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Std::chrono

lastmod 2018-08-17created 2015-03-1916 edits

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

Classes

  • duration: Describes a type that holds a time interval.
  • time_point: Describes a type that represents a point in time.

Structure

  • common_type: Describes specializations of the template class common_type for instantiations of duration and time_point.
  • duration_values: Provides specific values for the duration template parameter Rep.
  • steady_clock: Represents a steady clock.
  • system_clock: Represents a clock type that is based on the system's real-time clock.
  • treat_as_floating_point: Specifies whether a type can be treated as a floating-point type.

Functions

  • duration_cast: Casts a duration object to a specified type.
  • time_point_cast: Casts a time_point object to a specified type.

Now Milliseconds

To get the current time in milliseconds: 

unsigned long milliseconds_since_epoch =
    std::chrono::system_clock::now().time_since_epoch() / 
    std::chrono::milliseconds(1);

OR: 

auto duration = now.time_since_epoch();
auto millis = std::chrono::duration_cast<std::chrono::milliseconds>(duration).count();

time_t convert 

using namespace std;
using namespace chrono;

// time_point -> time_t
std::chrono::system_clock::time_point currTimePoint = system_clock::now();
time_t currTime = system_clock::to_time_t(currTimePoint);

// time_t -> time_point
time_t currTime = time(nullptr);
system_clock::time_point currTimePoint = system_clock::from_time_t(currTime);

#include <chrono>
#include <ctime>
#include <iostream>

template <typename Duration>
void print_time(tm t, Duration fraction) {
    using namespace std::chrono;
    std::printf("[%04u-%02u-%02u %02u:%02u:%02u.%03u]\n", t.tm_year + 1900,
                t.tm_mon + 1, t.tm_mday, t.tm_hour, t.tm_min, t.tm_sec,
                static_cast<unsigned>(fraction / milliseconds(1)));

    // VS2013's library has a bug which may require you to replace
    // "fraction / milliseconds(1)" with
    // "duration_cast<milliseconds>(fraction).count()"
}

int main() {
    using namespace std;
    using namespace std::chrono;

    system_clock::time_point now = system_clock::now();
    system_clock::duration tp = now.time_since_epoch();

    tp -= duration_cast<seconds>(tp);

    time_t tt = system_clock::to_time_t(now);

    print_time(*gmtime(&tt), tp);
    print_time(*localtime(&tt), tp);
}

Category

See also

Favorite site

References

  1. Sweeper.egloos.com-cpp11_chrono.pdf ↩

  2. The_C++Standard_Library-Utilities-_Clocks_and_Timers.pdf ↩

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