XDate

XDate includes implementation of the classes CGregorianDate, CIsoDate, and CFiscalDate. Please click on the following links for more information:

CGregorianDate: manipulating dates in the Gregorian calendar
CIsoDate: manipulating ISO-8601 dates; and XDateCalc, a calculator to display Gregorian and ISO dates
CFiscalDate: manipulating fiscal dates, weeks, quarters, and years; and XFisCal, a program that lets you create a printable fiscal calendar

Historical Background

The calendar in use in most of the world today is the Gregorian calendar, which came into common use beginning in 1582 AD, when it was decreed by Pope Gregory XIII, after whom it was named. Prior to that, the Julian calendar - introduced by Julius Caesar in 46 BC - was in continuous use, and remained in use into the 20th century in some parts of the world.

In modern times, there have been several attempts to standardize the formatting of dates. The most successful of these efforts is ISO 8601. This comprehensive standard is now widely used in timestamping documents, log files, emails, and other computer-generated files. It also introduced what has been called the ISO date/time, which is actually a set of rules for the representation of dates and times.

ISO 8601 uses YYYY-MM-DD big-endian date notation, and also introduced the idea of ISO week dates, which are specified by the ISO week-numbered year in the format YYYY, a week number in the format ww prefixed by the letter W, and the weekday number, a digit from 1 through 7, beginning with Monday and ending with Sunday.

CGregorianDate

To work with dates in any software program, you first have to decide how you will store dates internally. Currently, there are several standard date types to choose from:

time_t - a 32-bit long integer used to store time values (seconds since midnight January 1, 1970 AD). There is also a 64-bit version. The 32-bit version wraps on January 18, 2038 AD.
struct tm - this struct contains easily-accessible members for date and time.
DATE - this type implements date and time as a floating point number and is the basis for COleDateTime. Its range is January 1, 100 AD, to December 31, 9999 AD.
SYSTEMTIME - This struct is used system-wide for date and time storage. It has handy members for accessing individual time elements. Its range is 1601 AD through 30827 AD.
FILETIME - this struct is normally used only for dealing with filesystem times. To actually use it, you would normally convert it to a SYSTEMTIME. Note that FAT records times on disk in local time, while NTFS records times on disk in UTC (aka GMT).
CTime - a very popular MFC class based on time_t, has a corresponding CTimeSpan class.
COleDateTime - another popular MFC class with a larger range than CTime, has a corresponding COleDateTimeSpan class. See also this article.
DateTime - this struct is used in the .Net framework to represent date and time. It has many handy member functions. Its range is January 1, 1 AD to December 31, 9999 AD.

Terminology I follow two conventions in this article: first, I use AD instead of the more recent CE, because sometimes people think I am referring to Windows CE when I use CE. Second, I use UTC (Coordinated Universal Time) interchangeably with GMT. You can read more about UTC here.

Date Types

Unfortunately, none of these date types offer a comprehensive way of handling all the varieties of dates that commonly occur in today's electronic documents. Here are some that are not handled:

ISO 8601 week date formats - The ISO 8601 standard can be found here and here. While ISO 8601 specifies many formats that use the Gregorian calendar, it also introduces an entirely new date representation called ISO week dates. You can read the details in ISO 8601, ¶2.2.10 and ¶3.2.2.
In the ISO 8601 system of calendar weeks, there can be 52 or 53 weeks in an ISO 8601 year. The first week of the ISO year (just like all ISO weeks) begins on a Monday, and specifically includes January 4 (ISO 8601 ¶3.2.2). ISO 8601 week dates can be represented by YYYY-Www-D, where YYYY is the ISO year, ww is the 2-digit week number( 1..53), and D is the day number (1..7) within the week (Monday = 1, Sunday = 7). Thus, an ISO year may include up to three days from the preceding Gregorian year (if January 4 falls on a Sunday). In the same way, the end of an ISO year may include up to three days from the following Gregorian year. Example of this format: 1994-W52-7, which is January 1, 1995.
ISO 8601 ordinal dates - Another ISO 8601 date format is YYYY-DDD, where YYYY is the year and DDD is the sequential day number (1..366) within the year. ISO 8601 (see ¶4.1.3ff) calls this an ordinal date. Example of this format: 1985-102.
Julian day numbers - Julian day numbers (or, as JR Stockton points out, chronological Julian day numbers, since integer Julian day numbers do not include the fractional time, but are simply a count of days; read more about this here and here) are useful because they are simple to manipulate. Since Julian day numbers (I will omit "chronological" for brevity) are a monotonic sequence of integers, it is very easy to determine date differences using them. There are standard formulas for calculating Julian day numbers; see here.
Day and month names - You can obtain the day and month names (both full and abbreviated) by using the Win32 function GetLocaleInfo(). But what if you're in New York and wanted to retrieve and output the names appropriate for Europe or Asia? Or wanted to always output the US names, regardless of where you're located? Or wanted to output the names that are appropriate for some other area? The CGregorianDate class provides this flexibility in a convenient, unified manner.
Fiscal calendars - There are many different types of calendars used by accounting and government entities, for both budgeting and scheduling purposes. These fiscal calendars are not always aligned on the Gregorian year; they differ in the start date (some start on January 1, others October 1, etc.); in whether the first week of the fiscal year starts on the first full week; and in whether weeks start on Sunday or Monday. Fiscal calendars are obviously crucial to businesses and governments, and yet none of the above date types provide any support for them.

In addition, it is obvious that there is a basic requirement to easily convert between different date formats; for example, to go from Gregorian date to ISO date, in order to output an ISO week date. Or if you were trying to extract dates from a log file, to be able to convert ISO week dates to Gregorian dates, in order to store the dates in a standard system date format.

To meet these various requirements, I created XDate.h.

XDate.h

The file XDate.h includes implementation of the classes CGregorianDate, CIsoDate, and CFiscalDate. This article discusses CGregorianDate; Parts 2 and 3 discuss CIsoDate and CFiscalDate. At the end of this article, there is a list of CGregorianDate class members.

The classes contained in XDate.h do not handle time in any way; they do not store or convert time; only dates. They do not calculate Easter or any other civil or religious holiday. They do not deal with any calendar except Gregorian, Julian (in a limited way), and ISO 8601 (if you consider that a calendar). And they accept only dates after 1582 AD.

CGregorianDate implements a class based on the Gregorian calendar. Its data members are:

//=============================================================================
// Data
//=============================================================================
private:

// Note that all m-d-y values are one-based

    int month;   // 1 = January, ..., 12 = December
    int day;     // 1..LastDayOfMonth()
    int year;    // 1583..INT_MAX

Besides the usual month-day-year (MDY), CGregorianDate has constructors for many commonly used date types:

DATE
FILETIME
Julian day number
ordinal date YYYYDDD
SYSTEMTIME
time_t
struct tm

There are also retrieval functions that return the current CGregorianDate date in these formats. CGregorianDate implements overloaded math operators for +, -, ++, --, +=, and -=, as well as logical compare operators ==, !=, <, >, <=, and >=.

One of 24 carved wheels at the Konark Sun Temple in Orissa, India, built by King Narasimhadeva about 1250 AD to honor the sun god Surya. The temple symbolizes the passage of time, which is under the sun god's control. It takes the form of a huge chariot for the sun god, with 12 pairs of stone-carved wheels (representing the 12 months of the year) and a team of seven galloping horses (representing the days of the week).

CGregorianDate Construction

Examples of CGregorianDate construction:

Construction from Gregorian date MM/DD/YYYY
```
    CGregorianDate gd(3, 17, 2009);
```

Construction from CGregorianDate object

    CGregorianDate gd(3, 17, 2009);
    CGregorianDate gd2(gd);
or
    CGregorianDate gd2 = gd;

Construction from current time

    CGregorianDate gd(CGregorianDate::GetCurrentTime());
or
    CGregorianDate gd = CGregorianDate::GetCurrentTime();

Construction from time_t

    time_t t;
    time(&t);
    CGregorianDate gd(t);

Construction from struct tm

    time_t t;
    time(&t);
    struct tm now = *localtime(&t);
    CGregorianDate gd(now);

Construction from SYSTEMTIME

    SYSTEMTIME st;
    GetLocalTime(&st);
    CGregorianDate gd(st);

Construction from Julian day number
```
    CGregorianDate gd(2454908);
```
Construction from ordinal date YYYYDDD
```
    CGregorianDate gd(2009, 76);
```

CGregorianDate Usage

Once you have created a CGregorianDate object, you can use class functions to find out if the date is a leap year (IsLeapYear()), get its Julian day number (GetJulianDayNumber()), get its Excel serial date (GetExcelSerialDatePC()), and get month name (GetMonthNameForLocale()) and day name (GetDayNameForLocale()) for the date. Of course, at any time you can retrieve the date information (GetDay(), GetMonth(), GetYear()), or check if the date is valid (IsValidDate()).

Example: Find a Recurring Date

Your club meets on the second Tuesday of every month. You want to list all the club meeting dates for 2009:

    // from XDateTestDlg.cpp
    TCHAR szDayName[100];
    TCHAR szMonthName[100];
    CGregorianDate gd8(1, 6, 2009);        // Tuesday
    gd8.GetDayNameForLocale(szDayName, sizeof(szDayName)/sizeof(TCHAR)-1);

    m_List.Printf(CXListBox::Blue, CXListBox::White, 0,
        _T("Test 8:  Find recurring date - 2nd %s of the month"), szDayName);

    for (m = 1; m <= 12; m++)
    {
        gd8.Set(m, 1, 2009);
        gd8.GetMonthNameForLocale(szMonthName, sizeof(szMonthName)/sizeof(TCHAR)-1);
        for (int nTuesdays = 0; nTuesdays < 2; gd8++)
        {
            if (gd8.GetDayOfWeek() == CGregorianDate::Tuesday)
                nTuesdays++;
        }
        gd8--;
        m_List.Printf(CXListBox::Black, CXListBox::White, 0, 
            _T("    %s %d"), szMonthName, gd8.GetDay());
    }

The above code produces this output:

Test 8:  Find recurring date - 2nd Tuesday of the month
    January 13
    February 10
    March 10
    April 14
    May 12
    June 9
    July 14
    August 11
    September 8
    October 13
    November 10
    December 8

Example: Determining the Delivery Date

You need to find the delivery date for a package that you are sending. You know it will take 14 business days to get there (today is May 1):

    // from XDateTestDlg.cpp
    m_List.Printf(CXListBox::Blue, CXListBox::White, 0,
        _T("Test 9:  Find delivery date"));

    gd8 = CGregorianDate::GetCurrentTime();
    gd8.AddBusinessDays(14);
    m_List.Printf(CXListBox::Black, CXListBox::White, 0, 
        _T("    Delivery will be on %d/%d/%d"),
        gd8.GetYear(), gd8.GetMonth(), gd8.GetDay());

The above code produces this output:

Test 9:  Find delivery date
    Delivery will be on 2009/5/21

Example: Find all the Mondays in October

You want to find all the Mondays in October:

    // from XDateTestDlg.cpp
    TCHAR szMonthName[100];
    gd8.Set(10, 5, 2009);        // Monday
    gd8.GetDayNameForLocale(szDayName, sizeof(szDayName)/sizeof(TCHAR)-1);
    gd8.GetMonthNameForLocale(szMonthName, sizeof(szMonthName)/sizeof(TCHAR)-1);
    m_List.Printf(CXListBox::Blue, CXListBox::White, 0,
        _T("Test 10:  Find %ss in %s"), szDayName, szMonthName);

    gd8.Set(10, 1, 2009);
    while (gd8.GetMonth() == 10)
    {
        if (gd8.GetDayOfWeek() == CGregorianDate::Monday)
            m_List.Printf(CXListBox::Black, CXListBox::White, 0, 
                _T("    %s %d"), szMonthName, gd8.GetDay());
        gd8++;
    }

The above code produces this output:

Test 10:  Find Mondays in October
    October 5
    October 12
    October 19
    October 26

Example: Days until Christmas

You want to find the number of days until Christmas:

    // from XDateTestDlg.cpp
    m_List.Printf(CXListBox::Blue, CXListBox::White, 0,
        _T("Test 11  Find days until Christmas"));

    gd8 = CGregorianDate::GetCurrentTime();
    n = gd8.GetDays(12, 25, gd8.GetYear());
    m_List.Printf(CXListBox::Black, CXListBox::White, 0, 
        _T("    Days until Christmas = %d"), n);

The above code produces this output:

Test 11  Find days until Christmas
    Days until Christmas = 261

Please see XDateTestDlg.cpp for more examples of how to use CGregorianDate.

CGregorianDate Date Formatting

CGregorianDate uses strftime() to implement date formatting. Here are some sample formats that can be used with CGregorianDate::Format():

To get this date string	Use this format
March 17, 2009	%B %#d, %Y
March 2009	%B %Y
Tuesday, March 17, 2009	%A, %B %#d, %Y
Tue 17	%a %#d
17 Mar 2009	%#d %b %Y
17/3/2009	%#d/%#m/%Y
3/17/2009	%#m/%#d/%Y
03/17/09	%m/%d/%y
3/17	%#m/%#d
17/03/09	%d/%m/%y
2009076	%Y%j
09076	%y%j
2009-03-17	%Y-%m-%d

The # in the formats means "suppress leading zeros".

CGregorianDate Debugging

CGregorianDate provides the following debugging facilities:

virtual void Trace(LPCTSTR lpszMsg = NULL) const - This virtual function can be called anytime to write the month, day, and year, along with an optional message, to OutputDebugString(). The non-MFC XTrace.h is used to write the output when _DEBUG is defined, just like MFC's TRACE. To enable this, un-comment the line that is highlighted below:

//=============================================================================
// TRACE output
//=============================================================================

// if you want to see the TRACE output, un-comment this line:
//#define XDATE_ENABLE_TRACE


#undef TRACE_XDATE
#ifdef XDATE_ENABLE_TRACE
#include "XTrace.h"			// non-MFC TRACE
#define TRACE_XDATE TRACE
#else
#define TRACE_XDATE __noop
#endif

virtual void AssertValid() const - This virtual function can be called anytime to verify the date and display a diagnostic message via _ASSERTE (when _DEBUG is defined).
virtual void Dump() const - This virtual function may be overriden to provide custom debug output.

If you want to use the CGregorianDate Trace facility, don't forget to un-comment the line shown above, and also include XTrace.h in your project directory.

XDateTest

The demo application XDateTest.exe tests the various features and APIs of the XDate classes:

screenshot

How To Use

To integrate XDate into your own program, you first need to add XDate.h to your project. If you want to use the CGregorianDate Trace facility, also include XTrace.h in your project directory.

Next, include XDate.h in the module where you want to use the XDate classes.

For more details on how to use, please see XDateTestDlg.cpp.

CGregorianDate Class Members

Construction
	CGregorianDate()	Default constructor
	CGregorianDate(const CGregorianDate& gd)	Copy constructor
	CGregorianDate(const DATE date)	OLE DATE; used by COleDateTime
	CGregorianDate(const FILETIME& ft)	Filesystem FILETIME
	CGregorianDate(int jdn)	Chronological Julian day number
	CGregorianDate(int y, int d)	Ordinal date YYYYDDD
	CGregorianDate(int m, int d, int y)	Construction from month, day, year; earliest day is 1/1/1583 AD
	CGregorianDate(const struct tm& t)	C runtime; usually set from time_t
	CGregorianDate(const SYSTEMTIME& st)	System SYSTEMTIME
	CGregorianDate(time_t t)	C runtime; seconds since 1 Jan 1970
Assignment
	CGregorianDate& operator=(const CGregorianDate& gd)	CGregorianDate object
	CGregorianDate& operator=(const DATE& date)	OLE DATE; used by COleDateTime
	CGregorianDate& operator=(const FILETIME& ft)	Filesystem FILETIME
	CGregorianDate& operator=(const int& jdn)	Chronological Julian day number
	CGregorianDate& operator=(const struct tm& t)	C runtime; usually set from time_t
	CGregorianDate& operator=(const SYSTEMTIME& st)	System SYSTEMTIME
	CGregorianDate& operator=(const time_t& t)	C runtime; seconds since 1 Jan 1970
Attributes
	virtual bool GetAbbreviatedDayNameForLocale(LPTSTR lpszDayName, DWORD dwSize) const	Returns abbreviated day name for current day for system default locale as returned by GetLocaleInfo().
	virtual bool GetAbbreviatedDayNameForLocale(LCID locale, LPTSTR lpszDayName, DWORD dwSize) const	Returns abbreviated day name for current day for specified locale as returned by GetLocaleInfo().
	bool GetAbbreviatedDayNameForUS(LPTSTR lpszDayName, DWORD dwSize) const	Returns abbreviated day name for current day for US.
	virtual bool GetAbbreviatedMonthNameForLocale(LPTSTR lpszMonthName, DWORD dwSize) const	Returns abbreviated month name for system default locale for current month as returned by GetLocaleInfo().
	virtual bool GetAbbreviatedMonthNameForLocale(LCID locale, LPTSTR lpszMonthName, DWORD dwSize) const	Returns abbreviated month name for current month for specified locale as returned by GetLocaleInfo().
	bool GetAbbreviatedMonthNameForUS(LPTSTR lpszMonthName, DWORD dwSize) const	Returns abbreviated month name for current month for US.
	int GetBusinessDays(int m, int d, int y) const	Returns number of business days (see IsBusinessDay()) between the current date and the mdy date. Returns < 0 if mdy is in past, > 0 if mdy is in future.
	int GetBusinessDays(const CGregorianDate& gd) const	Returns number of business days (see IsBusinessDay()) between the current date and the gd date. Returns < 0 if gd is in past, > 0 if gd is in future.
	int GetCentury()	Returns century; eg, returns 19 for 1985.
	static CGregorianDate GetCurrentTime()	Returns a CGregorianDate object that represents the current time.
	int GetDay() const	Returns current day of month (1..31).
	int GetDayOfWeek() const	Returns day of week; Monday = 0, Sunday = 6.
	virtual bool GetDayNameForLocale(LPTSTR lpszDayName, DWORD dwSize) const	Returns day name for current day for the system default locale as returned by GetLocaleInfo().
	virtual bool GetDayNameForLocale(LCID locale, LPTSTR lpszDayName, DWORD dwSize) const	Returns day name for current day for the specified locale as returned by GetLocaleInfo().
	bool GetDayNameForUS(LPTSTR lpszDayName, DWORD dwSize) const	Returns day name for current day for US.
	int GetDays(int m, int d, int y) const	Returns number of days between the current date and the mdy date. Returns < 0 if mdy is in past, > 0 if mdy is in future.
	int GetDays(const CGregorianDate& gd) const	Returns number of days between the current date and the gd date. Returns < 0 if gd is in past, > 0 if gd is in future.
	static int GetExcelSerialDateMAC(int m, int d, int y)	Returns the MAC Excel serial date, a monotonic sequence of integers beginning with 0 = 1/1/1904.
	int GetExcelSerialDateMAC() const	Returns the MAC Excel serial date for the current date.
	static int GetExcelSerialDatePC(int m, int d, int y)	Returns the PC Excel serial date, a monotonic sequence of integers beginning with 1 = 1/1/1900. A special case is made for 2/29/1900 (an invalid date), because of a bug in Excel/Lotus 123.
	int GetExcelSerialDatePC() const	Returns the PC Excel serial date for the current date.
	bool GetGregorian(int& m, int& d, int& y) const	Returns the mdy values for the current date. Returns true if current date is valid.
	bool GetIso(int& w, int& d, int& y) const	Returns ISO week, day, and year for current date.
	static int GetJulianDayNumber(int m, int d, int y)	Returns Julian day number for mdy.
	int GetJulianDayNumber() const	Returns Julian day number for current date.
	int GetModifiedJulianDayNumber() const	Returns modified Julian day number for current date; this is the Julian day number - 2400001. It offers smaller magnitude numbers at a cost of reduced range.
	int GetMonth() const	Returns current month (1..12).
	virtual bool GetMonthNameForLocale(LPTSTR lpszMonthName, DWORD dwSize) const	Returns month name for current month for the system default locale as returned by GetLocaleInfo().
	virtual bool GetMonthNameForLocale(LCID locale, LPTSTR lpszMonthName, DWORD dwSize) const	Returns month name for current month for the specified locale as returned by GetLocaleInfo().
	bool GetMonthNameForUS(LPTSTR lpszMonthName, DWORD dwSize) const	Returns month name for current month for US.
	static int GetOrdinalDayOfYear(int m, int d, int y)	Returns day within year (1..366) for MDY.
	int GetOrdinalDayOfYear() const	Returns day within year (1..366) for current date.
	virtual TCHAR * GetOrdinalSuffix(int n) const	Returns pointer to suffix string for n; st for 1 *1st), nd for 2 (2nd), etc.
	bool GetOrdinalSuffixForDay(LPTSTR lpszSuffix, DWORD dwSize) const	Returns suffix string for current month day.
	bool GetSystemTime(SYSTEMTIME& SystemTime) const	Returns SYSTEMTIME value for current date. Returns false if date is not a valid SYSTEMTIME date (before 1602).
	bool GetTm(struct tm& t) const	Fills in tm struct with current month, day, and year. Returns false if date is not a valid C runtime date (before 1/1/1970).
	static int GetWeekNumber(int m, int d, int y, bool bMondayStart)	Returns week number (1..52) for MDY. If bMondayStart is true, week begins on Monday, otherwise week begins on Sunday.
	int GetWeekNumber(bool bMondayStart) const	Returns week number (1..52) for current date. If bMondayStart is true, week begins on Monday, otherwise week begins on Sunday.
	int GetYear() const	Returns current year (1583...).
	int GetYearWithoutCentury() const	Returns year without century; eg, returns 85 for 1985.
	virtual bool IsBusinessDay() const	Returns true if current date is a business day; the default implementation equates business days with week days that are not holidays.
	virtual bool IsHoliday() const	Returns true if current date is a holiday; the default implementation returns false.
	static bool IsIsoYearLong(int y)	Returns true if ISO year y contains 53 weeks, false if it contains 52.
	bool IsIsoYearLong() const	Returns true if ISO year of current date contains 53 weeks, false if it contains 52.
	static bool IsLeapYear(int y)	Returns true if year y is leap year, false if not.
	bool IsLeapYear() const	Returns true if year of current date is leap year, false if not.
	static bool IsValidDate(int m, int d, int y)	Returns true if mdy is a valid date, false if not.
	bool IsValidDate() const	Returns true if current date is a valid date, false if not.
	bool IsValidJulianDayNumber() const	Returns true if current date is a valid Julian day, false if not.
	virtual bool IsWeekDay() const	Returns true if current date is a week day; the default implementation equates week days with non-weekend days.
	virtual bool IsWeekEnd() const	Returns true if current date is a weekend day; the default implementation equates weekend days with Saturday or Sunday.
	static int LastDayOfMonth(int m, int y)	Returns last day (month size) of month m, year y.
	int LastDayOfMonth() const	Returns last day (month size) of current month.
	static bool OrdinalDateToGregorian(int ord_year, int ord_day, int& month, int& month_day)	Converts ISO date YYYYDDD to month and month day.
	bool Set(int m, int d, int y)	Sets the current month, day, and year. Returns true if date is valid
	void SetDay(int d)	Sets the current day to d.
	bool SetFromExcelSerialDateMAC(int esd) const	Sets the date from the MAC Excel serial date esd.
	bool SetFromExcelSerialDatePC(int esd) const	Sets the date from the PC Excel serial date esd. Serial dates below 61 are not allowed, because a bug in Excel caused 60 (2/29/1900) to be considered a valid date.
	bool SetFromIso(int w, int d, int y)	Sets the current date to ISO date wdy. Returns true if date is valid.
	bool SetFromJulianDayNumber(int jdn)	Sets the current date to Julian day number jdn. Returns true if date is valid.
	bool SetFromModifiedJulianDayNumber(int mjdn)	Sets the current date to the modified Julian day number mjdn. Returns true if date is valid.
	bool SetFromOrdinalDate(int ord_year, int ord_day)	Sets the current date to the ISO ordinal date YYYYDDD. Returns true if date is valid.
	bool SetFromSystemTime(const SYSTEMTIME& SystemTime)	Sets the current date to the date represented by the SYSTEMTIME SystemTime. Returns true if date is valid.
	bool SetFromSystemTime()	Sets the current date to the date returned by the system function GetLocalTime(). Returns true if date is valid.
	bool SetFromTm(const struct tm& t)	Sets the current date to the date represented by tm. Returns true if date is valid.
	void SetMonth(int m)	Sets the current month to m.
	void SetYear(int y)	Sets the current year to y.
Logical Operators
	bool operator==(const CGregorianDate& rhs) const	Returns true if dates are equal.
	bool operator!=(const CGregorianDate& rhs) const	Returns true if dates are not equal.
	bool operator<(const CGregorianDate& rhs) const	Returns true if lhs is less than rhs.
	bool operator>(const CGregorianDate& rhs) const	Returns true if lhs is greater than rhs.
	bool operator<=(const CGregorianDate& rhs) const	Returns true if lhs is less than or equal to rhs.
	bool operator>=(const CGregorianDate& rhs) const	Returns true if lhs is greater than or equal to rhs
Math Operators
	CGregorianDate& operator+(int days)	Add days to current date.
	CGregorianDate& operator-(int days)	Subtract days from current date.
	CGregorianDate& operator+=(int days)	Add days to current date.
	CGregorianDate& operator-=(int days)	Subtract days from current date.
	CGregorianDate& operator++()	Add one day to current date (prefix).
	CGregorianDate& operator--()	Subtract one day from current date (prefix).
	CGregorianDate& operator++(int)	Add one day to current date (postfix).
	CGregorianDate& operator--(int)	Subtract one day from current date (postfix).
Operations
	bool AddBusinessDays(int n)	Add n business days (see IsBusinessDay()) to current date. Returns true if resulting date is valid.
	bool AddDays(int n)	Add n days to current date. Returns true if resulting date is valid.
	bool AddMonths(int n)	Add n months to current date. Returns true if resulting date is valid.
	bool AddWeeks(int n)	Add n weeks to current date. Returns true if resulting date is valid.
	bool AddYears(int n)	Add n years to current date. Returns true if resulting date is valid.
	bool FindIsoYearStart()	Sets the current date to the start of the ISO year, as defined by ISO 8601. This is the first Monday that falls on or before January 4. Returns true if resulting date is valid.
	size_t Format(LPTSTR lpszDest, size_t maxsize, LPCTSTR format) const	Formats the current date with _tcsftime(). The date string is returned in lpszDest. Its size is returned by Format().
	static bool MDYFromOleDate(DATE dtSrc, int& m, int& d, int& y)	Returns MDY from OLE DATE value. Returns true if resulting date is valid.
	static bool OleDateFromMDY(DATE& dtDest, int m, int d, int y)	Returns OLE DATE value from MDY. Returns false if MDY is not a valid date (before 1583).
Dump/Trace
	virtual void AssertValid() const	Virtual function. By default returns true if current date is valid.
	virtual void Dump() const	Virtual function. By default outputs the current date using OutputDebugString().
	virtual void Trace(LPCTSTR lpszMsg = NULL) const	Virtual function. By default outputs an optional message and the current date using OutputDebugString().

References

Date and Time Formats, web site maintained by JR Stockton. Comprehensive and accurate discussion of date systems and formats.
The Hermetic Systems web site has many articles discussing dates and calendars. Very informative.
Gregorian calendar Wikipedia entry.
Julian calendar Wikipedia entry.
Wikipedia has some background on ISO 8601 here.
The ISO 8601 standard can be found here and here.

Revision History

Version 1.0

Initial release

Buy latest version

Buy XDate 1.0 license – $30.00 per developer. Includes full source code to XDateCalc.exe, XFisCal.exe, and XDateTest.exe.

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Date Types

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CGregorianDate Construction

CGregorianDate Usage

Example: Find a Recurring Date

Example: Determining the Delivery Date

Example: Find all the Mondays in October

Example: Days until Christmas

CGregorianDate Date Formatting

CGregorianDate Debugging

XDateTest

How To Use

CGregorianDate Class Members

References

Revision History

Version 1.0

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