Generate timestamps in C++

c++
1

C++ (using <chrono>, C++11 and later)

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

int main() {
    // Current time point
    auto now = std::chrono::system_clock::now();

    // Convert to time_t for calendar representation
    std::time_t now_c = std::chrono::system_clock::to_time_t(now);
    std::cout << "Unix timestamp: " << now_c << "\n";

    // Human-readable (UTC)
    std::cout << "UTC time: "
              << std::put_time(std::gmtime(&now_c), "%Y-%m-%dT%H:%M:%SZ")
              << "\n";

    // Human-readable (local time)
    std::cout << "Local time: "
              << std::put_time(std::localtime(&now_c), "%Y-%m-%d %H:%M:%S")
              << "\n";

    // Milliseconds since epoch
    auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(
                  now.time_since_epoch()).count();
    std::cout << "Milliseconds since epoch: " << ms << "\n";

    return 0;
}

C++20 (cleaner, with <chrono> calendar/timezone support)

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;

    auto now = system_clock::now();
    std::cout << "Timestamp: " << now << "\n"; // e.g. 2026-09-01 12:34:56.789012

    // Truncate to seconds
    auto now_sec = time_point_cast<seconds>(now);
    std::cout << "Seconds precision: " << now_sec << "\n";

    return 0;
}

(Requires a compiler with full C++20 <chrono> formatting support — GCC 13+/Clang 17+/MSVC are the safest bets; older compilers may need {fmt} as a fallback.)

Notes

  • localtime/gmtime return pointers to internal static buffers — not thread-safe. Use localtime_r/gmtime_r (POSIX) or localtime_s/gmtime_s (Windows/C11 Annex K) in multithreaded code.
  • For monotonic timing (measuring durations, not wall-clock time), prefer CLOCK_MONOTONIC in C or std::chrono::steady_clock in C++ — system_clock/CLOCK_REALTIME can jump due to NTP sync or manual clock changes.