QwtDate man page
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
'The week with January 1.1 in it.'
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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