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|Time and date predicates|
localto extract the local time,
'UTC'to extract a UTC time or an integer describing the seconds west of Greenwich.
?- date_time_stamp(date(2006,7,214,0,0,0,0,-,-), Stamp), stamp_date_time(Stamp, D, 0), date_time_value(date, D, Date). Date = date(2007, 1, 30)
When computing a time stamp from a local time specification, the UTC offset (arg 7), TZ (arg 8) and DST (arg 9) argument may be left unbound and are unified with the proper information. The example below, executed in Amsterdam, illustrates this behaviour. On the 25th of March at 01:00, DST does not apply. At 02.00, the clock is advanced by one hour and thus both 02:00 and 03:00 represent the same time stamp.
1 ?- date_time_stamp(date(2012,3,25,1,0,0,UTCOff,TZ,DST), Stamp). UTCOff = -3600, TZ = 'CET', DST = false, Stamp = 1332633600.0. 2 ?- date_time_stamp(date(2012,3,25,2,0,0,UTCOff,TZ,DST), Stamp). UTCOff = -7200, TZ = 'CEST', DST = true, Stamp = 1332637200.0. 3 ?- date_time_stamp(date(2012,3,25,3,0,0,UTCOff,TZ,DST), Stamp). UTCOff = -7200, TZ = 'CEST', DST = true, Stamp = 1332637200.0.
Note that DST and offset calculation are based on the POSIX function
mktime(). If mktime() returns an error, a representation_error
dst is generated.
|Calendar year as an integer|
|Calendar month as an integer 1..12|
|Calendar day as an integer 1..31|
|Clock hour as an integer 0..23|
|Clock minute as an integer 0..59|
|Clock second as a float 0.0..60.0|
|Offset to UTC in seconds (positive is west)|
|Name of timezone; fails if unknown|
date(Y,M,D,H,M,S,O,TZ,DST)or a term
fcan be prefixed by an integer to print the desired number of digits. E.g.,
%3fprints milliseconds. This format is not covered by any standard, but available with different format specifiers in various incarnations of the strftime() function.
pmin lower case.
'%a, %d %b %Y %T %z'). Our implementation supports
%:z, which modifies the output to HH:mm as required by XML-Schema. Note that both notations are valid in ISO 8601. The sequence
%:zis compatible to the GNU date(1) command.
The table below gives some format strings for popular time
representations. RFC1123 is used by HTTP. The full implementation of
as available from
library(http/http_header) is here.
http_timestamp(Time, Atom) :- stamp_date_time(Time, Date, 'UTC'), format_time(atom(Atom), '%a, %d %b %Y %T GMT', Date, posix).
posix, which currently only modifies the behaviour of the
Bformat specifiers. The predicate is used to be able to emit POSIX locale week and month names for emitting standardised time-stamps such as RFC1123.
parse_time(Text, _Format, Stamp). See parse_time/3.
Date = date(Year,Month,Day). Days of the week are numbered from one to seven: Monday = 1, Tuesday = 2, ... , Sunday = 7.