A collection of methods around date/time values. More...

#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. More...

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

anonymous enum

Enumerator
JulianDayForEpoch	The Julian day of "The Epoch".

◆ IntervalType

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.

◆ Week0Type

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

◆ ceil()

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()

◆ dateOfWeek0()

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()

◆ floor()

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()

◆ maxDate()

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

◆ minDate()

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()

◆ toDateTime()

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

◆ toDouble()

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.

◆ toString()

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

◆ utcOffset()

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

◆ weekNumber()

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

Public Types

Static Public Member Functions

Detailed Description

Member Enumeration Documentation

◆ anonymous enum

◆ IntervalType

◆ Week0Type

Member Function Documentation

◆ ceil()

◆ dateOfWeek0()

◆ floor()

◆ maxDate()

◆ minDate()

◆ toDateTime()

◆ toDouble()

◆ toString()

◆ utcOffset()

◆ weekNumber()