<chrono>

Include the standard header <chrono> to define classes and functions that represent and manipulate time durations and time instants.

Beginning in Visual Studio 2015, the implementation of steady_clock has changed to meet the C++ Standard requirements for steadiness and monotonicity:

• steady_clock is now based on QueryPerformanceCounter()
• high_resolution_clock is now a typedef for steady_clock In the Microsoft C++ implementation, steady_clock::time_point is now a typedef for chrono::time_point<steady_clock>. However, this isn't necessarily the case for other implementations.

Requirements

Header: <chrono>

Regional legislatures occasionally make changes to time zones, and an international standards body specifies when new leap seconds should be accounted for. A database of these changes was added to Windows 10. Specifically:

Feature	Client version	Server version
Leap second database updates	Windows 10 version 1809 or later	Windows Server 2019 or later
Time zone support	Windows 10 version 1903/19H1 or later	Windows Server 2022 or later

Using the time-zone facilities on older versions of Windows results in a runtime error.

Namespace: std

Calendrical types

Name	Description
common_type struct	Describes specializations of class template common_type for instantiations of duration and time_point.
day class	A day of the month. For example, the 25th day of the month.
duration class	A time interval.
duration_values struct	Provides specific values for the duration template parameter Rep.
hh_mm_ss class	Splits a duration into hours:minutes:seconds.
last_spec	Used to indicate the last item in a month such as last day of the week of a month (the last Tuesday of February 2020) or the last day of a month (the last day of April 2019).
leap_second class	A date and a value for an inserted leap second.
leap_second_info struct	The data returned by get_leap_second_info.
month class	A month of a year. For example, July.
month_day class	A specific day of a specific month. For example, July 30.
month_day_last class	The last day of a month.
month_weekday class	The nth weekday of a specific month.
month_weekday_last class	The nth weekday of a specific month.
time_point class	A point in time.
weekday class	A day of the week.
weekday_last class	The last weekday of a month.
weekday_indexed class	Combines a day of the week with an index that represents the weekday of the month.
year class	A year in the Gregorian calendar.
year_month class	A year and month. The day isn't specified.
year_month_day class	A year, month, and day.
year_month_day_last class	The last day of a specific month and year.
year_month_weekday class	A specific year, month, and nth weekday of the month.
year_month_weekday_last class	A specific year, month, and last weekday of the month.

Clocks

Name	Description
file_clock class	An alias for the clock used for std::filesystem::file_time_type, which is used to express file timestamps.
gps_clock class	A clock that keeps GPS time. Measures time starting from the first Sunday of January 1980 at 00:00:00 UTC.
high_resolution_clock struct	A clock with a nanosecond tick period.
local_t struct	A pseudo-clock used as an argument to the time_point template to indicate that the time_point represents local time.
steady_clock struct	A steady clock. This clock is preferred for measuring time intervals.
system_clock struct	A clock based on the real-time clock of the system.
tai_clock class	Measures International Atomic Time (TAI) starting from Thursday, January 1, 1958 at 00:00:00. This clock doesn't account for leap seconds.
utc_clock class	Measures time since 00:00:00 UTC on Thursday, January 1, 1970. This clock accounts for leap seconds, and is the time standard used around the world.

Time zones

Name	Description
choose	An enum that specifies how to resolve the ambiguous conversion of a local_time to a sys_time.
local_info	Provides a low-level interface to time zone information about the result of converting a local_time to a sys_time.
sys_info	Provides a low-level interface to time zone information about the result of converting a sys_time to a local_time.
time_zone class	All time zone transitions for a specific geographic area.
time_zone_link class	An alternative name for a time_zone.
tzdb struct	Represents a copy of the time zone database.
tzdb_list class	A singleton list of time zone databases.
zoned_time class	A pairing of a time_zone and a time_point with a specified precision.
zoned_traits struct	Used to associate a different default time zone with a zoned_time, and optionally map a custom name to that default time zone.

Exceptions

Name	Description
ambiguous_local_time	Error thrown when a local_time is converted to a sys_time and the result is ambiguous.
nonexistent_local_time	Error thrown when a local_time is converted to a sys_time and the result is a time that doesn't exist.

Functions

Name	Description
ceil(duration)	Returns the ceil of a duration object as a specified type.
ceil(time_point)	Returns the ceil of a time_point object as a specified type.
clock_cast	Converts a time_point from one clock to an equivalent time_point for another clock.
duration_cast	Casts a duration object to a specified type.
floor(duration)	Returns the floor of a duration object as a specified type.
floor(time_point)	Returns the floor of a time_point object as a specified type.
from_stream()	Parse the input stream into one of the std::chrono time or interval types such as day, month, weekday, year, and so on, using the specified format.
get_leap_second_info	Gets a leap_second_info struct.
is_am	Whether an hours object is AM.
is_pm	Whether an hours object is PM.
locate_zone	Gets a specified time zone.
make12	Returns an hours in 12-hour form.
make24	Returns an hours in 24-hour form.
round(duration)	Returns a duration object rounded as a specified type.
round(time_point)	Returns a time_point object rounded as a specified type.
time_point_cast	Casts a time_point object to a specified type.

Time zone related

Name	Description
current_zone	Gets the current time zone.
get_tzdb	Gets the first time zone database entry.
get_tzdb_list	Gets the list of time zone database entries.
reload_tzdb	Gets an updated time zone database entry.
remote_version	Checks for an updated time zone database entry.

Operators

Name	Description
operator-	Subtract or negate various <chrono> objects.
operator!=	Inequality operator that is used with various <chrono> objects.
operator modulo	Operator for modulo operations on duration objects.
operator*	Multiplication operator for duration objects.
operator/	Division operator for duration objects.
operator/	Provides syntax to create calendar dates.
operator+	Add to various <chrono> objects.
operator<	Determines whether various <chrono> objects are less than another.
operator<=	Determines whether various <chrono> objects are less than or equal to another.
operator==	Determines whether various <chrono> objects are equal to each other.
operator>	Determines whether various <chrono> objects are greater than another.
operator>=	Determines whether various <chrono> objects are greater than or equal to another.

Typedefs

For more information about ratio types that are used in the following typedefs, see <ratio>.

Convenience duration types

Name	Description
typedef duration<long long, nano> nanoseconds;	Synonym for a duration type that has a tick period of one billionth (1/1,000,000,000) of a second.
typedef duration<long long, micro> microseconds;	Synonym for a duration type that has a tick period of one-millionth (1/1,000,000) of a second.
typedef duration<long long, milli> milliseconds;	Synonym for a duration type that has a tick period of one-thousandth (1/1,000) of a second.
typedef duration<long long> seconds;	Synonym for a duration type that has a tick period of 1 second.
typedef duration<int, ratio<60>> minutes;	Synonym for a duration type that has a tick period of 1 minute.
typedef duration<int, ratio<3600>> hours;	Synonym for a duration type that has a tick period of 1 hour.

Convenience time_point types

Name	Description
file_time	A synonym for time_point<file_clock, Duration>. Represents a time_point for a file_clock. You specify the Duration, for example, file_time<seconds> ft;.
gps_seconds	A synonym for gps_time<seconds>; A count of seconds, represented by a time_point that is associated with a gps_clock.
gps_time	A synonym for time_point<gps_clock, Duration>. Represents a time_point for a gps_clock. You specify the Duration, for example, gps_time<milliseconds> gps;.
local_days	A synonym for local_time<days>. A count of days, represented by a time_point that isn't associated with any time zone.
local_seconds	A synonym for local_time<seconds>.
local_time	A synonym for time_point<local_t, Duration>. Represents a time_point for a local time that isn't associated with a time zone yet. You specify the Duration, for example, local_time<seconds> lt;. A local_time is a local time somewhere. It isn't the current local time of your computer's clock. Only when you pair a local_time with a time_zone do you get a point in time that can be converted to UTC time, or the time in a specific time zone.
sys_days	A synonym for sys_time<days>. A count of days since the system_clock's epoch, represented by a time_point that is associated with a system_clock.
sys_seconds	A synonym for sys_time<seconds>. A count of non-leap seconds since the epoch of system_clock (Jan 1, 1970 00:00:00 UTC), represented by a time_point that is associated with a system_clock.
sys_time	A synonym for time_point<system_clock, Duration>. You specify the Duration, for example, sys_time<seconds> st;. Represents a time_point returned from system_clock::now(). It represents Unix time, which closely approximates UTC time.
tai_seconds	A synonym for tai_time<seconds>. A count of seconds, represented by a time_point that is associated with a tai_clock.
tai_time	A synonym for time_point<tai_clock, Duration>. You provide the Duration, for example, tai_time<seconds> tt;. Represents a time_point for a tai_clock.
utc_seconds	A synonym for utc_time<seconds>;
utc_time	A synonym for time_point<utc_clock, Duration>. You provide the Duration, for example, utc_time<seconds> ut;. Represents a time_point for a utc_clock.

Type traits

Name	Description
clock_time_conversion	A trait that specifies how to convert a time_point from one clock to another.
is_clock	Check if a type is a clock.
treat_as_floating_point	Check if a duration can be converted to another duration that has a different tick period.

Literals

(C++11) The <chrono> header defines the following user-defined literals that you can use for greater convenience, type-safety, and maintainability of your code. These literals are defined in the literals::chrono_literals inline namespace and are in scope when std::chrono is in scope.

Declaration	Description
hours operator "" h(unsigned long long Val)	Specifies hours as an integral value.
duration<double, ratio<3600>> operator "" h(long double Val)	Specifies hours as a floating-point value.
minutes (operator "" min)(unsigned long long Val)	Specifies minutes as an integral value.
duration<double, ratio<60>> (operator "" min)( long double Val)	Specifies minutes as a floating-point value.
seconds operator "" s(unsigned long long Val)	Specifies minutes as an integral value.
duration<double> operator "" s(long double Val)	Specifies seconds as a floating-point value.
milliseconds operator "" ms(unsigned long long Val)	Specifies milliseconds as an integral value.
duration<double, milli> operator "" ms(long double Val)	Specifies milliseconds as a floating-point value.
microseconds operator "" us(unsigned long long Val)	Specifies microseconds as an integral value.
duration<double, micro> operator "" us(long double Val)	Specifies microseconds as a floating-point value.
nanoseconds operator "" ns(unsigned long long Val)	Specifies nanoseconds as an integral value.
duration<double, nano> operator "" ns(long double Val)	Specifies nanoseconds as a floating-point value.

The following examples show how to use <chrono> literals:

constexpr auto day = 24h;
constexpr auto week = 24h* 7;
constexpr auto my_duration_unit = 108ms;

See also

Header Files Reference