BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Minutes Between          BorlandTalk.com Forum Index -> C++ Builder (Students) View previous topic :: View next topic   Author Message bar Guest Posted: Thu Apr 05, 2007 2:01 pm    Post subject: Minutes Between Hello all The following code MinutesBetween("30/04/2007 08:00","30/04/2007 08:30") is returning 29 minutes,which is supposed to 30. Thanks for suggestion SA Back to top Stephan Laska Guest Posted: Thu Apr 05, 2007 7:21 pm    Post subject: Re: Minutes Between "bar" <shaikakbar250281 (AT) yahoo (DOT) co.in> wrote in message news:4614bace (AT) newsgroups (DOT) borland.com... Quote: Hello all The following code MinutesBetween("30/04/2007 08:00","30/04/2007 08:30") is returning 29 minutes,which is supposed to 30. Thanks for suggestion what are you doing inside MinutesBetween()? Back to top Koen Guest Posted: Thu Apr 05, 2007 9:24 pm    Post subject: Re: Minutes Between bar wrote: Quote: Hello all The following code MinutesBetween("30/04/2007 08:00","30/04/2007 08:30") is returning 29 minutes,which is supposed to 30. Thanks for suggestion SA A TDateTime uses a floating point value to store it's date, since floating points can't store every real number, it has to round the value. Your experience is an effect of that. Also see http://tinyurl.com/2tfuy7 A very interesting article is "What Every Computer Scientist Should Know About Floating-Point Arithmetic": http://docs.sun.com/source/806-3568/ncg_goldberg.html Back to top Remy Lebeau (TeamB) Guest Posted: Thu Apr 05, 2007 9:47 pm    Post subject: Re: Minutes Between "Stephan Laska" <Ask & maybe I'll Tell> wrote in message news:461505d4$1 (AT) newsgroups (DOT) borland.com... Quote: what are you doing inside MinutesBetween()? MinutesBetween() is a Borland function that was introduced in BCB 6. There is a new DateUtils unit that contains all sorts of date/time related functions. Gambit Back to top bar Guest Posted: Mon Apr 16, 2007 6:39 pm    Post subject: Re: Minutes Between long int TotalMinutes=MinutesBetween(D2->DateTime,D1->DateTime); where D1, D2 are datetime picker controls Thanks "Stephan Laska" <Ask & maybe I'll Tell> wrote in message news:461505d4$1 (AT) newsgroups (DOT) borland.com... Quote: "bar" <shaikakbar250281 (AT) yahoo (DOT) co.in> wrote in message news:4614bace (AT) newsgroups (DOT) borland.com... Hello all The following code MinutesBetween("30/04/2007 08:00","30/04/2007 08:30") is returning 29 minutes,which is supposed to 30. Thanks for suggestion what are you doing inside MinutesBetween()? Back to top Thorsten Kettner Guest Posted: Tue Apr 17, 2007 8:11 am    Post subject: Re: Minutes Between "bar" <shaikakbar250281 (AT) yahoo (DOT) co.in> wrote: Quote: The following code MinutesBetween("30/04/2007 08:00","30/04/2007 08:30") is returning 29 minutes,which is supposed to 30. Koen has answered the question: The VCL uses the type double to represent a datetime internally. And as he pointed out, one has to be quite careful when working with floating point types. It is certainly a very bad design to use double for datetimes. Well, usually it is exact enough to represent a date, but when it comes to precise calculations it fails. Subtracting one TDateTime from another gives you the fraction of days. Simply multiplying it with 24 (hours) and 60 (minutes) gives you the elapsed time in minutes, in your case 29,9999999930151. As MinutesBetween is designed to only count completely elapsed minutes, it gives you 29. The solution is to do the calculation yourself. The following gives you the elapsed minutes rounded to the nearest integer: TDateTime DateTime1 = EncodeDateTime(2007, 4, 30, 8, 0, 0, 0); TDateTime DateTime2 = EncodeDateTime(2007, 4, 30, 8, 30, 0, 0); int Minutes = RoundTo( static_cast<double>(DateTime2-DateTime1)*24.0*60.0 ,0); If you don't want say 10.6 minutes counted as 11 but just 10 however, then you would have to do the desired rounding by yourself too (e.g. by adding 0.1 and then cast to int, thus making 10.9==11 and 10.8==10). 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