Chrono usage notes

chrono Use notes
chrono Is a namespace , For time-dependent libraries .
Include
Durations: Duration class
Durations The implementation classes of are as follows ：
hours when
minutes branch
seconds second
milliseconds millisecond
microseconds Microsecond
nanoseconds nanosecond

Time points Point in time , Record a moment
Clocks
A framework that associates a point in time with actual physical time .

The library provides at least three clocks , They provide a way to express the current time as a point in time ：system_clock( The system clock )、steady_clock( Stabilize the clock ) and high_resolution_clock( High resolution clock ).

Durations Example ：

#include <iostream>
#include <ratio>
#include <chrono>

int main ()
{
    
  typedef std::chrono::duration<int> seconds_type;
  typedef std::chrono::duration<int,std::milli> milliseconds_type;
  typedef std::chrono::duration<int,std::ratio<60*60>> hours_type;

  hours_type h_oneday (24);                  // 24h
  seconds_type s_oneday (60*60*24);          // 86400s
  milliseconds_type ms_oneday (s_oneday);    // 86400000ms

  seconds_type s_onehour (60*60);            // 3600s
//hours_type h_onehour (s_onehour); // NOT VALID (type truncates), use:
  hours_type h_onehour (std::chrono::duration_cast<hours_type>(s_onehour));
  milliseconds_type ms_onehour (s_onehour);  // 3600000ms (ok, no type truncation)

  std::cout << ms_onehour.count() << "ms in 1h" << std::endl;

  return 0;
}

// duration::zero
#include <iostream>
#include <chrono>

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

  steady_clock::time_point t1 = steady_clock::now();

  std::cout << "Printing out something...\n";

  steady_clock::time_point t2 = steady_clock::now();

  steady_clock::duration d = t2 - t1;

  if ( d == steady_clock::duration::zero() )
    std::cout << "The internal clock did not tick.\n";

  else
    std::cout << "The internal clock advanced " << d.count() << " periods.\n";

  return 0;
}

// duration::min/max
#include <iostream>
#include <chrono>

int main ()
{
    
  std::cout << "system_clock durations can represent:\n";
  std::cout << "min: " << std::chrono::system_clock::duration::min().count() << "\n";
  std::cout << "max: " << std::chrono::system_clock::duration::max().count() << "\n";
  return 0;
}

Clocks Example ：

// system_clock example
#include <iostream>
#include <ctime>
#include <ratio>
#include <chrono>

// Get the current time converted to a string 
int main ()
{
    
  using std::chrono::system_clock;

  std::chrono::duration<int,std::ratio<60*60*24> > one_day (1);

  system_clock::time_point today = system_clock::now();
  system_clock::time_point tomorrow = today + one_day;

  std::time_t tt;

  tt = system_clock::to_time_t ( today );
  std::cout << "today is: " << ctime(&tt);

  tt = system_clock::to_time_t ( tomorrow );
  std::cout << "tomorrow will be: " << ctime(&tt);

  return 0;
}

// Calculate the time interval

// system_clock::from_time_t
#include <iostream>
#include <ctime>
#include <ratio>
#include <chrono>

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

  // create tm with 1/1/2000:
  std::tm timeinfo = std::tm();
  timeinfo.tm_year = 100;   // year: 2000
  timeinfo.tm_mon = 0;      // month: january
  timeinfo.tm_mday = 1;     // day: 1st
  std::time_t tt = std::mktime (&timeinfo);

  system_clock::time_point tp = system_clock::from_time_t (tt);
  system_clock::duration d = system_clock::now() - tp;

  // convert to number of days:
  typedef duration<int,std::ratio<60*60*24>> days_type;
  days_type ndays = duration_cast<days_type> (d);

  // display result:
  std::cout << ndays.count() << " days have passed since 1/1/2000";
  std::cout << std::endl;

  return 0;
}

…

duration_cast Time conversion
More reference chrono