datetime ++

An attempt to port Python Datetime in C++. Finally easy datetime management in C++ !

It consists of a header-only file datetime.h which relies on Howard Hinnant's date libraries, precisely date and tz.

This is an ongoing work! So expect mistakes for the moment and changes.

A little showcase

You can get the C++ source code and the equivalent Python code.

auto x1 = Date::today();
cout << "Today's date is " << x1 << endl;

auto x2 = DateTime<>::now(); // same result as DateTime<>::today()
cout << "Today's datetime is " << x2 << endl;

auto time_delta = TimeDelta(date::weeks(1), date::days(2), hours(3), seconds(240), microseconds(10000)); // arguments order does not matter
cout << "Here the delta time we want to add " << time_delta << endl;

cout << "Here the added result " << x2 + time_delta << endl;

// The C++ version can allow seconds only precision and can directly take a timezone string
auto x3 = DateTime<std::chrono::seconds>::now("Asia/Tehran");
cout << "Time in " << x3.tzinfo() << " is " << x3 << endl;

auto x4 = DateTime<>::strptime("21/11/92 16:30", "%d/%m/%y %H:%M");
cout << "datime from strptime is " << x4 << endl;

auto x5 = DateTime<>::utcfromtimestamp(1497252490.0282006);
std::cout << "UTC datetime from timestamp is " << x5 << ". Check timestamp back: " << x5.timestamp() << std::endl;

std::cout << "You can substract two datetimes into a timedelta " << x5 - x4 << std::endl;

outputs for me:

Today's date is 2017-06-14
Today's datetime is 2017-06-14 10:12:35.651158550 CEST
Here the delta time we want to add 9 days, 03:04:00.010000
Here the added result 2017-06-23 13:16:35.661158550 CEST
Time in Asia/Tehran is 2017-06-14 12:42:36 +0430
datime from strptime is 1992-11-21 16:30:00.000000000 UTC
UTC datetime from timestamp is 2017-06-12 07:28:10.028200626 UTC. Check timestamp back: 1497252490.028201
You can substract two datetimes into a timedelta 8968 days, 14:58:10.028200

Class datetime::TimeDelta public interface

Constructors

    template <class Duration>
    TimeDelta(const Duration& d);

    template<class Duration, class ... Durations>
    TimeDelta(const Duration& d, const Durations&... durations);

Member functions

    const date::days::rep                   days()          const
    const std::chrono::seconds::rep         seconds()       const
    const std::chrono::microseconds::rep    microseconds()  const
    const std::chrono::seconds::rep         total_seconds() const

Non member functions

    TimeDelta operator+(const TimeDelta&  x, const TimeDelta& y);
    TimeDelta operator-(const TimeDelta&  x, const TimeDelta& y);

    template<class Scalar, typename std::enable_if<std::is_floating_point<Scalar>::value>::type* = nullptr>
    TimeDelta operator*(Scalar s, const TimeDelta& x);

    template<class Scalar, typename std::enable_if<std::is_integral<Scalar>::value>::type* = nullptr>
    TimeDelta operator*(Scalar s, const TimeDelta& x);

    template<class Scalar, typename std::enable_if<std::is_floating_point<Scalar>::value>::type* = nullptr>
    TimeDelta operator*(const TimeDelta& x, Scalar s);

    template<class Scalar, typename std::enable_if<std::is_integral<Scalar>::value>::type* = nullptr>
    TimeDelta operator*(const TimeDelta& x, Scalar s);

    template<class CharT, class Traits>
    std::basic_ostream<CharT, Traits>&
    operator<<(std::basic_ostream<CharT, Traits>& os, const TimeDelta& td);

Not implemented (yet)

operator/, operator%, divmod, min, max, resolution

Remarks

• Currently, negative timedeltas do not follow Python unusual behaviour. For instance, in Python, timedelta(hours=-1) gives -1 day, 23:00:00 whereas in C++, auto x = TimeDelta(std::chrono::hours(-1)) will output 0 days, -01:00:00.00

Class datetime::Date public interface

Constructors

    Date() = default;
    Date(const date::year_month_day& ymd);
    Date(const date::year& y, const date::month& m, const date::day& d);

Member functions

    const date::year            year()              const;
    const date::month           month()             const;
    const date::day             day()               const;
    const date::year_month_day& year_month_day()    const;

    date::weekday   objweekday()    const; // extra method : no equivalent in Python
    unsigned        weekday()       const;
    unsigned        isoweekday()    const;
    std::string     ctime()         const;
    std::string     isoformat()     const;
    std::string     strftime(const std::string& format) const;

Non member functions

    Date operator+(const Date& d, const TimeDelta& td);
    Date operator+(const TimeDelta& td, const Date& d);
    Date operator-(const Date& d, const TimeDelta& td);
    TimeDelta operator-(const Date& x, const Date& y);

    template<class CharT, class Traits>
    std::basic_ostream<CharT, Traits>&
    operator<<(std::basic_ostream<CharT, Traits>& os, const Date& date);

Not implemented (yet)

fromordinal, replace, timetuple, toordinal, isocalendar, min, max, resolution

Remarks

• objweekday() returns a date::weekday object

Class datetime::DateTime public interface

Constructor

DateTime(const date::zoned_time<common_duration>& zt)

Member functions

    const date::zoned_time<common_duration>& zoned_time() const;  // extra method : no equivalent in Python

    Date        date()  const;
    const date::year  year()  const;
    const date::month month() const;
    const date::day   day()   const;

    const date::time_zone* time_zone() const; // extra method : no equivalent in Python
    const std::string& tzinfo() const; // differs from Python

    TimeDelta utcoffset() const;

    std::string timestamp() const;

    std::string ctime() const;
    std::string isoformat(const std::string& sep="T") const;
    std::string strftime(const std::string& format) const;

Non member functions

    static DateTime<typename std::common_type<Duration, std::chrono::seconds>::type> 
    today();
    
    static DateTime<typename std::common_type<Duration, std::chrono::seconds>::type> 
    now(const std::string& timezone_name = "");

    static DateTime<typename std::common_type<Duration, std::chrono::seconds>::type> 
    utcnow();
    
    template <class Rep>
    static DateTime<typename std::common_type<Duration, std::chrono::seconds>::type> 
    fromtimestamp(Rep timestamp, const std::string& timezone_name = "");

    template <class Rep>
    static DateTime<typename std::common_type<Duration, std::chrono::seconds>::type> 
    utcfromtimestamp(Rep timestamp);

    template <class Duration>
    DateTime<Duration> operator+(const DateTime<Duration>&  x, const TimeDelta& y);

    template <class Duration>
    DateTime<Duration> operator+(const DateTime<Duration>&  x, const TimeDelta& y);

    template <class Duration>
    DateTime<Duration> operator-(const TimeDelta& y, const DateTime<Duration>&  x);

    template <class Duration>
    TimeDelta operator-(const DateTime<Duration>&  x, const DateTime<Duration>& y);

    template <class Duration>
    bool operator<(const DateTime<Duration>&  x, const DateTime<Duration>& y);

    template<class CharT, class Traits, class Duration>
    std::basic_ostream<CharT, Traits>&
    operator<<(std::basic_ostream<CharT, Traits>& os, const DateTime<Duration>& date);

Not implemented (yet)

fromordinal, combine, fold, replace, utcoffset, dst, timetuple, utctimetuple, toordinal, min, max, resolution, tzset

Remarks

• The C++ version allows an optional Duration template parameter which will represents the time precision (e.g. std::chrono::milliseconds)
• The C++ version of tzinfo returns a string which is the time zone name
• time_zone() method gives time_zone* object from tz.

To work on

• Time class
• Tests
• Constexpr compile time possibilities
• No exception safety?