// Purpose: topic overview
// Author: wxWidgets team
// RCS-ID: $Id$
-// Licence: wxWindows license
+// Licence: wxWindows licence
/////////////////////////////////////////////////////////////////////////////
-/*!
+/**
- @page overview_datetime Date and time classes overview
+@page overview_datetime Date and Time
- Classes: wxDateTime, wxDateSpan, wxTimeSpan, wxCalendarCtrl
+@tableofcontents
- @li @ref overview_datetime_introduction
- @li @ref overview_datetime_classes
- @li @ref overview_datetime_characteristics
- @li @ref overview_datetime_timespandiff
- @li @ref overview_datetime_arithmetics
- @li @ref overview_datetime_timezones
- @li @ref overview_datetime_dst
- @li @ref overview_datetime_holidays
- @li @ref overview_datetime_compat
+wxWidgets provides a set of powerful classes to work with dates and times. Some
+of the supported features of wxDateTime class are:
+@li Wide range: the range of supported dates goes from about 4714 B.C. to
+ some 480 million years in the future.
+@li Precision: not using floating point calculations anywhere ensures that
+ the date calculations don't suffer from rounding errors.
+@li Many features: not only all usual calculations with dates are supported,
+ but also more exotic week and year day calculations, work day testing,
+ standard astronomical functions, conversion to and from strings in either
+ strict or free format.
+@li Efficiency: objects of wxDateTime are small (8 bytes) and working with
+ them is fast
+
+There are 3 main classes declared in @c wx/datetime.h: except wxDateTime itself
+which represents an absolute moment in time, there are also two classes -
+wxTimeSpan and wxDateSpan - which represent the intervals of time.
+
+There are also helper classes which are used together with wxDateTime:
+wxDateTimeHolidayAuthority which is used to determine whether a given date is a
+holiday or not and wxDateTimeWorkDays which is a derivation of this class for
+which (only) Saturdays and Sundays are the holidays. See more about these
+classes in the discussion of the holidays (see
+@ref overview_datetime_holidays).
- <hr>
+Finally, in other parts of this manual you may find mentions of wxDate and
+wxTime classes. @ref overview_datetime_compat are obsolete and superseded by
+wxDateTime.
- @section overview_datetime_introduction Introduction
- wxWidgets provides a set of powerful classes to work with dates and times. Some
- of the supported features of wxDateTime class are:
+@section overview_datetime_characteristics wxDateTime Characteristics
+
+wxDateTime stores the time as a signed number of
+milliseconds since the Epoch which is fixed, by convention, to Jan 1, 1970 -
+however this is not visible to the class users (in particular, dates prior to
+the Epoch are handled just as well (or as bad) as the dates after it). But it
+does mean that the best resolution which can be achieved with this class is 1
+millisecond.
- @li Wide range: the range of supported dates goes from about 4714 B.C. to
- some 480 million years in the future.
+The size of wxDateTime object is 8 bytes because it is represented as a 64 bit
+integer. The resulting range of supported dates is thus approximatively 580
+million years, but due to the current limitations in the Gregorian calendar
+support, only dates from Nov 24, 4714BC are supported (this is subject to
+change if there is sufficient interest in doing it).
+
+Finally, the internal representation is time zone independent (always in GMT)
+and the time zones only come into play when a date is broken into
+year/month/day components. See more about timezones below
+(see @ref overview_datetime_timezones).
+
+Currently, the only supported calendar is Gregorian one (which is used even
+for the dates prior to the historic introduction of this calendar which was
+first done on Oct 15, 1582 but is, generally speaking, country, and even
+region, dependent). Future versions will probably have Julian calendar support
+as well and support for other calendars (Maya, Hebrew, Chinese...) is not
+ruled out.
+
+
+
+@section overview_datetime_timespandiff wxDateSpan and wxTimeSpan
+
+While there is only one logical way to represent an absolute moment in the
+time (and hence only one wxDateTime class), there are at least two methods to
+describe a time interval.
+
+First, there is the direct and self-explaining way implemented by
+wxTimeSpan: it is just a difference in milliseconds
+between two moments in time. Adding or subtracting such an interval to
+wxDateTime is always well-defined and is a fast operation.
+
+But in the daily life other, calendar-dependent time interval specifications are
+used. For example, 'one month later' is commonly used. However, it is clear
+that this is not the same as wxTimeSpan of 60*60*24*31 seconds because 'one
+month later' Feb 15 is Mar 15 and not Mar 17 or Mar 16 (depending on whether
+the year is leap or not).
+
+This is why there is another class for representing such intervals called
+wxDateSpan. It handles these sort of operations in the
+most natural way possible, but note that manipulating with intervals of
+this kind is not always well-defined. Consider, for example, Jan 31 + '1
+month': this will give Feb 28 (or 29), i.e. the last day of February and not
+the non-existent Feb 31. Of course, this is what is usually wanted, but you
+still might be surprised to notice that now subtracting back the same
+interval from Feb 28 will result in Jan 28 and @b not Jan 31 we started
+with!
+
+So, unless you plan to implement some kind of natural language parsing in the
+program, you should probably use wxTimeSpan instead of wxDateSpan (which is
+also more efficient). However, wxDateSpan may be very useful in situations
+when you do need to understand what 'in a month' means (of course, it is
+just @c wxDateTime::Now() + wxDateSpan::Month()).
- @li Precision: not using floating point calculations anywhere ensures that
- the date calculations don't suffer from rounding errors.
- @li Many features: not only all usual calculations with dates are supported,
- but also more exotic week and year day calculations, work day testing, standard
- astronomical functions, conversion to and from strings in either strict or free
- format.
- @li Efficiency: objects of wxDateTime are small (8 bytes) and working with
- them is fast
+@section overview_datetime_arithmetics Date Arithmetics
+Many different operations may be performed with the dates, however not all of
+them make sense. For example, multiplying a date by a number is an invalid
+operation, even though multiplying either of the time span classes by a number
+is perfectly valid.
+Here is what can be done:
- @section overview_datetime_classes All date/time classes at a glance
+@li @b Addition: a wxTimeSpan or wxDateSpan can be added to wxDateTime
+ resulting in a new wxDateTime object and also 2 objects of the same span class
+ can be added together giving another object of the same class.
+@li @b Subtraction: the same types of operations as above are
+ allowed and, additionally, a difference between two wxDateTime objects can be
+ taken and this will yield wxTimeSpan.
+@li @b Multiplication: a wxTimeSpan or wxDateSpan object can be
+ multiplied by an integer number resulting in an object of the same type.
+@li <b>Unary minus</b>: a wxTimeSpan or wxDateSpan object may finally be
+ negated giving an interval of the same magnitude but of opposite time
+ direction.
- There are 3 main classes declared in @c wx/datetime.h: except wxDateTime itself
- which represents an absolute moment in time, there are also two classes -
- wxTimeSpan and wxDateSpan - which represent the intervals of time.
+For all these operations there are corresponding global (overloaded) operators
+and also member functions which are synonyms for them: Add(), Subtract() and
+Multiply(). Unary minus as well as composite assignment operations (like +=)
+are only implemented as members and Neg() is the synonym for unary minus.
- There are also helper classes which are used together with wxDateTime:
- wxDateTimeHolidayAuthority which is used to determine whether a given date
- is a holiday or not and wxDateTimeWorkDays which is a derivation of this
- class for which (only) Saturdays and Sundays are the holidays. See more about
- these classes in the discussion of the holidays (see @ref overview_datetime_holidays).
- Finally, in other parts of this manual you may find mentions of wxDate and
- wxTime classes. @ref overview_datetime_compat are obsolete and
- superseded by wxDateTime.
+@section overview_datetime_timezones Time Zone Considerations
+Although the time is always stored internally in GMT, you will usually work in
+the local time zone. Because of this, all wxDateTime constructors and setters
+which take the broken down date assume that these values are for the local
+time zone. Thus, @c wxDateTime(1, wxDateTime::Jan, 1970) will not
+correspond to the wxDateTime Epoch unless you happen to live in the UK.
+All methods returning the date components (year, month, day, hour, minute,
+second...) will also return the correct values for the local time zone by
+default, so, generally, doing the natural things will lead to natural and
+correct results.
- @section overview_datetime_characteristics wxDateTime characteristics
+If you only want to do this, you may safely skip the rest of this section.
+However, if you want to work with different time zones, you should read it to
+the end.
- wxDateTime stores the time as a signed number of
- milliseconds since the Epoch which is fixed, by convention, to Jan 1, 1970 -
- however this is not visible to the class users (in particular, dates prior to
- the Epoch are handled just as well (or as bad) as the dates after it). But it
- does mean that the best resolution which can be achieved with this class is 1
- millisecond.
+In this (rare) case, you are still limited to the local time zone when
+constructing wxDateTime objects, i.e. there is no way to construct a
+wxDateTime corresponding to the given date in, say, Pacific Standard Time.
+To do it, you will need to call wxDateTime::ToTimezone or wxDateTime::MakeTimezone
+methods to adjust the date for the target time zone. There are also special
+versions of these functions wxDateTime::ToUTC and wxDateTime::MakeUTC for
+the most common case - when the date should be constructed in UTC.
- The size of wxDateTime object is 8 bytes because it is represented as a 64 bit
- integer. The resulting range of supported dates is thus approximatively 580
- million years, but due to the current limitations in the Gregorian calendar
- support, only dates from Nov 24, 4714BC are supported (this is subject to
- change if there is sufficient interest in doing it).
+You also can just retrieve the value for some time zone without converting the
+object to it first. For this you may pass TimeZone argument to any of the
+methods which are affected by the time zone (all methods getting date
+components and the date formatting ones, for example). In particular, the
+Format() family of methods accepts a TimeZone parameter and this allows to
+simply print time in any time zone.
- Finally, the internal representation is time zone independent (always in GMT)
- and the time zones only come into play when a date is broken into
- year/month/day components. See more about timezones below
- (see @ref overview_datetime_timezones).
+To see how to do it, the last issue to address is how to construct a TimeZone
+object which must be passed to all these methods. First of all, you may construct
+it manually by specifying the time zone offset in seconds from GMT, but
+usually you will just use one of the @ref overview_datetime and
+let the conversion constructor do the job.
- Currently, the only supported calendar is Gregorian one (which is used even
- for the dates prior to the historic introduction of this calendar which was
- first done on Oct 15, 1582 but is, generally speaking, country, and even
- region, dependent). Future versions will probably have Julian calendar support
- as well and support for other calendars (Maya, Hebrew, Chinese...) is not
- ruled out.
+I.e. you would just write
+@code
+wxDateTime dt(...whatever...);
+printf("The time is %s in local time zone", dt.FormatTime().c_str());
+printf("The time is %s in GMT", dt.FormatTime(wxDateTime::GMT).c_str());
+@endcode
- @section overview_datetime_timespandiff Difference between wxDateSpan and wxTimeSpan
- While there is only one logical way to represent an absolute moment in the
- time (and hence only one wxDateTime class), there are at least two methods to
- describe a time interval.
+@section overview_datetime_dst Daylight Saving Time (DST)
- First, there is the direct and self-explaining way implemented by
- wxTimeSpan: it is just a difference in milliseconds
- between two moments in time. Adding or subtracting such an interval to
- wxDateTime is always well-defined and is a fast operation.
+DST (a.k.a. 'summer time') handling is always a delicate task which is better
+left to the operating system which is supposed to be configured by the
+administrator to behave correctly. Unfortunately, when doing calculations with
+date outside of the range supported by the standard library, we are forced to
+deal with these issues ourselves.
- But in the daily life other, calendar-dependent time interval specifications are
- used. For example, 'one month later' is commonly used. However, it is clear
- that this is not the same as wxTimeSpan of 60*60*24*31 seconds because 'one
- month later' Feb 15 is Mar 15 and not Mar 17 or Mar 16 (depending on whether
- the year is leap or not).
+Several functions are provided to calculate the beginning and end of DST in
+the given year and to determine whether it is in effect at the given moment or
+not, but they should not be considered as absolutely correct because, first of
+all, they only work more or less correctly for only a handful of countries
+(any information about other ones appreciated!) and even for them the rules
+may perfectly well change in the future.
- This is why there is another class for representing such intervals called
- wxDateSpan. It handles these sort of operations in the
- most natural way possible, but note that manipulating with intervals of
- this kind is not always well-defined. Consider, for example, Jan 31 + '1
- month': this will give Feb 28 (or 29), i.e. the last day of February and not
- the non-existent Feb 31. Of course, this is what is usually wanted, but you
- still might be surprised to notice that now subtracting back the same
- interval from Feb 28 will result in Jan 28 and @b not Jan 31 we started
- with!
+The time zone handling methods (see @ref overview_datetime_timezones) use
+these functions too, so they are subject to the same limitations.
- So, unless you plan to implement some kind of natural language parsing in the
- program, you should probably use wxTimeSpan instead of wxDateSpan (which is
- also more efficient). However, wxDateSpan may be very useful in situations
- when you do need to understand what 'in a month' means (of course, it is
- just @c wxDateTime::Now() + wxDateSpan::Month()).
+@section overview_datetime_holidays wxDateTime and Holidays
- @section overview_datetime_arithmetics Date arithmetics
+@todo WRITE THIS DOC PARAGRAPH.
- Many different operations may be performed with the dates, however not all of
- them make sense. For example, multiplying a date by a number is an invalid
- operation, even though multiplying either of the time span classes by a number
- is perfectly valid.
- Here is what can be done:
- @li @b Addition: a wxTimeSpan or wxDateSpan can be added to wxDateTime
- resulting in a new wxDateTime object and also 2 objects of the same span class
- can be added together giving another object of the same class.
+@section overview_datetime_compat Compatibility
- @li @b Subtraction: the same types of operations as above are
- allowed and, additionally, a difference between two wxDateTime objects can be
- taken and this will yield wxTimeSpan.
-
- @li @b Multiplication: a wxTimeSpan or wxDateSpan object can be
- multiplied by an integer number resulting in an object of the same type.
-
- @li <b>Unary minus</b>: a wxTimeSpan or wxDateSpan object may finally be
- negated giving an interval of the same magnitude but of opposite time
- direction.
-
- For all these operations there are corresponding global (overloaded) operators
- and also member functions which are synonyms for them: Add(), Subtract() and
- Multiply(). Unary minus as well as composite assignment operations (like +=)
- are only implemented as members and Neg() is the synonym for unary minus.
-
-
-
- @section overview_datetime_timezones Time zone considerations
-
- Although the time is always stored internally in GMT, you will usually work in
- the local time zone. Because of this, all wxDateTime constructors and setters
- which take the broken down date assume that these values are for the local
- time zone. Thus, @c wxDateTime(1, wxDateTime::Jan, 1970) will not
- correspond to the wxDateTime Epoch unless you happen to live in the UK.
- All methods returning the date components (year, month, day, hour, minute,
- second...) will also return the correct values for the local time zone by
- default, so, generally, doing the natural things will lead to natural and
- correct results.
-
- If you only want to do this, you may safely skip the rest of this section.
- However, if you want to work with different time zones, you should read it to
- the end.
-
- In this (rare) case, you are still limited to the local time zone when
- constructing wxDateTime objects, i.e. there is no way to construct a
- wxDateTime corresponding to the given date in, say, Pacific Standard Time.
- To do it, you will need to call wxDateTime::ToTimezone or wxDateTime::MakeTimezone
- methods to adjust the date for the target time zone. There are also special
- versions of these functions wxDateTime::ToUTC and wxDateTime::MakeUTC for
- the most common case - when the date should be constructed in UTC.
-
- You also can just retrieve the value for some time zone without converting the
- object to it first. For this you may pass TimeZone argument to any of the
- methods which are affected by the time zone (all methods getting date
- components and the date formatting ones, for example). In particular, the
- Format() family of methods accepts a TimeZone parameter and this allows to
- simply print time in any time zone.
-
- To see how to do it, the last issue to address is how to construct a TimeZone
- object which must be passed to all these methods. First of all, you may construct
- it manually by specifying the time zone offset in seconds from GMT, but
- usually you will just use one of the @ref overview_datetime and
- let the conversion constructor do the job.
-
- I.e. you would just write
-
- @code
- wxDateTime dt(...whatever...);
- printf("The time is %s in local time zone", dt.FormatTime().c_str());
- printf("The time is %s in GMT", dt.FormatTime(wxDateTime::GMT).c_str());
- @endcode
-
-
-
- @section overview_datetime_dst Daylight saving time (DST)
-
- DST (a.k.a. 'summer time') handling is always a delicate task which is better
- left to the operating system which is supposed to be configured by the
- administrator to behave correctly. Unfortunately, when doing calculations with
- date outside of the range supported by the standard library, we are forced to
- deal with these issues ourselves.
-
- Several functions are provided to calculate the beginning and end of DST in
- the given year and to determine whether it is in effect at the given moment or
- not, but they should not be considered as absolutely correct because, first of
- all, they only work more or less correctly for only a handful of countries
- (any information about other ones appreciated!) and even for them the rules
- may perfectly well change in the future.
-
- The time zone handling methods (see @ref overview_datetime_timezones) use
- these functions too, so they are subject to the same limitations.
-
-
-
- @section overview_datetime_holidays wxDateTime and Holidays
-
- TODO.
-
-
-
- @section overview_datetime_compat Compatibility
-
- The old classes for date/time manipulations ported from wxWidgets version 1.xx
- are still included but are reimplemented in terms of wxDateTime. However, using
- them is strongly discouraged because they have a few quirks/bugs and were not
- 'Y2K' compatible.
+The old classes for date/time manipulations ported from wxWidgets version 1.xx
+are still included but are reimplemented in terms of wxDateTime. However, using
+them is strongly discouraged because they have a few quirks/bugs and were not
+'Y2K' compatible.
*/
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