Contents

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

Detailed Description

TheQDateTime class provides date and time functions.

AQDateTime object contains a calendar date and a clock time (a "datetime"). It is a combination of theQDate andQTime classes. It can read the current datetime from the system clock. It provides functions for comparing datetimes and for manipulating a datetime by adding a number of seconds, days, months, or years.

AQDateTime object is typically created either by giving a date and time explicitly in the constructor, or by using the static functioncurrentDateTime() that returns aQDateTime object set to the system clock's time. The date and time can be changed withsetDate() andsetTime(). A datetime can also be set using thesetTime_t() function that takes a POSIX-standard "number of seconds since 00:00:00 on January 1, 1970" value. ThefromString() function returns aQDateTime, given a string and a date format used to interpret the date within the string.

Thedate() andtime() functions provide access to the date and time parts of the datetime. The same information is provided in textual format by thetoString() function.

QDateTime provides a full set of operators to compare twoQDateTime objects where smaller means earlier and larger means later.

You can increment (or decrement) a datetime by a given number of milliseconds usingaddMSecs(), seconds usingaddSecs(), or days usingaddDays(). Similarly you can useaddMonths() andaddYears(). ThedaysTo() function returns the number of days between two datetimes,secsTo() returns the number of seconds between two datetimes, andmsecsTo() returns the number of milliseconds between two datetimes.

QDateTime can store datetimes aslocal time or asUTC.QDateTime::currentDateTime() returns aQDateTime expressed as local time; usetoUTC() to convert it to UTC. You can also usetimeSpec() to find out if aQDateTime object stores a UTC time or a local time. Operations such asaddSecs() andsecsTo() are aware of daylight saving time (DST).

Note:QDateTime does not account for leap seconds.

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.

The Gregorian calendar was introduced in different places around the world on different dates.QDateTime usesQDate to store the date, so it uses the Gregorian calendar for all locales, beginning on the date 15 October 1582. For dates up to and including 4 October 1582,QDateTime uses the Julian calendar. This means there is a 10-day gap in theQDateTime 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.

Use of System Timezone

QDateTime uses the system's time zone information to determine the offset of local time from UTC. If the system is not configured correctly or not up-to-date,QDateTime will give wrong results as well.

Daylight Savings Time (DST)

QDateTime takes into account the system's time zone information when dealing with DST. On modern Unix systems, this means it applies the correct historical DST data whenever possible. On Windows and Windows CE, where the system doesn't support historical DST data, historical accuracy is not maintained with respect to DST.

The range of valid dates taking DST into account is 1970-01-01 to the present, and rules are in place for handling DST correctly until 2037-12-31, but these could change. For dates falling outside that range,QDateTime makes abest guess using the rules for year 1970 or 2037, but we can't guarantee accuracy. This meansQDateTime doesn't take into account changes in a locale's time zone before 1970, even if the system's time zone database supports that information.

Member Function Documentation

QDateTime::QDateTime()

Constructs a null datetime (i.e. null date and null time). A null datetime is invalid, since the date is invalid.

See alsoisValid().

QDateTime::QDateTime(constQDate & date)

Constructs a datetime with the givendate, a valid time(00:00:00.000), and sets thetimeSpec() toQt::LocalTime.

QDateTime::QDateTime(constQDate & date, constQTime & time,Qt::TimeSpec spec = Qt::LocalTime)

Constructs a datetime with the givendate andtime, using the time specification defined byspec.

Ifdate is valid andtime is not, the time will be set to midnight.

QDateTime::QDateTime(constQDateTime & other)

Constructs a copy of theother datetime.

QDateTime::~QDateTime()

Destroys the datetime.

QDateTime QDateTime::addDays(int ndays) const

Returns aQDateTime object containing a datetimendays days later than the datetime of this object (or earlier ifndays is negative).

See alsodaysTo(),addMonths(),addYears(), andaddSecs().

QDateTime QDateTime::addMSecs(qint64 msecs) const

Returns aQDateTime object containing a datetimemsecs miliseconds later than the datetime of this object (or earlier ifmsecs is negative).

See alsoaddSecs(),msecsTo(),addDays(),addMonths(), andaddYears().

QDateTime QDateTime::addMonths(int nmonths) const

Returns aQDateTime object containing a datetimenmonths months later than the datetime of this object (or earlier ifnmonths is negative).

See alsodaysTo(),addDays(),addYears(), andaddSecs().

QDateTime QDateTime::addSecs(int s) const

Returns aQDateTime object containing a datetimes seconds later than the datetime of this object (or earlier ifs is negative).

See alsoaddMSecs(),secsTo(),addDays(),addMonths(), andaddYears().

QDateTime QDateTime::addYears(int nyears) const

Returns aQDateTime object containing a datetimenyears years later than the datetime of this object (or earlier ifnyears is negative).

See alsodaysTo(),addDays(),addMonths(), andaddSecs().

[static]QDateTime QDateTime::currentDateTime()

Returns the current datetime, as reported by the system clock, in the local time zone.

See alsocurrentDateTimeUtc(),QDate::currentDate(),QTime::currentTime(), andtoTimeSpec().

[static]QDateTime QDateTime::currentDateTimeUtc()

Returns the current datetime, as reported by the system clock, in UTC.

This function was introduced in Qt 4.7.

See alsocurrentDateTime(),QDate::currentDate(),QTime::currentTime(), andtoTimeSpec().

[static]qint64 QDateTime::currentMSecsSinceEpoch()

Returns the number of milliseconds since 1970-01-01T00:00:00 Universal Coordinated Time. This number is like the POSIX time_t variable, but expressed in milliseconds instead.

This function was introduced in Qt 4.7.

See alsocurrentDateTime(),currentDateTimeUtc(),toTime_t(), andtoTimeSpec().

QDate QDateTime::date() const

Returns the date part of the datetime.

See alsosetDate(),time(), andtimeSpec().

int QDateTime::daysTo(constQDateTime & other) const

Returns the number of days from this datetime to theother datetime. If theother datetime is earlier than this datetime, the value returned is negative.

See alsoaddDays(),secsTo(), andmsecsTo().

[static]QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs)

Returns a datetime whose date and time are the number of milliseconds,msecs, that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC). On systems that do not support time zones, the time will be set as if local time wereQt::UTC.

Note that there are possible values formsecs that lie outside the valid range ofQDateTime, both negative and positive. The behavior of this function is undefined for those values.

This function was introduced in Qt 4.7.

See alsotoTime_t() andsetTime_t().

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

Returns theQDateTime represented by thestring, using theformat given, or an invalid datetime if this is not possible.

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]QDateTime QDateTime::fromString(constQString & string, constQString & format)

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

These expressions may be used for the date part of the format string:

Note:Unlike the other version of this function, day and month names must be given in the user's local language. It is only possible to use the English names if the user's language is English.

These expressions may be used for the time part of the format string:

All other input characters will be treated as text. Any sequence of characters that are enclosed in singlequotes will also be treated as text and not be used as an expression.

QTime time1=QTime::fromString("131","HHh");// time1 is 13:00:00QTime time1=QTime::fromString("1apA","1amAM");// time1 is 01:00:00QDateTime dateTime2=QDateTime::fromString("M1d1y9800:01:02","'M'M'd'd'y'yyhh:mm:ss");// dateTime is 1 January 1998 00:01:02

If the format is not satisfied an invalidQDateTime is returned. The expressions that don't have leading zeroes (d, M, h, m, s, z) will be greedy. This means that they will use two digits even if this will put them outside the range and/or leave too few digits for other sections.

QDateTime dateTime=QDateTime::fromString("130","Mm");// invalid

This could have meant 1 January 00:30.00 but the M will grab two digits.

For any field that is not represented in the format the following defaults are used:

For example:

QDateTime dateTime=QDateTime::fromString("1.30.1","M.d.s");// dateTime is January 30 in 1900 at 00:00:01.

QDateTime::toString()QTime::toString()

See alsoQDate::fromString(),QTime::fromString(), andQDate::toString().

[static]QDateTime QDateTime::fromTime_t(uint seconds)

Returns a datetime whose date and time are the number ofseconds that have passed since 1970-01-01T00:00:00, Coordinated Universal Time (Qt::UTC). On systems that do not support time zones, the time will be set as if local time wereQt::UTC.

This function was introduced in Qt 4.2.

See alsotoTime_t() andsetTime_t().

bool QDateTime::isNull() const

Returns true if both the date and the time are null; otherwise returns false. A null datetime is invalid.

See alsoQDate::isNull(),QTime::isNull(), andisValid().

bool QDateTime::isValid() const

Returns true if both the date and the time are valid; otherwise returns false.

See alsoQDate::isValid() andQTime::isValid().

qint64 QDateTime::msecsTo(constQDateTime & other) const

Returns the number of milliseconds from this datetime to theother datetime. If theother datetime is earlier than this datetime, the value returned is negative.

Before performing the comparison, the two datetimes are converted toQt::UTC to ensure that the result is correct if one of the two datetimes has daylight saving time (DST) and the other doesn't.

This function was introduced in Qt 4.7.

See alsoaddMSecs(),daysTo(), andQTime::msecsTo().

int QDateTime::secsTo(constQDateTime & other) const

Returns the number of seconds from this datetime to theother datetime. If theother datetime is earlier than this datetime, the value returned is negative.

Before performing the comparison, the two datetimes are converted toQt::UTC to ensure that the result is correct if one of the two datetimes has daylight saving time (DST) and the other doesn't.

Example:

QDateTime now=QDateTime::currentDateTime();QDateTime xmas(QDate(now.date().year(),12,25),QTime(0,0));qDebug("There are %d seconds to Christmas", now.secsTo(xmas));

See alsoaddSecs(),daysTo(), andQTime::secsTo().

void QDateTime::setDate(constQDate & date)

Sets the date part of this datetime todate. If no time is set, it is set to midnight.

See alsodate(),setTime(), andsetTimeSpec().

void QDateTime::setMSecsSinceEpoch(qint64 msecs)

Sets the date and time given the number of milliseconds,msecs, that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC). On systems that do not support time zones this function will behave as if local time wereQt::UTC.

Note that there are possible values formsecs that lie outside the valid range ofQDateTime, both negative and positive. The behavior of this function is undefined for those values.

This function was introduced in Qt 4.7.

See alsotoMSecsSinceEpoch() andsetTime_t().

void QDateTime::setTime(constQTime & time)

Sets the time part of this datetime totime.

See alsotime(),setDate(), andsetTimeSpec().

void QDateTime::setTimeSpec(Qt::TimeSpec spec)

Sets the time specification used in this datetime tospec.

See alsotimeSpec(),setDate(),setTime(), andQt::TimeSpec.

void QDateTime::setTime_t(uint seconds)

Sets the date and time given the number ofseconds that have passed since 1970-01-01T00:00:00, Coordinated Universal Time (Qt::UTC). On systems that do not support time zones this function will behave as if local time wereQt::UTC.

See alsotoTime_t().

QTime QDateTime::time() const

Returns the time part of the datetime.

See alsosetTime(),date(), andtimeSpec().

Qt::TimeSpec QDateTime::timeSpec() const

Returns the time specification of the datetime.

See alsosetTimeSpec(),date(),time(), andQt::TimeSpec.

QDateTime QDateTime::toLocalTime() const

Returns a datetime containing the date and time information in this datetime, but specified using theQt::LocalTime definition.

See alsotoTimeSpec().

qint64 QDateTime::toMSecsSinceEpoch() const

Returns the datetime as the number of milliseconds that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC).

On systems that do not support time zones, this function will behave as if local time wereQt::UTC.

The behavior for this function is undefined if the datetime stored in this object is not valid. However, for all valid dates, this function returns a unique value.

This function was introduced in Qt 4.7.

See alsotoTime_t() andsetMSecsSinceEpoch().

QString QDateTime::toString(constQString & format) const

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

These expressions may be used for the date:

These expressions may be used for the time:

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 (assumed that theQDateTime is 21 May 2001 14:13:09):

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

See alsoQDate::toString() andQTime::toString().

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

This is an overloaded function.

Returns the datetime as a string in theformat given.

If theformat isQt::TextDate, the string is formatted in the default way.QDate::shortDayName(),QDate::shortMonthName(), andQTime::toString() are used to generate the string, so the day and month names will be localized names. An example of this formatting is "Wed May 20 03:40:13 1998".

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-DDTHH:mm:ss[Z|[+|-]HH:mm], depending on thetimeSpec() of theQDateTime. If thetimeSpec() isQt::UTC, Z will be appended to the string; if thetimeSpec() isQt::OffsetFromUTC the offset in hours and minutes from UTC will be appended to the string.

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

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 alsoQDate::toString(),QTime::toString(), andQt::DateFormat.

QDateTime QDateTime::toTimeSpec(Qt::TimeSpec specification) const

Returns a copy of this datetime configured to use the given timespecification.

See alsotimeSpec(),toUTC(), andtoLocalTime().

uint QDateTime::toTime_t() const

Returns the datetime as the number of seconds that have passed since 1970-01-01T00:00:00, Coordinated Universal Time (Qt::UTC).

On systems that do not support time zones, this function will behave as if local time wereQt::UTC.

Note:This function returns a 32-bit unsigned integer, so it does not support dates before 1970, but it does support dates after 2038-01-19T03:14:06, which may not be valid time_t values. Be careful when passing those time_t values to system functions, which could interpret them as negative dates.

If the date is outside the range 1970-01-01T00:00:00 to 2106-02-07T06:28:14, this function returns -1 cast to an unsigned integer (i.e., 0xFFFFFFFF).

To get an extended range, usetoMSecsSinceEpoch().

See alsotoMSecsSinceEpoch() andsetTime_t().

QDateTime QDateTime::toUTC() const

Returns a datetime containing the date and time information in this datetime, but specified using theQt::UTC definition.

See alsotoTimeSpec().

bool QDateTime::operator!=(constQDateTime & other) const

Returns true if this datetime is different from theother datetime; otherwise returns false.

Two datetimes are different if either the date, the time, or the time zone components are different.

See alsooperator==().

bool QDateTime::operator<(constQDateTime & other) const

Returns true if this datetime is earlier than theother datetime; otherwise returns false.

bool QDateTime::operator<=(constQDateTime & other) const

Returns true if this datetime is earlier than or equal to theother datetime; otherwise returns false.

QDateTime & QDateTime::operator=(constQDateTime & other)

Makes a copy of theother datetime and returns a reference to the copy.

bool QDateTime::operator==(constQDateTime & other) const

Returns true if this datetime is equal to theother datetime; otherwise returns false.

See alsooperator!=().

bool QDateTime::operator>(constQDateTime & other) const

Returns true if this datetime is later than theother datetime; otherwise returns false.

bool QDateTime::operator>=(constQDateTime & other) const

Returns true if this datetime is later than or equal to theother datetime; otherwise returns false.

Related Non-Members

QDataStream &operator<<(QDataStream & out, constQDateTime & dateTime)

WritesdateTime to theout stream.

See alsoSerializing Qt Data Types.

QDataStream &operator>>(QDataStream & in,QDateTime & dateTime)

Reads a datetime from the streamin intodateTime.

See alsoSerializing Qt Data Types.