UNIX Timestamp in C++ (Guaranteed in C++20; de facto standard pre-C++20)

timestamp.hpp

/// @file timestamp.hpp
/// @brief Return UNIX timestamp.
/// @author J. Arrieta <Juan.Arrieta@nablazerolabs.com>
/// @copyright (C) 2019 Nabla Zero Labs
/// @license MIT

#pragma once
#include <chrono>
#include <cstdint>

namespace nzl {

/// @brief Return total nanoseconds elapsed since Jan 01, 1970 00:00:00 UTC.
/// @note Guaranteed in C++20; de facto standard pre-C++20.
inline std::uint64_t unix_nanos() noexcept {
  using namespace std::chrono;
  const auto elapsed = system_clock::now().time_since_epoch();
  return duration_cast<nanoseconds>(elapsed).count();
}

}  // namespace nzl