Hello Codeforces,

This is an update to an old blog I wrote 15 months ago about measuring elapsed time between two events in C++ programs on real-time scale such as milliseconds using the std::chrono library classes and functions.

The following is the class declaration and implementation.

using namespace std::chrono;
template<class clock, class units = milliseconds>
class Timer {
    const units T; const time_point<clock> t0; bool stopped = false;
public:
    inline Timer(const units interval) :  T(interval), t0(clock::now()) {}
    inline units elapsed_time() const { return duration_cast<units>(clock::now()-t0); }
    inline bool expired() { return stopped ? true: elapsed_time() < T ? false: (stopped = true); } };

The template has two parameters: clock and units corresponding to the used std::chrono clock and time units of the timer interval, respectively. The value passed to clock should be high_resolution_clock, system_clock, or steady_clock. The default value for units is milliseconds. Other possible values for units include nanoseconds, microseconds, etc. check chrono::duration for more details.

The class has three public member functions:

Timer(const units interval);
units elapsed_time() const;
bool expired();

The first public member function Timer(const units interval) is the class constructor used to create a timer object. The second function elapsed_time() returns the elapsed time since the creation of the object. The third function expired() returns false if such elapsed time has not reached interval yet; otherwise, the function returns true.

The following is an example program to test the functionality of the class by creating a timer object with 1.5 sec interval.

#include <bits/stdc++.h>

// The C++ template class is included here

using namespace std;

int main() {
	const auto T = 1500ms;
	Timer<high_resolution_clock> timer(T); 
	int iterations = 0;
	while (!timer.expired())
		iterations++;
	const double interval = duration_cast<nanoseconds>(T).count();
	cout << "average iteration time = " << interval/iterations << " nsec."; 
	return 0; }

The following is the stdout printed results of the example program.

average iteration time = 19.0212 nsec.

Your constructive comments and feedback are welcome.

Update: The third parameter value_t was removed from the template to make the class declaration more compact.