Liren Large Software Subsidy 7/07.iso/c/c017/34.ddi/DATECLS3.ZIP/DATECLS3.DOC

Text File | 1991-07-15 | 5.6 KB | 124 lines

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.

Coincidentally, I developed a need for a universal date conversion routine
about the same time for use in a business project I was developing as well.
Browsing the same forum, I encountered Eric's class, which provided much of
the functionality I needed  - the basic julian-gregorian and day of week
conversion algorithms - relieving me of the task of researching or re-
inventing them. He had also added overloaded + and - operators for
incrementing date objects by integer days, as well as several print functions.

I needed additional features for my implementations, so I set about adding
to the class. As is my habit, I got carried away.

The class now has:

    1. A full set of constructors, allowing    construction and re-setting
    of any date object from a julian date (the universal kind, relative
    to 1/1/4713 B.C.E., not the YYDDD kind); from a date string (i.e.
    11/15/1991);from another date object (copy constructor); or from a
    "date" struct as defined in dos.h and returned by getdate(). A date
    object may also be set to the current system date by assigning it to
    the string "today" (case-insensitive).

    2. A full set of comparison operators ( <, <=, >, >=, ==, !=),
    defined as friend functions so that date objects may be freely
    compared to other date objects, to julian dates, or to strings.

    3. A full set of arithmetic operators ( +, -, ++, --, += and -=).
    Additionally, two date objects may now be subtracted to find the
    number of days between them.

    4. I have consolidated the print functions into one function,
    formatDate, which accepts an enum value as its format type.

    MDY  - returns a buffer with the date formatted as MM/DD/YYYY
    DAY  - returns a buffer with the day of the week name only
    MONTH- returns a buffer with the month name only
    FULL - returns a buffer with the date formatted as DAY MMMMM DD, YYYY
    EUROPEAN- returns a buffer with the date formatted as DD MMMMMM, YYYY

    5. The ostream << operator has been overloaded as a friend function
    to handle Date objects. In this implementation the format returned
    is fixed at MM/DD/YYYY, however an equivalent to the ios::setf
    function could be added to maintain a static member in the Date
    class to handle multiple formatting options. A companion << operator
    has been included to handle dos.h date structs, which are returned
    by the getDate() function.

    6. Several utility functions have been provided:

        isLeapYear - returns 1 if a leap year, 0 if not
        dayOfYear  - returns the day relative to Jan. 1
        eom        - returns a dos.h "date" struct (format YYYYDDMM)
                 with the last day of the month of the date object
        getDate    - returns a dos.h "date" struct (format YYYYDDMM)
                 equivalent to the date object


IMPLEMENTATION NOTES.

    I have attempted to optimize the code for the Borland C++ compiler,
    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.

    Those of you who are using Eric's version will note that I have
    capatilized the class name to Date, to avoid conflict with Borland's
    "date" struct defined in DOS.H, which is also used by two functions.
    Please be wary of the potential for capitalization errors here.
    Also, I have altered the capitalization    of several function names
    to conform with Borland's suggested convention.

    Also, I reorganized the source according to common distribution
    formats.

    Thus, this ZIP file contains:

        DATECLS3.HPP    -     the header file
        DATECLS3.CPP    -    the member functions
        DATEDEMO.CPP    -    a test program (and a messy one at that)
        DATECLS3.DOC    -    the file you're reading


Future possibilities for enhancement include:

    1. Maintenance of a static variable to handle global date format
       preferences (MDY, FULL, etc.) which would be used to control
       the overloaded << operator (now fixed at the MDY format). This
       would be more convenient than using the formatDate routine.

    2. Maintenance of a static variable to handle other print format
       preferences. (Ideas would be to strip the century from the
       MDY format (i.e 10/15/91 instead of 10/15/1991), print
       abbreviated day or month names (i.e. MON, TUE, JAN, FEB), and
       the like). This would probably be a set of bit flags which would
       work (and be set) like the ios::setf options.

    3. 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.

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. I thank Steve and Eric for their inspiration and generousity, and hereby
contribute my additions to the public domain.

I would welcome further comments, suggestions and enhancements as well.
Good luck!

                    Christopher Hill
                    72030,2606