datenum to UTC?

Question

MrKoberec 2018-10-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/426134-datenum-to-utc

评论： Peter Perkins 2018-10-31

采纳的回答： James Tursa

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Hi, I have

10-Oct-2013 15:59:00

and I need UTC time

1381435140

Is there any easy way? (time zone GTM-4)

Thanks!

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Guillaume 2018-10-25

That's not UTC time, that's a Unix Time Stamp

It also appears that your input is a datetime not a datenum.

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Answer 1

James Tursa 2018-10-25

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编辑：James Tursa 2018-10-25

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Are you just looking for how to convert from the former to the latter? E.g.,

s = '10-Oct-2013 15:59:00';
unix_m4 = (datenum(s) - datenum('01-Jan-1970'))*86400 + 4*3600;

or

unix_m4 = seconds((datetime(s) - datetime('01-Jan-1970')) + seconds(4*3600));

or

unix_m4 = seconds(datetime(s,'timezone','-4') - datetime('01-Jan-1970','timezone','UTC'));

This result isn't called UTC btw, it is called Unix time:

https://en.wikipedia.org/wiki/Unix_time

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MrKoberec 2018-10-26

Thank you, James. Your first suggestion did the job (thank you for including the timezone). I'm using an old version of Matlab (long story) and it does not know the datetime. Sorry I forgot to mention this. Thank you also for the link. I understand it better now.

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Answer 2

jonas 2018-10-25

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编辑：jonas 2018-10-25

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Yes, use datetime instead of datenum.

t = datetime('10-Oct-2013 15:59:00','timezone','-04:00')
t_unix = posixtime(t)

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Peter Perkins 2018-10-31

'-04:00' is a valid time zone, but perhaps a little dangerous. It's a time zone that does not observe4 DST. If the OP is in, say, Boston, then that would give the wrong answer for 10-Nov. Something like 'America/New_York' is probably the right choice.

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