savings was applied.
  local t_UTC = os.date("!*t", t_secs)  -- find out what UTC t was  
converted to.
  t_UTC.isdst = t.isdst                 -- apply DST to this time if  
necessary.
  local UTC_secs = os.time(t_UTC)       -- find out the converted  
time in seconds.

  -- The answer is our original answer plus the difference.
  return t_secs + os.difftime(t_secs, UTC_secs)
end