Simple high resolution timer in C++

timer-c++03.cpp

#include <iostream>
#include <ctime>

class Timer
{
public:
    Timer() { clock_gettime(CLOCK_REALTIME, &beg_); }

    double elapsed() {
        clock_gettime(CLOCK_REALTIME, &end_);
        return end_.tv_sec - beg_.tv_sec +
            (end_.tv_nsec - beg_.tv_nsec) / 1000000000.;
    }

    void reset() { clock_gettime(CLOCK_REALTIME, &beg_); }

private:
    timespec beg_, end_;
};

// Example code
int main()
{
    Timer tmr;
    double t = tmr.elapsed();
    std::cout << t << std::endl;

    tmr.reset();
    t = tmr.elapsed();
    std::cout << t << std::endl;
	return 0;
}

timer=c++11.cpp

#include <iostream>
#include <chrono>

class Timer {
public:
    Timer() :
            m_beg(clock_::now()) {
    }
    void reset() {
        m_beg = clock_::now();
    }

    double elapsed() const {
        return std::chrono::duration_cast<std::chrono::milliseconds>(
                clock_::now() - m_beg).count();
    }

private:
    typedef std::chrono::high_resolution_clock clock_;
    typedef std::chrono::duration<double, std::ratio<1> > second_;
    std::chrono::time_point<clock_> m_beg;
};

// Example code
int main()
{
    Timer tmr;
    double t = tmr.elapsed();
    std::cout << t << std::endl;

    tmr.reset();
    t = tmr.elapsed();
    std::cout << t << std::endl;
    return 0;
}