Get current time since epoch

currenttime.hpp

#include <chrono>
#include <iomanip>

template <typename Clock>
class CurrentTime
{
    template<struct tm* represent(const time_t *)>
    static std::string utc() {
        using namespace std::chrono;
        auto timer = Clock::to_time_t(Clock::now());
        std::tm bt = *represent(&timer);
        std::ostringstream oss;
        oss << std::put_time(&bt, "%F %T");
        return oss.str();
    }
    template<struct tm* represent(const time_t *)>
    static std::string utcWithMilli() {
        using namespace std::chrono;
        auto now = Clock::now();
        auto ms = duration_cast<std::chrono::milliseconds>(now.time_since_epoch()) % 1000;
        auto timer = Clock::to_time_t(now);
        std::tm bt = *represent(&timer);
        std::ostringstream oss;
        oss << std::put_time(&bt, "%F %T");
        oss << '.' << std::setfill('0') << std::setw(3) << ms.count();
        return oss.str();
    }
  public:
    static long long seconds() {
        using namespace std::chrono;
        return duration_cast<seconds>(Clock::now().time_since_epoch()).count();
    }
    static long long milliseconds() {
        using namespace std::chrono;
        return duration_cast<milliseconds>(Clock::now().time_since_epoch()).count();
    }
    static long long microseconds() {
        using namespace std::chrono;
        return duration_cast<microseconds>(Clock::now().time_since_epoch()).count();
    }
    static long long nanoseconds() {
        using namespace std::chrono;
        return duration_cast<nanoseconds>(Clock::now().time_since_epoch()).count();
    }
    static std::string utcTime() { return CurrentTime::utc<&std::time>(); }
    static std::string utcTimeWithMilli() { return CurrentTime::utcWithMilli<&std::time>(); }
    static std::string utcLocalTime() { return CurrentTime::utc<&std::localtime>(); }
    static std::string utcLocalTimeWithMilli() { return CurrentTime::utcWithMilli<&std::localtime>(); }
    static std::string utcGMTime() { return CurrentTime::utc<&std::gmtime>(); }
    static std::string utcGMTimeWithMilli() { return CurrentTime::utcWithMilli<&std::gmtime>(); }
};