怠惰な人のための時間計測クラス for C++11

stopwatch.hpp

#include <chrono>
#include <iostream>

namespace detail
{
    namespace chrono
    {
        template<typename P>
        struct UnitName;

#define DEF_UNIT_NAME(T, N) \
        template<> struct UnitName<std::chrono::T> { static constexpr const char *name = #N; }

        DEF_UNIT_NAME(hours, h);
        DEF_UNIT_NAME(minutes, m);
        DEF_UNIT_NAME(seconds, s);
        DEF_UNIT_NAME(milliseconds, ms);
        DEF_UNIT_NAME(microseconds, us);

#undef DEF_UNIT_NAME
    }
}

template<typename Prec>
class StopWatch final
{
    using time_point = std::chrono::time_point<std::chrono::system_clock>;

private:
    time_point start_;
    std::ostream *out_;

    void start()
    {
        start_ = std::chrono::system_clock::now();
    }
public:
    StopWatch()
    : out_(&std::cout)
    { start(); }

    StopWatch(std::ostream &out)
    : out_(&out)
    { start(); }

    ~StopWatch()
    {
        const time_point end = std::chrono::system_clock::now();
        (*out_)
            << "elapsed time: "
            << std::chrono::duration_cast<Prec>(end - start_).count()
            << " ["
            << detail::chrono::UnitName<Prec>::name
            << "]"
            << std::endl;
    }
};

/* こんな感じで
{
    StopWatch<std::chrono::milliseconds> sw;
    // なんか超重い処理...
}
*/