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(* $Id: SysClock.Mod,v 1.7 1999/09/02 13:42:24 acken Exp $ *)
MODULE SysClock [FOREIGN "C"; LINK FILE "SysClock.c" END];
(* SysClock - facilities for accessing a system clock that records the
date and time of day.
Copyright (C) 1996-1998 Michael Griebling
This module is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
This module is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*)
<* Warnings := FALSE *>
CONST
maxSecondParts* = 999; (* Most systems have just millisecond accuracy *)
zoneMin* = -780; (* time zone minimum minutes *)
zoneMax* = 720; (* time zone maximum minutes *)
localTime* = MIN(INTEGER); (* time zone is inactive & time is local *)
unknownZone* = localTime+1; (* time zone is unknown *)
(* daylight savings mode values *)
unknown* = -1; (* current daylight savings status is unknown *)
inactive* = 0; (* daylight savings adjustments are not in effect *)
active* = 1; (* daylight savings adjustments are being used *)
TYPE
(* The DateTime type is a system-independent time format whose fields
are defined as follows:
year > 0
month = 1 .. 12
day = 1 .. 31
hour = 0 .. 23
minute = 0 .. 59
second = 0 .. 59
fractions = 0 .. maxSecondParts
zone = -780 .. 720
*)
DateTime* =
RECORD
year*: INTEGER;
month*: SHORTINT;
day*: SHORTINT;
hour*: SHORTINT;
minute*: SHORTINT;
second*: SHORTINT;
summerTimeFlag*: SHORTINT; (* daylight savings mode (see above) *)
fractions*: INTEGER; (* parts of a second in milliseconds *)
zone*: INTEGER; (* Time zone differential factor which
is the number of minutes to add to
local time to obtain UTC or is set
to localTime when time zones are
inactive. *)
END;
PROCEDURE CanGetClock*(): BOOLEAN;
(* Returns TRUE if a system clock can be read; FALSE otherwise. *)
PROCEDURE CanSetClock*(): BOOLEAN;
(* Returns TRUE if a system clock can be set; FALSE otherwise. *)
PROCEDURE IsValidDateTime* (d: DateTime): BOOLEAN;
(* Returns TRUE if the value of `d' represents a valid date and time;
FALSE otherwise. *)
PROCEDURE GetClock* (VAR userData: DateTime);
(* If possible, assigns system date and time of day to `userData' (i.e.,
the local time is returned). Error returns 1 Jan 1970. *)
PROCEDURE SetClock* (userData: DateTime);
(* If possible, sets the system clock to the values of `userData'. *)
PROCEDURE MakeLocalTime * (VAR c: DateTime);
(* Fill in the daylight savings mode and time zone for calendar date `c'.
The fields `zone' and `summerTimeFlag' given in `c' are ignored, assuming
that the rest of the record describes a local time.
Note 1: On most Unix systems the time zone information is only available for
dates falling within approx. 1 Jan 1902 to 31 Dec 2037. Outside this range
the field `zone' will be set to the unspecified `localTime' value (see
above), and `summerTimeFlag' will be set to `unknown'.
Note 2: The time zone information might not be fully accurate for past (and
future) years that apply different DST rules than the current year.
Usually the current set of rules is used for _all_ years between 1902 and
2037.
Note 3: With DST there is one hour in the year that happens twice: the
hour after which the clock is turned back for a full hour. It is undefined
which time zone will be selected for dates refering to this hour, i.e.
whether DST or normal time zone will be chosen. *)
PROCEDURE GetTimeOfDay* (VAR sec, usec: LONGINT): LONGINT;
(* PRIVAT. Don't use this. Take Time.GetTime instead.
Equivalent to the C function `gettimeofday'. The return value is `0' on
success and `-1' on failure; in the latter case `sec' and `usec' are set to
zero. *)
END SysClock.
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