Is the DateFormat read only?

[Alex Tweedly]

Thanks Graham. That does indeed work - on your local system.

The issue I am trying to deal with (and maybe it's related to what David 
is doing) is dealing with time zone issues on a LC web server. If you 
want to timestamp when some event happens, you can do that as a UTC 
timestamp using a function like this one of yours; but that leaves you 
two problems.

  - presenting those timestamps back to the user - which should be in 
*their* local time
  - allowing the user to provide their own timestamp - again should be 
local for them.

Most advice I've found via Google, etc. suggests keeping the timestamps 
in UTC, and asking the user to provide their timezone - usually when 
they 'register'. You can then use PHP (or ...) functions to convert a 
date/time between UTC and their local zone.

You might hope to do that in LC using 'convert .. to internet date' - 
but that doesn't work because that conversion (seems to) assume a local 
time, and then simply fill in the time offset for the local system (i.e. 
the problem David reported).

You should be able to do it using the TimeZone library - but I haven't 
figured out how to to do that, or I'm using it wrong, or something. (I 
didn't know about the Timezone library until David mentioned it yesterday.)

I'm currently using an ugly (though working :-) workaround using e.g.

put "America/New_York" into timeZone

*put*shell("TZ=" & timeZone & " date") into tmp

and working it all out from there (assumes Unix server - don't know if 
it works on others).

Alex.



On 07/11/2020 10:27, Graham Samuel via use-livecode wrote:
> I am as confused as anyone else as to what you are trying to do, but just in case, this little function seems to work for me to get the ’standard’ UTC date format which I have to use in my app to put time stamps into GPX files. It apparently produces the correct time zone. Doubtless it could be more elegantly coded.
>
> Hope it helps - who knows?
>
> Graham
>
> function fUTCTime
>     local t1,t2,t3
>     -- this gets the current time and puts it into UTC format, i.e YYYY-MM-DDThh:mm:ssTZD
>     put word 5 to 6 of the internet date into t3 -- we are interested in the time and time zone
>     put the long time into t1
>     convert t1 to dateItems -- format is yyyy,m,d,h,m,s,day no.
>     put (item 1 of t1) & "-" & f2digits(item 2 of t1) & "-" & f2digits(item 3 of t1) &"T" & word 1 of t3 into t2
>     put word 2 of t3 into t1 -- the time zone indication
>     get char 1 of t1 — the code for 0 (zero) is Z, apparently
>     if it <> "+" and it <> "-“ then
>        put "Z" after t2
>     else
>        put t1 after t2
>     end if
>     return t2
> end fUTCTime
>
> function f2digits theNum
> -- add a leading zero. We don't check if there are more than two digits
>     if number of chars of theNum = 1 then
>        return ("0" & theNum)
>     else
>        return theNum
>     end if
> end f2digits
>
>
>> On 7 Nov 2020, at 01:34, Alex Tweedly via use-livecode <use-livecode at lists.runrev.com> wrote:
>>
>> I don't think it "strips" the TZ info - it simply ignores it. I think the key phrase is in the dictionary as :
>>
>>> *Note:* The *convert* command assumes all dates / times are in local
 time except for 'the seconds', which is taken to be universal time.
>>>
>> So it assume syou date is in local time (regardless of the +0300), and therefore your example returns +0000 for you (I assume you're in the UK, or equivalent,  now). It does the same for me, and returns the date with "+0000".
>>
>> However, the same code run on my LC server (wherever on-rev is these days), changes the +0300 to -0500 - i.e. it's taken as local time where the server is.
>>
>>
>> I assume you should be able to do something with the TimeZone library - but I'm struggling to figure that out.
>>
>>>     local tNow
>>>     put the seconds into tNow
>>>     put FromUniversalTime(tNow,"US/Central") into tt
>>>     put tNow && tt
>>>     put FromUniversalTime(tNow,"US/Alaska") into tt
>>>     put CR & tt after msg
>> gives me
>>
>> 1604709030 1604709030
>>
>> 1604709030
>>
>> so I don't have a clue  what it was trying to do !?!
>>
>> Alex.
>>
>> On 06/11/2020 21:28, David Bovill via use-livecode wrote:
>>> Why does:
>>>
>>> get "Fri, 06 Nov 2020 10:57:37 +0300"
>>> convert it to internet date
>>> put it
>>>
>>> — give
>>> "Fri, 06 Nov 2020 10:57:37 +0000"
>>>
>>> Just seems to strip the timezone info?
>>> On 30 Oct 2020, 21:29 +0000, How to use LiveCode <use-livecode at lists.runrev.com>, wrote:
>>>> ToUniversalTime
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