Switching TimeZone property in datetime function doesn't change output.

Question

Marius Kaffka 2022-1-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1634450-switching-timezone-property-in-datetime-function-doesn-t-change-output

回答： Peter Perkins 2022-2-16

采纳的回答： Peter Perkins

Hello,

I'm using this command to get a datetime output for a timetable.

startdatum=datetime(6.375400481428600e+10,...

'ConvertFrom','epochtime','Epoch','01.01.0001 00:00:00.000',...

'TimeZone','Europe/London',...

'Format','dd.MMM.yyyy HH:mm:ss.SSS', ...

'InputFormat','dd.MMM.yyyy HH:mm:ss.SSS');

Switching the property TimeZone to 'Europe/London' or even 'America/Denver' within the datetime function doesn't change the output?

Only after executing the command and entering startdatum.TimeZone = 'Europe/London'(or any other timezone) in the command window actually change the startdatum variable.

Could someone explain to me, if it's an error from Matlab or is it the way this command works using EpochTime?

I tried: startdatum=datetime(6.375400481428600e+10,...

'ConvertFrom','posixtime',...

'TimeZone','Europe/Zurich',...

'Format','dd.MMM.yyyy HH:mm:ss.SSS');

and changing the TimeZone resulted in different outputs.

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Answer 1

Peter Perkins 2022-2-16

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1634450-switching-timezone-property-in-datetime-function-doesn-t-change-output#answer_897675

在 MATLAB Online 中打开

Marius, here's what's happening:

The first few inputs of your code tell datetime that the instant of time you are talking about is 6.375400481428600e+10 seconds after 01-01-0001 00:00:00. That ends up looking like 14.Apr.2021 13:46:54.286. But there's no timezone attached to that origin, so at that point, it's unzoned. Then datetime sees 'TimeZone','Europe/London', and puts the instant into that TZ, but preserves the clockface time. In other words, if the epoch is specified as unzoned, then regardless of what you pass in as 'TimeZone', the result will always look like 14.Apr.2021 13:46:54.286.

Let's say 6.375400481428600e+10 is supposed to represent elapsed seconds UTC. Here's what you would do:

>> fmt = 'dd.MMM.yyyy HH:mm:ss.SSS z';
>> dt1UTC = datetime(0001,1,1,'TimeZone','UTC');
>> dt = datetime(6.375400481428600e+10, ...
    'ConvertFrom','epochtime','Epoch',dt1UTC, ...
    'Format',fmt, ...
    'TimeZone','Europe/London')
dt = 
  datetime
    14.Apr.2021 14:46:54.286 UTC+1
    
>> dt = datetime(6.375400481428600e+10, ...
    'ConvertFrom','epochtime','Epoch',dt1UTC, ...
    'Format',fmt, ...
    'TimeZone','Europe/Zurich')
dt = 
  datetime
    14.Apr.2021 15:46:54.286 UTC+2