A datetime array whose Format property was never set explicitly displays with one of two default formats, and this method chooses them. The choice between the two is made from the values: an array whose elements all sit at midnight uses the date-only default, and any other array uses the date-and-time default. The choice is made afresh on every display, so an array moves between the two when its components change.

datetime.setDefaultFormats ('default', fmt) sets the date-and-time default to fmt, and datetime.setDefaultFormats ('defaultdate', fmt) sets the date-only default. fmt is a display format, given as a character vector or string scalar, and is validated as the Format property is. Arrays that already exist take the new format on their next display; those with an explicitly set Format are unaffected.

datetime.setDefaultFormats ('reset') restores both factory formats, 'dd-MMM-uuuu HH:mm:ss' and 'dd-MMM-uuuu'.

Both formats persist across Octave sessions.

Deviation from MATLAB. MATLAB accepts a second argument after 'reset' and silently ignores it, resetting both defaults whatever it says, so datetime.setDefaultFormats ('reset', 'default') reads as a request to reset one and quietly resets two. Anything at all is accepted there, a number included. Here that is an error, since no correct program can depend on the argument being ignored.

Source Code: datetime