Contents

• Public Types
• Public Functions
• Static Public Members
• Related Non-Members
• Detailed Description
• Use of Gregorian and Julian Calendars

Detailed Description

TheQDate class provides date functions.

AQDate object contains a calendar date, i.e. year, month, and day numbers, in the Gregorian calendar. (seeUse of Gregorian and Julian Calendars for dates prior to 15 October 1582). It can read the current date from the system clock. It provides functions for comparing dates, and for manipulating dates. For example, it is possible to add and subtract days, months, and years to dates.

AQDate object is typically created either by giving the year, month, and day numbers explicitly. Note thatQDate interprets two digit years as is, i.e., years 0 - 99. AQDate can also be constructed with the static functioncurrentDate(), which creates aQDate object containing the system clock's date. An explicit date can also be set usingsetDate(). ThefromString() function returns aQDate given a string and a date format which is used to interpret the date within the string.

Theyear(),month(), andday() functions provide access to the year, month, and day numbers. Also,dayOfWeek() anddayOfYear() functions are provided. The same information is provided in textual format by thetoString(),shortDayName(),longDayName(),shortMonthName(), andlongMonthName() functions.

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

You can increment (or decrement) a date by a given number of days usingaddDays(). Similarly you can useaddMonths() andaddYears(). ThedaysTo() function returns the number of days between two dates.

ThedaysInMonth() anddaysInYear() functions return how many days there are in this date's month and year, respectively. TheisLeapYear() function indicates whether a date is in a leap year.

Use of Gregorian and Julian Calendars

QDate uses the Gregorian calendar in all locales, beginning on the date 15 October 1582. For dates up to and including 4 October 1582, the Julian calendar is used. This means there is a 10-day gap in the internal calendar between the 4th and the 15th of October 1582. When you useQDateTime for dates in that epoch, the day after 4 October 1582 is 15 October 1582, and the dates in the gap are invalid.

The Julian to Gregorian changeover date used here is the date when the Gregorian calendar was first introduced, by Pope Gregory XIII. That change was not universally accepted and some localities only executed it at a later date (if at all).QDateTime doesn't take any of these historical facts into account. If an application must support a locale-specific dating system, it must do so on its own, remembering to convert the dates using the Julian day.

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 0001-01-01 is December 31st, 1 BCE.

Range of Valid Dates

The range of valid dates is from January 2nd, 4713 BCE, to sometime in the year 11 million CE. The Julian Day returned byQDate::toJulianDay() is a number in the contiguous range from 1 tooverflow, even acrossQDateTime's "date holes". It is suitable for use in applications that must convert aQDateTime to a date in another calendar system, e.g., Hebrew, Islamic or Chinese.

Member Type Documentation

enum QDate::MonthNameType

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

This enum was introduced or modified in Qt 4.5.

Member Function Documentation

QDate::QDate()

Constructs a null date. Null dates are invalid.

See alsoisNull() andisValid().

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

Constructs a date with yeary, monthm and dayd.

If the specified date is invalid, the date is not set andisValid() returns false. A date before 2 January 4713 B.C. is considered invalid.

Warning: Years 0 to 99 are interpreted as is, i.e., years 0-99.

See alsoisValid().

QDate QDate::addDays(int ndays) const

Returns aQDate object containing a datendays later than the date of this object (or earlier ifndays is negative).

See alsoaddMonths(),addYears(), anddaysTo().

QDate QDate::addMonths(int nmonths) const

Returns aQDate object containing a datenmonths later than the date of this object (or earlier ifnmonths is negative).

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.

Warning:QDate has a date hole around the days introducing the Gregorian calendar (the days 5 to 14 October 1582, inclusive, do not exist). If the calculation ends in one of those days,QDate will return either October 4 or October 15.

See alsoaddDays() andaddYears().

QDate QDate::addYears(int nyears) const

Returns aQDate object containing a datenyears later than the date of this object (or earlier ifnyears is negative).

Note:If the ending day/month combination does not exist in the resulting year (i.e., 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 (that is, Feb 28).

See alsoaddDays() andaddMonths().

[static]QDate QDate::currentDate()

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

See alsoQTime::currentTime() andQDateTime::currentDateTime().

int QDate::day() const

Returns the day of the month (1 to 31) of this date.

See alsoyear(),month(), anddayOfWeek().

int QDate::dayOfWeek() const

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

See alsoday(),dayOfYear(), andQt::DayOfWeek.

int QDate::dayOfYear() const

Returns the day of the year (1 to 365 or 366 on leap years) for this date.

See alsoday() anddayOfWeek().

int QDate::daysInMonth() const

Returns the number of days in the month (28 to 31) for this date.

See alsoday() anddaysInYear().

int QDate::daysInYear() const

Returns the number of days in the year (365 or 366) for this date.

See alsoday() anddaysInMonth().

int QDate::daysTo(constQDate & d) const

Returns the number of days from this date tod (which is negative ifd is earlier than this date).

Example:

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

See alsoaddDays().

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

Converts the Julian dayjd to aQDate.

See alsotoJulianDay().

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

Returns theQDate represented by thestring, using theformat given, or an invalid date if the string cannot be parsed.

Note forQt::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.

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

Returns theQDate represented by thestring, using theformat given, or an invalid date if the string cannot be parsed.

These expressions may be used for the format:

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 invalidQDate 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:

The following examples demonstrate the default values:

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

See alsoQDateTime::fromString(),QTime::fromString(),QDate::toString(),QDateTime::toString(), andQTime::toString().

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

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

This function was introduced in Qt 4.5.

See alsoyear(),month(),day(), andisValid().

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

Returns true if the specifiedyear is a leap year; otherwise returns false.

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 toisValid().

See alsoisValid().

bool QDate::isValid() const

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

See alsoisNull().

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

This is an overloaded function.

Returns true if the specified date (year,month, andday) is valid; otherwise returns false.

Example:

QDate::isValid(2002,5,17);// trueQDate::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 alsoisNull() andsetDate().

[static]QString QDate::longDayName(int weekday)

Returns the long version of the name of theweekday. The returned name is in normal type which can be used for date formatting.

See alsotoString(),shortDayName(),shortMonthName(), andlongMonthName().

[static]QString QDate::longDayName(int weekday,MonthNameType type)

Returns the long name of theweekday for the representation specified bytype.

The days are enumerated using the following convention:

• 1 = "Monday"
• 2 = "Tuesday"
• 3 = "Wednesday"
• 4 = "Thursday"
• 5 = "Friday"
• 6 = "Saturday"
• 7 = "Sunday"

The day names will be localized according to the system's default locale settings.

This function was introduced in Qt 4.5.

See alsotoString(),shortDayName(),shortMonthName(), andlongMonthName().

[static]QString QDate::longMonthName(int month)

Returns the long version of the name of themonth. The returned name is in normal type which can be used for date formatting.

See alsotoString(),shortMonthName(),shortDayName(), andlongDayName().

[static]QString QDate::longMonthName(int month,MonthNameType type)

Returns the long name of themonth for the representation specified bytype.

The months are enumerated using the following convention:

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

The month names will be localized according to the system's default locale settings.

This function was introduced in Qt 4.5.

See alsotoString(),shortMonthName(),shortDayName(), andlongDayName().

int QDate::month() const

Returns the number corresponding to the month of this date, using the following convention:

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

See alsoyear() andday().

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

Sets the date'syear,month, andday. Returns true if the date is valid; otherwise returns false.

If the specified date is invalid, theQDate object is set to be invalid. Any date before 2 January 4713 B.C. is considered invalid.

This function was introduced in Qt 4.2.

See alsoisValid().

[static]QString QDate::shortDayName(int weekday)

Returns the short version of the name of theweekday. The returned name is in normal type which can be used for date formatting.

See alsotoString(),longDayName(),shortMonthName(), andlongMonthName().

[static]QString QDate::shortDayName(int weekday,MonthNameType type)

Returns the short name of theweekday for the representation specified bytype.

The days are enumerated using the following convention:

• 1 = "Mon"
• 2 = "Tue"
• 3 = "Wed"
• 4 = "Thu"
• 5 = "Fri"
• 6 = "Sat"
• 7 = "Sun"

The day names will be localized according to the system's default locale settings.

This function was introduced in Qt 4.5.

See alsotoString(),shortMonthName(),longMonthName(), andlongDayName().

[static]QString QDate::shortMonthName(int month)

Returns the short version of the name of themonth. The returned name is in normal type which can be used for date formatting.

See alsotoString(),longMonthName(),shortDayName(), andlongDayName().

[static]QString QDate::shortMonthName(int month,MonthNameType type)

Returns the short name of themonth for the representation specified bytype.

The months are enumerated using the following convention:

• 1 = "Jan"
• 2 = "Feb"
• 3 = "Mar"
• 4 = "Apr"
• 5 = "May"
• 6 = "Jun"
• 7 = "Jul"
• 8 = "Aug"
• 9 = "Sep"
• 10 = "Oct"
• 11 = "Nov"
• 12 = "Dec"

The month names will be localized according to the system's default locale settings.

This function was introduced in Qt 4.5.

See alsotoString(),longMonthName(),shortDayName(), andlongDayName().

int QDate::toJulianDay() const

Converts the date to a Julian day.

See alsofromJulianDay().

QString QDate::toString(constQString & format) const

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

These expressions may be used:

All other input characters will be ignored. Any sequence of characters that are enclosed in singlequotes will be treated as text and not be used as an expression. Two consecutive singlequotes ("''") are replaced by a singlequote in the output.

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

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

Warning: TheQt::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 alsoQDateTime::toString() andQTime::toString().

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

This is an overloaded function.

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

If theformat isQt::TextDate, the string is formatted in the default way.QDate::shortDayName() andQDate::shortMonthName() are used to generate the string, so the day and month names will be localized names using the default locale from the system. An example of this formatting is "Sat May 20 1995".

If theformat isQt::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 theformat isQt::SystemLocaleShortDate orQt::SystemLocaleLongDate, the string format depends on the locale settings of the system. Identical to callingQLocale::system().toString(date,QLocale::ShortFormat) orQLocale::system().toString(date,QLocale::LongFormat).

If theformat isQt::DefaultLocaleShortDate orQt::DefaultLocaleLongDate, the string format depends on the default application locale. This is the locale set withQLocale::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 date is invalid, an empty string will be returned.

Warning: TheQt::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 alsoshortDayName() andshortMonthName().

int QDate::weekNumber(int * yearNumber = 0) const

Returns the week number (1 to 53), and stores the year in *yearNumber unlessyearNumber is null (the default).

Returns 0 if the date is invalid.

In accordance with ISO 8601, weeks start on Monday and the first Thursday of a year is always in week 1 of that year. Most years have 52 weeks, but some have 53.

*yearNumber is not always the same asyear(). 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 alsoisValid().

int QDate::year() const

Returns the year of this date. Negative numbers indicate years before 1 A.D. = 1 C.E., such that year -44 is 44 B.C.

See alsomonth() andday().

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

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

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

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

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

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

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

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

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

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

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

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

Related Non-Members

QDataStream &operator<<(QDataStream & out, constQDate & date)

Writes thedate to streamout.

See alsoSerializing Qt Data Types.

QDataStream &operator>>(QDataStream & in,QDate & date)

Reads a date from streamin into thedate.

See alsoSerializing Qt Data Types.