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Text File | 1994-01-26 | 25.0 KB | 591 lines

======================================================= Documentation for "The Killer Date Class!" Version 4.00 ======================================================= History ======= In the beginning Steve Marcus (CIS 72007,1233) posted a basic date manipulation/arithmetic class produced with Borland C++ 2.0 in the BPROGB forum, with a request for suggestions and enhancements. This was on 6/19/91. A rather enterprising gentleman by the name of Eric Simon (CIS 70540,1522) accepted the challenge, and produced a new and improved version in the course of a project he was developing at work. He contributed the results to the forum on 6/29/91, also inviting enhancements and comments. About that time yet another enterprising gentleman named Christopher Hill developed a need for a universal date conversion routine for use in a business project he was developing as well. Browsing the same forum, he encountered Eric's class, which provided much of the functionality he needed - the basic julian-gregorian and day of week conversion algorithms - relieving him of the task of researching or re-inventing them. Eric had also added overloaded + and - operators for incrementing date objects by integer days, as well as several print functions. Chris needed additional features for his implementations, thus was born versions 3.0 and 3.1(Hill & Simon). Well, almost a year later I sent out an SOS for a date class so _I_ didn't have to re-invent the wheel and lo-and-behold Chris responded. Thus begins the saga of version 4.0! I would like to take this opportunity to do a little witnessing: I looked all over for a date class that would suit my needs! I reviewed many implementations from strangers and friends alike and I am here to tell ya' folks, "It don't 'git no bedder 'n dis!" This class is _VERY_ cool! Now I'm not trying to say that there's no more room for enhancements (I'd really be crazy then!), but I am saying that if your looking for a _GOOD_ date class (I'd say commercial quality because I have yet to see a commercial product that implemented a date class to my satisfaction!) then this is it! So jump in and add to it, make it better and we'll SAVE THE WORLD! (Ok, so I got a little carried away at the end. Just a little...) No, but really... This is a truly pleasing example of co-operation among professionals, and an "object" study in the code reusability of OOP, resulting in three releases of one class within a single month by three different analysts who have never met, and yet another upgrade almost a year later by a fourth analyst (myself) and none of us have yet to meet! Chris thanks Steve and Eric for their inspiration and generousity, and I thank all three as well and hereby contribute my additions to the public domain. I believe any of us would welcome further comments, suggestions and enhancements as well. Good luck! May the quest for the perfect date class continue! v4.9 Ly Minh Trí - 73062,512 01/26/94 v4.8 Clyde Ford - 71426,72 11/18/93 v4.7 Ly Minh Trí - 73062,512 09/20/93 v4.6 Ly Minh Trí - 73062,512 08/04/93 v4.5 Ly Minh Trí - 73062,512 06/21/93 v4.4 Ly Minh Trí - 73062,512 06/03/93 v4.3 Ly Minh Trí - 73062,512 03/24/93 v4.2 Ly Minh Trí - 73062,512 03/13/93 v4.1 Kenneth A. Argo - 71241,3635 03/07/93 v4.0 Charles Price - 70541,3651 06/27/92 v3.1 Hill & Simon - 08/05/91 v3.0 Christopher Hill - 72030,2606 07/11/91 v2.0 Eric Simon - 70540,1522 06/29/91 v1.0 Steve Marcus - 72007,1233 06/16/91 =============================================================================== TML - 01/26/94 Version 4.9 fixes the Date::AddMonths() member function. The problem was it did not adjust the day value after the new month's value have been calculated. For example, if the current date is '08/31/1993' and 6 months is added to it using Date::AddMonths(), then the result is: 02/31/1994. Date::AddMonths() will now set the day value as appropriate for the new month. If the day value is greater than the # of days in that month, then it will roll the month over to the next month and set the day value to the difference between the day value and the # of days in the that month. Thanks to Patrick Cunningham this bug. This version also expands the Date::isDST() functionality by adding two new member functions: Date::setDST() and Date::setSTD(). Date::setDST() sets the month and day on which DST date begins. Likewise, Date::setSTD() sets the month and day on which STD date begins. Thanks to Marcelos Cantos for this suggestion. *********************** WARNING TO BORLAND C++ USERS ********************* A couple of people have kindly informed me that the class Date is a pre-defined class in Borland C++. Thus, you will have to rename this class to another name like xDate, or DateCL or whatever is appropriate for your implementation!!! ******************************************************************************* =============================================================================== TML - 11/18/93 Version 4.8 adds a new member function Date::isDST() which was contributed by Clyde Ford (CIS 71426,72). Date::isDST() determines if the current date object is "within daylight savings time as defined in the United States". If so, then it will return 1, otherwise a 0 is returned. Please note that my CIS address has changed to 73062,512. If anyone have added new functions to DateClass and feel others may benefit from it, feel free to send me your code so I may incorporate it into future versions of DateClass. Or if you prefer, just incorporate the code, document your additions and upload it... =============================================================================== TML - 09/20/93 Version 4.7 un-fixes the serious bug in the code for unary operators ++/--. In other words, they were originally correct. I guess I got really confused when I last talked to Jorge. Thanks to James M. Curran for informing me of this change. Also, James has a new version of DateClass (5.0) currently in the works. I think all of us will be very impress and receptive of his version!!! =============================================================================== TML - 08/04/93 Version 4.6 fixes the Date::AddMonths() member function. It does not add or subtract the number of months correctly. Thanks to Patrick Cunningham for finding this bug! =============================================================================== TML - 06/21/93 Version 4.5 fixes a very serious bug in the code for unary operators ++/--. I confused myself with the formats for prefix and postfix operations. (I got them reversed.) Jorge Padron was kind enough to inform me of my mistake. I also removed the 'const' keyword from parameter statements for functions which require variables to be passed by values (as opposed to pass by reference.) For example, Date operator + (const long i); is changed to: Date operator + (long i); I did it in the first place because I was trying to be consistent, but I realize that this can be confusing (especially those that are just learning C++). Jorge also pointed this out to me. =============================================================================== TML - 06/03/93 Version 4.4 adds a little validation to the value of the day and month when an object is created via a string argument. For example, month must be from (1..12) and day must be from (1..n) where 'n' is the number of days for the given month. Thus, the following statements: Date myDate("02/31/1993"); cout << myDate.formatDate() << "\n"; will result in an "invalid date" output! =============================================================================== TML - 3/15/93 Well, I must say, this is quite an impressive Date class!!! And I must agree with Mr. Kenneth...it's probably one of the BEST (if not the best) Date class I've seen so far (but then again, I've not seen too many!). However, I thought it really could take more advantage of some of the better features of C++ (ie. encapsulation!!!). Thus, I decided to take on the challenge set forth by the aforementioned 'Date'-crazed group. My changes are listed below in the Version 4.2 section. Please let me know of any updates/changes that will happen in the future!!! And ofcourse, we all welcome any comments/suggestions/participations!!! Ly Minh Trí :) =============================================================================== Implementation Notes ==================== All versions prior to 4.0 were written specifically for a Borland C++ compiler. However, version 4.0 was written specifically for Microsoft C++ 7.0. I too have attempted to optimize the code including the specification of const where applicable, the passing of references where advisable, and the use of constructor initializers where needed. However, I have not made an exhaustive analysis of this subject either. To get the best overview of the class capabilities run the demo program. It may not look pretty, but with a printout of a sample run and the code you should be able to get a really good feel for it. I have included a samples run at the end of this file in case someone doesn't want to take the time to compile the demo program. This ZIP file contains: MAKEFILE - make file to compile & link the files for MSC 7.0 DATEDEMO.PRJ - project file for compiling under Borland C++ 3.1 DATECL48.DOC - this file DATECL.H - the header file DATECL.CPP - the member functions DATEDEMO.CPP - a test program (and a messy one at that!) DATECL.LIB - a lib file so you can use it even if you don't have MSC7.0, or you just don't feel like fussin' with it! (Added in v4.0) Future possibilities for enhancement include ============================================ 1. Adding a derived Time class, for those applications which require the ability to track more than just dates. This would allow the manipulation of times for all dates (not just since 1980), and arithmetic calculations as well. =============================================================================== Additions/Changes to Version 4.5 ================================ - Correct the implementation code for the unary operators ++ and --. These were reversed in version 4.2 to 4.3 (i.e. prefix was coded as postfix, and postfix was coded as prefix). - Removed 'const' keyword from parameter statments that requires variables to be passed by value. =============================================================================== Additions/Changes to Version 4.4 ================================ - Add a little validation to value of the day and month when an object is created via a string argument. =============================================================================== Additions/Changes to Version 4.3 ================================ - Add more flexibility in the constructor to support the many string formats that are used by the Date class. - Fix Date::Date(char *) and make it accept the string as a 'const' argument. Also, make a copy of the string ('dat') before passing it to strtok() since this function modifies its argument! - Remove the smaller buffer ('buf') and make use of only one buffer to save memory. - Re-code the type cast operator to call formatDate() so the current format and options will be applied to the resulting string. - Changed year to 'int' type to support B.C.E. dates. =============================================================================== Additions/Changes to Version 4.2 ================================ - Made it compatible to both Borland C++ (v 3.1) and Microsoft C++ (v 7.0) via #define switches. Define _BCC for Borland and _MSC for Microsoft. See the GO.BAT batch file! - Fix memory problems in Version 4.1. There were three 'deadly' memory threats introduced by Version 4.1: (a) In the destructor function, it is erroneous to delete buf without referring to it as a vector of characters. The proper method would be: delete [] buf; // Must have the brackets! Please review the section "The Free Store and Class Arrays" on page 95-99 of the _C++ Tutorial_ from Microsoft's C++ package! (b) In the Date::operator char *() function, variable buf was allocated space every time the function was called. This causes memory leaks when the same Date instance calls this operator function more than once during its lifetime. (c) Also in the Date::operator char *() function, variable buf was assigned the address of the constant string BadDate without prior release of the memory for buf. - Modified the following functions to return a Date object instead of a reference to a Date object! Date operator + (const long i); Date operator + (const int i); Date operator - (const long i); Date operator - (const int i); Date operator ++ (); Date operator ++ (int); Date operator -- (); Date operator -- (int); This is important because in Version 4.0 and before, the binary operators (+ and -) were declared to return references to Date objects since these functions dynamically creates a Date object when the function is called. However, there were no provisions for deleting these objects once they leave the scope of the function. In Version 4.1, Mr. Kenneth got rid of this problem of allocation by forcing the compiler to generate code to allocate stack space to return the objects. However, Mr. Kenneth 'forget?' to remove the references declaration. Why would this cause problem? Because when the calling program is expecting a reference in return (as opposed to a copy of the object), then that reference will be invalid since after the function terminates, the temporary object (used to return the value to the calling program) will also be terminated. Thus, the reference to the object is rendered obsolete. To test this, I wrote the following program: #include "datecls4.h" #include "iostream.h" void showDate(Date &dt) { cout << dt; // The (char *) type cast operator is in } // effect here! void main() { Date z("04/13/1967"); showDate(z+3); } RESULT: *** destructor called *** // Temporary oject is destroyed 237/7/21 *** destructor called *** // Object 'z' is destroyed As dictated by the result, the temporary object (created by the + operator) is destroyed before its values are displayed. By declaring the functions to return an actual Date object instead of a reference, we force the compiler to make a copy of it and return it to the calling program! - Fix implementation of the prefix/postfix operators to properly reflect the before/after syntax of the unary incrementor. (C++ provides only the the facility to determine which type of operator is being used, but the implementation is left to the programmer!) - Moved all buffer variables to the class level and made them private static member data. . for the Date::formatDate() function, the buffer is renamed to 'cbuf' . for the Date::Operator () function, the buffer is named 'buf' - Move all publically declared variables/enums into the public portion of the class. Also redefine the #define constants to an enum type. By doing this, we are taking advantage of C++'s encapsulation feature and reduce pollution of the global variable names. This concept is based on the ios class. (ie. ios::hex, ios::dec, etc.) - Also redeclare the 'friend' functions to be member functions (again, making use of encapsulation!) - Rewrote the Date::SetOption() function. (Made it more compact!) - Made use of the 'const' feature of C++ to ensure the references returned by most of the member functions will be non-modifiable by the calling program. (ie. force them to make a copy of it if they want to modify it!) - In the function Date::formatDate(), for the case Date::EUROPEAN and Date::EUROPEAN, fix the code (day_of_week < 0) to (day_of_week < 1). Also removed the statement strcat(cbuf, " ") and put the space into the sprintf() statement: sprintf( cbuf+strlen(cbuf), " %d", abs(year) ); =============================================================================== Additions/Changes to Version 4.1 ================================ Fixed date display when using the * operator to get a string pointer. The code would return xx/xx/ xx if you only supplied a 2 digit year. Optimized the * operator so Invalid Dates would use a common "invalid date" text pointer. Fixed the +, - and * operators to get rid cases where memory leaks would occur. Fixed some variable casts so the code can be compiled with /W4 Added a destructor tp delete items created dynamically on behalf of the object (ie. char *). Release Documentation for Version 4.0 ===================================== Most of the modifications made to version 3.1 were to expand the public interface. Below is a list of new features in v4.0: 1. Date &Set() - Sets self to current system date; this may also be accomplished by passing initializing a date object like so: Date oDate1("Today"); // See demo for examples 2. Date &Set(long lJulian) - Sets self to the specified julian date 3. Date &Set(int nMonth, int nDay, int nYear) - Sets self to specified month, day, and year. The year must be 4 numbers long, not 2. 4. Date &AddWeeks(int nCount = 1) - Add or subtract(use a negative int) a specified number of weeks to/from self 5. Date &AddMonths(int nCount = 1) - Add or subtract(use a negative int) a specified number of months to/from self 6. Date &AddYears(int nCount = 1); - Add or subtract(use a negative int) a specified number of years to/from self 7. int Day() const - Returns numeric day of the month for self 8. int DaysInMonth() - Returns number of days in month (1..31) 9. int FirstDOM() const - Returns the First Day Of Month for self as a numeric (1..7) 10. char *CDOW() - Returns character Day Of Week ('Sunday'..'Saturday') 11. int NDOW() const - Returns the numeric day of the week for self(1..7) 12. int WOM() - Returns numeric Week Of Month (1..6) 13. int WOY() - Returns numeric Week Of Year (1..52) 14. char *CMonth() - Character Month name ("January") 15. int NMonth() const - Month Number (1..12) 16. Date BOM() - Returns a new date object that is the First Date Of the Month in self. For example: Date oDate1; Date oDate2("Today"); oDate1 = oDate2.BOM(); 17. Date EOM() - Returns a new date object that is the Last Date Of the Month in self. (See example in 16 above) 18. int NYear4() const - Returns the numeric value of the year for self in the form 1992. 19. Date BOY() - Returns a new date object that is the First Date Of the Year in self. (See example 16 above) 20. Date EOY() - Returns a new date object that is the Last Date Of the Year in self. (See example 16 above) 21. Added overloaded operators for + and - to accept int's. 22. Added overloaded operators for ++ and -- for Postfix notation 23. Switched from the Borland style DOS date structure(date) to the Microsoft version(_dosdate_t). Suggestions and general comments are always welcome! Enjoy! Chuck :-} Release Documentation for Version 3.1 ===================================== Subsequent to release 3.00, we (Hill & Simon) decided to collaborate on several further releases of this date class. This, the first, contains two new features, as well as a few minor bug fixes. 1. There was a minor bug in the original Computer Language julian/gregorian date conversion routines having to do with negative years. 2. The isLeapYear function did not take into account that, prior to 1582, years ending in 00 were also leap years. 3. The two-dimensional array of the number of days in each month has been eliminated in favor of a computational approach. 4. The function Date::setFormat(XXXX) maintains a static variable (one occurance for all Date objects, which controls the format which the << operator uses to print objects. "XXXX" can be MONTH, MDY, DAY, FULL, or EUROPEAN. The setting defaults to MDY, but once altered, remains altered until reset by another call to setFormat. The function Date::setOption(Option, Action) maintains a similar static variable which enables certain print formatting options. Available options at this point are: NO_CENTURY -- Suppress the printing of the century when in the MDY format (ex: 01/01/91 instead of 01/01/1991). DATE_ABBR -- Abbreviate month and day names when printing in the MONTH, DAY, FULL or EUROPEAN formats. (ex. MON, TUE, JAN, FEB, etc.) The length or the abbreviation is controlled by a DEFINED constant in DATECL31.HPP named ABBR_LENGTH, preset to 3. "Action" is either ON or OFF, and defaults to ON. (Example, the call Date::setOption(NO_CENTURY) turns on the century suppression option, and it remains set until the call Date::setOption(NO_CENTURY, OFF) is made. More features, including further expanded print formatting features, the derived Time class mentioned above, conversion into various calendar formats (Jewish, Chinese, Arabic, etc.), ability to increment Date objects by years and months instead of merely days, holiday computations, and more are planned. Sample run of DATEDEMO.EXE v4.0 =============================== Date Class v4.0 Demo Saturday, October 20, 1962 Monday Tuesday, October 10, 1995 Tuesday, October 30, 1962 5 October 1962 -14 8/6/1991 Tommorrow= Sunday, July 14, 1991 a1 (7-14-91) < 8-01-91 ? ==> TRUE a1 (7-14-91) > 8-01-91 ? ==> FALSE a1 (7-14-91)== 7-14-91 ? ==> TRUE a1 (7-14-91)== a3 (7-14-91) ? ==> TRUE a1 (7-14-91)== a4 (7-15-91) ? ==> FALSE Today is: 6/28/1992 Today (a4) is: 6/28/1992 Today + 4 is: 7/2/1992 Today - 4 is: 6/24/1992 =========== Leap Year Test =========== Wednesday, January 15, 1992 Leap day of year: 15 Tuesday, February 16, 1993 non-Leap day of year: 47 =========== eom test ============== b1.eom() (s/b 2/28/91) ==> 2/28/1991 ================== getDate test ===================== a1.getDate() (s/b 2/16/1993) ==> 2/16/1993 ================== string assignment test ==================== a1 as a string (s/b 2/16/1993) ==> 2/16/1993 ================== setFormat test ============================ a1 (s/b FULL format) ==> Tuesday, February 16, 1993 a1 (s/b EUROPEAN format) ==> 16 February 1993 ================== setOption test ============================ Date abbreviation ON a1 (s/b MONTH format) ==> Feb a1 (s/b DAY format) ==> Tue a1 (s/b FULL format) ==> Tue, Feb 16, 1993 a1 (s/b EUROPEAN format) ==> 16 Feb 1993 Century suppression ON a1 (s/b MDY format) ==> 2/16/93 Century suppression OFF a1 (s/b MDY format) ==> 2/16/1993 Century suppression ON a1 (s/b MDY format) ==> 2/16/93 a1 (s/b FULL format) ==> Tue, Feb 16, 1993 =============== Version 4.0 Enhancement Test ================= ---------- Set Stuff ----------- First, 'Set' to today... Before 'Set' => Saturday, November 26, 1966 After 'Set' => Sunday, June 28, 1992 Set to 11/26/66 => Saturday, November 26, 1966 Current Julian => 2439455 Set to Julian 2450000L => Tuesday, October 10, 1995 See! => 2450000 ---------- Add Stuff ----------- Start => Tuesday, October 10, 1995 Add 4 Weeks => Tuesday, November 7, 1995 Sub 1 Month => Saturday, October 7, 1995 Add 2 Years => Tuesday, October 7, 1997 ---------- Misc Stuff ----------- The date aboves' day of the month is => 7 There are 31 days in this month. The first day of this month lands on 4 This day happens to be Tuesday the 3 day of the week, on the 41 week of the year, on the 2 week of the month, (which is October) the 10nth month in the year. The year alone is 1997 ---------- First and Last Stuff ----------- The first date of this month is Monday, June 1, 1992 The last date of this month is Tuesday, June 30, 1992 The first date of this year is Wednesday, January 1, 1992 The last date of this year is Thursday, December 31, 1992