QCalendar Class | Qt Core | Qt 6.10.1
Description: The QCalendar class describes calendar systems.

- Qt 6.10
- Qt Core
- C++ Classes
- QCalendar
- Qt 6.10.1 Reference Documentation

# QCalendar Class

The QCalendar class describes calendar systems. More...

Header: | `#include <QCalendar>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Types

`(since 6.2)` class | SystemId
enum class | System { Gregorian, Julian, Milankovic, Jalali, IslamicCivil }

## Public Functions

| QCalendar()
| QCalendar(QAnyStringView name)
| QCalendar(QCalendar::System system)
`(since 6.2)` | QCalendar(QCalendar::SystemId id)
QDate | dateFromParts(const QCalendar::YearMonthDay &parts) const
QDate | dateFromParts(int year, int month, int day) const
QString | dateTimeToString(QStringView format, const QDateTime &datetime, QDate dateOnly, QTime timeOnly, const QLocale &locale) const
int | dayOfWeek(QDate date) const
int | daysInMonth(int month, int year = Unspecified) const
int | daysInYear(int year) const
bool | hasYearZero() const
bool | isDateValid(int year, int month, int day) const
bool | isGregorian() const
bool | isLeapYear(int year) const
bool | isLunar() const
bool | isLuniSolar() const
bool | isProleptic() const
bool | isSolar() const
bool | isValid() const
`(since 6.7)` QDate | matchCenturyToWeekday(const QCalendar::YearMonthDay &parts, int dow) const
int | maximumDaysInMonth() const
int | maximumMonthsInYear() const
int | minimumDaysInMonth() const
QString | monthName(const QLocale &locale, int month, int year = Unspecified, QLocale::FormatType format = QLocale::LongFormat) const
int | monthsInYear(int year) const
QString | name() const
QCalendar::YearMonthDay | partsFromDate(QDate date) const
QString | standaloneMonthName(const QLocale &locale, int month, int year = Unspecified, QLocale::FormatType format = QLocale::LongFormat) const
QString | standaloneWeekDayName(const QLocale &locale, int day, QLocale::FormatType format = QLocale::LongFormat) const
QString | weekDayName(const QLocale &locale, int day, QLocale::FormatType format = QLocale::LongFormat) const

## Static Public Members

QStringList | availableCalendars()

## Detailed Description

A QCalendar object maps a year, month, and day-number to a specific day (ultimately identified by its Julian day number), using the rules of a particular system.

The default QCalendar() is a proleptic Gregorian calendar, which has no year zero. Other calendars may be supported by enabling suitable features or loading plugins. Calendars supported as features can be constructed by passing the QCalendar::System enumeration to the constructor. All supported calendars may be constructed by name, once they have been constructed. (Thus plugins instantiate their calendar backend to register it.) Built-in backends, accessible via QCalendar::System, are also always available by name. Calendars using custom backends may also be constructed using a unique ID allocated to the backend on construction.

A QCalendar value is immutable.

See also QDate and QDateTime.

## Member Type Documentation

### enum class QCalendar::System

This enumerated type is used to specify a choice of calendar system.

Constant | Value | Description
--- | --- | ---
`QCalendar::System::Gregorian` | `0` | The default calendar, used internationally.
`QCalendar::System::Julian` | `8` | An ancient Roman calendar.
`QCalendar::System::Milankovic` | `9` | A revised Julian calendar used by some Orthodox churches.
`QCalendar::System::Jalali` | `10` | The Solar Hijri calendar (also called Persian).
`QCalendar::System::IslamicCivil` | `11` | The (tabular) Islamic Civil calendar.

See also QCalendar and QCalendar::SystemId.

## Member Function Documentation

### `[explicit]` QCalendar::QCalendar()

### `[explicit]` QCalendar::QCalendar(QAnyStringView name)

### `[explicit]` QCalendar::QCalendar(QCalendar::System system)

Constructs a calendar object.

The choice of calendar to use may be indicated by system, using the enumeration QCalendar::System, or by name, using a string (either Unicode or Latin 1). Construction by name may depend on an instance of the given calendar being constructed by other means first. With no argument, the default constructor returns the Gregorian calendar.

Note: In Qt versions before 6.4, the constructor by name accepted only QStringView and QLatin1String, not QAnyStringView.

See also QCalendar, System, and isValid().

### QDate QCalendar::dateFromParts(const QCalendar::YearMonthDay &parts) const

### QDate QCalendar::dateFromParts(int year, int month, int day) const

Converts a year, month, and day to a QDate.

The year, month, and day may be passed as separate numbers or packaged together as the members of parts. Returns a QDate with the given year, month, and day of the month in this calendar, if there is one. Otherwise, including the case where any of the values is QCalendar::Unspecified, returns a QDate whose isNull() is true.

See also isDateValid() and partsFromDate().

### `[explicit, since 6.2]` QCalendar::QCalendar(QCalendar::SystemId id)

Constructs a calendar object.

When using a custom calendar implementation, its backend is allocated a unique ID when created; passing that as id to this constructor will get a QCalendar using that backend. This can be useful when the backend is not registered by name.

This is an overloaded function.

This function was introduced in Qt 6.2.

### `[static]` QStringList QCalendar::availableCalendars()

Returns a list of names of the available calendar systems.

These may be supplied by plugins or other code linked into an application, in addition to the ones provided by Qt, some of which are controlled by features.

### QString QCalendar::dateTimeToString(QStringView format, const QDateTime &datetime, QDate dateOnly, QTime timeOnly, const QLocale &locale) const

Returns a string representing a given date, time or date-time.

If datetime is valid, it is represented and format specifiers for both date and time fields are recognized; otherwise, if dateOnly is valid, it is represented and only format specifiers for date fields are recognized; finally, if timeOnly is valid, it is represented and only format specifiers for time fields are recognized. If none of these is valid, an empty string is returned.

See QDate::toString and QTime::toString() for the supported field specifiers. Characters in format that are recognized as field specifiers are replaced by text representing appropriate data from the date and/or time being represented. The texts to represent them may depend on the locale specified. Other charagers in format are copied verbatim into the returned string.

See also monthName(), weekDayName(), QDate::toString(), and QTime::toString().

### int QCalendar::dayOfWeek(QDate date) const

Returns the day of the week number for the given date.

Returns zero if the calendar is unable to represent the indicated date. Returns 1 for Monday through 7 for Sunday. Calendars with intercallary days may use other numbers to represent these.

See also partsFromDate() and Qt::DayOfWeek.

### int QCalendar::daysInMonth(int month, int year = Unspecified) const

Returns the number of days in the given month of the given year.

Months are numbered consecutively, starting with 1 for the first month of each year. If year is `Unspecified` (its default, if not passed), the month's greatest length in any year is returned.

See also maximumDaysInMonth() and minimumDaysInMonth().

### int QCalendar::daysInYear(int year) const

Returns the number of days in the given year.

Handling of `Unspecified` as year is undefined.

### bool QCalendar::hasYearZero() const

Returns `true` if this calendar has a year zero.

A calendar may represent years from its first year onwards but provide no way to describe years before its first; such a calendar has no year zero and is not proleptic.

A calendar which represents years before its first may number these years simply by following the usual integer counting, so that the year before the first is year zero, with negative-numbered years preceding this; such a calendar is proleptic and has a year zero. A calendar might also have a year zero (for example, the year of some great event, with subsequent years being the first year after that event, the second year after, and so on) without describing years before its year zero. Such a calendar would have a year zero without being proleptic.

Some calendars, however, represent years before their first by an alternate numbering; for example, the proleptic Gregorian calendar's first year is 1 CE and the year before it is 1 BCE, preceded by 2 BCE and so on. In this case, we use negative year numbers for this alternate numbering, with year -1 as the year before year 1, year -2 as the year before year -1 and so on. Such a calendar is proleptic but has no year zero.

See also isProleptic().

### bool QCalendar::isDateValid(int year, int month, int day) const

Returns `true` precisely if the given year, month, and day specify a valid date in this calendar.

Usually this means 1 <= month <= monthsInYear(year) and 1 <= day <= daysInMonth(month, year). However, calendars with intercallary days or months may complicate that.

### bool QCalendar::isGregorian() const

Returns `true` if this calendar object is the Gregorian calendar object used as default calendar by other Qt APIs, e.g. in QDate.

### bool QCalendar::isLeapYear(int year) const

Returns `true` if the given year is a leap year.

Since the year is not a whole number of days long, some years are longer than others. The difference may be a whole month or just a single day; the details vary between calendars.

See also isDateValid().

### bool QCalendar::isLunar() const

Returns `true` if this calendar is a lunar calendar.

A lunar calendar is one based primarily on the phases of the moon.

### bool QCalendar::isLuniSolar() const

Returns `true` if this calendar is luni-solar.

A luni-solar calendar expresses the phases of the moon but adapts itself to also keep track of the Sun's varying position in the sky, relative to the fixed stars.

### bool QCalendar::isProleptic() const

Returns `true` if this calendar is proleptic.

A proleptic calendar is able to describe years arbitrarily long before its first. These are represented by negative year numbers and possibly by a year zero.

See also hasYearZero().

### bool QCalendar::isSolar() const

Returns `true` if this calendar is solar.

A solar calendar is based primarily on the Sun's varying position in the sky, relative to the fixed stars.

### bool QCalendar::isValid() const

Returns true if this is a valid calendar object.

Constructing a calendar with an unrecognised calendar name may result in an invalid object. Use this method to check after creating a calendar by name.

### `[since 6.7]` QDate QCalendar::matchCenturyToWeekday(const QCalendar::YearMonthDay &parts, int dow) const

Adjusts the century of a date to match a given day of the week.

For use when given a date's day of week, day of month, month and last two digits of the year. Returns a QDate instance with the given dow as its dayOfWeek(), matching the given parts in month and day of the month. The returned QDate's year() shall differ from `parts.year` by a multiple of 100, preferring small multiples over larger and positive multiples over their negations.

If no date matches these conditions, an invalid QDate is returned: the day of week is incompatible with the other data given. This arises, for example, with the Gregorian calendar, whose 400-year cycle is a whole number of weeks long, so any given month and day of that month only ever falls, in years with a given last two digits, on four days of the week. (In the special case of February 29th at the turn of a century, when that is a leap year, only one day of the week is possible: Tuesday.)

This function was introduced in Qt 6.7.

### int QCalendar::maximumDaysInMonth() const

Returns the number of days in the longest month in the calendar, in any year.

See also daysInMonth() and minimumDaysInMonth().

### int QCalendar::maximumMonthsInYear() const

Returns the largest number of months that any year may contain.

See also monthName(), standaloneMonthName(), and monthsInYear().

### int QCalendar::minimumDaysInMonth() const

Returns the number of days in the shortest month in the calendar, in any year.

See also daysInMonth() and maximumDaysInMonth().

### QString QCalendar::monthName(const QLocale &locale, int month, int year = Unspecified, QLocale::FormatType format = QLocale::LongFormat) const

Returns a suitably localised name for a month.

The month is indicated by a number, with month = 1 meaning the first month of the year and subsequent months numbered accordingly. Returns an empty string if the month number is unrecognized.

The year may be Unspecified, in which case the mapping from numbers to names for a typical year's months should be used. Some calendars have leap months that aren't always at the end of the year; their mapping of month numbers to names may then depend on the placement of a leap month. Thus the year should normally be specified, if known.

The name is returned in the form that would normally be used in a full date, in the specified locale; the format determines how fully it shall be expressed (i.e. to what extent it is abbreviated).

See also standaloneMonthName(), maximumMonthsInYear(), and dateTimeToString().

### int QCalendar::monthsInYear(int year) const

Returns the number of months in the given year.

If year is `Unspecified`, returns the maximum number of months in a year.

See also maximumMonthsInYear().

### QString QCalendar::name() const

The primary name of this calendar.

The calendar may also be known by some aliases. A calendar instantiated by name may use such an alias, in which case its name() need not match the alias by which it was instantiated.

### QCalendar::YearMonthDay QCalendar::partsFromDate(QDate date) const

Converts a QDate to a year, month, and day of the month.

The returned structure's isValid() shall be false if the calendar is unable to represent the given date. Otherwise its year, month, and day members record the so-named parts of its representation.

See also dateFromParts(), isProleptic(), and hasYearZero().

### QString QCalendar::standaloneMonthName(const QLocale &locale, int month, int year = Unspecified, QLocale::FormatType format = QLocale::LongFormat) const

Returns a suitably localised standalone name for a month.

The month is indicated by a number, with month = 1 meaning the first month of the year and subsequent months numbered accordingly. Returns an empty string if the month number is unrecognized.

The year may be Unspecified, in which case the mapping from numbers to names for a typical year's months should be used. Some calendars have leap months that aren't always at the end of the year; their mapping of month numbers to names may then depend on the placement of a leap month. Thus the year should normally be specified, if known.

The name is returned in the form that would be used in isolation in the specified locale; the format determines how fully it shall be expressed (i.e. to what extent it is abbreviated).

See also monthName(), maximumMonthsInYear(), and dateTimeToString().

### QString QCalendar::standaloneWeekDayName(const QLocale &locale, int day, QLocale::FormatType format = QLocale::LongFormat) const

Returns a suitably localised standalone name for a day of the week.

The days of the week are numbered from 1 for Monday through 7 for Sunday. Some calendars may support higher numbers for other days (e.g. intercallary days, that are not part of any week). Returns an empty string if the day number is unrecognized.

The name is returned in the form that would be used in isolation (for example as a column heading in a calendar's tabular display of a month with successive weeks as rows) in the specified locale; the format determines how fully it shall be expressed (i.e. to what extent it is abbreviated).

See also weekDayName() and dayOfWeek().

### QString QCalendar::weekDayName(const QLocale &locale, int day, QLocale::FormatType format = QLocale::LongFormat) const

Returns a suitably localised name for a day of the week.

The days of the week are numbered from 1 for Monday through 7 for Sunday. Some calendars may support higher numbers for other days (e.g. intercallary days, that are not part of any week). Returns an empty string if the day number is unrecognized.

The name is returned in the form that would normally be used in a full date, in the specified locale; the format determines how fully it shall be expressed (i.e. to what extent it is abbreviated).

See also standaloneWeekDayName() and dayOfWeek().