cpp chrono basic

// cpp 20
//c++ - Number of seconds since midnight - Stack Overflow
//https://stackoverflow.com/questions/61273498/number-of-seconds-since-midnight
int main(int argc, char** argv)
{
    std::system("chcp 65001");
 
    using namespace std;
    using namespace std::chrono;
 
    // chrono time point to string
    auto chronoNow = chrono::system_clock::now();
    cout << chronoNow << endl;
    std::time_t tt = chrono::system_clock::to_time_t(chronoNow);
    char buffer[32];
    std::tm ttm;
    localtime_s(&ttm, &tt);
    strftime(buffer, 32, "%Y-%m-%d %H:%M:%S", &ttm);
    cout << buffer << endl;
    auto remainder = chrono::duration_cast<chrono::microseconds>(chronoNow.time_since_epoch()) % chrono::seconds(1);
    cout << remainder.count() << endl;
    string timeStr(buffer);
    timeStr += std::format(".{:06d}", remainder.count());
    cout << timeStr << endl;
 
    // milliseconds since epoch
    auto millisec_since_epoch = chrono::duration_cast<chrono::milliseconds>(chrono::system_clock::now().time_since_epoch());
    cout << millisec_since_epoch << endl;
    cout << millisec_since_epoch.count() << endl;
    cout << millisec_since_epoch / std::chrono::milliseconds(1) << endl;
 
    // milliseconds since start of the day
    auto now = chrono::system_clock::now();
    auto today = chrono::floor<chrono::days>(now);
    auto hours_since_midninght = duration_cast<hours>(now - today);
    int hours_since_midninght_int = hours_since_midninght.count();
    cout << hours_since_midninght << endl;
    cout << hours_since_midninght_int << endl;
 
    // chrono in local zone
    auto local_now = chrono::current_zone()->to_local(chrono::system_clock::now());
    auto local_today = chrono::floor<chrono::days>(local_now);
    auto local_hours_elapsed = chrono::duration_cast<chrono::hours>(local_now - local_today);
    cout << local_hours_elapsed << endl;
    cout << local_hours_elapsed.count() << endl;
 
    return 0;
}