C++20 introduced a guarantee that time_since_epoch
is relative to the UNIX epoch, and cppreference.com gives an example that I’ve distilled to the relevant code, and changed to units of seconds rather than hours:
#include <iostream> #include <chrono> int main() { const auto p1 = std::chrono::system_clock::now(); std::cout << "seconds since epoch: " << std::chrono::duration_cast<std::chrono::seconds>( p1.time_since_epoch()).count() << '\n'; }
Using C++17 or earlier, time()
is the simplest function – seconds since Epoch, which for Linux and UNIX at least would be the UNIX epoch. Linux manpage here.
The cppreference page linked above gives this example:
#include <ctime> #include <iostream> int main() { std::time_t result = std::time(nullptr); std::cout << std::asctime(std::localtime(&result)) << result << " seconds since the Epoch\n"; }