posix chrono casting

gistfile1.txt

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

using namespace std::chrono_literals;

namespace std
{
namespace chrono
{

namespace detail
{
template<typename From, typename To>
struct posix_time_point_cast;

template<typename Clock, typename Duration>
struct posix_time_point_cast<std::chrono::time_point<Clock, Duration>, timespec>
{
    static timespec cast(std::chrono::time_point<Clock, Duration> time_point)
    {
        auto seconds = std::chrono::duration_cast<std::chrono::seconds>(time_point.time_since_epoch());
        timespec result{ seconds.count(), 0 };
        return std::move(result);
    }
};

template<typename Clock, typename Duration>
struct posix_time_point_cast<timespec, std::chrono::time_point<Clock, Duration>>
{
    static timespec cast(timespec spec)
    {
        auto duration = seconds{ spec.tv_sec } + nanoseconds{ spec.tv_nsec };
        time_point<Clock, Duration> time = duration_cast<Duration>(duration);
        return std::move(time);
    }
};

} // detail

template<typename T, typename Clock, typename Duration>
auto time_point_cast(time_point<Clock, Duration> point) -> std::enable_if_t<std::is_same<T, timespec>::value, timespec>
{
    return detail::posix_time_point_cast<time_point<Clock, Duration>, timespec>::cast(point);
}

template<typename TimePoint>
TimePoint time_point_cast(timespec spec)
{
    return detail::posix_time_point_cast<timespec, TimePoint>::cast(spec);
}

}
}

auto getSystemTime()
{
    return std::chrono::system_clock::now();
}

void setSystemTime(std::chrono::system_clock::time_point timePoint)
{
    auto time = std::chrono::time_point_cast<timespec>(timePoint);
    std::cout << time.tv_sec << std::endl;
    if (clock_settime(CLOCK_REALTIME, &time) != 0)
    {
        throw std::system_error(errno, std::system_category());
    }
}

int main(int argc, char* argv[])
{
    auto now = getSystemTime();
    timespec ts = std::chrono::time_point_cast<timespec>(now);
    std::chrono::system_clock::time_point tp = std::chrono::time_point_cast<std::chrono::system_clock::time_point>(ts);
    setSystemTime(now);
    return 0;
}