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Consider a Qdate from 

QDate Mydate = ui->dateEdit->date();

For example, suppose we choose 2018/07/14 (today).

How to obtain the day of the first Friday (in this case, 6) on the chosen month (in this case, July)?

I suspect we have to use Mydate.dayOfWeek() computations.

Sigur
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  • What have you tried so far? – Nick Jul 14 '18 at 16:21
  • @Nick In my case, Friday is 5th day of week. So I tried to test if `Mydate.dayOfWeek()` is `5` or not. Then, I got lost when `Mydate.day()` is greater than the first Friday (like today, 14). I was not able to decide when stop subtracting from `14`. – Sigur Jul 14 '18 at 16:27

2 Answers2

2

There is probably a neater solution, but:

  1. Subtract dayOfWeek for current date/day from dayOfMonth.
  2. Add 5 (for Friday).
  3. If -ve add 7 or if +ve answer is modulus 7.

Code:

dayOfWeekToday = MyDate.dayOfWeek()
firstFriday = MyDate.day() - dayOfWeekToday + 5
firstFriday = (firstFriday <= 0) ? firstFriday + 7 : firstFriday % 7
Sigur
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Nick
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1

Adding to Nick's answer, there needs to be a special case where result of MyDate.day() - dayOfWeekToday + 5 is divisible by 7. Something like:

dayOfWeekToday = MyDate.dayOfWeek()
firstFriday = MyDate.day() - dayOfWeekToday + 5
firstFriday = (firstFriday <= 0) ? firstFriday + 7 
                                 : (firstFriday % 7 == 0) ? 7 : firstFriday % 7
user3470494
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