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‎docs/standard-library/chrono.md

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---
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description: "Learn more about: <chrono>"
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title: "<chrono>"
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ms.date: 06/16/2021
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description: "Learn more about: <chrono>"
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title: "<chrono>"
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ms.date: 07/01/2021
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f1_keywords: ["<chrono>", "chrono/std::chrono::nanoseconds", "chrono/std::chrono::minutes", "chrono/std::chrono::seconds", "chrono/std::chrono::hours", "chrono/std::chrono::milliseconds", "chrono/std::chrono::microseconds"]
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---
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# `<chrono>`
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Include the standard header `<chrono>` to define classes and functions that represent and manipulate time durations and time instants.
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**Namespace:** `std`
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## Members
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### Classes
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## Classes
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| Name | Description |
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|--|--|
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| [`day` class](../standard-library/day-class.md) | A day of the month. For example, the 25th day of the month. |
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| [`duration` class](../standard-library/duration-class.md) | A time interval. |
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| [`hh_mm_ss` class](../standard-library/hhmmss-class.md) | Splits a [`duration`](duration-class.md) into hours:minutes:seconds. |
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| [`leap_second` class](../standard-library/leap-second-class.md) | A date and a value for an inserted leap second. |
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| [`month` class](../standard-library/month-class.md) | A month of a year. For example, July. |
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| [`month_day` class](../standard-library/month-day-class.md) | A specific day of a specific month. For example, July 30th. |
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| [`month_day_last` class](../standard-library/month-day-last-class.md) | The last day of a month. |
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| [`month_weekday` class](../standard-library/month-day-last-class.md) | The nth weekday of a specific month. |
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| [`month_weekday_last` class](../standard-library/month-weekday-last-class.md) | The nth weekday of a specific month. |
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| [`time_point` class](../standard-library/time-point-class.md) | A point in time. |
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| [`time_zone` class](../standard-library/time-point-class.md) | All time zone transitions for a specific geographic area. |
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| [`weekday` class](../standard-library/weekday-class.md) | A day of the week. |
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| [`weekday_last` class](../standard-library/weekdaylast-class.md) | The last weekday of a month. |
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| [`weekday_indexed` class](../standard-library/weekdayindexed-class.md) | Combines a day of the week with an index that represents the weekday of the month. |
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| [`year` class](../standard-library/year-class.md) | A year in the [Gregorian calendar](https://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar).|
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| [`year_month` class](../standard-library/year-month-class.md) | A year and month. The day isn't specified.|
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| [`year_month_day` class](../standard-library/year-month-day-class.md) | A year, month, and day.|
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| [`year_month_day_last` class](../standard-library/year-month-day-last-class.md) | The last day of a specific month and year. |
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| [`year_month_weekday` class](../standard-library/year-month-weekday-class.md) | A specific year, month, and nth weekday of the month. |
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| [`year_month_weekday_last` class](../standard-library/year-month-weekday-last-class.md) | A specific year, month, and last weekday of the month. |
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### Structs
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| [`day` class](day-class.md) | A day of the month. For example, the 25th day of the month. |
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| [`duration` class](duration-class.md) | A time interval. |
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| [`hh_mm_ss` class](hhmmss-class.md) | Splits a [`duration`](duration-class.md) into hours:minutes:seconds. |
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| [`leap_second` class](leap-second-class.md) | A date and a value for an inserted leap second. |
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| [`month` class](month-class.md) | A month of a year. For example, July. |
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| [`month_day` class](month-day-class.md) | A specific day of a specific month. For example, July 30th. |
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| [`month_day_last` class](month-day-last-class.md) | The last day of a month. |
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| [`month_weekday` class](month-day-last-class.md) | The nth weekday of a specific month. |
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| [`month_weekday_last` class](month-weekday-last-class.md) | The nth weekday of a specific month. |
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| [`time_point` class](time-point-class.md) | A point in time. |
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| [`time_zone` class](time-point-class.md) | All time zone transitions for a specific geographic area. |
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| [`weekday` class](weekday-class.md) | A day of the week. |
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| [`weekday_last` class](weekdaylast-class.md) | The last weekday of a month. |
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| [`weekday_indexed` class](weekdayindexed-class.md) | Combines a day of the week with an index that represents the weekday of the month. |
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| [`year` class](year-class.md) | A year in the [Gregorian calendar](https://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar).|
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| [`year_month` class](year-month-class.md) | A year and month. The day isn't specified.|
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| [`year_month_day` class](year-month-day-class.md) | A year, month, and day.|
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| [`year_month_day_last` class](year-month-day-last-class.md) | The last day of a specific month and year. |
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| [`year_month_weekday` class](year-month-weekday-class.md) | A specific year, month, and nth weekday of the month. |
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| [`year_month_weekday_last` class](year-month-weekday-last-class.md) | A specific year, month, and last weekday of the month. |
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## Structs
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|Name|Description|
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|[`common_type` struct](../standard-library/common-type-structure.md)|Describes specializations of class template [`common_type`](../standard-library/common-type-class.md) for instantiations of `duration` and `time_point`.|
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|[`duration_values` struct](../standard-library/duration-values-structure.md)|Provides specific values for the `duration` template parameter `Rep`.|
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|[`high_resolution_clock` struct](../standard-library/high-resolution-clock-struct.md)| A clock with a nanosecond tick period. |
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|[`leap_second_info` struct](../standard-library/leap-second-info-struct.md) | The data returned by [`get_leap_second_info`](chrono-functions.md#std-chrono-get-leap-second-info). |
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|[`steady_clock` struct](../standard-library/steady-clock-struct.md)|A `steady` clock. Preferred for measuring time intervals. |
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|[`system_clock` struct](../standard-library/system-clock-structure.md)|A *`clock type`* that is based on the real-time clock of the system.|
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|[`treat_as_floating_point` struct](../standard-library/treat-as-floating-point-structure.md)|Specifies whether a type can be treated as a floating-point type.|
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|[`common_type` struct](common-type-structure.md)|Describes specializations of class template [`common_type`](common-type-class.md) for instantiations of `duration` and `time_point`.|
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|[`duration_values` struct](duration-values-structure.md)|Provides specific values for the `duration` template parameter `Rep`.|
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|[`high_resolution_clock` struct](high-resolution-clock-struct.md)| A clock with a nanosecond tick period. |
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|[`leap_second_info` struct](leap-second-info-struct.md) | The data returned by [`get_leap_second_info`](chrono-functions.md#std-chrono-get-leap-second-info). |
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|[`steady_clock` struct](steady-clock-struct.md)|A `steady` clock. Preferred for measuring time intervals. |
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|[`system_clock` struct](system-clock-structure.md)|A *`clock type`* that is based on the real-time clock of the system.|
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### Functions
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## Functions
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| Name | Description |
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|--|--|
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| [`ceil(duration)`](./chrono-functions.md#std-chrono-ceil-duration) | Returns the `ceil` of a `duration` object as a specified type. |
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| [`ceil(time_point)`](./chrono-functions.md#std-chrono-ceil-time-point) | Returns the `ceil` of a `time_point` object as a specified type. |
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| [`current_zone`](./chrono-functions.md#std-chrono-current-zone) | Gets the current time zone. |
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| [`duration_cast`](./chrono-functions.md#std-chrono-duration-cast) | Casts a `duration` object to a specified type. |
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| [`floor(duration)`](./chrono-functions.md#std-chrono-floor-duration) | Returns the `floor` of a `duration` object as a specified type. |
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| [`floor(time_point)`](./chrono-functions.md#std-chrono-floor-time-point) | Returns the `floor` of a `time_point` object as a specified type. |
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| [`from_stream()`](./chrono-functions.md#std-chrono-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. |
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| [`get_leap_second_info`](./chrono-functions.md#std-chrono-get-leap-second-info) | Gets a [`leap_second_info` struct](../standard-library/leap-second-info-struct.md). |
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| [`get_tzdb_list`](./chrono-functions.md#std-chrono-get-tzdb-list) | Gets the list of time zone database entries. |
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| [`get_tzdb`](./chrono-functions.md#std-chrono-get-tzdb) | Gets the first time zone database entry. |
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| [`is_am`](./chrono-functions.md#std-chrono-is-am) | Whether an `hours` object is AM. |
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| [`is_pm`](./chrono-functions.md#std-chrono-is-pm) | Whether an `hours` object is PM. |
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| [`locate_zone`](./chrono-functions.md#std-chrono-locate-zone) | Gets a specified time zone. |
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| [`make12`](./chrono-functions.md#std-chrono-make12) | Returns an `hours` in 12-hour form. |
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| [`make24`](./chrono-functions.md#std-chrono-make24) | Returns an `hours` in 24-hour form. |
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| [`reload_tzdb`](./chrono-functions.md#std-chrono-reload-tzdb) | Gets an updated time zone database entry. |
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| [`remote_version`](./chrono-functions.md#std-chrono-remote-version) | Checks for an updated time zone database entry. |
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| [`round(duration)`](./chrono-functions.md#std-chrono-round-duration) | Returns a `duration` object rounded as a specified type. |
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| [`round(time_point)`](./chrono-functions.md#std-chrono-round-time-point) | Returns a `time_point` object rounded as a specified type. |
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| [`time_point_cast`](./chrono-functions.md#std-chrono-time-point-cast) | Casts a `time_point` object to a specified type. |
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### Operators
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| [`ceil(duration)`](chrono-functions.md#std-chrono-ceil-duration) | Returns the `ceil` of a `duration` object as a specified type. |
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| [`ceil(time_point)`](chrono-functions.md#std-chrono-ceil-time-point) | Returns the `ceil` of a `time_point` object as a specified type. |
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| [`current_zone`](chrono-functions.md#std-chrono-current-zone) | Gets the current time zone. |
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| [`duration_cast`](chrono-functions.md#std-chrono-duration-cast) | Casts a `duration` object to a specified type. |
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| [`floor(duration)`](chrono-functions.md#std-chrono-floor-duration) | Returns the `floor` of a `duration` object as a specified type. |
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| [`floor(time_point)`](chrono-functions.md#std-chrono-floor-time-point) | Returns the `floor` of a `time_point` object as a specified type. |
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| [`from_stream()`](chrono-functions.md#std-chrono-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. |
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| [`get_leap_second_info`](chrono-functions.md#std-chrono-get-leap-second-info) | Gets a [`leap_second_info` struct](leap-second-info-struct.md). |
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| [`get_tzdb_list`](chrono-functions.md#std-chrono-get-tzdb-list) | Gets the list of time zone database entries. |
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| [`get_tzdb`](chrono-functions.md#std-chrono-get-tzdb) | Gets the first time zone database entry. |
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| [`is_am`](chrono-functions.md#std-chrono-is-am) | Whether an `hours` object is AM. |
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| [`is_pm`](chrono-functions.md#std-chrono-is-pm) | Whether an `hours` object is PM. |
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| [`locate_zone`](chrono-functions.md#std-chrono-locate-zone) | Gets a specified time zone. |
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| [`make12`](chrono-functions.md#std-chrono-make12) | Returns an `hours` in 12-hour form. |
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| [`make24`](chrono-functions.md#std-chrono-make24) | Returns an `hours` in 24-hour form. |
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| [`reload_tzdb`](chrono-functions.md#std-chrono-reload-tzdb) | Gets an updated time zone database entry. |
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| [`remote_version`](chrono-functions.md#std-chrono-remote-version) | Checks for an updated time zone database entry. |
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| [`round(duration)`](chrono-functions.md#std-chrono-round-duration) | Returns a `duration` object rounded as a specified type. |
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| [`round(time_point)`](chrono-functions.md#std-chrono-round-time-point) | Returns a `time_point` object rounded as a specified type. |
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| [`time_point_cast`](chrono-functions.md#std-chrono-time-point-cast) | Casts a `time_point` object to a specified type. |
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## Operators
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|[`operator-`](../standard-library/chrono-operators.md#op_minus)|Subtract or negate various <chrono> objects.|
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|[`operator!=`](../standard-library/chrono-operators.md#op_neq)|Inequality operator that is used with various <chrono> objects.|
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|[`operator modulo`](../standard-library/chrono-operators.md#op_modulo)|Operator for modulo operations on `duration` objects.|
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|[`operator*`](../standard-library/chrono-operators.md#op_star)|Multiplication operator for `duration` objects.|
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|[`operator/`](../standard-library/chrono-operators.md#op_div)|Division operator for `duration` objects.|
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|[`operator/`](../standard-library/chrono-operators.md#op_/)|Provides syntax to create calendar dates.|
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|[`operator+`](../standard-library/chrono-operators.md#op_add)|Add to various <chrono> objects.|
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|[`operator<`](../standard-library/chrono-operators.md#op_lt)|Determines whether various <chrono> objects are less than another.|
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|[`operator<=`](../standard-library/chrono-operators.md#op_lt_eq)|Determines whether various <chrono> objects are less than or equal to another.|
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|[`operator==`](../standard-library/chrono-operators.md#op_eq_eq)|Determines whether various <chrono> objects are equal to each other.|
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|[`operator>`](../standard-library/chrono-operators.md#op_gt)|Determines whether various <chrono> objects are greater than another.|
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|[`operator>=`](../standard-library/chrono-operators.md#op_gt_eq)|Determines whether various <chrono> objects are greater than or equal to another.|
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### Typedefs (Predefined Duration Types)
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For more information about ratio types that are used in the following typedefs, see [`<ratio>`](../standard-library/ratio.md).
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|[`operator-`](chrono-operators.md#op_minus)|Subtract or negate various <chrono> objects.|
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|[`operator!=`](chrono-operators.md#op_neq)|Inequality operator that is used with various <chrono> objects.|
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|[`operator modulo`](chrono-operators.md#op_modulo)|Operator for modulo operations on `duration` objects.|
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|[`operator*`](chrono-operators.md#op_star)|Multiplication operator for `duration` objects.|
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|[`operator/`](chrono-operators.md#op_div)|Division operator for `duration` objects.|
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|[`operator/`](chrono-operators.md#op_/)|Provides syntax to create calendar dates.|
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|[`operator+`](chrono-operators.md#op_add)|Add to various <chrono> objects.|
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|[`operator<`](chrono-operators.md#op_lt)|Determines whether various <chrono> objects are less than another.|
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|[`operator<=`](chrono-operators.md#op_lt_eq)|Determines whether various <chrono> objects are less than or equal to another.|
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|[`operator==`](chrono-operators.md#op_eq_eq)|Determines whether various <chrono> objects are equal to each other.|
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|[`operator>`](chrono-operators.md#op_gt)|Determines whether various <chrono> objects are greater than another.|
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|[`operator>=`](chrono-operators.md#op_gt_eq)|Determines whether various <chrono> objects are greater than or equal to another.|
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## Typedefs (Predefined duration types)
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For more information about ratio types that are used in the following typedefs, see [`<ratio>`](ratio.md).
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|`typedef duration<int, ratio<60>> minutes;`|Synonym for a `duration` type that has a tick period of 1 minute.|
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|`typedef duration<int, ratio<3600>> hours;`|Synonym for a `duration` type that has a tick period of 1 hour.|
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### Alias declarations
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## Type traits
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|Name|Description|
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|[is_clock](is-clock-struct.md) | See if a type is a clock. |
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|[treat_as_floating_point](treat-as-floating-point-structure.md) | See if a `duration` can be converted to another `duration` that has a different tick period.|
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## Alias declarations
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|`using local_days = local_time<days>;` | A count of days, represented by a [`time_point`](time-point-class.md) that is not associated with any time zone. |
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|`using sys_days = sys_time<days>;` | A count of days, represented by a `time_point` that is associated with a [`system_clock`](system-clock-structure.md), which has a 1/1/1970 epoch. |
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### Literals
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## Literals
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**(C++11)** The `<chrono>` header defines the following [user-defined literals](../cpp/user-defined-literals-cpp.md) 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.
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## See also
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[Header Files Reference](../standard-library/cpp-standard-library-header-files.md)
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[Header Files Reference](cpp-standard-library-header-files.md)

‎docs/standard-library/is-clock-struct.md

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---
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description: "Learn more about is_clock struct"
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title: "is_clock class"
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ms.date: 07/19/2021
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f1_keywords: ["chrono/std::is_clock"]
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helpviewer_keywords: ["std::chrono [C++], is_clock"]
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---
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# `is_clock` structure
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A type trait that determines whether the specified type meets the requirements to be a clock.
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## Syntax
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```cpp
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template<class T> struct is_clock; // c++ 20
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```
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**Helper variable template**
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```cpp
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template<class T> inline constexpr bool is_clock_v = is_clock<T>::value; // c++ 20
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```
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### Parameters
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*`T`*\
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The type to test.
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## Members
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|Name|Description|
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|----------|-----------------|
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| [`value`](#value) | Indicates whether `T` satisfies the requirements to be a clock. |
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| [`operator ()`](#op_parens) | Returns [`value`](#value). |
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| [`operator bool`](#op_bool) | Returns [`value`](#value). |
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## Remarks
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A clock has a `rep`, `period`, `duration`, `time_point`, `is_steady`, and a `now()` function.
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For more details about the requirements to be a C++17 clock, see [Cpp17Clock requirements](https://eel.is/c++draft/tab:time.clock).
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The following code works because `is_clock`, derives from `Cpp17UnaryTypeTrait`, which derives from `integral_constant`. This is where `value_type`, which is a `bool`, and `type`, which is a `std::integral_constant<bool, value>` come from.
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## Example
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```cpp
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#include <iostream>
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#include <chrono>
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using namespace std::chrono;
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int main()
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{
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is_clock<system_clock> ic;
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std::cout << std::boolalpha << ic.value << ", " << ic() << ", " << (bool)ic;
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return 0;
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}
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```
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```output
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true, true, true
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```
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## Requirements
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**Header:** \<`chrono`>
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**Namespace:** `std`
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**Compiler Option:** [`/std:c++latest`](../build/reference/std-specify-language-standard-version.md)
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## Value
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Get whether the specified type satisfies the requirements to be a clock.
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```cpp
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static constexpr T value;
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```
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### Return value
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`true` if specified type meets the requirements to be a clock. Otherwise, `false`.
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## <a name="op_parens"></a> `operator()`
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```cpp
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constexpr value_type operator()() const noexcept
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```
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Returns `value`, that is, whether the specified type meets the requirements to be a clock.
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### Return value
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`true` if specified type meets the requirements to be a clock. Otherwise, `false`.
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## <a name="op_bool"></a> `operator bool`
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```cpp
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constexpr operator value_type() const noexcept
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```
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Returns `value`, that is, whether the specified type meets the requirements to be a clock.
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### Return value
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`true` if specified type meets the requirements to be a clock. Otherwise, `false`.
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## See also
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[`<chrono>`](chrono.md)\
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[Header Files Reference](cpp-standard-library-header-files.md)

‎docs/standard-library/toc.yml

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href: ../standard-library/hhmmss-class.md
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- name: high_resolution_clock struct
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href: high-resolution-clock-struct.md
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- name: is_clock struct
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href: is-clock-struct.md
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- name: leap_second class
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href: ../standard-library/leap-second-class.md
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- name: leap_second_info struct

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