stopwatch.cc

class Stopwatch {
    using clock = std::chrono::high_resolution_clock;
    bool is_running() const { return stop_time_ == clock::time_point::min(); }
    clock::time_point end_time() const { return is_running() ? clock::now() : stop_time_; }
    clock::time_point begin_time_{clock::now()}, stop_time_{clock::time_point::min()};
public:
    void stop() { if (is_running()) stop_time_ = clock::now(); }
    clock::duration elapsed() const { return end_time() - begin_time_; }
};