datenum - Parse ISO 8601 timestamp without applying UTC offset

I'm using MATLAB R2014b-win64

When I call datenum with an ISO 8601 datenum, I get:

>> result = datenum('2015-05-01T00:00:01Z','yyyy-mm-ddTHH:MM:SSZ')

result =

            736084.666678241

But this is not correct--MATLAB assumed I wanted the time changed from UTC to my local time zone:

>> datestr(result)

ans =

30-Apr-2015 16:00:01

If I leave off the 'Z' from the formatIn field, I get the right datenum:

>> result = datenum('2015-05-01T00:00:01Z','yyyy-mm-ddTHH:MM:SS')

result =

            736085.000011574

>> datestr(result)

ans =

01-May-2015 00:00:01

I don't see anything about this in the documentation. Am I missing something?

Perhaps this is a bug?

[per isakson]

Neither "UTC" nor "Z" is described on the page datenum, Convert date and time to serial date number - as far as I can see. If so, we may not make any assumptions on the behavior.

Answer 1

[Peter Perkins]

Randall, this is indeed a bug, albeit for inputs that were never documented to work. Prior to R2013b, this generated an error. Although 'yyyymmddTHHMMSS' is a format documented to work in datenum/datevec/datestr, you've added a Z at the end, intended as "literal". That's the problem.

Two suggestions:

1) You're using R2014b. Consider using datetime instead of datenum:

>> datetime('2015-05-01T00:00:01Z','Format','yyyy-MM-dd''T''HH:mm:ss''Z''')
ans = 
   2015-05-01T00:00:01Z

Notice how I've "escaped" the two literals in the format. If you want to use time zones, datetime supports those, while datenum does not.

>> datetime('2015-05-01T00:00:01Z','TimeZone','local','Format','yyyy-MM-dd''T''HH:mm:ssz')
ans = 
   2015-04-30T20:00:01EDT
>> datetime('2015-05-01T00:00:01Z','TimeZone','UTC','Format','yyyy-MM-dd''T''HH:mm:ssXXX')
ans = 
   2015-05-01T00:00:01Z

2) Use strrep to strip the Z off your strings, and leave it out of the format.

Hope this helps.

[Randall Pittman]

Thanks, Peter. I guess I expected it to work with the 'Z' since it's a valid ISO 8601 date/time string, but I understand that it's not officially supported to be used that way.

I need to learn more about datetime. I'm so used to datenums that I haven't looked at it as of yet, but I will. Thanks.