Why Must the TimeZone be Specified for datetime when the Time Zone is Included in the DateString?

Suppose I have a date string

fu = "Mon Mar 3 12:20:40 EST 2025"

fu = "Mon Mar 3 12:20:40 EST 2025"

Converting to datetime causes an error because the TimeZone input is not specified

try
    d = datetime(fu,'InputFormat','eee MMM d HH:mm:ss z yyyy')
catch ME
    ME.message
end

ans = 'The format 'eee MMM d HH:mm:ss z yyyy' contains a field for time zone offset. When that field is present, you must use the 'TimeZone' input parameter to create the datetime array in a specific time zone. You can then convert that array to be unzoned by setting its 'TimeZone' property to ''.'

Why does TimeZone need to be specified if EST is included in the input?

Specifying the TimeZone then results in a warning, though I'm not sure what the "unexpected results" might be.

d = datetime(fu,'InputFormat','eee MMM d HH:mm:ss z yyyy','TimeZone','EST')

Warning: 'EST' specifies a time zone with a fixed offset from UTC, -05:00. This zone does not follow daylight saving time, and so may give unexpected results. See the datetime.TimeZone property for details about specifying time zones.

d = datetime
   03-Mar-2025 12:20:40

Answer 1

[Walter Roberson]

fu1 = "Mon Mar 3 12:20:40 EST 2025";
d1 = datetime(fu1,'InputFormat','eee MMM d HH:mm:ss z yyyy','TimeZone','-05:00')

d1 = datetime
   03-Mar-2025 12:20:40

d2 = datetime(fu1,'InputFormat','eee MMM d HH:mm:ss z yyyy','TimeZone','GMT')

d2 = datetime
   03-Mar-2025 17:20:40

fu2 = "Mon Mar 3 12:20:40 CST 2025";
d3 = datetime(fu2,'InputFormat','eee MMM d HH:mm:ss z yyyy','TimeZone','-05:00')

d3 = datetime
   03-Mar-2025 13:20:40

So the specified timezone in the datetime input has an effect on the output time.

And the TimeZone that is specified tells datetime() what the output timezone is to be.

[Paul]

Why doesn't TimeZone of d just default to the time zone in the input string?

Seems to me that if the input string contains a time zone, then that's the time zone the user wants absent any other action (like specifying TimeZone).

[Mark]

I'm wondering the same thing. It seems like the TimeZone of the datetime object should be assigned to the zone specified in the input string. As it is, it seems like there is no simple way to preserve this information from the input, as the forced conversion to another zone results in a loss of the data.