c++ time utils

time_utils.h

//*****************************************************
    // ConvertYYYYMMDDhhmmss_us
    //*****************************************************
    static std::string ConvertYYYYMMDDhhmmss_us(uint64_t intime,
                                                bool usegmtime = false)
    {
        char buff[50];
        memset(buff, '\0', sizeof(buff));

        std::string s_format = "%4d%02d%02d-%02d:%02d:%02d.%06d";
        int nano = intime % 1000000000LL;
        int micro = nano / 1000;
        time_t epoch = (time_t)intime / 1000000000LL;

        struct tm t;
        if (usegmtime)
        {
            gmtime_r(&epoch, &t);
        }
        else
        {
            localtime_r(&epoch, &t);
        }
        sprintf(buff, s_format.c_str(), t.tm_year + 1900, t.tm_mon + 1, t.tm_mday,
                t.tm_hour, t.tm_min, t.tm_sec, micro);

        return (std::string(buff));
    }