C++で現在時刻を表示する方法

<code class="cpp">#include <iostream>
#include <ctime>

int main() {
  time_t now = time(0);
  std::cout << "Current time: " << ctime(&now);
  return 0;
}</code>

<code class="cpp">#include <iostream>
#include <chrono>

int main() {
  auto now = std::chrono::system_clock::now();
  auto time_t_now = std::chrono::system_clock::to_time_t(now);
  std::cout << "Current time: " << ctime(&time_t_now);
  return 0;
}</code>

<code class="cpp">#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>

int main() {
  boost::posix_time::ptime now = boost::posix_time::second_clock::local_time();
  std::cout << "Current time: " << now;
  return 0;
}</code>