Re: Getting GMT time

Anonymous AtWork wrote:
> Bryan Oakley wrote:
>
>> Anonymous AtWork wrote:
>>
>>> I want to know what the GMT time is. If I do [clock seconds], I get
>>> the local time. I can add 5 hours, but what about DST when it is 6
>>> (or 4--whatever the difference is). There's probably some kind of
>>> non-portable craziness I could do to find out what TZ the computer is
>>> in and figure out the local algorithm for adjustment thereof, but
>>> since Tcl already knows all that (right?) it seems like it could do
>>> it for me.
>>>
>>> Is there a simple, 2-3 line way to do this?
>>
>>
>>
>> Look at the clock man page, especially where it mentions the -gmt
>> option to "clock format".
>>
>
> That will *format* the number of seconds I have as a GMT time. But the
> number of seconds I have isn't GMT, it's local. Given the local time, I
> want to know the GMT time.

I use following algoritm to determine the GMT time to calculate planet
positions

## let t be the local time
set t [clock seconds]
1136026469

clock format $t -format "%Y-%m-%d %H:%M:%S"
2005-12-31 11:54:29
## Belgium is GMT+1

clock format $t -format "%Y-%m-%d %H:%M:%S" -gmt 1
2005-12-31 10:54:29

## Following command will convert the local time t to GMT time

clock scan [clock format $t -format "%Y-%m-%d %H:%M:%S" -gmt 1]
1136022869
Received on Tue Jan 3 03:09:56 2006