C++ 软件开发中的时间

#include <chrono>inline std::string to_iso_8601(std::chrono::time_point<std::chrono::system_clock> t) {// convert to time_t which will represent the number of// seconds since the UNIX epoch, UTC 00:00:00 Thursday, 1st. January 1970auto epoch_seconds = std::chrono::system_clock::to_time_t(t); // Format this as date time to seconds resolution// e.g. 2016-08-30T08:18:51std::stringstream stream;stream << std::put_time(gmtime(&epoch_seconds), "%FT%T"); // If we now convert back to a time_point we will get the time truncated// to whole secondsauto truncated = std::chrono::system_clock::from_time_t(epoch_seconds); // Now we subtract this seconds count from the original time to// get the number of extra microseconds..auto delta_us = std::chrono::duration_cast<std::chrono::microseconds>(t - truncated).count(); // And append this to the output stream as fractional seconds// e.g. 2016-08-30T08:18:51.867479stream << "." << std::fixed << std::setw(6) << std::setfill('0') << delta_us; return stream.str();}

inline std::chrono::system_clock::time_point utc_from_iso_8601(std::string datetime_in_iso) {  std::tm t = {};  std::istringstream ss(datetime_in_iso);  ss >> std::get_time(&t, "%Y-%m-%dT%H:%M:%SZ");  auto epoch_seconds = std::mktime(&t) - _timezone; // only for Windows  if (-1 == epoch_seconds) return std::chrono::system_clock::time_point();
  int y, m, d, h, M;  float fraction_second = 0;  sscanf(datetime_in_iso.c_str(), "%d-%d-%dT%d:%d:%fZ", &y, &m, &d, &h, &M, &fraction_second);  float delta_s = fraction_second - t.tm_sec;
  auto truncated = std::chrono::system_clock::from_time_t(epoch_seconds);  auto precise_time = truncated + std::chrono::microseconds(int(delta_s * 1000000));
  return precise_time;}