#include <chrono>
#include <iostream>
#include <thread>
 
int main()
{
   using std::chrono::system_clock;
   using std::chrono::milliseconds;
   using std::chrono::nanoseconds;
   using std::chrono::duration_cast;
   const auto duration = milliseconds(100);
   const auto start = system_clock::now();
   std::this_thread::sleep_for(duration);
   const auto stop = system_clock::now();
   const auto d_correct = duration_cast<nanoseconds>(duration).count();
   const auto d_actual = duration_cast<nanoseconds>(stop - start).count();
   std::cout << "Difference is " << d_actual << ", and it should be roughly " << d_correct << "\n";
}
 

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