Function timestampToString

c++/test/TestConvertColumnReader.cc:1005–1030

  }

  static std::string timestampToString(int64_t seconds, int64_t nanos,
                                       const std::string& zoneName) {
    auto& timezone = getTimezoneByName(zoneName);
    seconds = timezone.convertToUTC(seconds);
    time_t t = static_cast<time_t>(seconds);
    char buffer[100];
    constexpr auto SECOND_IN_DAY = 3600 * 24;
    auto day = t < 0 ? (t - SECOND_IN_DAY + 1) / SECOND_IN_DAY : t / SECOND_IN_DAY;

    auto [y, m, d] = civil_from_days(day);
    auto second_in_day = t % (3600 * 24);
    if (second_in_day < 0) {
      second_in_day += 3600 * 24;
    }
    auto h = second_in_day % (3600 * 24) / 3600;
    auto min = second_in_day % 3600 / 60;
    auto s = second_in_day % 60;
    std::snprintf(buffer, sizeof(buffer), "%04d-%02d-%02d %02ld:%02ld:%02ld", y, m, d, h, min, s);
    std::string result(buffer);
    if (nanos) {
      while (nanos % 10 == 0) nanos /= 10;
      result = result + "." + std::to_string(nanos);
    }
    result = result + " " + zoneName;
    return result;
  }

  TEST(ConvertColumnReader, TestConvertStringVariantToTimestamp) {
    constexpr int DEFAULT_MEM_STREAM_SIZE = 10 * 1024 * 1024;