How to cast a double into std::chrono::milliseconds

user_9088126 0
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I am using boost::asio::steady_timer m_timer and if I am not mistaken, in order to call m_timer.expires_after(expiration_time_ms);, expiration_time_ms should be a std::chrono::milleseconds variable.

Nevertheless, in my case, I have the expiration time as a double. I would like to know if it is possible to cast a double into std::chrono::milliseconds

The aim is to call

void
setExpirationTime(my_casted_double) {
  boost::asio::steady_timer m_timer;
  m_timer.expires_after(my_casted_double)
}
chrono timer casting c++
2 Answers

One nice trick is to multiply your values with chrono literals:

using namespace std::chrono_literals;

double time = 82.0;
auto t_82ms = time * 1ms;
std::this_thread::sleep_for(t_82ms);

It also works the other way around:

double time = t_82ms / 1s; // time == 0.082
user_120410200

m_timer.expires_after will accept any duration which is convertible to boost::asio::steady_timer::duration it doesn't need to be std::chrono::milliseconds (and if you don't want to discard the fractional milliseconds from your duration you shouldn't be converting to std::chrono::milliseconds).

You can convert your double into a std::chrono::duration as follows:

double milliseconds = 0.1;
std::chrono::duration<double, std::milli> chrono_milliseconds{ milliseconds };

chrono_milliseconds can't however be passed automatically into expires_after as there is no automatic conversion from floating point durations to integer ones. You can fix this with a std::chrono::duration_cast:

m_timer.expires_after(
  std::chrono::duration_cast<boost::asio::steady_timer::duration>(chrono_milliseconds));
user_54943700
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