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Calculating number of days between two dates.

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Started by owl January 17, 2005 12:13 AM

39 comments, last by owl 19 years, 2 months ago

Brother Bob

10,350

January 17, 2005 03:48 AM

Quote:Original post by owl
Should I add 1 to the years passed or am I doing something wrong?

Just a shot in the dark, but you could try a nearest rounding instead of truncation when converting years to days.

(int)(year * 365.256 + 0.5)

instead of

(int)(year * 365.256)

I'm not entirely sure how my code does it (I'm converting dates to UNIX time), but I think it's using nearest rounding, and my times are off by just a second or so (just a rough implementation so far, so it works quite good in my oppinion) so it seems to handle leap years fine.

Zahlman

1,682

January 17, 2005 04:07 AM

Shouldn't the 'daysinmonth' be cumulative? o_O

owl

376

Author

January 17, 2005 04:10 AM

Quote:Original post by Zahlman
Shouldn't the 'daysinmonth' be cumulative? o_O

What you mean? daysinmont is an array[12] that holds how many days each month of a year has according to Gregory Peck. ;)

@Bob: If i round the calculation, the whole leap year thing will be gone. It will always return 365. If I substract 1 to each year passed then it works perfect.

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Nice Coder

366

January 17, 2005 04:11 AM

No.

Daysinmonth is an array, which holds the amount of days there are in the month (non-leap-year).

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owl

376

Author

January 17, 2005 05:28 AM

All I have to figure now is how to calculate the correct date that is the result of substracting n days from some other date taking leap years into account too.

01/01/0001 - n(days) = ??/??/????

I'm considering handling BC dates as negative years...

Advice on this will be appreciated too :D

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Kylotan

10,510

January 17, 2005 05:36 AM

I don't mean to rain on your parade, but I'm curious as to why you're duplicating the efforts in the Boost library?

owl

376

Author

January 17, 2005 05:51 AM

Quote:Original post by Kylotan
I don't mean to rain on your parade, but I'm curious as to why you're duplicating the efforts in the Boost library?

I dunno, for fun I guess. I don't want to make a huge complex library as Date_Time, just a simple/intuitive class (for dummies) that can perform the most common operations on any *Gregorian* kind of date (BC/AD).

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Sharlin

864

January 17, 2005 07:01 AM

Surely there's no reason to do time/date math by hand (a sure way to lose one's mind in the long run) when there are standard facilities in the <time.h> / <ctime> header just for that purpose!

I *strongly* recommend representing your dates as the standard type time_t (UNIX timestamp, number of seconds since 00:00:00 1970/01/01; a simple integer type on most systems). It's a *lot* easier, shorter, faster, less bug-prone and takes less memory than storing the parts separately as integers.

EDIT: Oh well, this approach won't do much good if you want to have dates outside the size_t's range...

owl

376

Author

January 17, 2005 07:05 AM

Quote:Original post by Sharlin
(UNIX timestamp, number of seconds since 00:00:00 1970/01/01; a simple integer type on most systems). It's a *lot* easier, shorter, faster, less bug-prone and takes less memory than storing the parts separately as integers.

But what would be of the poor historian-programmers then? :(

Or old programmers that want to remember the good ol' 50-60's?

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Sharlin

864

January 17, 2005 07:18 AM

Yeah, I realised that almost as I hit "reply", re-reading your original message and seeing the dates you used as an example... Edited my message to reflect that. Still, I'd say that a third-party library is better than doing all the dirty stuff yourself. If not boost, then something else.

Calculating number of days between two dates.

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Calculating number of days between two dates.

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