The CDATE and DATE system variables provide access to the current date and time. The TDCREATE, TDINDWG, TDUPDATE, and TDUSRTIMER system variables (and the $TDCREATE, $TDUCREATE, $TDUPDATE, and $TDUUPDATE DXF header variables) provide access to times and dates associated with the current drawing. The values are represented as real numbers with special meanings, as described below.
DATE is the current date and time represented as a Julian date and fraction of a day in a real number.
<Julian date>.<Fraction of day>
For example, on December 31, 1999, at 9:58:35 p.m. GMT, the DATE variable contains
2451544.91568287
The date and time are taken from the computer's clock when the variable is read. The time is represented as a fraction of a day, and the times returned by DATE may be truly subtracted to compute differences in time. To extract the seconds since midnight from the value returned by DATE, use the AutoLISP expressions
(setq s (getvar "DATE"))
(setq seconds (* 86400.0 (- s (fix s))))
Note that DATE returns only a true Julian date if the system's clock is set to UTC/Zulu (Greenwich Mean Time). TDCREATE and TDUPDATE have the same format as DATE, but their values represent the creation time and last update time of the current drawing.
TDINDWG and TDUSRTIMER (and the $TDINDWG and $TDUSRTIMER DXF header variables) use a format similar to that of DATE, but their values represent elapsed times, as in
<Number of days>.<Fraction of day>
CDATE is the current date and time in calendar and clock format. The value is returned as a real number in the form
YYYYMMDD.HHMMSShsec
hsec = hundredths of a second (00-99)
For example, if the current date is December 31, 2005, and the time is 9:58:35.75 p.m., CDATE would return the value:
20051231.21583575
Note that CDATE values can be compared for later and earlier values but that subtracting them yields numbers that are not meaningful.