Examples Delphi

domFirst - First occurrence in a Month.

domSecond - Second occurrence in a Month.

domThird - Third occurrence in a Month.

domFourth - Fourth occurrence in a Month.

domLast - Last occurrence in a Month.
@param DOMType the desired Day of Month Type.
@param DOW the Day of Week, 1 = Sunday, 7 = Saturady.
@param Month the month of the year, 1 = Jan, 12 = Dec.
@param Year 4-digit year such as 1999.
@returns the Date uniquely defined by the above.
@cat DTMath
@cat MonthMath
}
function DayOfMonth2Date (const DOMType: TESBDOMType; const DOW: Byte;
const Month, Year: Word): TDateTime;
var
Ofs: Integer;
DT: TDateTime;
begin
if DOMType < domLast then
begin
DT := GetFirstDayOfMonth (Month, Year);
Ofs := DOW - DayOfWeek (DT);
if Ofs < 0 then
Ofs := Ofs + 7;
Result := DT + Ofs + 7 * Integer (DOMType);
end
else
begin
DT := GetLastDayOfMonth (Month, Year);
Ofs := DayofWeek (DT) - DOW;
if Ofs < 0 then
Ofs := Ofs + 7;
Result := DT - Ofs;
end;
end;
You will need routines to return the First and Last Days of the Month/Year
for the above...
You may also want to check out our FREE ESBDates which also includes
GPTimeZone which includes another way of doing the above :)
HTH
Glenn Crouch mailto:glenn@esbconsult.com.au ICQ:36017076
ESB Consultancy, http://www.esbconsult.com.au
Home of ESBPCS, ESBStats, ESBPDF Analysis & ESBCalc
Kalgoorlie-Boulder, Western Australia
(TeamND, TeamOE, Addict Support, eLists.org Management)
********************************************************************************
unit RelDate;
interface
uses
Controls;
type
TDayOfWeek = (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday);
function RelativeDate(Date: TDate; WeekDay: TDayOfWeek; Which: integer): TDate;
implementation
uses
SysUtils;
function FindDay(Date: TDate; WeekDay: TDayOfWeek; Delta: integer): TDate;
var
Count: longint;
begin
Count := Trunc(Date) + Delta;
Result := (Count - ((Count - Ord(WeekDay) + 6) mod 7)) * 1.0;
end;
function RelativeDate(Date: TDate; WeekDay: TDayOfWeek; Which: integer): TDate;
{e.g.
RelativeDate(Now, Wednesday, 1) will find the first Wednesday in the current month
RelativeDate(Now, Sunday, -1) will find the last Sunday in the current month
RelativeDate(Now, Monday, -2) will find the penultimate Monday in the current month
}
var
Year, Month, Day: word;
Count: longint;
Delta: shortint;
begin
DecodeDate(Date, Year, Month, Day);
if Which > 0 then
begin
Count := Trunc(Date) - Day + 7;
Delta := -1;
end
else
begin
Count := Trunc(Date) - Day + MonthDays[IsLeapYear(Year), Month];
Delta := 1;
end;
Result := (FindDay(Count * 1.0, WeekDay, 0) + ((Which + Delta) * 7)) * 1.0;
end;
end.
Regards,
Russell Hewitt
***************************************************************************
Glenn Crouch - ESB wrote:
> > function GetLastDayOfMonth(Mo, Yr: Word): TDateTime;
> > begin
> > // find first day of subsequent month and subtract a day
> > Result := EncodeDate(Yr, Mo + 1, 1) - 1.0;
> > end;
>
> Not good option for December (Mo = 12) ... But basically yes :)
Ooops, good point, seems like I always miss those wrap-around situations, how
about:
function GetLastDayOfMonth(Mo, Yr: Word): TDateTime;
var
TempYr, TempMo: Word;
begin
// find first day of subsequent month and subtract a day
TempYr := Yr;
TempMo := Mo + 1;
if TempMo = 13 then begin // Whoa Nellie, next month is next year!
TempMo := 1; // January
Inc(TempYr); // subsequent year
end;
Result := EncodeDate(TempYr, TempMo, 1) - 1.0;
end;
Thanks for catching that! ;-)
Of course an even more robust solution would check that Mo was in the range
1..12 to begin with, which I haven't done.
What is a sensible "bad date" value to return on an error like that? Since
TDateTime is a type alias for an IEEE double, one could use NaN I guess?
Stephen Posey
slposey@concentric.net
*******************************************************
Glenn Crouch - ESB wrote:
>
> The following is from our ESBPCS:
Interesting, I note that your definition only implicitly includes the fifth
occurence of a day via the domLast value; there's no way to explicitly ask for
the 5th occurence and perhaps get some kind of exception or an error value back
indicating that it doesn't exist, you'd have to ask for both domFourth and
domLast and check whether they were the same.
E.g. for January 2001:
DayOfMonth2Date(domFourth, 4, 1, 2001) will return Jan. 24
DayOfMonth2Date(domLast, 4, 1, 2001) will return Jan. 31
but
DayOfMonth2Date(domFourth, 5, 1, 2001) and
DayOfMonth2Date(domLast, 5, 1, 2001) will both return Jan. 25
> type
> TESBDOMType = (domFirst, domSecond, domThird, domFourth, domLast);
>
> {: Returns the Given Occurrence (Day of Month) of a Day of Week in a given
> Month/Year. Thus can be used to find the first Wednesday, Last Monday,
> etc. DOMType can be one of the following:

> domFirst - First occurrence in a Month.

> domSecond - Second occurrence in a Month.

> domThird - Third occurrence in a Month.

> domFourth - Fourth occurrence in a Month.