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Difference between revisions of "cpp/chrono/duration"

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< cpp‎ | chrono
m (apply DR23: P3235R3. more std::enable_nonlocking_formatter_optimization specializations)
(→‎Member types: arithmetic type is too strict, I believe types such as boost::safe_numerics::safe<int> are allowed here)
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{{dsc|{{tt|rep}}|{{tt|Rep}}, an arithmetic type representing the number of ticks}}
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{{dsc|{{tt|rep}}|{{tt|Rep}}, an arithmetic type, or a class emulating an arithmetic type, representing the number of ticks}}
 
{{dsc|{{tt|period}}|{{rev inl|until=c++17|{{tt|Period}}}}{{rev inl|since=c++17|{{c/core|typename Period::type}}}}, a {{lc|std::ratio}} representing the tick period (i.e. the number of second's fractions per tick)}}
 
{{dsc|{{tt|period}}|{{rev inl|until=c++17|{{tt|Period}}}}{{rev inl|since=c++17|{{c/core|typename Period::type}}}}, a {{lc|std::ratio}} representing the tick period (i.e. the number of second's fractions per tick)}}
 
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Revision as of 01:31, 24 July 2024

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Date and time utilities
Time point
(C++11)
(C++20)
Duration
duration
(C++11)
Clocks
(C++11)
(C++11)
(C++20)
(C++20)
(C++20)
(C++20)
Time of day
(C++20)(C++20)
(C++20)(C++20)
(C++20)

Calendar
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)(C++20)
Time zone
(C++20)
(C++20)
(C++20)(C++20)(C++20)(C++20)  
(C++20)
chrono I/O
(C++20)
C-style date and time
 
std::chrono::duration
Member functions
Non-member functions
(C++17)
(C++17)
(C++17)
(C++17)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++20)

Helper classes
 
Defined in header <chrono>
template<

    class Rep,
    class Period = std::ratio<1>

> class duration;
 (since C++11)

Class template std::chrono::duration represents a time interval.

It consists of a count of ticks of type Rep and a tick period, where the tick period is a compile-time rational fraction representing the time in seconds from one tick to the next.

The only data stored in a duration is a tick count of type Rep. If Rep is floating point, then the duration can represent fractions of ticks. Period is included as part of the duration's type, and is only used when converting between different durations.

Contents

Member types

Member type Definition
rep Rep, an arithmetic type, or a class emulating an arithmetic type, representing the number of ticks
period Period(until C++17)typename Period::type(since C++17), a std::ratio representing the tick period (i.e. the number of second's fractions per tick)

Member functions

 constructs new duration
(public member function) [edit]
assigns the contents
(public member function) [edit]
returns the count of ticks
(public member function) [edit]
[static]
 returns the special duration value zero
(public static member function) [edit]
[static]
 returns the special duration value min
(public static member function) [edit]
[static]
 returns the special duration value max
(public static member function) [edit]
implements unary + and unary -
(public member function) [edit]
increments or decrements the tick count
(public member function) [edit]
implements compound assignment between two durations
(public member function) [edit]

Non-member functions

(C++11)
 implements arithmetic operations with durations as arguments
(function template) [edit]
(C++11)(C++11)(removed in C++20)(C++11)(C++11)(C++11)(C++11)(C++20)
 compares two durations
(function template) [edit]
(C++11)
 converts a duration to another, with a different tick interval
(function template) [edit]
(C++17)
 converts a duration to another, rounding down
(function template) [edit]
(C++17)
 converts a duration to another, rounding up
(function template) [edit]
(C++17)
 converts a duration to another, rounding to nearest, ties to even
(function template) [edit]
(C++17)
 obtains the absolute value of the duration
(function template) [edit]
(C++20)
 performs stream output on a duration
(function template) [edit]
(C++20)
 parses a duration from a stream according to the provided format
(function template) [edit]

Helper types

A type /* intXX */ used in the table below means a signed integer type of at least XX bits.

Type Definition
std::chrono::nanoseconds std::chrono::duration</* int64 */, std::nano>
std::chrono::microseconds std::chrono::duration</* int55 */, std::micro>
std::chrono::milliseconds std::chrono::duration</* int45 */, std::milli>
std::chrono::seconds std::chrono::duration</* int35 */>
std::chrono::minutes std::chrono::duration</* int29 */, std::ratio<60>>
std::chrono::hours std::chrono::duration</* int23 */, std::ratio<3600>>
std::chrono::days (since C++20) std::chrono::duration</* int25 */, std::ratio<86400>>
std::chrono::weeks (since C++20) std::chrono::duration</* int22 */, std::ratio<604800>>
std::chrono::months (since C++20) std::chrono::duration</* int20 */, std::ratio<2629746>>
std::chrono::years (since C++20) std::chrono::duration</* int17 */, std::ratio<31556952>>

Note: each of the predefined duration types up to hours covers a range of at least ±292 years.

Each of the predefined duration types days, weeks, months and years covers a range of at least ±40000 years. years is equal to 365.2425 days (the average length of a Gregorian year). months is equal to 30.436875 days (exactly 1/12 of years).

(since C++20)

Helper classes

(C++11)
 specializes the std::common_type trait
(class template specialization) [edit]
(C++11)
 indicates that a duration is convertible to duration with different tick period
(class template) [edit]
(C++11)
 constructs zero, min, and max values of a tick count of given type
(class template) [edit]
(C++20)
 formatting support for duration
(class template specialization) [edit]
(C++26)
 hash support for std::chrono::duration
(class template specialization)

Helper specializations

template< class Rep, class Period >

inline constexpr bool enable_nonlocking_formatter_optimization<chrono::duration<Rep, Period>>

 = enable_nonlocking_formatter_optimization<Rep>;
 (since C++23)

This specialization of std::enable_nonlocking_formatter_optimization enables efficient implementation of std::print and std::println for printing a chrono::duration object when the template parameter Rep enables it.

Literals

Defined in inline namespace std::literals::chrono_literals
(C++14)
 a std::chrono::duration literal representing hours
(function) [edit]
(C++14)
 a std::chrono::duration literal representing minutes
(function) [edit]
(C++14)
 a std::chrono::duration literal representing seconds
(function) [edit]
(C++14)
 a std::chrono::duration literal representing milliseconds
(function) [edit]
(C++14)
 a std::chrono::duration literal representing microseconds
(function) [edit]
(C++14)
 a std::chrono::duration literal representing nanoseconds
(function) [edit]

Note: the literal suffixes d and y do not refer to days and years but to day and year, respectively.

(since C++20)

Notes

The actual time interval (in seconds) that is held by a duration object d is roughly equal to d.count() * D::period::num / D::period::den, where D is of type chrono::duration<> and d is an object of such type.

Feature-test macro Value Std Feature
__cpp_lib_chrono_udls 201304L (C++14) User-defined literals for time types

Example

This example shows how to define several custom duration types and convert between types:

Run this code
#include <chrono>
#include <iostream>
 
using namespace std::chrono_literals;
 
template<typename T1, typename T2>
using mul = std::ratio_multiply<T1, T2>;
 
int main()
{
    using microfortnights = std::chrono::duration<float,
        mul<mul<std::ratio<2>, std::chrono::weeks::period>, std::micro>>;
    using nanocenturies = std::chrono::duration<float,
        mul<mul<std::hecto, std::chrono::years::period>, std::nano>>;
    using fps_24 = std::chrono::duration<double, std::ratio<1, 24>>;
 
    std::cout << "1 second is:\n";
 
    // integer scale conversion with no precision loss: no cast
    std::cout << std::chrono::milliseconds(1s).count() << " milliseconds\n"
              << std::chrono::microseconds(1s).count() << " microseconds\n"
              << std::chrono::nanoseconds(1s).count() << " nanoseconds\n";
 
    // integer scale conversion with precision loss: requires a cast
    std::cout << std::chrono::duration_cast<std::chrono::minutes>(1s).count()
              << " minutes\n";
 
    // floating-point scale conversion: no cast
    std::cout << microfortnights(1s).count() << " microfortnights\n"
              << nanocenturies(1s).count() << " nanocenturies\n"
              << fps_24(1s).count() << " frames at 24fps\n";
}

Output: 

1 second is:
1000 milliseconds
1000000 microseconds
1000000000 nanoseconds
0 minutes
0.82672 microfortnights
0.316887 nanocenturies
24 frames at 24fps
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