QDateTime 类

QDateTime 类提供日期和时间功能。 更多...

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

• 所有成员列表，包括继承成员
• 弃用成员
• QDateTime is part of 隐式共享类 .

此类 weakly comparable .

注意： 此类的所有函数 可重入 .

公共类型

(从 6.7 起) enum class	TransitionResolution { Reject, RelativeToBefore, RelativeToAfter, PreferBefore, PreferAfter, …, LegacyBehavior }
enum class	YearRange { First, Last }

公共函数

	QDateTime ()
	QDateTime (QDate date , QTime time , const QTimeZone & timeZone , QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
(从 6.5 起)	QDateTime (QDate date , QTime time , QDateTime::TransitionResolution resolve = TransitionResolution::LegacyBehavior)
	QDateTime (const QDateTime & other )
	QDateTime (QDateTime && other )
	~QDateTime ()
QDateTime	addDays (qint64 ndays ) const
(从 6.4 起) 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
(从 6.5 起) QTimeZone	timeRepresentation () const
Qt::TimeSpec	timeSpec () const
QTimeZone	timeZone () const
QString	timeZoneAbbreviation () const
CFDateRef	toCFDate () const
QDateTime	toLocalTime () const
qint64	toMSecsSinceEpoch () const
NSDate *	toNSDate () const
QDateTime	toOffsetFromUtc (int offsetSeconds ) const
qint64	toSecsSinceEpoch () const
(从 6.4 起) std::chrono::sys_time<std::chrono::milliseconds>	toStdSysMilliseconds () const
(从 6.4 起) std::chrono::sys_seconds	toStdSysSeconds () const
QString	toString (const QString & format , QCalendar cal ) const
QString	toString (Qt::DateFormat format = Qt::TextDate) const
QString	toString (const QString & format ) const
QString	toString (QStringView format ) const
QString	toString (QStringView format , QCalendar cal ) const
QDateTime	toTimeZone (const QTimeZone & timeZone ) const
QDateTime	toUTC () const
(从 6.4 起) QDateTime &	operator+= (std::chrono::milliseconds duration )
(从 6.4 起) QDateTime &	operator-= (std::chrono::milliseconds duration )
QDateTime &	operator= (const QDateTime & other )

静态公共成员

(从 6.5 起) QDateTime	currentDateTime (const QTimeZone & zone )
QDateTime	currentDateTime ()
QDateTime	currentDateTimeUtc ()
qint64	currentMSecsSinceEpoch ()
qint64	currentSecsSinceEpoch ()
QDateTime	fromCFDate (CFDateRef date )
QDateTime	fromMSecsSinceEpoch (qint64 msecs , const QTimeZone & timeZone )
(从 6.5 起) QDateTime	fromMSecsSinceEpoch (qint64 msecs )
QDateTime	fromNSDate (const NSDate * date )
QDateTime	fromSecsSinceEpoch (qint64 secs , const QTimeZone & timeZone )
(从 6.5 起) QDateTime	fromSecsSinceEpoch (qint64 secs )
(从 6.4 起) QDateTime	fromStdLocalTime (const std::chrono::local_time<std::chrono::milliseconds> & time )
(从 6.4 起) QDateTime	fromStdTimePoint (const std::chrono::time_point<Clock, Duration> & time )
(从 6.4 起) QDateTime	fromStdTimePoint (std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds> time )
(从 6.4 起) QDateTime	fromStdTimePoint (const std::chrono::local_time<std::chrono::milliseconds> & time )
(从 6.4 起) QDateTime	fromStdZonedTime (const int & time )
QDateTime	fromString (const QString & string , Qt::DateFormat format = Qt::TextDate)
(从 6.0 起) QDateTime	fromString (QStringView string , Qt::DateFormat format = Qt::TextDate)
(从 6.0 起) QDateTime	fromString (QStringView string , QStringView format , QCalendar cal )
(从 6.0 起) QDateTime	fromString (const QString & string , QStringView format , QCalendar cal )
QDateTime	fromString (const QString & string , const QString & format , QCalendar cal )
(从 6.7 起) QDateTime	fromString (QStringView string , QStringView format , int baseYear = QLocale::DefaultTwoDigitBaseYear)
(从 6.7 起) QDateTime	fromString (QStringView string , QStringView format , int baseYear , QCalendar cal )
(从 6.7 起) QDateTime	fromString (const QString & string , QStringView format , int baseYear = QLocale::DefaultTwoDigitBaseYear)
(从 6.0 起) QDateTime	fromString (const QString & string , QStringView format , int baseYear , QCalendar cal )
(从 6.7 起) QDateTime	fromString (const QString & string , const QString & format , int baseYear = QLocale::DefaultTwoDigitBaseYear)
QDateTime	fromString (const QString & string , const QString & format , int baseYear , QCalendar cal )

相关非成员

bool	operator!= (const QDateTime & lhs , const QDateTime & rhs )
(从 6.4 起) QDateTime	operator+ (const QDateTime & dateTime , std::chrono::milliseconds duration )
(从 6.4 起) QDateTime	operator+ (std::chrono::milliseconds duration , const QDateTime & dateTime )
(从 6.4 起) std::chrono::milliseconds	operator- (const QDateTime & lhs , const QDateTime & rhs )
(从 6.4 起) 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 )

详细描述

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

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 () 和 addYears ()。 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.

使用 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 () 是 Qt::TimeZone ) to use that instead.

备注

注意： QDateTime does not account for leap seconds.

注意： All conversion to and from string formats is done using the C locale. For localized conversions, see QLocale .

注意： 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.

注意： 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.

有效日期范围

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 文档编制了解更多细节。

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 () 和 secsTo () know the true time interval. Likewise, addMSecs () 和 addSecs () correspond directly to elapsed time, where addDays (), addMonths () 和 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.

注意： 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 () 和 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.

另请参阅 QDate , QTime , QDateTimeEdit ，和 QTimeZone .

成员类型文档编制

[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 () 或 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.

常量	值	描述
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 () 或 addYears (), the behavior is and (mostly) was to use RelativeToBefore if adding a positive adjustment and RelativeToAfter if adding a negative adjustment.

注意： 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	后于	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).

注意： 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 () 和 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 ) 和 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 ).

该枚举在 Qt 6.7 引入。

另请参阅 Timezone transitions and QDateTime::TransitionResolution.

enum class QDateTime:: YearRange

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

常量	值	描述
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.

注意： 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.

另请参阅 isValid () 和 QDate .

成员函数文档编制

QString QDateTime:: toString ( QStringView format , QCalendar cal ) const

QString QDateTime:: toString (const QString & format , QCalendar cal ) const

以字符串形式返回 datetime。 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 () 和 QDate::toString () for the supported specifiers for time and date, respectively, in the format 参数。

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):

格式	结果
dd.MM.yyyy	21.05.2001
ddd MMMM d yy	Tue May 21 01
hh:mm:ss.zzz	14:13:09.120
hh:mm:ss.z	14:13:09.12
h:m:s ap	2:13:9 pm

若日期时间无效，返回空字符串。

注意： Day and month names as well as AM/PM indicators are given in English (C locale). To get localized month and day names and localized forms of AM/PM, use QLocale::system ().toDateTime().

另请参阅 fromString (), QDate::toString (), QTime::toString ()，和 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.

另请参阅 isValid (), setMSecsSinceEpoch (), setDate (), setTime ()，和 setTimeZone ().

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

构造日期时间采用给定 date and time , using the time representation described by timeZone .

若 date 有效和 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.

注意： 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)

这是重载函数。

构造日期时间采用给定 date and time , using local time.

若 date 有效和 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.

注意： 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.

该函数在 Qt 6.5 引入。

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

构造副本为 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 ()

销毁日期时间。

QDateTime QDateTime:: addDays ( qint64 ndays ) const

返回 QDateTime 对象包含日期时间 ndays days later than the datetime of this object (or earlier if ndays is negative).

若 timeSpec () 是 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).

另请参阅 daysTo (), addMonths (), addYears (), addSecs ()，和 Timezone transitions .

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

返回 QDateTime 对象包含日期时间 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.

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

该函数在 Qt 6.4 引入。

另请参阅 addMSecs (), msecsTo (), addDays (), addMonths ()，和 addYears ().

QDateTime QDateTime:: addMSecs ( qint64 msecs ) const

返回 QDateTime 对象包含日期时间 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.

另请参阅 addSecs (), msecsTo (), addDays (), addMonths ()，和 addYears ().

QDateTime QDateTime:: addMonths ( int nmonths ) const

返回 QDateTime 对象包含日期时间 nmonths months later than the datetime of this object (or earlier if nmonths is negative).

若 timeSpec () 是 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).

另请参阅 daysTo (), addDays (), addYears (), addSecs ()，和 Timezone transitions .

QDateTime QDateTime:: addSecs ( qint64 s ) const

返回 QDateTime 对象包含日期时间 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.

另请参阅 addMSecs (), secsTo (), addDays (), addMonths ()，和 addYears ().

QDateTime QDateTime:: addYears ( int nyears ) const

返回 QDateTime 对象包含日期时间 nyears years later than the datetime of this object (or earlier if nyears is negative).

若 timeSpec () 是 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).

另请参阅 daysTo (), addDays (), addMonths (), addSecs ()，和 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 。若 zone is omitted, local time is used.

该函数在 Qt 6.5 引入。

另请参阅 currentDateTimeUtc (), QDate::currentDate (), QTime::currentTime ()，和 toTimeSpec ().

[static] QDateTime QDateTime:: currentDateTime ()

这是重载函数。

[static] QDateTime QDateTime:: currentDateTimeUtc ()

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

相当于 currentDateTime(QTimeZone::UTC) .

另请参阅 currentDateTime (), QDate::currentDate (), QTime::currentTime ()，和 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.

另请参阅 currentDateTime (), currentDateTimeUtc ()，和 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.

另请参阅 currentMSecsSinceEpoch ().

QDate QDateTime:: date () const

返回 datetime 的日期部分。

另请参阅 setDate (), time ()，和 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.

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

范例：

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);
					

另请参阅 addDays (), secsTo ()，和 msecsTo ().

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

构造新的 QDateTime containing a copy of the CFDate date .

另请参阅 toCFDate ().

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

这是重载函数。

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.

另请参阅 fromSecsSinceEpoch (), toMSecsSinceEpoch ()，和 setMSecsSinceEpoch ().

[static, since 6.5] QDateTime QDateTime:: fromMSecsSinceEpoch ( qint64 msecs )

这是重载函数。

该函数在 Qt 6.5 引入。

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

构造新的 QDateTime containing a copy of the NSDate date .

另请参阅 toNSDate ().

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

这是重载函数。

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.

另请参阅 fromMSecsSinceEpoch (), toSecsSinceEpoch ()，和 setSecsSinceEpoch ().

[static, since 6.5] QDateTime QDateTime:: fromSecsSinceEpoch ( qint64 secs )

这是重载函数。

该函数在 Qt 6.5 引入。

[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 ).

注意： This function requires C++20.

该函数在 Qt 6.4 引入。

另请参阅 toStdSysMilliseconds () 和 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 ，使用 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.

注意： This function requires C++20.

该函数在 Qt 6.4 引入。

另请参阅 toStdSysMilliseconds () 和 fromMSecsSinceEpoch ().

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

这是重载函数。

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

该函数在 Qt 6.4 引入。

[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 ).

注意： This function requires C++20.

该函数在 Qt 6.4 引入。

另请参阅 toStdSysMilliseconds () 和 fromMSecsSinceEpoch ().

[static, since 6.4] QDateTime QDateTime:: fromStdZonedTime (const int & time )

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

注意： This function requires C++20.

该函数在 Qt 6.4 引入。

另请参阅 QTimeZone , toStdSysMilliseconds ()，和 fromMSecsSinceEpoch ().

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

返回 QDateTime 表示通过 string ，使用 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.

另请参阅 toString () 和 QLocale::toDateTime ().

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

这是重载函数。

该函数在 Qt 6.0 引入。

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

这是重载函数。

该函数在 Qt 6.0 引入。

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

这是重载函数。

该函数在 Qt 6.0 引入。

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

这是重载函数。

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

这是重载函数。

Uses a default-constructed QCalendar .

该函数在 Qt 6.7 引入。

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

这是重载函数。

该函数在 Qt 6.7 引入。

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

这是重载函数。

Uses a default-constructed QCalendar .

该函数在 Qt 6.7 引入。

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

这是重载函数。

该函数在 Qt 6.0 引入。

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

这是重载函数。

Uses a default-constructed QCalendar .

该函数在 Qt 6.7 引入。

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

返回 QDateTime 表示通过 string ，使用 format given, or an invalid datetime if the string cannot be parsed.

使用日历 cal 若有供给，否则高利历 (公历)。

当 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 () 了解细节。

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

表达式	输出
t	the timezone (offset, name, "Z" or offset with "UTC" prefix)
tt	the timezone in offset format with no colon between hours and minutes (for example "+0200")
ttt	the timezone in offset format with a colon between hours and minutes (for example "+02:00")
tttt	the timezone name (for example "Europe/Berlin"). The name recognized are those known to QTimeZone , which may depend on the operating system in use.

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 () 和 QTime::fromString ().

例如：

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);
					

注意： Day and month names as well as AM/PM indicators must be given in English (C locale). If localized month and day names or localized forms of AM/PM are to be recognized, use QLocale::system ().toDateTime().

注意： If a format character is repeated more times than the longest expression in the table above using it, this part of the format will be read as several expressions with no separator between them; the longest above, possibly repeated as many times as there are copies of it, ending with a residue that may be a shorter expression. Thus 'tttttt' would match "Europe/BerlinEurope/Berlin" and set the zone to Berlin time; if the datetime string contained "Europe/BerlinZ" it would "match" but produce an inconsistent result, leading to an invalid datetime.

另请参阅 toString (), QDate::fromString (), QTime::fromString ()，和 QLocale::toDateTime ().

bool QDateTime:: isDaylightTime () const

Returns if this datetime falls in Daylight-Saving Time.

若 Qt::TimeSpec 不是 Qt::LocalTime or Qt::TimeZone then will always return false.

另请参阅 timeSpec ().

bool QDateTime:: isNull () const

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

另请参阅 QDate::isNull (), QTime::isNull ()，和 isValid ().

bool QDateTime:: isValid () const

返回 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.

另请参阅 QDateTime::YearRange , QDate::isValid ()，和 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.

返回 0 若日期时间无效。

另请参阅 addMSecs (), daysTo ()，和 QTime::msecsTo ().

int QDateTime:: offsetFromUtc () const

Returns this datetime's Offset From UTC in seconds.

结果从属 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).

另请参阅 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.

返回 0 若日期时间无效。

范例：

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

另请参阅 addSecs (), daysTo ()，和 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.

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

注意： 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.

另请参阅 date (), setTime ()，和 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() ) 到 msecs 将产生未定义行为。

另请参阅 setSecsSinceEpoch (), toMSecsSinceEpoch ()，和 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 .

另请参阅 setMSecsSinceEpoch (), toSecsSinceEpoch ()，和 fromSecsSinceEpoch ().

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

Sets the time part of this datetime to time 。若 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());
					

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

注意： 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.

另请参阅 time (), setDate ()，和 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 () 和 time ().

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

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

注意： 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.

另请参阅 timeRepresentation (), timeZone ()，和 Qt::TimeSpec .

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

Swaps this datetime with other 。此操作非常快且从不失败。

QTime QDateTime:: time () const

Returns the time part of the datetime.

另请参阅 setTime (), date ()，和 timeRepresentation ().

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

返回 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 () 是 Qt::OffsetFromUTC , the returned QTimeZone 's fixedSecondsAheadOfUtc() supplies the offset. When timeSpec () 是 Qt::TimeZone ， QTimeZone object itself is the full representation of that time zone.

该函数在 Qt 6.5 引入。

另请参阅 timeZone (), setTimeZone ()，和 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() .

另请参阅 setTimeSpec (), timeRepresentation (), date ()，和 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 () 是 Qt::TimeZone .

当 timeSpec () 是 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.

另请参阅 timeRepresentation (), setTimeZone (), Qt::TimeSpec ，和 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.

注意： 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.

另请参阅 timeSpec () 和 QTimeZone::abbreviation ().

CFDateRef QDateTime:: toCFDate () const

创建 CFDate 从 QDateTime .

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

另请参阅 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.

范例：

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);
					

另请参阅 toTimeZone (), toUTC ()，和 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.

另请参阅 toSecsSinceEpoch (), setMSecsSinceEpoch ()，和 fromMSecsSinceEpoch ().

NSDate *QDateTime:: toNSDate () const

创建 NSDate 从 QDateTime .

The NSDate object is autoreleased.

另请参阅 fromNSDate ().

QDateTime QDateTime:: toOffsetFromUtc ( int offsetSeconds ) const

Returns a copy of this datetime converted to a spec of Qt::OffsetFromUTC 采用给定 offsetSeconds . Equivalent to toTimeZone(QTimeZone::fromSecondsAheadOfUtc(offsetSeconds)) .

若 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.

另请参阅 setOffsetFromUtc (), offsetFromUtc ()，和 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.

另请参阅 toMSecsSinceEpoch (), fromSecsSinceEpoch ()，和 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.

注意： This function requires C++20.

该函数在 Qt 6.4 引入。

另请参阅 fromStdTimePoint () 和 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.

注意： This function requires C++20.

该函数在 Qt 6.4 引入。

另请参阅 fromStdTimePoint () 和 toSecsSinceEpoch ().

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

这是重载函数。

以字符串形式返回日期时间按 format 给定。

若 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 ().

若 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 () 对于 QDateTime 。若 timeSpec () 是 Qt::UTC , Z will be appended to the string; if the timeSpec () 是 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].

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

若日期时间无效，返回空字符串。

警告： The Qt::ISODate format is only valid for years in the range 0 to 9999.

另请参阅 fromString (), QDate::toString (), QTime::toString ()，和 QLocale::toString ().

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

这是重载函数。

QString QDateTime:: toString ( QStringView format ) const

这是重载函数。

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);
					

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

另请参阅 timeRepresentation (), toLocalTime (), toUTC ()，和 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.

范例：

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);
					

另请参阅 toTimeZone (), toLocalTime ()，和 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.

该函数在 Qt 6.4 引入。

另请参阅 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.

该函数在 Qt 6.4 引入。

另请参阅 addMSecs .

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

拷贝 other datetime into this and returns this copy.

相关非成员

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

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

返回 QDateTime 对象包含日期时间 duration milliseconds later than dateTime (or earlier if duration is negative).

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

该函数在 Qt 6.4 引入。

另请参阅 addMSecs ().

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

返回 true if lhs is different from rhs ；否则返回 false .

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date () 和 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.

另请参阅 operator== ().

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

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

返回 0 若日期时间无效。

该函数在 Qt 6.4 引入。

另请参阅 msecsTo ().

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

返回 QDateTime 对象包含日期时间 duration milliseconds earlier than dateTime (or later if duration is negative).

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

该函数在 Qt 6.4 引入。

另请参阅 addMSecs ().

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

返回 true if lhs is earlier than rhs ；否则返回 false .

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date () 和 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.

另请参阅 operator== ().

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

写入 dateTime 到 out stream.

另请参阅 序列化 Qt 数据类型 .

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

返回 true if lhs is earlier than or equal to rhs ；否则返回 false .

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date () 和 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.

另请参阅 operator== ().

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

返回 true if lhs represents the same moment in time as rhs ；否则返回 false .

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date () 和 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.

另请参阅 operator!= (), operator< (), operator<= (), operator> ()，和 operator>= ().

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

返回 true if lhs is later than rhs ；否则返回 false .

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date () 和 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.

另请参阅 operator== ().

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

返回 true if lhs is later than or equal to rhs ；否则返回 false .

Two datetimes using different time representations can have different offsets from UTC. In this case, they may compare equivalent even if their date () 和 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.

另请参阅 operator== ().

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

Reads a datetime from the stream in into dateTime .

另请参阅 序列化 Qt 数据类型 .

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