Chrono

Duration

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 form 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.

• 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 seconds’s fraction per tick)

• Member functions

(constructor)	constructs new duration
operator=	assigns the contents
count	returns the count of ticks
zero (static)	returns the special duration value zero
min (static)	returns the special duration value min
max (static)	returns the special duration value max
operator+ / operator-	implements unary + and unary -
operator++ / operator–	increments or decrements the tick count
operator+= / operator-= / operator*= / operator/= / operator%=	implements compound assignment between two durations

• Non-member functions

operator+ / operator- / operator* / operator/ / operator%	implements arithmetic operations with durations as arguments
operator== / operator!= / operator< / operator<= / operator> / operator>= operator<=>	compares two durations
duration_cast (c++11)	converts a duration to another, with a firrerent tick interval
floor (c++17)	converts a duration to another, rounding down
ceil (c++17)	converts a duration to another rounding up
round (c++17)	converts a duration to another, rounding to nearest, ties to even
abs (c++17)	obtains the absolute value of the duration
operator<< (c++20)	performs stream output on a duration
from_stream (c++20)	parses a duration from a stream according to the provided format

• Example:

#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";

  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 no precision loss: no cast
  std::cout << std::chrono::duration_cast<std::chrono::minutes>(1s).count()
            << " minutes\n";

  // alternative to duration_cast
  std::cout << 1s / 1min << " minutes\n";

  // floating-poimy scale conversion: no cast
  std::cout << microfortnights(1s).count() << "mcrofortnights\n"
            << nanocenturies(1s).count() << " nanocenturies\n"
            << fps_24(1s).count() << " frames at 24fps\n";

  std::cout << std::chrono::system_clock::now() << " \n";

  std::cout << std::format("{:%Y-%m-%d %H:%M:%S}",
                           std::chrono::system_clock::now())
            << " \n";
}