time during standard to DST transition

Scott Atwood scott.roy.atwood at gmail.com
Wed Dec 10 19:26:06 UTC 2008

On Wed, Dec 10, 2008 at 10:43 AM, Jennifer Wang (jennifwa) <
jennifwa at cisco.com> wrote:

>  Hello,
> We ran into a problem when setting time to the "missing hour" during
> transition from standard time to DST time.  For example, setting time to Mar
> 8, 2009 at 2:10am using America/Los_Angeles time zone results in error.
> Should mktime() skip forward in this case and set the time to Mar 8, 2009
> 3:10am?

To me, it seems to make sense to return an error.  The time 2:10am Mar 8,
2009 in America/Los_Angeles really is an ambiguous time.  You can't
determine the intension of the caller.  She could either be counting forward
one hour from 1:10am, or she could be counting back one hour from 3:10am,
which result in different answers.  Likewise, calling mktime() with 2:10am,
Nov 2, 2008 in America/Los_Angeles and a negative value of tm_isdst is
similarly ambiguous.

I think both of these cases should return an error.


Scott Atwood

Cycle tracks will abound in Utopia.  ~H.G. Wells
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