QDateTime Class

Member Function Documentation

Returns the datetime as a string. The format parameter determines the format of the result string. If cal is supplied, it determines the calendar used to represent the date; it defaults to Gregorian. Prior to Qt 5.14, there was no cal parameter and the Gregorian calendar was always used. See QTime::toString() and QDate::toString() for the supported specifiers for time and date, respectively, in the format parameter.

Any sequence of characters enclosed in single quotes will be included verbatim in the output string (stripped of the quotes), even if it contains formatting characters. Two consecutive single quotes ("''") are replaced by a single quote in the output. All other characters in the format string are included verbatim in the output string.

Formats without separators (e.g. "ddMM") are supported but must be used with care, as the resulting strings aren't always reliably readable (e.g. if "dM" produces "212" it could mean either the 2nd of December or the 21st of February).

Example format strings (assumed that the QDateTime is 21 May 2001 14:13:09.120):

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

See also fromString(), QDate::toString(), QTime::toString(), and QLocale::toString().

[noexcept] QDateTime::QDateTime()

Constructs a null datetime, nominally using local time.

A null datetime is invalid, since its date and time are invalid.

See also isValid(), setMSecsSinceEpoch(), setDate(), setTime(), and setTimeZone().

[until 6.9] QDateTime::QDateTime(QDate date, QTime time, Qt::TimeSpec spec, int offsetSeconds = 0)

This function is scheduled for deprecation in version 6.9.

Use QDateTime(date, time) or QDateTime(date, time, QTimeZone::fromSecondsAheadOfUtc(offsetSeconds)).

Constructs a datetime with the given date and time, using the time representation implied by spec and offsetSeconds seconds.

If date is valid and time is not, the time will be set to midnight.

If spec is not Qt::OffsetFromUTC then offsetSeconds will be ignored. If spec is Qt::OffsetFromUTC and offsetSeconds is 0 then the timeSpec() will be set to Qt::UTC, i.e. an offset of 0 seconds.

If spec is Qt::TimeZone then the spec will be set to Qt::LocalTime, i.e. the current system time zone. To create a Qt::TimeZone datetime use the correct constructor.

If date lies outside the range of dates representable by QDateTime, the result is invalid. If spec is Qt::LocalTime and the system's time-zone skipped over the given date and time, the result is invalid.

QDateTime::QDateTime(QDate date, QTime time, const QTimeZone &timeZone, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)

Constructs a datetime with the given date and time, using the time representation described by timeZone.

If date is valid and time is not, the time will be set to midnight. If timeZone is invalid then the datetime will be invalid. If date and time describe a moment close to a transition for timeZone, resolve controls how that situation is resolved.

[since 6.5] QDateTime::QDateTime(QDate date, QTime time, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)

This is an overloaded function.

Constructs a datetime with the given date and time, using local time.

If date is valid and time is not, midnight will be used as the time. If date and time describe a moment close to a transition for local time, resolve controls how that situation is resolved.

This function was introduced in Qt 6.5.

[noexcept] QDateTime::QDateTime(const QDateTime &other)

Constructs a copy of the other datetime.

[noexcept] QDateTime::QDateTime(QDateTime &&other)

Moves the content of the temporary other datetime to this object and leaves other in an unspecified (but proper) state.

[noexcept] QDateTime::~QDateTime()

Destroys the datetime.

QDateTime QDateTime::addDays(qint64 ndays) const

Returns a QDateTime object containing a datetime ndays days later than the datetime of this object (or earlier if ndays is negative).

If the timeSpec() is Qt::LocalTime or Qt::TimeZone and the resulting date and time fall in the Standard Time to Daylight-Saving Time transition hour then the result will be just beyond this gap, in the direction of change. If the transition is at 2am and the clock goes forward to 3am, the result of aiming between 2am and 3am will be adjusted to fall before 2am (if ndays < 0) or after 3am (otherwise).

See also daysTo(), addMonths(), addYears(), addSecs(), and Timezone transitions.

[since 6.4] QDateTime QDateTime::addDuration(std::chrono::milliseconds msecs) const

Returns a QDateTime object containing a datetime msecs milliseconds later than the datetime of this object (or earlier if msecs is negative).

If this datetime is invalid, an invalid datetime will be returned.

This function was introduced in Qt 6.4.

See also addMSecs(), msecsTo(), addDays(), addMonths(), and addYears().

QDateTime QDateTime::addMSecs(qint64 msecs) const

Returns a QDateTime object containing a datetime msecs milliseconds later than the datetime of this object (or earlier if msecs is negative).

If this datetime is invalid, an invalid datetime will be returned.

See also addSecs(), msecsTo(), addDays(), addMonths(), and addYears().

QDateTime QDateTime::addMonths(int nmonths) const

Returns a QDateTime object containing a datetime nmonths months later than the datetime of this object (or earlier if nmonths is negative).

If the timeSpec() is Qt::LocalTime or Qt::TimeZone and the resulting date and time fall in the Standard Time to Daylight-Saving Time transition hour then the result will be just beyond this gap, in the direction of change. If the transition is at 2am and the clock goes forward to 3am, the result of aiming between 2am and 3am will be adjusted to fall before 2am (if nmonths < 0) or after 3am (otherwise).

See also daysTo(), addDays(), addYears(), addSecs(), and Timezone transitions.

QDateTime QDateTime::addSecs(qint64 s) const

Returns a QDateTime object containing a datetime s seconds later than the datetime of this object (or earlier if s is negative).

If this datetime is invalid, an invalid datetime will be returned.

See also addMSecs(), secsTo(), addDays(), addMonths(), and addYears().

QDateTime QDateTime::addYears(int nyears) const

Returns a QDateTime object containing a datetime nyears years later than the datetime of this object (or earlier if nyears is negative).

If the timeSpec() is Qt::LocalTime or Qt::TimeZone and the resulting date and time fall in the Standard Time to Daylight-Saving Time transition hour then the result will be just beyond this gap, in the direction of change. If the transition is at 2am and the clock goes forward to 3am, the result of aiming between 2am and 3am will be adjusted to fall before 2am (if nyears < 0) or after 3am (otherwise).

See also daysTo(), addDays(), addMonths(), addSecs(), and Timezone transitions.

[static, since 6.5] QDateTime QDateTime::currentDateTime(const QTimeZone &zone)

Returns the system clock's current datetime, using the time representation described by zone. If zone is omitted, local time is used.

This function was introduced in Qt 6.5.

See also currentDateTimeUtc(), QDate::currentDate(), QTime::currentTime(), and toTimeSpec().

[static] QDateTime QDateTime::currentDateTime()

This is an overloaded function.

[static] QDateTime QDateTime::currentDateTimeUtc()

Returns the system clock's current datetime, expressed in terms of UTC.

Equivalent to currentDateTime(QTimeZone::UTC).

See also currentDateTime(), QDate::currentDate(), QTime::currentTime(), and toTimeSpec().

[static noexcept] qint64 QDateTime::currentMSecsSinceEpoch()

Returns the current number of milliseconds since the start, in UTC, of the year 1970.

This number is like the POSIX time_t variable, but expressed in milliseconds instead of seconds.

See also currentDateTime(), currentDateTimeUtc(), and toTimeSpec().

[static noexcept] qint64 QDateTime::currentSecsSinceEpoch()

Returns the number of seconds since the start, in UTC, of the year 1970.

This number is like the POSIX time_t variable.

See also currentMSecsSinceEpoch().

QDate QDateTime::date() const

Returns the date part of the datetime.

See also setDate(), time(), and timeRepresentation().

qint64 QDateTime::daysTo(const QDateTime &other) const

Returns the number of days from this datetime to the other datetime. The number of days is counted as the number of times midnight is reached between this datetime to the other datetime. This means that a 10 minute difference from 23:55 to 0:05 the next day counts as one day.

If the other datetime is earlier than this datetime, the value returned is negative.

Example:

 QDateTime startDate(QDate(2012, 7, 6), QTime(8, 30, 0));
 QDateTime endDate(QDate(2012, 7, 7), QTime(16, 30, 0));
 qDebug() << "Days from startDate to endDate: " << startDate.daysTo(endDate);

 startDate = QDateTime(QDate(2012, 7, 6), QTime(23, 55, 0));
 endDate = QDateTime(QDate(2012, 7, 7), QTime(0, 5, 0));
 qDebug() << "Days from startDate to endDate: " << startDate.daysTo(endDate);

 qSwap(startDate, endDate); // Make endDate before startDate.
 qDebug() << "Days from startDate to endDate: " << startDate.daysTo(endDate);

See also addDays(), secsTo(), and msecsTo().

[static] QDateTime QDateTime::fromCFDate(CFDateRef date)

Constructs a new QDateTime containing a copy of the CFDate date.

See also toCFDate().

[static] QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs, const QTimeZone &timeZone)

Returns a datetime representing a moment the given number msecs of milliseconds after the start, in UTC, of the year 1970, described as specified by timeZone. The default time representation is local time.

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

See also fromSecsSinceEpoch(), toMSecsSinceEpoch(), and setMSecsSinceEpoch().

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

This is an overloaded function.

[static, until 6.9] QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs, Qt::TimeSpec spec, int offsetSeconds = 0)

This function is scheduled for deprecation in version 6.9.

This is an overloaded function.

Pass a QTimeZone instead, or omit spec and offsetSeconds.

Returns a datetime representing a moment the given number msecs of milliseconds after the start, in UTC, of the year 1970, described as specified by spec and offsetSeconds.

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

If the spec is not Qt::OffsetFromUTC then the offsetSeconds will be ignored. If the spec is Qt::OffsetFromUTC and the offsetSeconds is 0 then Qt::UTC will be used as the spec, since UTC has zero offset.

If spec is Qt::TimeZone then Qt::LocalTime will be used in its place, equivalent to using the current system time zone (but differently represented).

See also fromSecsSinceEpoch(), toMSecsSinceEpoch(), and setMSecsSinceEpoch().

[static] QDateTime QDateTime::fromNSDate(const NSDate *date)

Constructs a new QDateTime containing a copy of the NSDate date.

See also toNSDate().

[static] QDateTime QDateTime::fromSecsSinceEpoch(qint64 secs, const QTimeZone &timeZone)

Returns a datetime representing a moment the given number secs of seconds after the start, in UTC, of the year 1970, described as specified by timeZone. The default time representation is local time.

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

See also fromMSecsSinceEpoch(), toSecsSinceEpoch(), and setSecsSinceEpoch().

[static] QDateTime QDateTime::fromSecsSinceEpoch(qint64 secs)

This is an overloaded function.

[static, until 6.9] QDateTime QDateTime::fromSecsSinceEpoch(qint64 secs, Qt::TimeSpec spec, int offsetSeconds = 0)

This function is scheduled for deprecation in version 6.9.

This is an overloaded function.

Pass a QTimeZone instead, or omit spec and offsetSeconds.

Returns a datetime representing a moment the given number secs of seconds after the start, in UTC, of the year 1970, described as specified by spec and offsetSeconds.

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

If the spec is not Qt::OffsetFromUTC then the offsetSeconds will be ignored. If the spec is Qt::OffsetFromUTC and the offsetSeconds is 0 then Qt::UTC will be used as the spec, since UTC has zero offset.

If spec is Qt::TimeZone then Qt::LocalTime will be used in its place, equivalent to using the current system time zone (but differently represented).

See also fromMSecsSinceEpoch(), toSecsSinceEpoch(), and setSecsSinceEpoch().

[static, since 6.4] QDateTime QDateTime::fromStdLocalTime(const std::chrono::local_time<std::chrono::milliseconds> &time)

Constructs a datetime whose date and time are the number of milliseconds represented by time, counted since 1970-01-01T00:00:00.000 in local time (Qt::LocalTime).

This function was introduced in Qt 6.4.

See also toStdSysMilliseconds() and fromMSecsSinceEpoch().

[static, since 6.4] QDateTime QDateTime::fromStdTimePoint(const std::chrono::local_time<std::chrono::milliseconds> &time)

Constructs a datetime whose date and time are the number of milliseconds represented by time, counted since 1970-01-01T00:00:00.000 in local time (Qt::LocalTime).

This function was introduced in Qt 6.4.

See also toStdSysMilliseconds() and fromMSecsSinceEpoch().

[static, since 6.4] template <typename Clock, typename Duration> QDateTime QDateTime::fromStdTimePoint(const std::chrono::time_point<Clock, Duration> &time)

Constructs a datetime representing the same point in time as time, using Qt::UTC as its time representation.

The clock of time must be compatible with std::chrono::system_clock; in particular, a conversion supported by std::chrono::clock_cast must exist. After the conversion, the duration type of the result must be convertible to std::chrono::milliseconds.

If this is not the case, the caller must perform the necessary clock conversion towards std::chrono::system_clock and the necessary conversion of the duration type (cast/round/floor/ceil/...) so that the input to this function satisfies the constraints above.

This function was introduced in Qt 6.4.

See also toStdSysMilliseconds() and fromMSecsSinceEpoch().

[static, since 6.4] QDateTime QDateTime::fromStdTimePoint(std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds> time)

This is an overloaded function.

Constructs a datetime representing the same point in time as time, using Qt::UTC as its time representation.

This function was introduced in Qt 6.4.

[static, since 6.4] QDateTime QDateTime::fromStdZonedTime(const std::chrono::zoned_time<std::chrono::milliseconds, const std::chrono::time_zone *> &time)

Constructs a datetime representing the same point in time as time. The result will be expressed in time's time zone.

This function was introduced in Qt 6.4.

See also QTimeZone, toStdSysMilliseconds(), and fromMSecsSinceEpoch().

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

Returns the QDateTime represented by the string, using the format given, or an invalid datetime if this is not possible.

Note for Qt::TextDate: only English short month names (e.g. "Jan" in short form or "January" in long form) are recognized.

See also toString() and QLocale::toDateTime().

[static] QDateTime QDateTime::fromString(const QString &string, const QString &format, int baseYear, QCalendar cal)

Returns the QDateTime represented by the string, using the format given, or an invalid datetime if the string cannot be parsed.

Uses the calendar cal if supplied, else Gregorian.

When format only specifies the last two digits of a year, the 100 years starting at baseYear are the candidates first considered. Prior to 6.7 there was no baseYear parameter and 1900 was always used. This is the default for baseYear, selecting a year from then to 1999. In some cases, other fields may lead to the next or previous century being selected, to get a result consistent with all fields given. See QDate::fromString() for details.

In addition to the expressions, recognized in the format string to represent parts of the date and time, by QDate::fromString() and QTime::fromString(), this method supports:

If no 't' format specifier is present, the system's local time-zone is used. For the defaults of all other fields, see QDate::fromString() and QTime::fromString().

For example:

 QDateTime dateTime = QDateTime::fromString("1.30.1", "M.d.s");
 // dateTime is January 30 in 1900 at 00:00:01.
 dateTime = QDateTime::fromString("12", "yy");
 // dateTime is January 1 in 1912 at 00:00:00.

All other input characters will be treated as text. Any non-empty sequence of characters enclosed in single quotes will also be treated (stripped of the quotes) as text and not be interpreted as expressions.

 QTime time1 = QTime::fromString("131", "HHh");
 // time1 is 13:00:00
 QTime time1 = QTime::fromString("1apA", "1amAM");
 // time1 is 01:00:00

 QDateTime 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 invalid QDateTime is returned. If the format is satisfied but string represents an invalid datetime (e.g. in a gap skipped by a time-zone transition), an valid QDateTime is returned, that represents a near-by datetime that is valid.

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 (or three, for z) 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.

Incorrectly specified fields of the string will cause an invalid QDateTime to be returned. For example, consider the following code, where the two digit year 12 is read as 1912 (see the table below for all field defaults); the resulting datetime is invalid because 23 April 1912 was a Tuesday, not a Monday:

 QString string = "Monday, 23 April 12 22:51:41";
 QString format = "dddd, d MMMM yy hh:mm:ss";
 QDateTime invalid = QDateTime::fromString(string, format);

The correct code is:

 QString string = "Tuesday, 23 April 12 22:51:41";
 QString format = "dddd, d MMMM yy hh:mm:ss";
 QDateTime valid = QDateTime::fromString(string, format);

See also toString(), QDate::fromString(), QTime::fromString(), and QLocale::toDateTime().

[static, since 6.0] QDateTime QDateTime::fromString(QStringView string, Qt::DateFormat format = Qt::TextDate)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static, since 6.0] QDateTime QDateTime::fromString(QStringView string, QStringView format, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static, since 6.7] QDateTime QDateTime::fromString(QStringView string, QStringView format, int baseYear = QLocale::DefaultTwoDigitBaseYear)

This is an overloaded function.

Uses a default-constructed QCalendar.

This function was introduced in Qt 6.7.

[static, since 6.0] QDateTime QDateTime::fromString(const QString &string, QStringView format, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static, since 6.7] QDateTime QDateTime::fromString(const QString &string, QStringView format, int baseYear = QLocale::DefaultTwoDigitBaseYear)

This is an overloaded function.

Uses a default-constructed QCalendar.

This function was introduced in Qt 6.7.

[static] QDateTime QDateTime::fromString(const QString &string, const QString &format, QCalendar cal)

This is an overloaded function.

[static, since 6.7] QDateTime QDateTime::fromString(const QString &string, const QString &format, int baseYear = QLocale::DefaultTwoDigitBaseYear)

This is an overloaded function.

Uses a default-constructed QCalendar.

This function was introduced in Qt 6.7.

[static, since 6.7] QDateTime QDateTime::fromString(QStringView string, QStringView format, int baseYear, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.7.

[static, since 6.0] QDateTime QDateTime::fromString(const QString &string, QStringView format, int baseYear, QCalendar cal)

This is an overloaded function.

This function was introduced in Qt 6.0.

bool QDateTime::isDaylightTime() const

Returns if this datetime falls in Daylight-Saving Time.

If the Qt::TimeSpec is not Qt::LocalTime or Qt::TimeZone then will always return false.

See also timeSpec().

bool QDateTime::isNull() const

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

See also QDate::isNull(), QTime::isNull(), and isValid().

bool QDateTime::isValid() const

Returns true if this datetime represents a definite moment, otherwise false.

A datetime is valid if both its date and its time are valid and the time representation used gives a valid meaning to their combination. When the time representation is a specific time-zone or local time, there may be times on some dates that the zone skips in its representation, as when a daylight-saving transition skips an hour (typically during a night in spring). For example, if DST ends at 2am with the clock advancing to 3am, then datetimes from 02:00:00 to 02:59:59.999 on that day are invalid.

See also QDateTime::YearRange, QDate::isValid(), and QTime::isValid().

qint64 QDateTime::msecsTo(const QDateTime &other) const

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

Before performing the comparison, the two datetimes are converted to Qt::UTC to ensure that the result is correct if daylight-saving (DST) applies to one of the two datetimes and but not the other.

Returns 0 if either datetime is invalid.

See also addMSecs(), daysTo(), and QTime::msecsTo().

int QDateTime::offsetFromUtc() const

Returns this datetime's Offset From UTC in seconds.

The result depends on timeSpec():

• Qt::UTC The offset is 0.
• Qt::OffsetFromUTC The offset is the value originally set.
• Qt::LocalTime The local time's offset from UTC is returned.
• Qt::TimeZone The offset used by the time-zone is returned.

For the last two, the offset at this date and time will be returned, taking account of Daylight-Saving Offset. The offset is the difference between the local time or time in the given time-zone and UTC time; it is positive in time-zones ahead of UTC (East of The Prime Meridian), negative for those behind UTC (West of The Prime Meridian).

See also setOffsetFromUtc().

qint64 QDateTime::secsTo(const QDateTime &other) const

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

Before performing the comparison, the two datetimes are converted to Qt::UTC to ensure that the result is correct if daylight-saving (DST) applies to one of the two datetimes but not the other.

Returns 0 if either datetime is invalid.

Example:

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

See also addSecs(), daysTo(), and QTime::secsTo().

void QDateTime::setDate(QDate date, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)

Sets the date part of this datetime to date.

If no time is set yet, it is set to midnight. If date is invalid, this QDateTime becomes invalid.

If date and time() describe a moment close to a transition for this datetime's time representation, resolve controls how that situation is resolved.

See also date(), setTime(), and setTimeZone().

void QDateTime::setMSecsSinceEpoch(qint64 msecs)

Sets the datetime to represent a moment a given number, msecs, of milliseconds after the start, in UTC, of the year 1970.

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

Note that passing the minimum of qint64 (std::numeric_limits<qint64>::min()) to msecs will result in undefined behavior.

See also setSecsSinceEpoch(), toMSecsSinceEpoch(), and fromMSecsSinceEpoch().

[until 6.9] void QDateTime::setOffsetFromUtc(int offsetSeconds)

This function is scheduled for deprecation in version 6.9.

Use setTimeZone(QTimeZone::fromSecondsAheadOfUtc(offsetSeconds)) instead

Sets the timeSpec() to Qt::OffsetFromUTC and the offset to offsetSeconds. The datetime may refer to a different point in time.

The maximum and minimum offset is 14 positive or negative hours. If offsetSeconds is larger or smaller than that, then the result is undefined.

If offsetSeconds is 0 then the timeSpec() will be set to Qt::UTC.

See also setTimeZone(), isValid(), offsetFromUtc(), and toOffsetFromUtc().

void QDateTime::setSecsSinceEpoch(qint64 secs)

Sets the datetime to represent a moment a given number, secs, of seconds after the start, in UTC, of the year 1970.

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

See also setMSecsSinceEpoch(), toSecsSinceEpoch(), and fromSecsSinceEpoch().

void QDateTime::setTime(QTime time, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)

Sets the time part of this datetime to time. If time is not valid, this function sets it to midnight. Therefore, it's possible to clear any set time in a QDateTime by setting it to a default QTime:

 QDateTime dt = QDateTime::currentDateTime();
 dt.setTime(QTime());

If date() and time describe a moment close to a transition for this datetime's time representation, resolve controls how that situation is resolved.

See also time(), setDate(), and setTimeZone().

[until 6.9] void QDateTime::setTimeSpec(Qt::TimeSpec spec)

This function is scheduled for deprecation in version 6.9.

Use setTimeZone() instead

Sets the time specification used in this datetime to spec. The datetime may refer to a different point in time.

If spec is Qt::OffsetFromUTC then the timeSpec() will be set to Qt::UTC, i.e. an effective offset of 0.

If spec is Qt::TimeZone then the spec will be set to Qt::LocalTime, i.e. the current system time zone.

Example:

 QDateTime local(QDateTime::currentDateTime());
 qDebug() << "Local time is:" << local;

 QDateTime UTC(local);
 UTC.setTimeSpec(Qt::UTC);
 qDebug() << "UTC time is:" << UTC;

 qDebug() << "There are" << local.secsTo(UTC) << "seconds difference between the datetimes.";

See also setTimeZone(), timeSpec(), toTimeSpec(), setDate(), and setTime().

void QDateTime::setTimeZone(const QTimeZone &toZone, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)

Sets the time zone used in this datetime to toZone.

The datetime may refer to a different point in time. It uses the time representation of toZone, which may change the meaning of its unchanged date() and time().

If toZone is invalid then the datetime will be invalid. Otherwise, this datetime's timeSpec() after the call will match toZone.timeSpec().

If date() and time() describe a moment close to a transition for toZone, resolve controls how that situation is resolved.

See also timeRepresentation(), timeZone(), and Qt::TimeSpec.

[noexcept] void QDateTime::swap(QDateTime &other)

Swaps this datetime with other. This operation is very fast and never fails.

QTime QDateTime::time() const

Returns the time part of the datetime.

See also setTime(), date(), and timeRepresentation().

[since 6.5] QTimeZone QDateTime::timeRepresentation() const

Returns a QTimeZone identifying how this datetime represents time.

The timeSpec() of the returned QTimeZone will coincide with that of this datetime; if it is not Qt::TimeZone then the returned QTimeZone is a time representation. When their timeSpec() is Qt::OffsetFromUTC, the returned QTimeZone's fixedSecondsAheadOfUtc() supplies the offset. When timeSpec() is Qt::TimeZone, the QTimeZone object itself is the full representation of that time zone.

This function was introduced in Qt 6.5.

See also timeZone(), setTimeZone(), and QTimeZone::asBackendZone().

Qt::TimeSpec QDateTime::timeSpec() const

Returns the time specification of the datetime.

This classifies its time representation as local time, UTC, a fixed offset from UTC (without indicating the offset) or a time zone (without giving the details of that time zone). Equivalent to timeRepresentation().timeSpec().

See also setTimeSpec(), timeRepresentation(), date(), and time().

QTimeZone QDateTime::timeZone() const

Returns the time zone of the datetime.

The result is the same as timeRepresentation().asBackendZone(). In all cases, the result's timeSpec() is Qt::TimeZone.

When timeSpec() is Qt::LocalTime, the result will describe local time at the time this method was called. It will not reflect subsequent changes to the system time zone, even when the QDateTime from which it was obtained does.

See also timeRepresentation(), setTimeZone(), Qt::TimeSpec, and QTimeZone::asBackendZone().

QString QDateTime::timeZoneAbbreviation() const

Returns the Time Zone Abbreviation for this datetime.

The returned string depends on timeSpec():

• For Qt::UTC it is "UTC".
• For Qt::OffsetFromUTC it will be in the format "UTC±00:00".
• For Qt::LocalTime, the host system is queried.
• For Qt::TimeZone, the associated QTimeZone object is queried.

See also timeSpec() and QTimeZone::abbreviation().

CFDateRef QDateTime::toCFDate() const

Creates a CFDate from a QDateTime.

The caller owns the CFDate object and is responsible for releasing it.

See also fromCFDate().

QDateTime QDateTime::toLocalTime() const

Returns a copy of this datetime converted to local time.

The result represents the same moment in time as, and is equal to, this datetime.

Example:

 QDateTime UTC(QDateTime::currentDateTimeUtc());
 QDateTime local(UTC.toLocalTime());
 qDebug() << "UTC time is:" << UTC;
 qDebug() << "Local time is:" << local;
 qDebug() << "No difference between times:" << UTC.secsTo(local);

See also toTimeZone(), toUTC(), and toOffsetFromUtc().

qint64 QDateTime::toMSecsSinceEpoch() const

Returns the datetime as a number of milliseconds after the start, in UTC, of the year 1970.

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

See also toSecsSinceEpoch(), setMSecsSinceEpoch(), and fromMSecsSinceEpoch().

NSDate *QDateTime::toNSDate() const

Creates an NSDate from a QDateTime.

The NSDate object is autoreleased.

See also fromNSDate().

QDateTime QDateTime::toOffsetFromUtc(int offsetSeconds) const

Returns a copy of this datetime converted to a spec of Qt::OffsetFromUTC with the given offsetSeconds. Equivalent to toTimeZone(QTimeZone::fromSecondsAheadOfUtc(offsetSeconds)).

If the offsetSeconds equals 0 then a UTC datetime will be returned.

The result represents the same moment in time as, and is equal to, this datetime.

See also setOffsetFromUtc(), offsetFromUtc(), and toTimeZone().

qint64 QDateTime::toSecsSinceEpoch() const

Returns the datetime as a number of seconds after the start, in UTC, of the year 1970.

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

See also toMSecsSinceEpoch(), fromSecsSinceEpoch(), and setSecsSinceEpoch().

[since 6.4] std::chrono::sys_time<std::chrono::milliseconds> QDateTime::toStdSysMilliseconds() const

Converts this datetime object to the equivalent time point expressed in milliseconds, using std::chrono::system_clock as a clock.

This function was introduced in Qt 6.4.

See also fromStdTimePoint() and toMSecsSinceEpoch().

[since 6.4] std::chrono::sys_seconds QDateTime::toStdSysSeconds() const

Converts this datetime object to the equivalent time point expressed in seconds, using std::chrono::system_clock as a clock.

This function was introduced in Qt 6.4.

See also fromStdTimePoint() and toSecsSinceEpoch().

QString QDateTime::toString(QStringView format) const

This is an overloaded function.

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

This is an overloaded function.

Returns the datetime as a string in the format given.

If the format is Qt::TextDate, the string is formatted in the default way. The day and month names will be in English. An example of this formatting is "Wed May 20 03:40:13 1998". For localized formatting, see QLocale::toString().

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-ddTHH:mm:ss[Z|±HH:mm], depending on the timeSpec() of the QDateTime. If the timeSpec() is Qt::UTC, Z will be appended to the string; if the timeSpec() is Qt::OffsetFromUTC, the offset in hours and minutes from UTC will be appended to the string. To include milliseconds in the ISO 8601 date, use the format Qt::ISODateWithMs, which corresponds to yyyy-MM-ddTHH:mm:ss.zzz[Z|±HH:mm].

If the format is Qt::RFC2822Date, the string is formatted following RFC 2822.

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

See also fromString(), QDate::toString(), QTime::toString(), and QLocale::toString().

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

This is an overloaded function.

[until 6.9] QDateTime QDateTime::toTimeSpec(Qt::TimeSpec spec) const

This function is scheduled for deprecation in version 6.9.

Use toTimeZone() instead.

Returns a copy of this datetime converted to the given time spec.

The result represents the same moment in time as, and is equal to, this datetime.

If spec is Qt::OffsetFromUTC then it is set to Qt::UTC. To set to a fixed offset from UTC, use toTimeZone() or toOffsetFromUtc().

If spec is Qt::TimeZone then it is set to Qt::LocalTime, i.e. the local Time Zone. To set a specified time-zone, use toTimeZone().

Example:

 QDateTime local(QDateTime::currentDateTime());
 QDateTime UTC(local.toTimeSpec(Qt::UTC));
 qDebug() << "Local time is:" << local;
 qDebug() << "UTC time is:" << UTC;
 qDebug() << "No difference between times:" << local.secsTo(UTC);

See also setTimeSpec(), timeSpec(), and toTimeZone().

QDateTime QDateTime::toTimeZone(const QTimeZone &timeZone) const

Returns a copy of this datetime converted to the given timeZone.

The result represents the same moment in time as, and is equal to, this datetime.

The result describes the moment in time in terms of timeZone's time representation. For example:

 QDateTime local(QDateTime::currentDateTime());
 QDateTime UTC(local.toTimeSpec(QTimeZone::UTC));
 qDebug() << "Local time is:" << local;
 qDebug() << "UTC time is:" << UTC;
 qDebug() << "No difference between times represented:" << local.secsTo(UTC);

If timeZone is invalid then the datetime will be invalid. Otherwise the returned datetime's timeSpec() will match timeZone.timeSpec().

See also timeRepresentation(), toLocalTime(), toUTC(), and toOffsetFromUtc().

QDateTime QDateTime::toUTC() const

Returns a copy of this datetime converted to UTC.

The result represents the same moment in time as, and is equal to, this datetime.

Example:

 QDateTime local(QDateTime::currentDateTime());
 QDateTime UTC(local.toUTC());
 qDebug() << "Local time is:" << local;
 qDebug() << "UTC time is:" << UTC;
 qDebug() << "No difference between times:" << local.secsTo(UTC);

See also toTimeZone(), toLocalTime(), and toOffsetFromUtc().

[since 6.4] QDateTime &QDateTime::operator+=(std::chrono::milliseconds duration)

Modifies this datetime object by adding the given duration. The updated object will be later if duration is positive, or earlier if it is negative.

If this datetime is invalid, this function has no effect.

Returns a reference to this datetime object.

This function was introduced in Qt 6.4.

See also addMSecs().

[since 6.4] QDateTime &QDateTime::operator-=(std::chrono::milliseconds duration)

Modifies this datetime object by subtracting the given duration. The updated object will be earlier if duration is positive, or later if it is negative.

If this datetime is invalid, this function has no effect.

Returns a reference to this datetime object.

This function was introduced in Qt 6.4.

See also addMSecs.

[noexcept] QDateTime &QDateTime::operator=(const QDateTime &other)

Copies the other datetime into this and returns this copy.