Compute the timestamp from a date/9 term. Values for month, day,
hour, minute or second may be left unbound from the right, i.e., seconds
may be unbound, or seconds and minutes, etc. It is not allowed to
specify the seconds and leave one of the more significant fields
unbound. Unbound values unified to their lowest possible value.
Values for month, day, hour, minute or second need not be
normalized. This flexibility allows for easy computation of the
time at any given number of these units from a given timestamp.
Normalization can be achieved following this call with
stamp_date_time/3.
This example computes the date 200 days after 2006-07-14:
?- 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.
