DateTime in C++

/*
 * Initializes the object with the values taken from the formatted string like:
 * "YYYY-MM-DD hh:mm:ss"
 * "YYYY-MM-DD hh:mm"
 * "YYYY-MM-DD"
 * "hh:mm:ss"
 * "hh:mm"
 * where number of the seconds is 0 by default
 */
DateTime(const char* datetime);
DateTime(const string& datetime);

/*
 * Copy constructor
 */
DateTime(const DateTime& datetime);

/*
 * Assignment operator
 */
DateTime& operator =(const DateTime& datetime);

enum Format
{
    INVALID = 0,
    DATETIME,
    DATE,
    TIME
};

enum TimeUnit
{
    SECONDS,
    MINUTES,
    HOURS,
    DAYS,
    MONTHS,
    YEARS,
};

enum DatePart
{
    NONE = -1,
    SECOND = 0,
    MINUTE,
    HOUR,
    TIME_HM,
    TIME_HMS,
    DATE_TIME_HM,
    DATE_TIME_HMS,
    DATE_ONLY,
    DAY_OF_WEEK,
    DAY_OF_MONTH,
    DAY_OF_YEAR,
    MONTH_OF_YEAR,
    MONTH_AND_DAY,
    QUARTER,
    YEAR,
    YEAR_AND_MONTH,
    YEAR_AND_QUARTER,
};

/*
 * Returns the part of date
 *
 * E.g. if the initial date is 01/01/1973 00:00:00
 * getDatePart(YEAR) returns 1973
 * getDatePart(MONTH) returns 1
 * getDatePart(DAY_OF_MONTH) returns 1
 */
DatePartValue getDatePart(DatePart part);

/*
 * Returns the number of the required date/time unit since the epoch
 * (currently is 00:00:00 November 17, 1858)
 * If the format is TIME, returns the 0 for all date units.
 *
 * E.g. if the initial date is 01/01/1973 00:00:00
 * getValue( HOURS ) returns the number of hours since the epoch
 * getValue( SECONDS ) returns the number of seconds since the epoch
 */
Value getValue(TimeUnit unit);

/*
 * Returns one of the datetime formats, see the Format enumeration
 */
Format getFormat();

/*
 * Returns the date and time in format "YYYY-MM-DD hh:mm:ss"
 */
string toString();

/*
 * Increments the date/time value. The offset is expressed in the time units
 * specified in timeUnit.
 */
void increment(int offset, TimeUnit timeUnit);

/*
 * Returns the modified Julian date (the number of days since 17/11/1858)
 * of the date specified by the day/month/year
 */
static Value getMJDFromDate(short day, short month, short year);

/*
 * Returns the date structure given the number of days since 17/11/1858
 * Note that the tm_year member already contains the right year (not the year minus 1900),
 * and the tm_mon member starts with 1, not 0.
 */
static struct tm getDateFromMJD(Value days);

/*
 * Returns the quarter number given the month number
 */
static short getQuarterFromMonth(short month);

/*
 * Returns the day of week (1 - Monday, 2 - Tuesday, ... 7 - Sunday)
 * of the date specified by the day/month/year
 */
static short getDayOfWeek(short day, short month, short year);

/*
 * Returns the absolute value of the difference between two dates
 * specified by day/month/year in the specified time units
 * Warning: only DAYS, MONTHS and YEARS units accepted
 * otherwise returns 0
 */
static Value getDateDiff
(
    short day1, short month1, short year1,
    short day2, short month2, short year2,
    TimeUnit unit
);

/*
 * Returns true if the specified year is a leap year
 */
static bool isLeapYear(short year);

/*
 * Returns the number of days in the specified month/year
 */
static short getDaysInMonth(short month, short year);

/*
 * Returns the number of days in the specified month/year
 */
static short getMonthNumberByName(const char *name);