chrono basic usage

chrono.cpp

# include <iostream>
# include <chrono>

int main() {
  auto start = std::chrono::system_clock::now(); // use auto to skip typing std::chrono::system_clock::time_point
  /* do something */
  auto end = std::chrono::system_clock::now();
  auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end-start).count();
  /*
    Trasnlate time unit to nanoseconds.
    Other units are microseconds, milliseconds, seconds, minutes, hours.
   */
  std::cout << elapsed << std::endl;
}