# Need advanced date and day calculations in C++

We are developing a proprietary task scheduler (just like windows scheduler) for a product.
I desperately need a ready-made source code or algorithms or anything that will help me.

I need something like: First/Second/Third/Fourth/Last  Monday/Tuesday/Wed/Thur...Sunday of a particular Month.

Task will be customised to run at any one of above combinations chosen by user.

Any help will be greatly appreciated.

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Commented:
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Commented:
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Author Commented:

Actually we have already developed the code for the schedular.What we are interested in dates calculation part of the schedular.we need to get the dates calculation in Terms of Monthly,weekly and Daily , those are aviable with the windows
schedular.

Thanks ,
Uma
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Commented:
The following should do the job.

#include <windows.h>
#include <time.h>

enum Weekday { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY };
enum DayInMonth { FIRSTDAY, SECONDDAY, THIRDDAY, FOURTHDAY, LASTDAY  };

int daysMonth[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

int getDayOfMonth(int year, int month, Weekday wd, DayInMonth dim)
{
struct tm tm = { 0 };
tm.tm_mday = 1;
tm.tm_mon  = month-1;
tm.tm_year = year - 1900;
time_t  tt = mktime(&tm);
struct tm* ptm = localtime(&tt); // get day of week to struct tm

// calculate first weekday
int day = 1 + (wd - ptm->tm_wday);
if (dim != LASTDAY)
return day + 7 * dim;

day += 28;
if (day <= daysMonth[month-1])
return day;
if (month == 2 && day == 29 && year%4 == 0)
return 29;
return day - 7;
}

Regards, Alex
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Commented:
I was looking for code that does this very thing, and I came across this thread.
The code submitted by "itsmeandnobodyelse" does not work.  Perhaps there is a typo somewhere, but I don't see how it can possibly work.
As an example, I cut and pasted the code into a simple program, and I get peculiar results:
e.g. second Sunday in 3/2008 is the 2nd, an obviously invalid result:
from code:  Second Sun  in 3/2008 is: 2

If we go through the algorithm for the second Sunday in 3/2008:
desired day, wd, is Sunday=0.
First day of 3/2008 is a Saturday=6 should be in ptm->tm_wday.
day = 1 + (wd - ptm->tm_wday) = 1 + (0 - 6), so day = -5
dim (i.e. SECONDAY = 1) is not equal to LASTDAY (4), so we are returning day+7*dim = -5+7*1 = 2

The rest of the code is garbage, too, including the incorrectly handled leap year calculation (no leap  year in years ending with 00).

DOES ANYONE CHECK THIS STUFF?
#include <iostream>
#include <time.h>
#include <string>

enum Weekday { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY };
enum DayInMonth { FIRSTDAY, SECONDDAY, THIRDDAY, FOURTHDAY, LASTDAY  };

int daysMonth[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

int getDayOfMonth(int year, int month, Weekday wd, DayInMonth dim)
{
struct tm tm = { 0 };
tm.tm_mday = 1;
tm.tm_mon  = month-1;
tm.tm_year = year - 1900;
time_t  tt = mktime(&tm);
struct tm* ptm = localtime(&tt); // get day of week to struct tm

// calculate first weekday
int day = 1 + (wd - ptm->tm_wday);
if (dim != LASTDAY)
return day + 7 * dim;

day += 28;
if (day <= daysMonth[month-1])
return day;
if (month == 2 && day == 29 && year%4 == 0)
return 29;
return day - 7;
}

int main()
{
std::string weekDayName[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
std::string whichDay[] = { "First", "Second", "Third", "Fourth", "Last" };

int year = 2008;
int month = 3;
Weekday wday = SUNDAY;
DayInMonth which = SECONDDAY;

int dayOfMonth = getDayOfMonth(year, month, wday, which);

std::cout << whichDay[which] << " " << weekDayName[wday] << "  " << "in " << month << "/" << year ;
std::cout << " is: " << dayOfMonth << std::endl;
return 0;
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Commented:
>>>> int day = 1 + (wd - ptm->tm_wday);

The prog should work correct if changing the above line into

int day = 1 + ((7+ wd - ptm->tm_wday)%7);

>>>> The rest of the code is garbage, too, including the incorrectly handled leap

2000 was a leap year because it can be divided by 400 without rest. So the above algorithm covers all years between 1901 and 2099 what seems to be a sufficient range for normal date calculations.

You could make it work for all dates by

if (month == 2 && day == 29 &&
(year%4 == 0 && (year%100 != 0 || year%400 == 0)))
return 29;

I currently am on vacancies and can't compile and test the above.

Regards, Alex
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