std::chrono::duration<Rep,Period>::duration
constexpr duration() = default; | (1) | (since C++11) |
duration( const duration& ) = default; | (2) | (since C++11) |
template< class Rep2 > constexpr explicit duration( const Rep2& r ); | (3) | (since C++11) |
template< class Rep2, class Period2 > constexpr duration( const duration<Rep2,Period2>& d ); | (4) | (since C++11) |
Constructs a new duration
from one of several optional data sources.
1) The default constructor is defaulted.
2) The copy constructor is defaulted (makes a bitwise copy of the tick count).
3) Constructs a duration with
r
ticks. Note that this constructor only participates in overload resolution if Rep2
(the argument type) is implicitly convertible to rep
(the type of this duration's ticks) and-
std::chrono::treat_as_floating_point<rep>::value
is true, or -
std::chrono::treat_as_floating_point<Rep2>::value
is false.
(that is, a duration with an integer tick count cannot be constructed from a floating-point value, but a duration with a floating-point tick count can be constructed from an integer value)
4) Constructs a duration by converting
d
to an appropriate period and tick count, as if by std::chrono::duration_cast<duration>(d).count()
. In order to prevent truncation during conversion, this constructor only participates in overload resolution if computation of the conversion factor (by std::ratio_divide<Period2, Period>
) does not overflow and:-
std::chrono::treat_as_floating_point<rep>::value == true
or both:
-
std::ratio_divide<Period2, period>::den == 1
, and -
std::chrono::treat_as_floating_point<Rep2>::value == false
.
(that is, either the duration uses floating-point ticks, or
Period2
is exactly divisible by period)Parameters
r | - | a tick count |
d | - | a duration to copy from |
Example
The following code shows several examples (both valid and invalid) of how to construct durations:
#include <chrono> int main() { std::chrono::hours h(1); // one hour std::chrono::milliseconds ms{3}; // 3 milliseconds std::chrono::duration<int, std::kilo> ks(3); // 3000 seconds // error: treat_as_floating_point<int>::value == false, // This duration allows whole tick counts only // std::chrono::duration<int, std::kilo> d3(3.5); // 30Hz clock using fractional ticks std::chrono::duration<double, std::ratio<1, 30>> hz30(3.5); // 3000 microseconds constructed from 3 milliseconds std::chrono::microseconds us = ms; // error: 1/1000000 is not divisible by 1/1000 // std::chrono::milliseconds ms2 = us std::chrono::duration<double, std::milli> ms2 = us; // 3.0 milliseconds }
See also
assigns the contents (public member function) |
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