Provided by: libqwt-doc_6.1.3-1_all 
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, IntervalType intervalType) [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 (int year, Week0Type type) [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, IntervalType intervalType) [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 (double value, Qt::TimeSpec timeSpec = 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, Week0Type
week0Type) [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 )
As week 1 usually starts in the previous year a special rule is applied for formats, where
the year is expected to match the week number - even if the date belongs to the previous
year.
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, Week0Type type) [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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