QDate Class

Member Function Documentation

Constructs a QDate representing the same date as date. This allows for easy interoperability between the Standard Library calendaring classes and Qt datetime classes.

For example:

// 23 April 2012:
QDate date = std::chrono::year_month_day(std::chrono::year(2012),
                                         std::chrono::month(4),
                                         std::chrono::day(23));

// Same, under `using std::chrono` convenience:
QDate dateWithLiterals1 = 23 / April / 2012y;
QDate dateWithLiterals2 = 2012y / April / 23;

// Last day of February 2000
QDate lastDayFeb2020 = 2000y / February / last;

// First Monday of January 2020:
QDate firstMonday = 2020y / January / Monday[0];

// Last Monday of January 2020:
QDate lastMonday = 2020y / January / Monday[last];

This function was introduced in Qt 6.4.

Returns the date as a string. The format parameter determines the format of the result string. If cal is supplied, it determines the calendar used to represent the date; it defaults to Gregorian. Prior to Qt 5.14, there was no cal parameter and the Gregorian calendar was always used.

These expressions may be used in the format parameter:

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):

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

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

[constexpr] QDate::QDate()

Constructs a null date. Null dates are invalid.

See also isNull() and isValid().

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.

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

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().

[since 6.4] QDate QDate::addDuration(std::chrono::days 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.

This function was introduced in Qt 6.4.

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.

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.

See also addDays() and addMonths().

QDate QDate::addYears(int nyears) const

This is an overloaded function.

[static] QDate QDate::currentDate()

Returns the system clock's current date.

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(), dayOfWeek(), and QCalendar::partsFromDate().

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(), QCalendar::dayOfWeek(), 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(), dayOfWeek(), and QCalendar::daysInYear().

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(), daysInYear(), QCalendar::daysInMonth(), QCalendar::maximumDaysInMonth(), and QCalendar::minimumDaysInMonth().

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(), daysInMonth(), QCalendar::daysInYear(), and QCalendar::maximumMonthsInYear().

int QDate::daysInYear() const

This is an overloaded function.

qint64 QDate::daysTo(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().

QDateTime QDate::endOfDay(const QTimeZone &zone) const

Returns the end-moment of the day.

When a day ends depends on a how time is described: each day starts and ends earlier for those in time-zones further west and later for those in time-zones further east. The time representation to use can be specified by an optional time zone. The default time representation is the system's local time.

Usually, the end of the day is one millisecond before the midnight, 24:00: however, if a time-zone transition causes the given date to skip over that moment (e.g. a DST spring-forward skipping over 23:00 and the following hour), the actual latest time in the day is returned. This can only arise when the time representation is a time-zone or local time.

When zone has a timeSpec() of Qt::OffsetFromUTC or Qt::UTC, the time representation has no transitions so the end of the day is QTime(23, 59, 59, 999).

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 an invalid time-zone as zone will also produce an invalid result, as shall dates that end outside the range representable by QDateTime.

See also startOfDay().

[since 6.5] QDateTime QDate::endOfDay() const

This is an overloaded function.

This function was introduced in Qt 6.5.

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

Converts the Julian day jd to a QDate.

See also toJulianDay().

[static constexpr noexcept, since 6.4] QDate QDate::fromStdSysDays(const std::chrono::sys_days &days)

Returns a QDate days days after January 1st, 1970 (the UNIX epoch). If days is negative, the returned date will be before the epoch.

This function was introduced in Qt 6.4.

See also toStdSysDays().

[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: only English month names (e.g. "Jan" in short form or "January" in long form) are recognized.

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

[static, since 6.0] QDate QDate::fromString(QStringView string, Qt::DateFormat format = Qt::TextDate)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static, since 6.0] QDate QDate::fromString(QStringView string, QStringView format, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static, since 6.0] QDate QDate::fromString(const QString &string, QStringView format, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.0.

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

This is an overloaded function.

[static, since 6.7] QDate QDate::fromString(QStringView string, QStringView format, int baseYear = QLocale::DefaultTwoDigitBaseYear)

This is an overloaded function.

Uses a default-constructed QCalendar.

This function was introduced in Qt 6.7.

[static, since 6.7] QDate QDate::fromString(QStringView string, QStringView format, int baseYear, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.7.

[static, since 6.7] QDate QDate::fromString(const QString &string, QStringView format, int baseYear = QLocale::DefaultTwoDigitBaseYear)

This is an overloaded function.

Uses a default-constructed QCalendar.

This function was introduced in Qt 6.7.

[static, since 6.0] QDate QDate::fromString(const QString &string, QStringView format, int baseYear, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static, since 6.7] QDate QDate::fromString(const QString &string, const QString &format, int baseYear = QLocale::DefaultTwoDigitBaseYear)

This is an overloaded function.

Uses a default-constructed QCalendar.

This function was introduced in Qt 6.7.

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

All other input characters will be treated as text. Any non-empty sequence of characters enclosed in single quotes will also be treated (stripped of the quotes) as text and not be interpreted as expressions. 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:

When format only specifies the last two digits of a year, the 100 years starting at baseYear are the candidates first considered. Prior to 6.7 there was no baseYear parameter and 1900 was always used. This is the default for baseYear, selecting a year from then to 1999. Passing 1976 as baseYear will select a year from 1976 through 2075, for example. When the format also includes month, day (of month) and day-of-week, these suffice to imply the century. In such a case, a matching date is selected in the nearest century to the one indicated by baseYear, prefering later over earlier. See QCalendar::matchCenturyToWeekday() and Date ambiguities for further details,

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

Date ambiguities

Different cultures use different formats for dates and, as a result, users may mix up the order in which date fields should be given. For example, "Wed 28-Nov-01" might mean either 2028 November 1st or the 28th of November, 2001 (each of which happens to be a Wednesday). Using format "ddd yy-MMM-dd" it shall be interpreted the first way, using "ddd dd-MMM-yy" the second. However, which the user meant may depend on the way the user normally writes dates, rather than the format the code was expecting.

The example considered above mixed up day of the month and a two-digit year. Similar confusion can arise over interchanging the month and day of the month, when both are given as numbers. In these cases, including a day of the week field in the date format can provide some redundancy, that may help to catch errors of this kind. However, as in the example above, this is not always effective: the interchange of two fields (or their meanings) may produce dates with the same day of the week.

Including a day of the week in the format can also resolve the century of a date specified using only the last two digits of its year. Unfortunately, when combined with a date in which the user (or other source of data) has mixed up two of the fields, this resolution can lead to finding a date which does match the format's reading but isn't the one intended by its author. Likewise, if the user simply gets the day of the week wrong, in an otherwise correct date, this can lead a date in a different century. In each case, finding a date in a different century can turn a wrongly-input date into a wildly different one.

The best way to avoid date ambiguities is to use four-digit years and months specified by name (whether full or abbreviated), ideally collected via user interface idioms that make abundantly clear to the user which part of the date they are selecting. Including a day of the week can also help by providing the means to check consistency of the data. Where data comes from the user, using a format supplied by a locale selected by the user, it is best to use a long format as short formats are more likely to use two-digit years. Of course, it is not always possible to control the format - data may come from a source you do not control, for example.

As a result of these possible sources of confusion, particularly when you cannot be sure an unambiguous format is in use, it is important to check that the result of reading a string as a date is not just valid but reasonable for the purpose for which it was supplied. If the result is outside some range of reasonable values, it may be worth getting the user to confirm their date selection, showing the date read from the string in a long format that does include month name and four-digit year, to make it easier for them to recognize any errors.

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.

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().

[constexpr] bool QDate::isNull() const

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

See also isValid().

[constexpr] 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(), day(), and QCalendar::partsFromDate().

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.

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.

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

QDateTime QDate::startOfDay(const QTimeZone &zone) const

Returns the start-moment of the day.

When a day starts depends on a how time is described: each day starts and ends earlier for those in time-zones further west and later for those in time-zones further east. The time representation to use can be specified by an optional time zone. The default time representation is the system's local time.

Usually, the start of the day is midnight, 00:00: however, if a time-zone transition causes the given date to skip over that midnight (e.g. a DST spring-forward skipping over the first hour of the day day), the actual earliest time in the day is returned. This can only arise when the time representation is a time-zone or local time.

When zone has a timeSpec() of is Qt::OffsetFromUTC or Qt::UTC, the time representation has no transitions so the start of the day is QTime(0, 0).

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 an invalid time-zone as zone will also produce an invalid result, as shall dates that start outside the range representable by QDateTime.

See also endOfDay().

[since 6.5] QDateTime QDate::startOfDay() const

This is an overloaded function.

This function was introduced in Qt 6.5.

[constexpr] qint64 QDate::toJulianDay() const

Converts the date to a Julian day.

See also fromJulianDay().

[constexpr noexcept] std::chrono::sys_days QDate::toStdSysDays() const

Returns the number of days between January 1st, 1970 (the UNIX epoch) and this date, represented as a std::chrono::sys_days object. If this date is before the epoch, the number of days will be negative.

See also fromStdSysDays() and daysTo().

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 in English. An example of this formatting is "Sat May 20 1995". For localized formatting, see QLocale::toString().

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::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.

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

QString QDate::toString(const QString &format) const

This is an overloaded function.

QString QDate::toString(QStringView format) const

This is an overloaded function.

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.

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(), QCalendar::isProleptic(), and QCalendar::partsFromDate().

int QDate::year() const

This is an overloaded function.