- Qt 6.9
- Qt Core
- C++ Classes
- QDateTime
- Qt 6.9.2 Reference Documentation

# QDateTime Class

The QDateTime class provides date and time functions. More...

Header: | `#include <QDateTime>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`

- List of all members, including inherited members
- Deprecated members
- QDateTime is part of Implicitly Shared Classes.

This class is weakly comparable.

Note: All functions in this class are reentrant.

## Public Types

`(since 6.7)` enum class | TransitionResolution { Reject, RelativeToBefore, RelativeToAfter, PreferBefore, PreferAfter, …, LegacyBehavior }
enum class | YearRange { First, Last }

## Public Functions

| QDateTime()
| QDateTime(QDate date, QTime time, const QTimeZone &timeZone, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
`(since 6.5)` | QDateTime(QDate date, QTime time, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
| QDateTime(const QDateTime &other)
| QDateTime(QDateTime &&other)
| ~QDateTime()
QDateTime | addDays(qint64 ndays) const
`(since 6.4)` QDateTime | addDuration(std::chrono::milliseconds msecs) const
QDateTime | addMSecs(qint64 msecs) const
QDateTime | addMonths(int nmonths) const
QDateTime | addSecs(qint64 s) const
QDateTime | addYears(int nyears) const
QDate | date() const
qint64 | daysTo(const QDateTime &other) const
bool | isDaylightTime() const
bool | isNull() const
bool | isValid() const
qint64 | msecsTo(const QDateTime &other) const
int | offsetFromUtc() const
qint64 | secsTo(const QDateTime &other) const
void | setDate(QDate date, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
void | setMSecsSinceEpoch(qint64 msecs)
void | setSecsSinceEpoch(qint64 secs)
void | setTime(QTime time, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
void | setTimeZone(const QTimeZone &toZone, QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
void | swap(QDateTime &other)
QTime | time() const
`(since 6.5)` QTimeZone | timeRepresentation() const
Qt::TimeSpec | timeSpec() const
QString | timeZoneAbbreviation() const
CFDateRef | toCFDate() const
QDateTime | toLocalTime() const
qint64 | toMSecsSinceEpoch() const
NSDate * | toNSDate() const
QDateTime | toOffsetFromUtc(int offsetSeconds) const
qint64 | toSecsSinceEpoch() const
`(since 6.4)` std::chrono::sys_time<std::chrono::milliseconds> | toStdSysMilliseconds() const
`(since 6.4)` std::chrono::sys_seconds | toStdSysSeconds() const
QDateTime | toTimeZone(const QTimeZone &timeZone) const
QDateTime | toUTC() const
`(since 6.4)` QDateTime & | operator+=(std::chrono::milliseconds duration)
`(since 6.4)` QDateTime & | operator-=(std::chrono::milliseconds duration)
QDateTime & | operator=(const QDateTime &other)

## Static Public Members

`(since 6.5)` QDateTime | currentDateTime(const QTimeZone &zone)
QDateTime | currentDateTime()
QDateTime | currentDateTimeUtc()
qint64 | currentMSecsSinceEpoch()
qint64 | currentSecsSinceEpoch()
QDateTime | fromCFDate(CFDateRef date)
QDateTime | fromMSecsSinceEpoch(qint64 msecs, const QTimeZone &timeZone)
QDateTime | fromMSecsSinceEpoch(qint64 msecs)
QDateTime | fromNSDate(const NSDate *date)
QDateTime | fromSecsSinceEpoch(qint64 secs, const QTimeZone &timeZone)
QDateTime | fromSecsSinceEpoch(qint64 secs)
`(since 6.4)` QDateTime | fromStdLocalTime(const std::chrono::local_time<std::chrono::milliseconds> &time)
`(since 6.4)` QDateTime | fromStdTimePoint(const std::chrono::local_time<std::chrono::milliseconds> &time)
`(since 6.4)` QDateTime | fromStdTimePoint(const std::chrono::time_point<Clock, Duration> &time)
`(since 6.4)` QDateTime | fromStdTimePoint(std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds> time)

## Related Non-Members

bool | operator!=(const QDateTime &lhs, const QDateTime &rhs)
`(since 6.4)` QDateTime | operator+(const QDateTime &dateTime, std::chrono::milliseconds duration)
`(since 6.4)` QDateTime | operator+(std::chrono::milliseconds duration, const QDateTime &dateTime)
`(since 6.4)` std::chrono::milliseconds | operator-(const QDateTime &lhs, const QDateTime &rhs)
`(since 6.4)` QDateTime | operator-(const QDateTime &dateTime, std::chrono::milliseconds duration)
bool | operator<(const QDateTime &lhs, const QDateTime &rhs)
QDataStream & | operator<<(QDataStream &out, const QDateTime &dateTime)
bool | operator<=(const QDateTime &lhs, const QDateTime &rhs)
bool | operator==(const QDateTime &lhs, const QDateTime &rhs)
bool | operator>(const QDateTime &lhs, const QDateTime &rhs)
bool | operator>=(const QDateTime &lhs, const QDateTime &rhs)
QDataStream & | operator>>(QDataStream &in, QDateTime &dateTime)

## Detailed Description

A QDateTime object encodes a calendar date and a clock time (a "datetime") in accordance with a time representation. It combines features of the QDate and QTime 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.

QDateTime can describe datetimes with respect to local time, to UTC, to a specified offset from UTC or to a specified time zone. Each of these time representations can be encapsulated in a suitable instance of the QTimeZone class. For example, a time zone of "Europe/Berlin" will apply the daylight-saving rules as used in Germany. In contrast, a fixed offset from UTC of +3600 seconds is one hour ahead of UTC (usually written in ISO standard notation as "UTC+01:00"), with no daylight-saving complications. When using either local time or a specified time zone, time-zone transitions (see below) are taken into account. A QDateTime's timeSpec() will tell you which of the four types of time representation is in use; its timeRepresentation() provides a full description of that time representation, as a QTimeZone.

A QDateTime object is typically created either by giving a date and time explicitly in the constructor, or by using a static function such as currentDateTime() or fromMSecsSinceEpoch(). The date and time can be changed with setDate() and setTime(). A datetime can also be set using the setMSecsSinceEpoch() function that takes the time, in milliseconds, since the start, in UTC, of the year 1970. The fromString() function returns a QDateTime, given a string and a date format used to interpret the date within the string.

QDateTime::currentDateTime() returns a QDateTime that expresses the current date and time with respect to a specific time representation, such as local time (its default). QDateTime::currentDateTimeUtc() returns a QDateTime that expresses the current date and time with respect to UTC; it is equivalent to `QDateTime::currentDateTime(QTimeZone::UTC)`.

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

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

You can increment (or decrement) a datetime by a given number of milliseconds using addMSecs(), seconds using addSecs(), or days using addDays(). Similarly, you can use addMonths() and addYears(). The daysTo() function returns the number of days between two datetimes, secsTo() returns the number of seconds between two datetimes, and msecsTo() returns the number of milliseconds between two datetimes. These operations are aware of daylight-saving time (DST) and other time-zone transitions, where applicable.

Use toTimeZone() to re-express a datetime in terms of a different time representation. By passing a lightweight QTimeZone that represents local time, UTC or a fixed offset from UTC, you can convert the datetime to use the corresponding time representation; or you can pass a full time zone (whose timeSpec() is `Qt::TimeZone`) to use that instead.

### Remarks

QDateTime does not account for leap seconds.

All conversions to and from string formats are done using the C locale. For localized conversions, see QLocale.

There is no year 0 in the Gregorian calendar. Dates in that year are considered invalid. The year -1 is the year "1 before Christ" or "1 before common era." The day before 1 January 1 CE is 31 December 1 BCE.

Using local time (the default) or a specified time zone implies a need to resolve any issues around transitions. As a result, operations on such QDateTime instances (notably including constructing them) may be more expensive than the equivalent when using UTC or a fixed offset from it.

#### Range of Valid Dates

The range of values that QDateTime can represent is dependent on the internal storage implementation. QDateTime is currently stored in a qint64 as a serial msecs value encoding the date and time. This restricts the date range to about ±292 million years, compared to the QDate range of ±2 billion years. Care must be taken when creating a QDateTime with extreme values that you do not overflow the storage. The exact range of supported values varies depending on the time representation used.

#### Use of Timezones

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

QDateTime likewise uses system-provided information to determine the offsets of other timezones from UTC. If this information is incomplete or out of date, QDateTime will give wrong results. See the QTimeZone documentation for more details.

On modern Unix systems, this means QDateTime usually has accurate information about historical transitions (including DST, see below) whenever possible. On Windows, where the system doesn't support historical timezone data, historical accuracy is not maintained with respect to timezone transitions, notably including DST. However, building Qt with the ICU library will equip QTimeZone with the same timezone database as is used on Unix.

#### Timezone transitions

QDateTime takes into account timezone transitions, both the transitions between Standard Time and Daylight-Saving Time (DST) and the transitions that arise when a zone changes its standard offset. For example, if the transition is at 2am and the clock goes forward to 3am, then there is a "missing" hour from 02:00:00 to 02:59:59.999. Such a transition is known as a "spring forward" and the times skipped over have no meaning. When a transition goes the other way, known as a "fall back", a time interval is repeated, first in the old zone (usually DST), then in the new zone (usually Standard Time), so times in this interval are ambiguous.

Some zones use "reversed" DST, using standard time in summer and daylight-saving time (with a lowered offset) in winter. For such zones, the spring forward still happens in spring and skips an hour, but is a transition out of daylight-saving time, while the fall back still repeats an autumn hour but is a transition to daylight-saving time.

When converting from a UTC time (or a time at fixed offset from UTC), there is always an unambiguous valid result in any timezone. However, when combining a date and time to make a datetime, expressed with respect to local time or a specific time-zone, the nominal result may fall in a transition, making it either invalid or ambiguous. Methods where this situation may arise take a `resolve` parameter: this is always ignored if the requested datetime is valid and unambiguous. See TransitionResolution for the options it lets you control. Prior to Qt 6.7, the equivalent of its LegacyBehavior was selected.

For a spring forward's skipped interval, interpreting the requested time with either offset yields an actual time at which the other offset was in use; so passing `TransitionResolution::RelativeToBefore` for `resolve` will actually result in a time after the transition, that would have had the requested representation had the transition not happened. Likewise, `TransitionResolution::RelativeToAfter` for `resolve` results in a time before the transition, that would have had the requested representation, had the transition happened earlier.

When QDateTime performs arithmetic, as with addDay() or addSecs(), it takes care to produce a valid result. For example, on a day when there is a spring forward from 02:00 to 03:00, adding one second to 01:59:59 will get 03:00:00. Adding one day to 02:30 on the preceding day will get 03:30 on the day of the transition, while subtracting one day, by calling `addDay(-1)`, to 02:30 on the following day will get 01:30 on the day of the transition. While addSecs() will deliver a time offset by the given number of seconds, addDays() adjusts the date and only adjusts time if it would otherwise get an invalid result. Applying `addDays(1)` to 03:00 on the day before the spring-forward will simply get 03:00 on the day of the transition, even though the latter is only 23 hours after the former; but `addSecs(24 * 60 * 60)` will get 04:00 on the day of the transition, since that's 24 hours later. Typical transitions make some days 23 or 25 hours long.

For datetimes that the system `time_t` can represent (from 1901-12-14 to 2038-01-18 on systems with 32-bit `time_t`; for the full range QDateTime can represent if the type is 64-bit), the standard system APIs are used to determine local time's offset from UTC. For datetimes not handled by these system APIs (potentially including some within the `time_t` range), QTimeZone::systemTimeZone() is used, if available, or a best effort is made to estimate. In any case, the offset information used depends on the system and may be incomplete or, for past times, historically inaccurate. Furthermore, for future dates, the local time zone's offsets and DST rules may change before that date comes around.

##### Whole day transitions

A small number of zones have skipped or repeated entire days as part of moving The International Date Line across themselves. For these, daysTo() will be unaware of the duplication or gap, simply using the difference in calendar date; in contrast, msecsTo() and secsTo() know the true time interval. Likewise, addMSecs() and addSecs() correspond directly to elapsed time, where addDays(), addMonths() and addYears() follow the nominal calendar, aside from where landing in a gap or duplication requires resolving an ambiguity or invalidity due to a duplication or omission.

Note: Days "lost" during a change of calendar, such as from Julian to Gregorian, do not affect QDateTime. Although the two calendars describe dates differently, the successive days across the change are described by consecutive QDate instances, each one day later than the previous, as described by either calendar or by their toJulianDay() values. In contrast, a zone skipping or duplicating a day is changing its description of time, not date, for all that it does so by a whole 24 hours.

#### Offsets From UTC

Offsets from UTC are measured in seconds east of Greenwich. The moment described by a particular date and time, such as noon on a particular day, depends on the time representation used. Those with a higher offset from UTC describe an earlier moment, and those with a lower offset a later moment, by any given combination of date and time.

There is no explicit size restriction on an offset from UTC, but there is an implicit limit imposed when using the toString() and fromString() methods which use a ±hh:mm format, effectively limiting the range to ± 99 hours and 59 minutes and whole minutes only. Note that currently no time zone has an offset outside the range of ±14 hours and all known offsets are multiples of five minutes. Historical time zones have a wider range and may have offsets including seconds; these last cannot be faithfully represented in strings.

See also QDate, QTime, QDateTimeEdit, and QTimeZone.

## Member Type Documentation

### `[since 6.7]` enum class QDateTime::TransitionResolution

This enumeration is used to resolve datetime combinations which fall in Timezone transitions.

When constructing a datetime, specified in terms of local time or a time-zone that has daylight-saving time, or revising one with setDate(), setTime() or setTimeZone(), the given parameters may imply a time representation that either has no meaning or has two meanings in the zone. Such time representations are described as being in the transition. In either case, we can simply return an invalid datetime, to indicate that the operation is ill-defined. In the ambiguous case, we can alternatively select one of the two times that could be meant. When there is no meaning, we can select a time either side of it that might plausibly have been meant. For example, when advancing from an earlier time, we can select the time after the transition that is actually the specified amount of time after the earlier time in question. The options specified here configure how such selection is performed.

Constant | Value | Description
--- | --- | ---
`QDateTime::TransitionResolution::Reject` | `0` | Treat any time in a transition as invalid. Either it really is, or it is ambiguous.
`QDateTime::TransitionResolution::RelativeToBefore` | `1` | Selects a time as if stepping forward from a time before the transition. This interprets the requested time using the offset in effect before the transition and, if necessary, converts the result to the offset in effect at the resulting time.
`QDateTime::TransitionResolution::RelativeToAfter` | `2` | Select a time as if stepping backward from a time after the transition. This interprets the requested time using the offset in effect after the transition and, if necessary, converts the result to the offset in effect at the resulting time.
`QDateTime::TransitionResolution::PreferBefore` | `3` | Selects a time before the transition,
`QDateTime::TransitionResolution::PreferAfter` | `4` | Selects a time after the transition.
`QDateTime::TransitionResolution::PreferStandard` | `5` | Selects a time on the standard time side of the transition.
`QDateTime::TransitionResolution::PreferDaylightSaving` | `6` | Selects a time on the daylight-saving-time side of the transition.
`QDateTime::TransitionResolution::LegacyBehavior` | `RelativeToBefore` | An alias for RelativeToBefore, which is used as default for TransitionResolution parameters, as this most closely matches the behavior prior to Qt 6.7.

For addDays(), addMonths() or addYears(), the behavior is and (mostly) was to use `RelativeToBefore` if adding a positive adjustment and `RelativeToAfter` if adding a negative adjustment.

Note: In time zones where daylight-saving increases the offset from UTC in summer (known as "positive DST"), PreferStandard is an alias for RelativeToAfter and PreferDaylightSaving for RelativeToBefore. In time zones where the daylight-saving mechanism is a decrease in offset from UTC in winter (known as "negative DST"), the reverse applies, provided the operating system reports - as it does on most platforms - whether a datetime is in DST or standard time. For some platforms, where transition times are unavailable even for Qt::TimeZone datetimes, QTimeZone is obliged to presume that the side with lower offset from UTC is standard time, effectively assuming positive DST.

The following tables illustrate how a QDateTime constructor resolves a request for 02:30 on a day when local time has a transition between 02:00 and 03:00, with a nominal standard time LST and daylight-saving time LDT on the two sides, in the various possible cases. The transition type may be to skip an hour or repeat it. The type of transition and value of a parameter `resolve` determine which actual time on the given date is selected. First, the common case of positive daylight-saving, where:

Before | 02:00–03:00 | After | `resolve` | selected
--- | --- | --- | --- | ---
LST | skip | LDT | RelativeToBefore | 03:30 LDT
LST | skip | LDT | RelativeToAfter | 01:30 LST
LST | skip | LDT | PreferBefore | 01:30 LST
LST | skip | LDT | PreferAfter | 03:30 LDT
LST | skip | LDT | PreferStandard | 01:30 LST
LST | skip | LDT | PreferDaylightSaving | 03:30 LDT
LDT | repeat | LST | RelativeToBefore | 02:30 LDT
LDT | repeat | LST | RelativeToAfter | 02:30 LST
LDT | repeat | LST | PreferBefore | 02:30 LDT
LDT | repeat | LST | PreferAfter | 02:30 LST
LDT | repeat | LST | PreferStandard | 02:30 LST
LDT | repeat | LST | PreferDaylightSaving | 02:30 LDT

Second, the case for negative daylight-saving, using LDT in winter and skipping an hour to transition to LST in summer, then repeating an hour at the transition back to winter:

LDT | skip | LST | RelativeToBefore | 03:30 LST
LDT | skip | LST | RelativeToAfter | 01:30 LDT
LDT | skip | LST | PreferBefore | 01:30 LDT
LDT | skip | LST | PreferAfter | 03:30 LST
LDT | skip | LST | PreferStandard | 03:30 LST
LDT | skip | LST | PreferDaylightSaving | 01:30 LDT
LST | repeat | LDT | RelativeToBefore | 02:30 LST
LST | repeat | LDT | RelativeToAfter | 02:30 LDT
LST | repeat | LDT | PreferBefore | 02:30 LST
LST | repeat | LDT | PreferAfter | 02:30 LDT
LST | repeat | LDT | PreferStandard | 02:30 LST
LST | repeat | LDT | PreferDaylightSaving | 02:30 LDT

Reject can be used to prompt relevant QDateTime APIs to return an invalid datetime object so that your code can deal with transitions for itself, for example by alerting a user to the fact that the datetime they have selected is in a transition interval, to offer them the opportunity to resolve a conflict or ambiguity. Code using this may well find the other options above useful to determine relevant information to use in its own (or the user's) resolution. If the start or end of the transition, or the moment of the transition itself, is the right resolution, QTimeZone's transition APIs can be used to obtain that information. You can determine whether the transition is a repeated or skipped interval by using secsTo() to measure the actual time between noon on the previous and following days. The result will be less than 48 hours for a skipped interval (such as a spring-forward) and more than 48 hours for a repeated interval (such as a fall-back).

Note: When a resolution other than Reject is specified, a valid QDateTime object is returned, if possible. If the requested date-time falls in a gap, the returned date-time will not have the time() requested - or, in some cases, the date(), if a whole day was skipped. You can thus detect when a gap is hit by comparing date() and time() to what was requested.

##### Relation to other datetime software

The Python programming language's datetime APIs have a `fold` parameter that corresponds to `RelativeToBefore` (`fold = True`) and `RelativeToAfter` (`fold = False`).

The `Temporal` proposal to replace JavaScript's `Date` offers four options for how to resolve a transition, as value for a `disambiguation` parameter. Its `'reject'` raises an exception, which roughly corresponds to `Reject` producing an invalid result. Its `'earlier'` and `'later'` options correspond to `PreferBefore` and `PreferAfter`. Its `'compatible'` option corresponds to `RelativeToBefore` (and Python's `fold = True`).

This enum was introduced in Qt 6.7.

See also Timezone transitions and QDateTime::TransitionResolution.

### enum class QDateTime::YearRange

This enumerated type describes the range of years (in the Gregorian calendar) representable by QDateTime:

Constant | Value | Description
--- | --- | ---
`QDateTime::YearRange::First` | `-292275056` | The later parts of this year are representable
`QDateTime::YearRange::Last` | `+292278994` | The earlier parts of this year are representable

All dates strictly between these two years are also representable. Note, however, that the Gregorian Calendar has no year zero.

Note: QDate can describe dates in a wider range of years. For most purposes, this makes little difference, as the range of years that QDateTime can support reaches 292 million years either side of 1970.

See also isValid() and QDate.

## Member Function Documentation

### `[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().

### 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.

Note: Prior to Qt 6.7, the version of this function lacked the resolve parameter so had no way to resolve the ambiguities related to transitions.

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

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.

Note: Prior to Qt 6.7, the version of this function lacked the resolve parameter so had no way to resolve the ambiguities related to transitions.

This is an overloaded function.

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.

Note: Adding durations expressed in `std::chrono::months` or `std::chrono::years` does not yield the same result obtained by using addMonths() or addYears(). The former are fixed durations, calculated in relation to the solar year; the latter use the Gregorian calendar definitions of months/years.

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 toTimeZone().

### `[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 toTimeZone().

### `[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 toTimeZone().

### `[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]` 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, 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).

Note: This function requires C++20.

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).

Note: This function requires C++20.

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.

Note: This function requires C++20.

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)

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

This is an overloaded function.

This function was introduced in Qt 6.4.

### 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 setTimeZone().

### 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.

Note: Prior to Qt 6.7, the version of this function lacked the resolve parameter so had no way to resolve the ambiguities related to transitions.

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().

### 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.

Note: Prior to Qt 6.7, the version of this function lacked the resolve parameter so had no way to resolve the ambiguities related to transitions.

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

### 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.

Note: Prior to Qt 6.7, the version of this function lacked the resolve parameter so had no way to resolve the ambiguities related to transitions.

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 setTimeZone(), timeRepresentation(), date(), and time().

### 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.

Note: The abbreviation is not guaranteed to be unique, i.e. different time zones may have the same abbreviation. For Qt::LocalTime and Qt::TimeZone, when returned by the host system, the abbreviation may be localized.

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 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.

Note: This function requires C++20.

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.

Note: This function requires C++20.

This function was introduced in Qt 6.4.

See also fromStdTimePoint() and toSecsSinceEpoch().

### 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.toTimeZone(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.

## Related Non-Members

### `[since 6.4]` QDateTime operator+(const QDateTime &dateTime, std::chrono::milliseconds duration)

### `[since 6.4]` QDateTime operator+(std::chrono::milliseconds duration, const QDateTime &dateTime)

Returns a QDateTime object containing a datetime duration milliseconds later than dateTime (or earlier if duration is negative).

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

This function was introduced in Qt 6.4.

See also addMSecs().

### `[noexcept]` bool operator!=(const QDateTime &lhs, const QDateTime &rhs)

Returns `true` if lhs is different from rhs; otherwise returns `false`.

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date() and time() differ, if that difference matches the difference in UTC offset. If their `date()` and `time()` coincide, the one with higher offset from UTC is less (earlier) than the one with lower offset. As a result, datetimes are only weakly ordered.

Since 5.14, all invalid datetimes are equivalent and less than all valid datetimes.

See also operator==().

### `[since 6.4]` std::chrono::milliseconds operator-(const QDateTime &lhs, const QDateTime &rhs)

Returns the number of milliseconds between lhs and rhs. If lhs is earlier than rhs, the result will be negative.

Returns 0 if either datetime is invalid.

This function was introduced in Qt 6.4.

See also msecsTo().

### `[since 6.4]` QDateTime operator-(const QDateTime &dateTime, std::chrono::milliseconds duration)

Returns a QDateTime object containing a datetime duration milliseconds earlier than dateTime (or later if duration is negative).

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

This function was introduced in Qt 6.4.

See also addMSecs().

### `[noexcept]` bool operator<(const QDateTime &lhs, const QDateTime &rhs)

Returns `true` if lhs is earlier than rhs; otherwise returns `false`.

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date() and time() differ, if that difference matches the difference in UTC offset. If their `date()` and `time()` coincide, the one with higher offset from UTC is less (earlier) than the one with lower offset. As a result, datetimes are only weakly ordered.

Since 5.14, all invalid datetimes are equivalent and less than all valid datetimes.

See also operator==().

### QDataStream &operator<<(QDataStream &out, const QDateTime &dateTime)

Writes dateTime to the out stream.

See also Serializing Qt Data Types.

### `[noexcept]` bool operator<=(const QDateTime &lhs, const QDateTime &rhs)

Returns `true` if lhs is earlier than or equal to rhs; otherwise returns `false`.

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date() and time() differ, if that difference matches the difference in UTC offset. If their `date()` and `time()` coincide, the one with higher offset from UTC is less (earlier) than the one with lower offset. As a result, datetimes are only weakly ordered.

Since 5.14, all invalid datetimes are equivalent and less than all valid datetimes.

See also operator==().

### `[noexcept]` bool operator==(const QDateTime &lhs, const QDateTime &rhs)

Returns `true` if lhs represents the same moment in time as rhs; otherwise returns `false`.

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date() and time() differ, if that difference matches the difference in UTC offset. If their `date()` and `time()` coincide, the one with higher offset from UTC is less (earlier) than the one with lower offset. As a result, datetimes are only weakly ordered.

Since 5.14, all invalid datetimes are equivalent and less than all valid datetimes.

See also operator!=(), operator<(), operator<=(), operator>(), and operator>=().

### `[noexcept]` bool operator>(const QDateTime &lhs, const QDateTime &rhs)

Returns `true` if lhs is later than rhs; otherwise returns `false`.

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date() and time() differ, if that difference matches the difference in UTC offset. If their `date()` and `time()` coincide, the one with higher offset from UTC is less (earlier) than the one with lower offset. As a result, datetimes are only weakly ordered.

Since 5.14, all invalid datetimes are equivalent and less than all valid datetimes.

See also operator==().

### `[noexcept]` bool operator>=(const QDateTime &lhs, const QDateTime &rhs)

Returns `true` if lhs is later than or equal to rhs; otherwise returns `false`.

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date() and time() differ, if that difference matches the difference in UTC offset. If their `date()` and `time()` coincide, the one with higher offset from UTC is less (earlier) than the one with lower offset. As a result, datetimes are only weakly ordered.

Since 5.14, all invalid datetimes are equivalent and less than all valid datetimes.

See also operator==().

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

Reads a datetime from the stream in into dateTime.

See also Serializing Qt Data Types.