QDateTime Class

Member Function Documentation

Returns the datetime as a string. The format parameter determines the format of the result string. If cal is supplied, it determines the calendar used to represent the date; it defaults to Gregorian. See QTime::toString() and QDate::toString() for the supported specifiers for time and date, respectively.

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

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

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

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

Note: If localized month and day names are desired, please switch to using QLocale::system().toString() as QDateTime methods shall change to use English (C locale) names at Qt 6.

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

QDateTime::QDateTime(QDateTime &&other)

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

This function was introduced in Qt 5.8.

QDateTime::QDateTime(const QDateTime &other)

Constructs a copy of the other datetime.

QDateTime::QDateTime(const QDate &date, const QTime &time, const QTimeZone &timeZone)

Constructs a datetime with the given date and time, using the Time Zone specified by timeZone.

If date is valid and time is not, the time will be set to 00:00:00.

If timeZone is invalid then the datetime will be invalid.

This function was introduced in Qt 5.2.

QDateTime::QDateTime(const QDate &date, const QTime &time, Qt::TimeSpec spec, int offsetSeconds)

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

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

If the spec is not Qt::OffsetFromUTC then offsetSeconds will be ignored.

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

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

This function was introduced in Qt 5.2.

QDateTime::QDateTime(const QDate &date, const QTime &time, Qt::TimeSpec spec = Qt::LocalTime)

Constructs a datetime with the given date and time, using the time specification defined by spec.

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

If spec is Qt::OffsetFromUTC then it will be set to Qt::UTC, i.e. an offset of 0 seconds. To create a Qt::OffsetFromUTC datetime use the correct constructor.

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

QDateTime::QDateTime(const QDate &date)

Constructs a datetime with the given date, using Qt::LocalTime as the timeSpec() and the time at the start of that date.

See also QDate::startOfDay().

QDateTime::QDateTime()

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

See also isValid().

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

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

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 and the resulting date and time fall in the Standard Time to Daylight-Saving Time transition hour then the result will be adjusted accordingly, i.e. if the transition is at 2am and the clock goes forward to 3am and the result falls between 2am and 3am then the result will be adjusted to fall after 3am.

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

QDateTime QDateTime::addMSecs(qint64 msecs) const

Returns a QDateTime object containing a datetime msecs miliseconds 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 and the resulting date and time fall in the Standard Time to Daylight-Saving Time transition hour then the result will be adjusted accordingly, i.e. if the transition is at 2am and the clock goes forward to 3am and the result falls between 2am and 3am then the result will be adjusted to fall after 3am.

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

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 and the resulting date and time fall in the Standard Time to Daylight-Saving Time transition hour then the result will be adjusted accordingly, i.e. if the transition is at 2am and the clock goes forward to 3am and the result falls between 2am and 3am then the result will be adjusted to fall after 3am.

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

[static] QDateTime QDateTime::currentDateTime()

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

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

[static] QDateTime QDateTime::currentDateTimeUtc()

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

This function was introduced in Qt 4.7.

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

[static] qint64 QDateTime::currentMSecsSinceEpoch()

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

This function was introduced in Qt 4.7.

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

[static] qint64 QDateTime::currentSecsSinceEpoch()

Returns the number of seconds since 1970-01-01T00:00:00 Universal Coordinated Time.

This function was introduced in Qt 5.8.

See also currentMSecsSinceEpoch().

QDate QDateTime::date() const

Returns the date part of the datetime.

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

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.

This function was introduced in Qt 5.5.

See also toCFDate().

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

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

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.

This function was introduced in Qt 4.7.

See also toMSecsSinceEpoch() and setMSecsSinceEpoch().

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

Returns a datetime whose date and time are the number of milliseconds msecs that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC) and converted to the given spec.

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

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

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

This function was introduced in Qt 5.2.

See also toMSecsSinceEpoch() and setMSecsSinceEpoch().

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

Returns a datetime whose date and time are the number of milliseconds msecs that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC) and with the given timeZone.

This function was introduced in Qt 5.2.

See also fromSecsSinceEpoch().

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

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

This function was introduced in Qt 5.5.

See also toNSDate().

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

Returns a datetime whose date and time are the number of seconds secs that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC) and converted to the given spec.

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

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

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

This function was introduced in Qt 5.8.

See also toSecsSinceEpoch() and setSecsSinceEpoch().

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

Returns a datetime whose date and time are the number of seconds secs that have passed since 1970-01-01T00:00:00.000, Coordinated Universal Time (Qt::UTC) and with the given timeZone.

This function was introduced in Qt 5.8.

See also fromMSecsSinceEpoch().

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

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

Note for Qt::TextDate: It is recommended that you use the English short month names (e.g. "Jan"). Although localized month names can also be used in Qt 5, they depend on the user's locale settings.

Note: Support for localized dates, including the format options Qt::SystemLocaleDate, Qt::SystemLocaleShortDate, Qt::SystemLocaleLongDate, Qt::LocaleDate, Qt::DefaultLocaleShortDate, and Qt::DefaultLocaleLongDate, shall be removed in Qt 6. Use QLocale::toDateTime() instead.

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

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

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

Uses the calendar cal if supplied, else Gregorian.

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

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

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

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

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);

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

For example:

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

Note: If localized month and day names are used, please switch to using QLocale::system().toDateTime() as QDateTime methods shall change to only recognize English (C locale) names at Qt 6.

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

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.

This function was introduced in Qt 5.2.

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 both the date and the time are valid and they are valid in the current Qt::TimeSpec, otherwise returns false.

If the timeSpec() is Qt::LocalTime or Qt::TimeZone then the date and time are checked to see if they fall in the Standard Time to Daylight-Saving Time transition hour, i.e. if the transition is at 2am and the clock goes forward to 3am then the time from 02:00:00 to 02:59:59.999 is considered to be 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 date-time'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 unless the date precedes the start of 1970. 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).

This function was introduced in Qt 5.2.

See also setOffsetFromUtc().

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

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

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

Returns 0 if either datetime is invalid.

Example:

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

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

void QDateTime::setDate(const QDate &date)

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.

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

void QDateTime::setMSecsSinceEpoch(qint64 msecs)

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

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

This function was introduced in Qt 4.7.

See also toMSecsSinceEpoch() and setSecsSinceEpoch().

void QDateTime::setOffsetFromUtc(int offsetSeconds)

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

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

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

This function was introduced in Qt 5.2.

See also isValid() and offsetFromUtc().

void QDateTime::setSecsSinceEpoch(qint64 secs)

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

This function was introduced in Qt 5.8.

See also toSecsSinceEpoch() and setMSecsSinceEpoch().

void QDateTime::setTime(const QTime &time)

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());

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

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

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

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

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

Example:

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

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

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

See also timeSpec(), setDate(), setTime(), setTimeZone(), and Qt::TimeSpec.

void QDateTime::setTimeZone(const QTimeZone &toZone)

Sets the time zone used in this datetime to toZone. The datetime will refer to a different point in time.

If toZone is invalid then the datetime will be invalid.

This function was introduced in Qt 5.2.

See also timeZone() and Qt::TimeSpec.

void QDateTime::swap(QDateTime &other)

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

This function was introduced in Qt 5.0.

QTime QDateTime::time() const

Returns the time part of the datetime.

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

Qt::TimeSpec QDateTime::timeSpec() const

Returns the time specification of the datetime.

See also setTimeSpec(), date(), time(), and Qt::TimeSpec.

QTimeZone QDateTime::timeZone() const

Returns the time zone of the datetime.

If the timeSpec() is Qt::LocalTime then an instance of the current system time zone will be returned. Note however that if you copy this time zone the instance will not remain in sync if the system time zone changes.

This function was introduced in Qt 5.2.

See also setTimeZone() and Qt::TimeSpec.

QString QDateTime::timeZoneAbbreviation() const

Returns the Time Zone Abbreviation for the datetime.

If the timeSpec() is Qt::UTC this will be "UTC".

If the timeSpec() is Qt::OffsetFromUTC this will be in the format "UTC[+-]00:00".

If the timeSpec() is Qt::LocalTime then the host system is queried for the correct abbreviation.

Note that abbreviations may or may not be localized.

Note too that the abbreviation is not guaranteed to be a unique value, i.e. different time zones may have the same abbreviation.

This function was introduced in Qt 5.2.

See also timeSpec().

CFDateRef QDateTime::toCFDate() const

Creates a CFDate from a QDateTime. The caller owns the CFDate object and is responsible for releasing it.

This function was introduced in Qt 5.5.

See also fromCFDate().

QDateTime QDateTime::toLocalTime() const

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

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 toTimeSpec().

qint64 QDateTime::toMSecsSinceEpoch() const

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

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

This function was introduced in Qt 4.7.

See also toSecsSinceEpoch() and setMSecsSinceEpoch().

NSDate *QDateTime::toNSDate() const

Creates an NSDate from a QDateTime. The NSDate object is autoreleased.

This function was introduced in Qt 5.5.

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.

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

This function was introduced in Qt 5.2.

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

qint64 QDateTime::toSecsSinceEpoch() const

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

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

This function was introduced in Qt 5.8.

See also toMSecsSinceEpoch() and setSecsSinceEpoch().

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

This is an overloaded function.

Returns the datetime as a string in the format given.

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

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

The format options Qt::SystemLocaleDate, Qt::SystemLocaleShortDate and Qt::SystemLocaleLongDate shall be removed in Qt 6. Their use should be replaced with QLocale::system().toString(datetime, QLocale::ShortFormat) or QLocale::system().toString(datetime, QLocale::LongFormat).

The format options Qt::LocaleDate, Qt::DefaultLocaleShortDate and Qt::DefaultLocaleLongDate shall be removed in Qt 6. Their use should be replaced with QLocale().toString(datetime, QLocale::ShortFormat) or QLocale().toString(datetime, QLocale::LongFormat).

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

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

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

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

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

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

If spec is Qt::OffsetFromUTC then it is set to Qt::UTC. To set to a spec of Qt::OffsetFromUTC use toOffsetFromUtc().

If spec is Qt::TimeZone then it is set to Qt::LocalTime, i.e. the local Time Zone.

Example:

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

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

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

Returns a copy of this datetime converted to the given timeZone

This function was introduced in Qt 5.2.

See also timeZone() and toTimeSpec().

QDateTime QDateTime::toUTC() const

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

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 toTimeSpec().

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

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

Two datetimes are different if either the date, the time, or the time zone components are different. Since 5.14, any invalid datetime is less than all valid datetimes.

See also operator==().

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

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

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

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

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

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

Since 5.14, all invalid datetimes are equal to one another and differ from all other datetimes.

See also operator!=().

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

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

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

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