[tz] tz abbreviations / zdump for programmers

Ian Abbott abbotti at mev.co.uk
Wed Jun 6 17:05:07 UTC 2012

On 2012-06-06 17:00, Zefram wrote:
> Ian Abbott wrote:
>> I also noticed that Windows 7 displays the same zone name to the user
>> as "(UTC) Dublin, Edinburgh, Lisbon, London"
> So they've moved on from "GMT" to "UTC".  The parenthesised part
> previously referred, and presumably still refers, to the zone's "standard"
> (non-DST) offset from UT.  So for London it's "GMT" and for Paris it's
> "GMT+1", for example, regardless of whether DST is in effect.

Yes, you're correct.  My excuse for not noticing is that I live in the 
UK. ;-)

> It seems extremely unlikely that they're making any meaningful distinction
> between GMT and UTC (i.e., the sub-second difference between flavours
> of UT).  Of course, hardly anyone else makes that distinction in a
> timezone context anyway.
>>                                             Perhaps the use of "UTC"
>> to mean "legal time in Eire, Scotland, Portugal and England" is even
>> more confusing than "GMT"!
> Are they doing that?  The existing misuse of "GMT" is in the strings
> "GMT Standard Time" and "GMT Daylight Time", which name the two states
> of the timezone.  Have those changed to "UTC Standard Time" and "UTC
> Daylight Time"?

No, they're still "GMT Standard Time" and "GMT Daylight Time" in the 
registry 'Std' and 'Dlt' registry values in the timezone registry key 
'GMT Standard Time'.  (I think the 'Std' and 'Dlt' registry values get 
used by the strftime's "%Z" format specifier in the Microsoft CRT and 
its char *_tzname[2] array if the TZ environment variable is unset, 
although the registry also contains references to items within a 
resource DLL ("tzrez.dll"), so maybe the strings in the resource DLL get 
used sometimes.  I don't know the order of preference for the different 

>  The "(GMT) ... London", as I noted above, is describing
> one of the offsets, and neither that nor "(UTC) ... London" is incorrect
> for that purpose.  Albeit a bit misleading: its purpose would be clearer
> if it had an explicit "+0".

All the zones at UTC+0 (or at least the three I looked at casually) 
appear to have displayed names beginning "(UTC)" instead of 
"(UTC+00:00)" or "(UTC-00:00)".  The same appears to be true for XP 
except for the UTC/GMT substitution in the displayed names.  Windows 7 
also has a zone called "UTC" that XP lacks.

-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti at mev.co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-

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