These functions convert time values (see Time of Day) to Lisp timestamps, or into calendrical information and vice versa.
Many 32-bit operating systems are limited to system times containing 32 bits of information in their seconds component; these systems typically handle only the times from 1901-12-13 20:45:52 through 2038-01-19 03:14:07 Universal Time. However, 64-bit and some 32-bit operating systems have larger seconds components, and can represent times far in the past or future.
Calendrical conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 BC, and do not skip zero as traditional Gregorian years do; for example, the year number -37 represents the Gregorian year 38 BC.
This function converts a time value into a Lisp timestamp.
The optional form argument specifies the timestamp form to be
returned. If form is the symbol
integer, this function
returns an integer count of seconds. If form is a positive
integer, it specifies a clock frequency and this function returns an
. form).25 If form is
t, this function treats it as a positive integer suitable for
representing the timestamp; for example, it is treated as 1000000000
if time is nil and the platform timestamp has nanosecond
resolution. If form is
list, this function returns an
(high low micro pico).
Although an omitted or
nil form currently acts like
list, this is planned to change in a future Emacs version, so
callers requiring list timestamps should pass
If time is infinite or a NaN, this function signals an error.
Otherwise, if time cannot be represented exactly, conversion
truncates it toward minus infinity. When form is
conversion is always exact so no truncation occurs, and the returned
clock resolution is no less than that of time. By way of
float-time can convert any Lisp time value without
signaling an error, although the result might not be exact.
See Time of Day.
For efficiency this function might return a value that is
time, or that otherwise shares structure with time.
(time-convert nil nil) is equivalent to
(current-time), the latter may be a bit faster.
(setq a (time-convert nil t)) ⇒ (1564826753904873156 . 1000000000)
(time-convert a 100000) ⇒ (156482675390487 . 100000)
(time-convert a 'integer) ⇒ 1564826753
(time-convert a 'list) ⇒ (23877 23681 904873 156000)
This function converts a time value into calendrical information. If you don’t specify time, it decodes the current time, and similarly zone defaults to the current time zone rule. See Time Zone Rules. The operating system limits the range of time and zone values.
The form argument controls the form of the returned seconds element, as described below. The return value is a list of nine elements, as follows:
(seconds minutes hour day month year dow dst utcoff)
Here is what the elements mean:
The number of seconds past the minute, with form described below.
The number of minutes past the hour, as an integer between 0 and 59.
The hour of the day, as an integer between 0 and 23.
The day of the month, as an integer between 1 and 31.
The month of the year, as an integer between 1 and 12.
The year, an integer typically greater than 1900.
The day of week, as an integer between 0 and 6, where 0 stands for Sunday.
t if daylight saving time is effect,
nil if it is not
in effect, and -1 if this information is not available.
An integer indicating the Universal Time offset in seconds, i.e., the number of seconds east of Greenwich.
The seconds element is a Lisp timestamp that is nonnegative and
less than 61; it is less than 60 except during positive leap seconds
(assuming the operating system supports leap seconds). If the
optional form argument is
t, seconds uses the same
precision as time; if form is
seconds is truncated to an integer. For example, if time
is the timestamp
(1566009571321 . 1000), which represents
2019-08-17 02:39:31.321 UTC on typical systems that lack leap seconds,
(decode-time time t t) returns
((31321 . 1000)
39 2 17 8 2019 6 nil 0), whereas
(decode-time time t
(31 39 2 17 8 2019 6 nil 0). If form
is omitted or
nil, it currently defaults to
this default may change in future Emacs releases, so callers requiring
a particular form should specify form.
Common Lisp Note: Common Lisp has different meanings for dow and utcoff, and its second is an integer between 0 and 59 inclusive.
To access (or alter) the elements in the time value, the
decoded-time-zone accessors can be used.
For instance, to increase the year in a decoded time, you could say:
(setf (decoded-time-year decoded-time) (+ (decoded-time-year decoded-time) 4))
Also see the following function.
This function takes a decoded time structure and adds delta
(also a decoded time structure) to it. Elements in delta that
nil are ignored.
For instance, if you want “same time next month”, you could say:
(let ((time (decode-time nil nil t)) (delta (make-decoded-time :month 2))) (encode-time (decoded-time-add time delta)))
If this date doesn’t exist (if you’re running this on January 31st, for instance), then the date will be shifted back until you get a valid date (which will be February 28th or 29th, depending).
Fields are added in a most to least significant order, so if the adjustment described above happens, it happens before adding days, hours, minutes or seconds.
The values in delta can be negative to subtract values instead.
The return value is a decoded time structure.
Return a decoded time structure with only the given keywords filled
out, leaving the rest
nil. For instance, to get a structure
that represents “two months”, you could say:
(make-decoded-time :month 2)
This function converts time to a Lisp timestamp.
It can act as the inverse of
Ordinarily the first argument is a list
(second minute hour day month
year ignored dst zone) that specifies a
decoded time in the style of
decode-time, so that
(encode-time (decode-time ...)) works. For the meanings of
these list members, see the table under
As an obsolescent calling convention, this function can be given six
or more arguments. The first six arguments second,
minute, hour, day, month, and year
specify most of the components of a decoded time. If there are more
than six arguments the last argument is used as zone and
any other extra arguments are ignored, so that
#'encode-time (decode-time ...)) works. In this obsolescent
convention, zone defaults to the current time zone rule
(see Time Zone Rules), and dst is treated as if it was
Year numbers less than 100 are not treated specially. If you want them
to stand for years above 1900, or years above 2000, you must alter them
yourself before you call
The operating system limits the range of time and zone values.
encode-time function acts as a rough inverse to
decode-time. For example, you can pass the output of
the latter to the former as follows:
(encode-time (decode-time …))
You can perform simple date arithmetic by using out-of-range values for seconds, minutes, hour, day, and month; for example, day 0 means the day preceding the given month.
Currently a positive integer form should be at least 65536 if the returned value is intended to be given to standard functions expecting Lisp timestamps.