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std::chrono..._since_epoch(3)  C++ Standard Libary std::chrono..._since_epoch(3)

NAME
     std::chrono::time_point::time_since_epoch				       -
     std::chrono::time_point::time_since_epoch

Synopsis
	duration time_since_epoch() const;  (since C++11)
					    (constexpr since C++14)

	Returns a duration representing the amount of time between *this and the
     clock's
	epoch.

Parameters
	(none)

Return value
	The amount of time between this time_point and the clock's epoch.

Example
     // Run this code

      #include <chrono>
      #include <ctime>
      #include <iostream>

      int main()
      {
	  const auto p0 = std::chrono::time_point<std::chrono::system_clock>{};
	  const auto p1 = std::chrono::system_clock::now();
	  const auto p2 = p1 - std::chrono::hours(24);

	  std::time_t epoch_time = std::chrono::system_clock::to_time_t(p0);
	  std::cout << "epoch: " << std::ctime(&epoch_time);
	  std::time_t today_time = std::chrono::system_clock::to_time_t(p1);
	  std::cout << "today: " << std::ctime(&today_time);

	  std::cout << "hours since epoch: "
		    << std::chrono::duration_cast<std::chrono::hours>(
			   p1.time_since_epoch()).count()
		    << '\n';
	  std::cout << "yesterday, hours since epoch: "
		    << std::chrono::duration_cast<std::chrono::hours>(
			   p2.time_since_epoch()).count()
		    << '\n';
      }

Possible output:
      epoch: Thu Jan  1 00:00:00 1970
      today: Fri Jun 30 10:44:11 2017
      hours since epoch: 416338
      yesterday, hours since epoch: 416314

http://cppreference.com 	   2024.06.10	   std::chrono..._since_epoch(3)

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