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NAME

       QwtDate -

       A collection of methods around date/time values.

SYNOPSIS

       #include <qwt_date.h>

   Public Types
       enum Week0Type { FirstThursday, FirstDay }
       enum IntervalType { Millisecond, Second, Minute, Hour, Day, Week, Month, Year }
       enum { JulianDayForEpoch = 2440588 }

   Static Public Member Functions
       static QDate minDate ()
       static QDate maxDate ()
       static QDateTime toDateTime (double value, Qt::TimeSpec=Qt::UTC)
       static double toDouble (const QDateTime &)
       static QDateTime ceil (const QDateTime &, IntervalType)
       static QDateTime floor (const QDateTime &, IntervalType)
       static QDate dateOfWeek0 (int year, Week0Type)
           Date of the first day of the first week for a year.
       static int weekNumber (const QDate &, Week0Type)
       static int utcOffset (const QDateTime &)
       static QString toString (const QDateTime &, const QString &format, Week0Type)

Detailed Description

       A collection of methods around date/time values.

       Qt offers convenient classes for dealing with date/time values, but Qwt uses coordinate
       systems that are based on doubles. QwtDate offers methods to translate from QDateTime to
       double and v.v.

       A double is interpreted as the number of milliseconds since 1970-01-01T00:00:00 Universal
       Coordinated Time - also known as 'The Epoch'.

       While the range of the Julian day in Qt4 is limited to [0, MAX_INT], Qt5 stores it as
       qint64 offering a huge range of valid dates. As the significance of a double is below this
       ( assuming a fraction of 52 bits ) the translation is not bijective with rounding errors
       for dates very far from Epoch. For a resolution of 1 ms those start to happen for dates
       above the year 144683.

       An axis for a date/time interval is expected to be aligned and divided in time/date units
       like seconds, minutes, ... QwtDate offers several algorithms that are needed to calculate
       these axes.

       See Also:
           QwtDateScaleEngine, QwtDateScaleDraw, QDate, QTime

Member Enumeration Documentation

   anonymous enum
       Enumerator

       JulianDayForEpoch
              The Julian day of 'The Epoch'.

   enum QwtDate::IntervalType
       Classification of an time interval

       Time intervals needs to be classified to decide how to align and divide it.

       Enumerator

       Millisecond
              The interval is related to milliseconds.

       Second The interval is related to seconds.

       Minute The interval is related to minutes.

       Hour   The interval is related to hours.

       Day    The interval is related to days.

       Week   The interval is related to weeks.

       Month  The interval is related to months.

       Year   The interval is related to years.

   enum QwtDate::Week0Type
       How to identify the first week of year differs between countries.

       Enumerator

       FirstThursday
              According to ISO 8601 the first week of a year is defined as 'the week with the
              year's first Thursday in it'.

       FirstThursday corresponds to the numbering that is implemented in QDate::weekNumber().

       FirstDay

       In the U.S. this definition is more common than FirstThursday.

Member Function Documentation

   QDateTime QwtDate::ceil (const QDateTime &dateTime, IntervalTypeintervalType) [static]
       Ceil a datetime according the interval type

       Parameters:
           dateTime Datetime value
           intervalType Interval type, how to ceil. F.e. when intervalType = QwtDate::Months, the
           result will be ceiled to the next beginning of a month

       Returns:
           Ceiled datetime

       See Also:
           floor()

   QDate QwtDate::dateOfWeek0 (intyear, Week0Typetype) [static]
       Date of the first day of the first week for a year. The first day of a week depends on the
       current locale ( QLocale::firstDayOfWeek() ).

       Parameters:
           year Year
           type Option how to identify the first week

       Returns:
           First day of week 0

       See Also:
           QLocale::firstDayOfWeek(), weekNumber()

   QDateTime QwtDate::floor (const QDateTime &dateTime, IntervalTypeintervalType) [static]
       Floor a datetime according the interval type

       Parameters:
           dateTime Datetime value
           intervalType Interval type, how to ceil. F.e. when intervalType = QwtDate::Months, the
           result will be ceiled to the next beginning of a month

       Returns:
           Floored datetime

       See Also:
           floor()

   QDate QwtDate::maxDate () [static]
       Maximum for the supported date range

       The range of valid dates depends on how QDate stores the Julian day internally.

       · For Qt4 it is 'Tue Jun 3 5874898'

       · For Qt5 it is 'Tue Dec 31 2147483647'

       Returns:
           maximum of the date range

       See Also:
           minDate()

       Note:
           The maximum differs between Qt4 and Qt5

   QDate QwtDate::minDate () [static]
       Minimum for the supported date range

       The range of valid dates depends on how QDate stores the Julian day internally.

       · For Qt4 it is 'Tue Jan 2 -4713'

       · For Qt5 it is 'Thu Jan 1 -2147483648'

       Returns:
           minimum of the date range

       See Also:
           maxDate()

   QDateTime QwtDate::toDateTime (doublevalue, Qt::TimeSpectimeSpec = Qt::UTC) [static]
       Translate from double to QDateTime

       Parameters:
           value Number of milliseconds since the epoch, 1970-01-01T00:00:00 UTC
           timeSpec Time specification

       Returns:
           Datetime value

       See Also:
           toDouble(), QDateTime::setMSecsSinceEpoch()

       Note:
           The return datetime for Qt::OffsetFromUTC will be Qt::UTC

   double QwtDate::toDouble (const QDateTime &dateTime) [static]
       Translate from QDateTime to double

       Parameters:
           dateTime Datetime value

       Returns:
           Number of milliseconds since 1970-01-01T00:00:00 UTC has passed.

       See Also:
           toDateTime(), QDateTime::toMSecsSinceEpoch()

       Warning:
           For values very far below or above 1970-01-01 UTC rounding errors will happen due to
           the limited significance of a double.

   QString QwtDate::toString (const QDateTime &dateTime, const QString &format,
       Week0Typeweek0Type) [static]
       Translate a datetime into a string

       Beside the format expressions documented in QDateTime::toString() the following
       expressions are supported:

       · w
          week number: ( 1 - 53 )

       · ww
          week number with a leading zero ( 01 - 53 )

       Parameters:
           dateTime Datetime value
           format Format string
           week0Type Specification of week 0

       Returns:
           Datetime string

       See Also:
           QDateTime::toString(), weekNumber(), QwtDateScaleDraw

   int QwtDate::utcOffset (const QDateTime &dateTime) [static]
       Offset in seconds from Coordinated Universal Time

       The offset depends on the time specification of dateTime:

       · Qt::UTC 0, dateTime has no offset

       · Qt::OffsetFromUTC returns dateTime.utcOffset()

       · Qt::LocalTime: number of seconds from the UTC

       For Qt::LocalTime the offset depends on the timezone and daylight savings.

       Parameters:
           dateTime Datetime value

       Returns:
           Offset in seconds

   int QwtDate::weekNumber (const QDate &date, Week0Typetype) [static]
       Find the week number of a date

       · QwtDate::FirstThursday
          Corresponding to ISO 8601 ( see QDate::weekNumber() ).

       · QwtDate::FirstDay
          Number of weeks that have begun since dateOfWeek0().

       Parameters:
           date Date
           type Option how to identify the first week

       Returns:
           Week number, starting with 1

Author

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