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QDate Class Reference
[QtCore module]

The QDate class provides date functions. More...

 #include <QDate>

Note: All functions in this class are reentrant.

• List of all members, including inherited members
• Obsolete members
• Qt 3 support members

Public Types

Public Functions

Static Public Members

Related Non-Members

Detailed Description

The QDate class provides date functions.

A QDate object contains a calendar date, i.e. year, month, and day numbers, in the Gregorian calendar. (see Use 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.

A QDate object is typically created either by giving the year, month, and day numbers explicitly. Note that QDate interprets two digit years as is, i.e., years 0 - 99. 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.

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 use QDateTime 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 by QDate::toJulianDay() is a number in the contiguous range from 1 to overflow, even across QDateTime's "date holes". It is suitable for use in applications that must convert a QDateTime to a date in another calendar system, e.g., Hebrew, Islamic or Chinese.

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.

This enum was introduced in Qt 4.5.

Member Function Documentation

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.

If the specified date is invalid, the date is not set and isValid() 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 also isValid().

QDate QDate::addDays ( int ndays ) const

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

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.

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 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().

QDate QDate::currentDate ()   [static]

This is an overloaded function.

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

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

int QDate::day () const

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

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

int QDate::dayOfWeek () const

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

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.

See also day() and dayOfWeek().

int QDate::daysInMonth () const

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

See also day() and daysInYear().

int QDate::daysInYear () const

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

See also day() and daysInMonth().

int 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).

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().

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

Converts the Julian day jd to a QDate.

See also toJulianDay().

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

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.

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

Returns the QDate represented by the string, using the format 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 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:

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 QDateTime::fromString(), QTime::fromString(), QDate::toString(), QDateTime::toString(), and QTime::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 also year(), month(), day(), and isValid().

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

Returns true if the specified year 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 to isValid().

See also isValid().

bool QDate::isValid () const

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

See also isNull().

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

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().

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

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

See also toString(), shortDayName(), shortMonthName(), and longMonthName().

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

Returns the long name of the weekday for the representation specified by type.

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 locale settings.

This function was introduced in Qt 4.5.

See also toString(), shortDayName(), shortMonthName(), and longMonthName().

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

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

See also toString(), shortMonthName(), shortDayName(), and longDayName().

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

Returns the long name of the month for the representation specified by type.

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 locale settings.

This function was introduced in Qt 4.5.

See also toString(), shortMonthName(), shortDayName(), and longDayName().

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 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. Any date before 2 January 4713 B.C. is considered invalid.

This function was introduced in Qt 4.2.

See also isValid().

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

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

See also toString(), longDayName(), shortMonthName(), and longMonthName().

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

Returns the short name of the weekday for the representation specified by type.

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 locale settings.

This function was introduced in Qt 4.5.

See also toString(), shortMonthName(), longMonthName(), and longDayName().

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

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

See also toString(), longMonthName(), shortDayName(), and longDayName().

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

Returns the short name of the month for the representation specified by type.

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 locale settings.

This function was introduced in Qt 4.5.

See also toString(), longMonthName(), shortDayName(), and longDayName().

int QDate::toJulianDay () const

Converts the date to a Julian day.

See also fromJulianDay().

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

Returns the date as a string. The format 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 the QDate is the 20 July 1969):

If the datetime 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 QDateTime::toString() and QTime::toString().

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. QDate::shortDayName() and QDate::shortMonthName() are used to generate the string, so the day and month names will be localized names. 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 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 shortDayName() and shortMonthName().

int QDate::weekNumber ( int * yearNumber = 0 ) 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 A.D. = 1 C.E., such that year -44 is 44 B.C.

See also month() and day().

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.

Related Non-Members

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

Writes the date to stream out.

See also Format of the QDataStream operators.

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

Reads a date from stream in into the date.

See also Format of the QDataStream operators.