QDate Class

The QDate class provides date functions. More...

Header:	#include <QDate>
qmake:	QT += core

• List of all members, including inherited members
• Obsolete members

Note: All functions in this class are reentrant.

Public Types

enum	MonthNameType { DateFormat, StandaloneFormat }

Public Functions

	QDate(int y, int m, int d)
	QDate()
QDate	addDays(qint64 ndays) const
QDate	addMonths(int nmonths, QCalendar cal) const
QDate	addMonths(int nmonths) const
QDate	addYears(int nyears, QCalendar cal) const
QDate	addYears(int nyears) const
int	day(QCalendar cal) const
int	day() const
int	dayOfWeek(QCalendar cal) const
int	dayOfWeek() const
int	dayOfYear(QCalendar cal) const
int	dayOfYear() const
int	daysInMonth(QCalendar cal) const
int	daysInMonth() const
int	daysInYear(QCalendar cal) const
int	daysInYear() const
qint64	daysTo(const QDate &d) const
QDateTime	endOfDay(Qt::TimeSpec spec = Qt::LocalTime, int offsetSeconds = 0) const
QDateTime	endOfDay(const QTimeZone &zone) const
void	getDate(int *year, int *month, int *day) const
bool	isNull() const
bool	isValid() const
int	month(QCalendar cal) const
int	month() const
bool	setDate(int year, int month, int day)
bool	setDate(int year, int month, int day, QCalendar cal)
QDateTime	startOfDay(Qt::TimeSpec spec = Qt::LocalTime, int offsetSeconds = 0) const
QDateTime	startOfDay(const QTimeZone &zone) const
qint64	toJulianDay() const
QString	toString(const QString &format) const
QString	toString(Qt::DateFormat format = Qt::TextDate) const
QString	toString(QStringView format) const
int	weekNumber(int *yearNumber = nullptr) const
int	year(QCalendar cal) const
int	year() const
bool	operator!=(const QDate &d) const
bool	operator<(const QDate &d) const
bool	operator<=(const QDate &d) const
bool	operator==(const QDate &d) const
bool	operator>(const QDate &d) const
bool	operator>=(const QDate &d) const

Static Public Members

QDate	currentDate()
QDate	fromJulianDay(qint64 jd)
QDate	fromString(const QString &string, Qt::DateFormat format = Qt::TextDate)
QDate	fromString(const QString &string, const QString &format)
QDate	fromString(const QString &string, const QString &format, QCalendar cal)
bool	isLeapYear(int year)
bool	isValid(int year, int month, int day)

Related Non-Members

QDataStream &	operator<<(QDataStream &out, const QDate &date)
QDataStream &	operator>>(QDataStream &in, QDate &date)

Detailed Description

A QDate object represents a particular date. This can be expressed as a calendar date, i.e. year, month, and day numbers, in the proleptic Gregorian calendar.

A QDate object is typically created by giving the year, month, and day numbers explicitly. Note that QDate interprets year numbers less than 100 as presented, i.e., as years 1 through 99, without adding any offset. The static function currentDate() creates a QDate object containing the date read from the system clock. An explicit date can also be set using setDate(). The fromString() function returns a QDate given a string and a date format which is used to interpret the date within the string.

The year(), month(), and day() functions provide access to the year, month, and day numbers. Also, dayOfWeek() and dayOfYear() functions are provided. The same information is provided in textual format by toString(). The day and month numbers can be mapped to names using QLocale.

QDate provides a full set of operators to compare two QDate objects where smaller means earlier, and larger means later.

You can increment (or decrement) a date by a given number of days using addDays(). Similarly you can use addMonths() and addYears(). The daysTo() function returns the number of days between two dates.

The daysInMonth() and daysInYear() functions return how many days there are in this date's month and year, respectively. The isLeapYear() function indicates whether a date is in a leap year.

Remarks

No Year 0

There is no year 0. Dates in that year are considered invalid. The year -1 is the year "1 before Christ" or "1 before current era." The day before 1 January 1 CE, QDate(1, 1, 1), is 31 December 1 BCE, QDate(-1, 12, 31).

Range of Valid Dates

Dates are stored internally as a Julian Day number, an integer count of every day in a contiguous range, with 24 November 4714 BCE in the Gregorian calendar being Julian Day 0 (1 January 4713 BCE in the Julian calendar). As well as being an efficient and accurate way of storing an absolute date, it is suitable for converting a date into other calendar systems such as Hebrew, Islamic or Chinese. The Julian Day number can be obtained using QDate::toJulianDay() and can be set using QDate::fromJulianDay().

The range of dates able to be stored by QDate as a Julian Day number is for technical reasons limited to between -784350574879 and 784354017364, which means from before 2 billion BCE to after 2 billion CE.

See also QTime, QDateTime, QCalendar, QDateTime::YearRange, QDateEdit, QDateTimeEdit, and QCalendarWidget.

Member Type Documentation

enum QDate::MonthNameType

This enum describes the types of the string representation used for the month name.

Constant	Value	Description
QDate::DateFormat	0	This type of name can be used for date-to-string formatting.
QDate::StandaloneFormat	1	This type is used when you need to enumerate months or weekdays. Usually standalone names are represented in singular forms with capitalized first letter.

This enum was introduced or modified in Qt 4.5.

Member Function Documentation

Returns the date as a string. The format parameter determines the format of the result string.

These expressions may be used:

Expression	Output
d	The day as a number without a leading zero (1 to 31)
dd	The day as a number with a leading zero (01 to 31)
ddd	The abbreviated localized day name (e.g. 'Mon' to 'Sun'). Uses the system locale to localize the name, i.e. QLocale::system().
dddd	The long localized day name (e.g. 'Monday' to 'Sunday'). Uses the system locale to localize the name, i.e. QLocale::system().
M	The month as a number without a leading zero (1 to 12)
MM	The month as a number with a leading zero (01 to 12)
MMM	The abbreviated localized month name (e.g. 'Jan' to 'Dec'). Uses the system locale to localize the name, i.e. QLocale::system().
MMMM	The long localized month name (e.g. 'January' to 'December'). Uses the system locale to localize the name, i.e. QLocale::system().
yy	The year as a two digit number (00 to 99)
yyyy	The year as a four digit number. If the year is negative, a minus sign is prepended, making five characters.

Any sequence of characters enclosed in single quotes will be included verbatim in the output string (stripped of the quotes), even if it contains formatting characters. Two consecutive single quotes ("''") are replaced by a single quote in the output. All other characters in the format string are included verbatim in the output string.

Formats without separators (e.g. "ddMM") are supported but must be used with care, as the resulting strings aren't always reliably readable (e.g. if "dM" produces "212" it could mean either the 2nd of December or the 21st of February).

Example format strings (assuming that the QDate is the 20 July 1969):

Format	Result
dd.MM.yyyy	20.07.1969
ddd MMMM d yy	Sun July 20 69
'The day is' dddd	The day is Sunday

If the datetime is invalid, an empty string will be returned.

See also fromString(), QDateTime::toString(), QTime::toString(), and QLocale::toString().

Returns the end-moment of the day. Usually, this is one millisecond before the midnight at the end of the day: however, if a time-zone transition causes the given date to skip over that midnight (e.g. a DST spring-forward skipping from just before 23:00 to the start of the next day), the actual latest time in the day is returned. This can only arise when the start-moment is specified in terms of a time-zone (by passing its QTimeZone as zone) or in terms of local time (by passing Qt::LocalTime as spec; this is its default).

The offsetSeconds is ignored unless spec is Qt::OffsetFromUTC, when it gives the implied zone's offset from UTC. As UTC and such zones have no transitions, the end of the day is QTime(23, 59, 59, 999) in these cases.

In the rare case of a date that was entirely skipped (this happens when a zone east of the international date-line switches to being west of it), the return shall be invalid. Passing Qt::TimeZone as spec (instead of passing a QTimeZone) will also produce an invalid result, as shall dates that end outside the range representable by QDateTime.

This documentation was introduced in Qt 5.14.

See also startOfDay().

Returns the start-moment of the day. Usually, this shall be midnight at the start of the day: however, if a time-zone transition causes the given date to skip over that midnight (e.g. a DST spring-forward skipping from the end of the previous day to 01:00 of the new day), the actual earliest time in the day is returned. This can only arise when the start-moment is specified in terms of a time-zone (by passing its QTimeZone as zone) or in terms of local time (by passing Qt::LocalTime as spec; this is its default).

The offsetSeconds is ignored unless spec is Qt::OffsetFromUTC, when it gives the implied zone's offset from UTC. As UTC and such zones have no transitions, the start of the day is QTime(0, 0) in these cases.

In the rare case of a date that was entirely skipped (this happens when a zone east of the international date-line switches to being west of it), the return shall be invalid. Passing Qt::TimeZone as spec (instead of passing a QTimeZone) or passing an invalid time-zone as zone will also produce an invalid result, as shall dates that start outside the range representable by QDateTime.

This documentation was introduced in Qt 5.14.

See also endOfDay().

QDate::QDate(int y, int m, int d)

Constructs a date with year y, month m and day d.

The date is understood in terms of the Gregorian calendar. If the specified date is invalid, the date is not set and isValid() returns false.

Warning: Years 1 to 99 are interpreted as is. Year 0 is invalid.

See also isValid() and QCalendar::dateFromParts().

QDate::QDate()

Constructs a null date. Null dates are invalid.

See also isNull() and isValid().

QDate QDate::addDays(qint64 ndays) const

Returns a QDate object containing a date ndays later than the date of this object (or earlier if ndays is negative).

Returns a null date if the current date is invalid or the new date is out of range.

See also addMonths(), addYears(), and daysTo().

QDate QDate::addMonths(int nmonths, QCalendar cal) const

Returns a QDate object containing a date nmonths later than the date of this object (or earlier if nmonths is negative).

Uses cal as calendar, if supplied, else the Gregorian calendar.

Note: If the ending day/month combination does not exist in the resulting month/year, this function will return a date that is the latest valid date in the selected month.

See also addDays() and addYears().

QDate QDate::addMonths(int nmonths) const

This is an overloaded function.

QDate QDate::addYears(int nyears, QCalendar cal) const

Returns a QDate object containing a date nyears later than the date of this object (or earlier if nyears is negative).

Uses cal as calendar, if supplied, else the Gregorian calendar.

Note: If the ending day/month combination does not exist in the resulting year (e.g., for the Gregorian calendar, if the date was Feb 29 and the final year is not a leap year), this function will return a date that is the latest valid date in the given month (in the example, Feb 28).

See also addDays() and addMonths().

QDate QDate::addYears(int nyears) const

This is an overloaded function.

[static] QDate QDate::currentDate()

Returns the current date, as reported by the system clock.

See also QTime::currentTime() and QDateTime::currentDateTime().

int QDate::day(QCalendar cal) const

Returns the day of the month for this date.

Uses cal as calendar if supplied, else the Gregorian calendar (for which the return ranges from 1 to 31). Returns 0 if the date is invalid.

See also year(), month(), and dayOfWeek().

int QDate::day() const

This is an overloaded function.

int QDate::dayOfWeek(QCalendar cal) const

Returns the weekday (1 = Monday to 7 = Sunday) for this date.

Uses cal as calendar if supplied, else the Gregorian calendar. Returns 0 if the date is invalid. Some calendars may give special meaning (e.g. intercallary days) to values greater than 7.

See also day(), dayOfYear(), and Qt::DayOfWeek.

int QDate::dayOfWeek() const

This is an overloaded function.

int QDate::dayOfYear(QCalendar cal) const

Returns the day of the year (1 for the first day) for this date.

Uses cal as calendar if supplied, else the Gregorian calendar. Returns 0 if either the date or the first day of its year is invalid.

See also day() and dayOfWeek().

int QDate::dayOfYear() const

This is an overloaded function.

int QDate::daysInMonth(QCalendar cal) const

Returns the number of days in the month for this date.

Uses cal as calendar if supplied, else the Gregorian calendar (for which the result ranges from 28 to 31). Returns 0 if the date is invalid.

See also day() and daysInYear().

int QDate::daysInMonth() const

This is an overloaded function.

int QDate::daysInYear(QCalendar cal) const

Returns the number of days in the year for this date.

Uses cal as calendar if supplied, else the Gregorian calendar (for which the result is 365 or 366). Returns 0 if the date is invalid.

See also day() and daysInMonth().

int QDate::daysInYear() const

This is an overloaded function.

qint64 QDate::daysTo(const QDate &d) const

Returns the number of days from this date to d (which is negative if d is earlier than this date).

Returns 0 if either date is invalid.

Example:

QDate d1(1995, 5, 17);  // May 17, 1995
QDate d2(1995, 5, 20);  // May 20, 1995
d1.daysTo(d2);          // returns 3
d2.daysTo(d1);          // returns -3

See also addDays().

[static] QDate QDate::fromJulianDay(qint64 jd)

Converts the Julian day jd to a QDate.

See also toJulianDay().

[static] QDate QDate::fromString(const QString &string, Qt::DateFormat format = Qt::TextDate)

Returns the QDate represented by the string, using the format given, or an invalid date if the string cannot be parsed.

Note for Qt::TextDate: It is recommended that you use the English short month names (e.g. "Jan"). Although localized month names can also be used, they depend on the user's locale settings.

See also toString() and QLocale::toDate().

[static] QDate QDate::fromString(const QString &string, const QString &format)

This is an overloaded function.

[static] QDate QDate::fromString(const QString &string, const QString &format, QCalendar cal)

Returns the QDate represented by the string, using the format given, or an invalid date if the string cannot be parsed.

Uses cal as calendar if supplied, else the Gregorian calendar. Ranges of values in the format descriptions below are for the latter; they may be different for other calendars.

These expressions may be used for the format:

Expression	Output
d	The day as a number without a leading zero (1 to 31)
dd	The day as a number with a leading zero (01 to 31)
ddd	The abbreviated localized day name (e.g. 'Mon' to 'Sun'). Uses the system locale to localize the name, i.e. QLocale::system().
dddd	The long localized day name (e.g. 'Monday' to 'Sunday'). Uses the system locale to localize the name, i.e. QLocale::system().
M	The month as a number without a leading zero (1 to 12)
MM	The month as a number with a leading zero (01 to 12)
MMM	The abbreviated localized month name (e.g. 'Jan' to 'Dec'). Uses the system locale to localize the name, i.e. QLocale::system().
MMMM	The long localized month name (e.g. 'January' to 'December'). Uses the system locale to localize the name, i.e. QLocale::system().
yy	The year as a two digit number (00 to 99)
yyyy	The year as a four digit number, possibly plus a leading minus sign for negative years.

Note: Unlike the other version of this function, day and month names must be given in the user's local language. It is only possible to use the English names if the user's language is English.

All other input characters will be treated as text. Any sequence of characters that are enclosed in single quotes will also be treated as text and will not be used as an expression. For example:

QDate date = QDate::fromString("1MM12car2003", "d'MM'MMcaryyyy");
// date is 1 December 2003

If the format is not satisfied, an invalid QDate is returned. The expressions that don't expect leading zeroes (d, M) will be greedy. This means that they will use two digits even if this will put them outside the accepted range of values and leaves too few digits for other sections. For example, the following format string could have meant January 30 but the M will grab two digits, resulting in an invalid date:

QDate date = QDate::fromString("130", "Md"); // invalid

For any field that is not represented in the format the following defaults are used:

Field	Default value
Year	1900
Month	1
Day	1

The following examples demonstrate the default values:

QDate::fromString("1.30", "M.d");           // January 30 1900
QDate::fromString("20000110", "yyyyMMdd");  // January 10, 2000
QDate::fromString("20000110", "yyyyMd");    // January 10, 2000

See also toString(), QDateTime::fromString(), QTime::fromString(), and QLocale::toDate().

void QDate::getDate(int *year, int *month, int *day) const

Extracts the date's year, month, and day, and assigns them to *year, *month, and *day. The pointers may be null.

Returns 0 if the date is invalid.

Note: In Qt versions prior to 5.7, this function is marked as non-const.

This function was introduced in Qt 4.5.

See also year(), month(), day(), isValid(), and QCalendar::partsFromDate().

[static] bool QDate::isLeapYear(int year)

Returns true if the specified year is a leap year in the Gregorian calendar; otherwise returns false.

See also QCalendar::isLeapYear().

bool QDate::isNull() const

Returns true if the date is null; otherwise returns false. A null date is invalid.

Note: The behavior of this function is equivalent to isValid().

See also isValid().

bool QDate::isValid() const

Returns true if this date is valid; otherwise returns false.

See also isNull() and QCalendar::isDateValid().

[static] bool QDate::isValid(int year, int month, int day)

This is an overloaded function.

Returns true if the specified date (year, month, and day) is valid in the Gregorian calendar; otherwise returns false.

Example:

QDate::isValid(2002, 5, 17);  // true
QDate::isValid(2002, 2, 30);  // false (Feb 30 does not exist)
QDate::isValid(2004, 2, 29);  // true (2004 is a leap year)
QDate::isValid(2000, 2, 29);  // true (2000 is a leap year)
QDate::isValid(2006, 2, 29);  // false (2006 is not a leap year)
QDate::isValid(2100, 2, 29);  // false (2100 is not a leap year)
QDate::isValid(1202, 6, 6);   // true (even though 1202 is pre-Gregorian)

See also isNull(), setDate(), and QCalendar::isDateValid().

int QDate::month(QCalendar cal) const

Returns the month-number for the date.

Numbers the months of the year starting with 1 for the first. Uses cal as calendar if supplied, else the Gregorian calendar, for which the month numbering is as follows:

• 1 = "January"
• 2 = "February"
• 3 = "March"
• 4 = "April"
• 5 = "May"
• 6 = "June"
• 7 = "July"
• 8 = "August"
• 9 = "September"
• 10 = "October"
• 11 = "November"
• 12 = "December"

Returns 0 if the date is invalid. Note that some calendars may have more than 12 months in some years.

See also year() and day().

int QDate::month() const

This is an overloaded function.

bool QDate::setDate(int year, int month, int day)

Sets this to represent the date, in the Gregorian calendar, with the given year, month and day numbers. Returns true if the resulting date is valid, otherwise it sets this to represent an invalid date and returns false.

This function was introduced in Qt 4.2.

See also isValid() and QCalendar::dateFromParts().

bool QDate::setDate(int year, int month, int day, QCalendar cal)

Sets this to represent the date, in the given calendar cal, with the given year, month and day numbers. Returns true if the resulting date is valid, otherwise it sets this to represent an invalid date and returns false.

This function was introduced in Qt 5.14.

See also isValid() and QCalendar::dateFromParts().

qint64 QDate::toJulianDay() const

Converts the date to a Julian day.

See also fromJulianDay().

QString QDate::toString(Qt::DateFormat format = Qt::TextDate) const

This is an overloaded function.

Returns the date as a string. The format parameter determines the format of the string.

If the format is Qt::TextDate, the string is formatted in the default way. The day and month names will be localized names using the system locale, i.e. QLocale::system(). An example of this formatting is "Sat May 20 1995".

If the format is Qt::ISODate, the string format corresponds to the ISO 8601 extended specification for representations of dates and times, taking the form yyyy-MM-dd, where yyyy is the year, MM is the month of the year (between 01 and 12), and dd is the day of the month between 01 and 31.

If the format is Qt::SystemLocaleShortDate or Qt::SystemLocaleLongDate, the string format depends on the locale settings of the system. Identical to calling QLocale::system().toString(date, QLocale::ShortFormat) or QLocale::system().toString(date, QLocale::LongFormat).

If the format is Qt::DefaultLocaleShortDate or Qt::DefaultLocaleLongDate, the string format depends on the default application locale. This is the locale set with QLocale::setDefault(), or the system locale if no default locale has been set. Identical to calling QLocale().toString(date, QLocale::ShortFormat) or QLocale().toString(date, QLocale::LongFormat).

If the format is Qt::RFC2822Date, the string is formatted in an RFC 2822 compatible way. An example of this formatting is "20 May 1995".

If the date is invalid, an empty string will be returned.

Warning: The Qt::ISODate format is only valid for years in the range 0 to 9999. This restriction may apply to locale-aware formats as well, depending on the locale settings.

See also fromString() and QLocale::toString().

int QDate::weekNumber(int *yearNumber = nullptr) const

Returns the ISO 8601 week number (1 to 53).

Returns 0 if the date is invalid. Otherwise, returns the week number for the date. If yearNumber is not nullptr (its default), stores the year as *yearNumber.

In accordance with ISO 8601, each week falls in the year to which most of its days belong, in the Gregorian calendar. As ISO 8601's week starts on Monday, this is the year in which the week's Thursday falls. Most years have 52 weeks, but some have 53.

Note: *yearNumber is not always the same as year(). For example, 1 January 2000 has week number 52 in the year 1999, and 31 December 2002 has week number 1 in the year 2003.

See also isValid().

int QDate::year(QCalendar cal) const

Returns the year of this date.

Uses cal as calendar, if supplied, else the Gregorian calendar.

Returns 0 if the date is invalid. For some calendars, dates before their first year may all be invalid.

If using a calendar which has a year 0, check using isValid() if the return is 0. Such calendars use negative year numbers in the obvious way, with year 1 preceded by year 0, in turn preceded by year -1 and so on.

Some calendars, despite having no year 0, have a conventional numbering of the years before their first year, counting backwards from 1. For example, in the proleptic Gregorian calendar, successive years before 1 CE (the first year) are identified as 1 BCE, 2 BCE, 3 BCE and so on. For such calendars, negative year numbers are used to indicate these years before year 1, with -1 indicating the year before 1.

See also month(), day(), QCalendar::hasYearZero(), and QCalendar::isProleptic().

int QDate::year() const

This is an overloaded function.

bool QDate::operator!=(const QDate &d) const

Returns true if this date is different from d; otherwise returns false.

bool QDate::operator<(const QDate &d) const

Returns true if this date is earlier than d; otherwise returns false.

bool QDate::operator<=(const QDate &d) const

Returns true if this date is earlier than or equal to d; otherwise returns false.

bool QDate::operator==(const QDate &d) const

Returns true if this date is equal to d; otherwise returns false.

bool QDate::operator>(const QDate &d) const

Returns true if this date is later than d; otherwise returns false.

bool QDate::operator>=(const QDate &d) const

Returns true if this date is later than or equal to d; otherwise returns false.