QDate Class

The QDate class provides date functions. More...

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

Note: All functions in this class are reentrant.

Public Types

enum MonthNameType { DateFormat, StandaloneFormat }

Public Functions

QDate(int y, int m, int d)
QDate addDays(qint64 ndays) const
QDate addMonths(int nmonths) const
QDate addYears(int nyears) const
int day() const
int dayOfWeek() const
int dayOfYear() const
int daysInMonth() const
int daysInYear() const
qint64 daysTo(const QDate &d) const
void getDate(int *year, int *month, int *day) const
int month() const
bool setDate(int year, int month, int day)
int weekNumber(int *yearNumber = nullptr) const
int year() const

Static Public Members

bool isValid(int year, int month, int day)
QDataStream &operator<<(QDataStream &out, const QDate &date)
QDataStream &operator>>(QDataStream &in, QDate &date)

Detailed Description

A QDate object encodes a calendar date, i.e. year, month, and day numbers, in the proleptic Gregorian calendar by default. 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.

A QDate object is typically created by giving the year, month, and day numbers explicitly. Note that QDate interprets two digit years as presented, i.e., as years 0 through 99, without adding any offset. A QDate can also be constructed with the static function currentDate(), which creates a QDate object containing the system clock's date. 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 the toString(), shortDayName(), longDayName(), shortMonthName(), and longMonthName() functions.

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, QDateEdit, QDateTimeEdit, and QCalendarWidget.

Member Type Documentation

enum QDate::MonthNameType

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

ConstantValueDescription
QDate::DateFormat0This type of name can be used for date-to-string formatting.
QDate::StandaloneFormat1This 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

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

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

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().

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) const

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

See also addDays() and addYears().

QDate QDate::addYears(int nyears) const

Returns a QDate object containing a date nyears later than the date of this object (or earlier if nyears 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 also addDays() and addMonths().

int QDate::day() const

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

Returns 0 if the date is invalid.

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

int QDate::dayOfWeek() const

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

Returns 0 if the date is invalid.

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

int QDate::dayOfYear() const

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

Returns 0 if the date is invalid.

See also day() and dayOfWeek().

int QDate::daysInMonth() const

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

Returns 0 if the date is invalid.

See also day() and daysInYear().

int QDate::daysInYear() const

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

Returns 0 if the date is invalid.

See also day() and daysInMonth().

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().

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(), and isValid().

[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; 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() and setDate().

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"

Returns 0 if the date is invalid.

See also year() and day().

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

Sets the date's year, month, and day. Returns true if the date is valid; otherwise returns false.

If the specified date is invalid, the QDate object is set to be invalid.

This function was introduced in Qt 4.2.

See also isValid().

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

Returns the week number (1 to 53), and stores the year in *yearNumber unless yearNumber 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 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() const

Returns the year of this date. Negative numbers indicate years before 1 CE, such that year -44 is 44 BCE.

Returns 0 if the date is invalid.

See also month() and day().

Related Non-Members

QDataStream &QDate::operator<<(QDataStream &out, const QDate &date)

Writes the date to stream out.

See also Serializing Qt Data Types.

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

Reads a date from stream in into the date.

See also Serializing Qt Data Types.