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TimeZoneRule Class Reference

#include <timezonerule.h>

Public Member Functions

 TimeZoneRule ()
 TimeZoneRule (const QString &smonth, const QString &sday, const QTime &stime, const QString &rmonth, const QString &rday, const QTime &rtime, const double &offset=1.00)
double deltaTZ () const
bool equals (TimeZoneRule *r)
bool isDSTActive (const KStarsDateTime &date)
bool isEmptyRule () const
KStarsDateTime nextDSTChange () const
KStarsDateTime nextDSTChange_LTime () const
void reset_with_ltime (KStarsDateTime &ltime, const double TZoffset, const bool time_runs_forward, const bool automaticDSTchange=false)
void setDST (bool activate=true)

Detailed Description

This class provides the information needed to determine whether Daylight Savings Time (DST; a.k.a.

"Summer Time") is currently active at a given location. There are (at least) 25 different "rules" which govern DST around the world; a string identifying the appropriate rule is attached to each city in citydb.sqlite.

The rules themselves are stored in the TZrulebook.dat file, which is read on startup; each line in the file creates a TimeZoneRule object.

TimeZoneRule consists of QStrings identifying the months and days on which DST starts and ends, QTime objects identifying the time at which the changes occur, and a double indicating the size of the offset in hours (probably always 1.00).

Month names should be the English three-letter abbreviation, uncapitalized. Day names are either an integer indicating the calendar date (i.e., "15" is the fifteenth of the month), or a number paired with a three-letter abbreviation for a weekday. This indicates the Nth weekday of the month (i.e., "2sun" is the second Sunday of the Month). Finally, the weekday string on its own indicates the last weekday of the month (i.e., "mon" is the last Monday of the month).

The isDSTActive(KStarsDateTime) function returns true if DST is active for the DateTime given as an argument.

The nextDSTChange(KStarsDateTime) function returns the KStarsDateTime of the moment at which the next DST change will occur for the current location.

Jason Harris

Definition at line 47 of file timezonerule.h.

Constructor & Destructor Documentation

◆ TimeZoneRule() [1/2]

TimeZoneRule::TimeZoneRule ( )

Default Constructor.

Makes the "empty" time zone rule (i.e., no DST correction)

Definition at line 14 of file timezonerule.cpp.

◆ TimeZoneRule() [2/2]

TimeZoneRule::TimeZoneRule ( const QString & smonth,
const QString & sday,
const QTime & stime,
const QString & rmonth,
const QString & rday,
const QTime & rtime,
const double & offset = 1.00 )


Create a TZ rule according to the arguments.

smonththe three-letter code for the month in which DST starts
sdaya string encoding the day on which DST starts (see the class description)
stimethe time at which DST starts
rmonththe three-letter code for the month in which DST reverts
rdaya string encoding the day on which DST reverts (see the class description)
rtimethe time at which DST reverts
offsetthe offset between normal time and DS time (always 1.00?)

Definition at line 19 of file timezonerule.cpp.

Member Function Documentation

◆ deltaTZ()

double TimeZoneRule::deltaTZ ( ) const
the current Timezone offset, compared to the timezone's Standard Time. This is typically 0.0 if DST is inactive, and 1.0 if DST is active.

Definition at line 80 of file timezonerule.h.

◆ equals()

bool TimeZoneRule::equals ( TimeZoneRule * r)
true if this rule is the same as the argument.
rthe rule to check for equivalence

Definition at line 557 of file timezonerule.cpp.

◆ isDSTActive()

bool TimeZoneRule::isDSTActive ( const KStarsDateTime & date)

Determine whether DST is in effect for the given DateTime, according to this rule.

datethe date/time to test for DST

Definition at line 283 of file timezonerule.cpp.

◆ isEmptyRule()

bool TimeZoneRule::isEmptyRule ( ) const
true if the rule is the "empty" TZ rule.

Definition at line 71 of file timezonerule.h.

◆ nextDSTChange()

KStarsDateTime TimeZoneRule::nextDSTChange ( ) const
computed value for next DST change in universal time.

Definition at line 95 of file timezonerule.h.

◆ nextDSTChange_LTime()

KStarsDateTime TimeZoneRule::nextDSTChange_LTime ( ) const
computed value for next DST change in local time.

Definition at line 98 of file timezonerule.h.

◆ reset_with_ltime()

void TimeZoneRule::reset_with_ltime ( KStarsDateTime & ltime,
const double TZoffset,
const bool time_runs_forward,
const bool automaticDSTchange = false )

Recalculate next dst change and if DST is active by a given local time with timezone offset and time direction.

ltimethe time to be tested
time_runs_forwardtime direction
TZoffsetoffset of timezone in some fictional unit
automaticDSTchangeis automatic DST change?
Check dox for TZoffset

There are some problems using local time for getting next daylight saving change time.

  1. The local time is the start time of DST change. So the local time doesn't exists and must corrected.
  2. The local time is the revert time. So the local time exists twice.
  3. Neither start time nor revert time. There is no problem.

Problem #1 is more complicated and we have to change the local time by reference. Problem #2 we just have to reset status of DST.

automaticDSTchange should only set to true if DST status changed due to running automatically over a DST change time. If local time will changed manually the automaticDSTchange should always set to false, to hold current DST status if possible (just on start and revert time possible).

Definition at line 432 of file timezonerule.cpp.

◆ setDST()

void TimeZoneRule::setDST ( bool activate = true)

Toggle DST on/off.

The activate argument should probably be isDSTActive()

activateif true, then set DST active; otherwise, deactivate DST

Definition at line 61 of file timezonerule.cpp.

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