std::chrono::time_point::time_since_epoch

From cppreference.com


duration time_since_epoch() const;

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

[edit] Parameters

(none)

[edit] Return value

the amount of time between this time_point and the clock's epoch

[edit] Example

#include <iostream>
#include <chrono>
#include <ctime>
 
int main()
{
    std::chrono::time_point<std::chrono::system_clock> p1, p2, p3;
 
    p2 = std::chrono::system_clock::now();
    p3 = p2 - std::chrono::hours(24);
 
    std::time_t epoch_time = std::chrono::system_clock::to_time_t(p1);
    std::cout << "epoch: " << std::ctime(&epoch_time);
    std::time_t today_time = std::chrono::system_clock::to_time_t(p2);
    std::cout << "today: " << std::ctime(&today_time);
 
    std::cout << "hours since epoch: "
              << std::chrono::duration_cast<std::chrono::hours>(
                   p2.time_since_epoch()).count() 
              << '\n';
    std::cout << "yesterday, hours since epoch: "
              << std::chrono::duration_cast<std::chrono::hours>(
                   p3.time_since_epoch()).count() 
              << '\n';
}

Possible output:

epoch: Wed Dec 31 19:00:00 1969
today: Tue Jun 19 12:05:37 2012
hours since epoch: 372256
yesterday, hours since epoch: 372232

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