Qt 4.3: QDate Class Reference

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# QDate Class Reference
[QtCore module]

The QDate class provides date functions. More...

     #include <QDate>

Note: All the functions in this class are reentrant.

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

### Public Functions

- QDate ()
- QDate ( int y, int m, int d )
- QDate addDays ( int 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
- int daysTo ( const QDate & d ) const
- bool isNull () const
- bool isValid () const
- int month () const
- bool setDate ( int year, int month, int day )
- int toJulianDay () const
- QString toString ( const QString & format ) const
- QString toString ( Qt::DateFormat format = Qt::TextDate ) const
- int weekNumber ( int * yearNumber = 0 ) 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 ( int jd )
- QDate fromString ( const QString & string, Qt::DateFormat format = Qt::TextDate )
- QDate fromString ( const QString & string, const QString & format )
- bool isLeapYear ( int year )
- bool isValid ( int year, int month, int day )
- QString longDayName ( int weekday )
- QString longMonthName ( int month )
- QString shortDayName ( int weekday )
- QString shortMonthName ( int month )

### Related Non-Members

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

## 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 (Julian calendar for dates before 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, or by using the static function currentDate() that 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 this date is in a leap year.

Note that the Gregorian calendar was introduced at different dates in different countries and regions. QDate uses the Gregorian calendar starting from 15 October 1582, and uses the Julian calendar for dates up to 4 October 1582.

See also QTime, QDateTime, QDateEdit, QDateTimeEdit, and QCalendarWidget.

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

Warning: Years 0 to 99 are interpreted as is. If you want to specify the year 2010, you must write 2010, not 10.

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).

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).

See also addDays() and addMonths().

### QDate QDate::currentDate () `[static]`

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) 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.

Warning: Qt::LocalDate cannot be used here.

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

This is an overloaded member function, provided for convenience.

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:

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 QDate::shortDayName().
dddd | The long localized day name (e.g. 'Monday' to 'Sunday'). Uses QDate::longDayName().
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 QDate::shortMonthName().
MMMM | The long localized month name (e.g. 'January' to 'December'). Uses QDate::longMonthName().
yy | The year as two digit number (00 to 99)
yyyy | The year as four digit number

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 QDateTime::fromString(), QTime::fromString(), QDate::toString(), QDateTime::toString(), and QTime::toString().

### 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.

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 member function, provided for convenience.

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 name of the weekday 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.

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

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

Returns the long name of the month 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.

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 name of the weekday 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.

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

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

Returns the name of the month 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.

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:

Expression | Output
--- | ---
d | the day as number without a leading zero (1 to31)
dd | the day as number with a leading zero (01 to 31)
ddd | the abbreviated localized day name (e.g. 'Mon' to 'Sun'). Uses QDate::shortDayName().
dddd | the long localized day name (e.g. 'Qt::Monday' to 'Qt::Sunday'). Uses QDate::longDayName().
M | the month as number without a leading zero (1-12)
MM | the month as number with a leading zero (01-12)
MMM | the abbreviated localized month name (e.g. 'Jan' to 'Dec'). Uses QDate::shortMonthName().
MMMM | the long localized month name (e.g. 'January' to 'December'). Uses QDate::longMonthName().
yy | the year as two digit number (00 to 99)
yyyy | the year as four digit number

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):

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.

Warning: This function is only valid for years in the range 0 to 9999.

See also QDateTime::toString() and QTime::toString().

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

This is an overloaded member function, provided for convenience.

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::LocalDate or Qt::SystemLocaleDate, the string format depends on the locale settings of the system. Identical to calling QLocale::system().toString(date, QLocale::ShortFormat). Qt::LocalDate has been deprecated, please use Qt::SystemLocaleDate instead.

If the format is Qt::LocaleDate, 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);

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 Qt::LocalDate 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 Qt::Monday and the first Qt::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.

Copyright (c) 1989 The Regents of the University of California. All rights reserved.

Redistribution and use in source and binary forms are permitted provided that the above copyright notice and this paragraph are duplicated in all such forms and that any documentation, advertising materials, and other materials related to such distribution and use acknowledge that the software was developed by the University of California, Berkeley. The name of the University may not be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

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 )

This is an overloaded member function, provided for convenience.

Writes the date to stream out.

See also Format of the QDataStream operators.

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

This is an overloaded member function, provided for convenience.

Reads a date from stream in into the date.

See also Format of the QDataStream operators.