Public Types | Static Public Member Functions | List of all members
QwtDate Class Reference

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

#include <qwt_date.h>

Public Types

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

Static Public Member Functions

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

Definition at line 42 of file qwt_date.h.

Member Enumeration Documentation

anonymous enum
Enumerator
JulianDayForEpoch 

The Julian day of "The Epoch".

Definition at line 102 of file qwt_date.h.

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.

Definition at line 75 of file qwt_date.h.

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.

Definition at line 49 of file qwt_date.h.

Member Function Documentation

QDateTime QwtDate::ceil ( const QDateTime &  dateTime,
IntervalType  intervalType 
)
static

Ceil a datetime according the interval type

Parameters
dateTimeDatetime value
intervalTypeInterval 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()

Definition at line 391 of file qwt_date.cpp.

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
yearYear
typeOption how to identify the first week
Returns
First day of week 0
See also
QLocale::firstDayOfWeek(), weekNumber()

Definition at line 610 of file qwt_date.cpp.

QDateTime QwtDate::floor ( const QDateTime &  dateTime,
IntervalType  intervalType 
)
static

Floor a datetime according the interval type

Parameters
dateTimeDatetime value
intervalTypeInterval 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()

Definition at line 493 of file qwt_date.cpp.

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

Definition at line 589 of file qwt_date.cpp.

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()

Definition at line 567 of file qwt_date.cpp.

QDateTime QwtDate::toDateTime ( double  value,
Qt::TimeSpec  timeSpec = Qt::UTC 
)
static

Translate from double to QDateTime

Parameters
valueNumber of milliseconds since the epoch, 1970-01-01T00:00:00 UTC
timeSpecTime specification
Returns
Datetime value
See also
toDouble(), QDateTime::setMSecsSinceEpoch()
Note
The return datetime for Qt::OffsetFromUTC will be Qt::UTC

Definition at line 329 of file qwt_date.cpp.

double QwtDate::toDouble ( const QDateTime &  dateTime)
static

Translate from QDateTime to double

Parameters
dateTimeDatetime 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.

Definition at line 366 of file qwt_date.cpp.

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
dateTimeDatetime value
formatFormat string
week0TypeSpecification of week 0
Returns
Datetime string
See also
QDateTime::toString(), weekNumber(), QwtDateScaleDraw

Definition at line 750 of file qwt_date.cpp.

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
dateTimeDatetime value
Returns
Offset in seconds

Definition at line 703 of file qwt_date.cpp.

int QwtDate::weekNumber ( const QDate &  date,
Week0Type  type 
)
static

Find the week number of a date

Parameters
dateDate
typeOption how to identify the first week
Returns
Week number, starting with 1

Definition at line 653 of file qwt_date.cpp.


The documentation for this class was generated from the following files:


plotjuggler
Author(s): Davide Faconti
autogenerated on Sat Jul 6 2019 03:44:18