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Re: What about my last date functions? there are some error?

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On 08/11/16 19:16, jadill33@gmail.com wrote:

<snip>

> I'm curious, if you don't mind, what's your use-case on calculating a
> Julian date when the Gregorian calendar is primarily what we use these
> days?

Oh, I don't care about it being Julian. In fact, that's just a name as 
far as I'm concerned. What I find useful is simply the fact that the 
date is represented as a single integer, such that to get tomorrow's 
date from today's, all I have to do is ++d, without worrying about 
whether this is the last day of the month or the last day of the year.

Consider how we might prepare a list of dates, 30 days apart, starting 
from next Tuesday, and continuing until 17th January 2021. We might do 
it like this (I'm assuming C90 here, for maximum portability):

time_t tmtstart = {0};
time_t tmtend = {0};

struct tm start_date = {0};
struct tm end_date = {0};

start_date.tm_year = 116; /* tm_year is 1900-based! */
start_date.tm_mon = 10; /* November, not October! tm_mon is 0-11 */
start_date.tm_mday = 15; /* 15th, not 14th! tm_mday is 1-31 */
end_date.tm_year = 121;
end_date.tm_mon = 0;
end_date.tm_mday = 17;
tmtstart = mktime(&start_date);
tmtend = mktime(&end_date);

while(difftime(tmtend, tmtstart) > 0.0)
{
   /* I could use strftime here, but it seems unnecessary for such a 
simple printf */
   printf("%02d/%02d/%04d\n",
          tmtstart.tm_mday,
          tmtstart.tm_mon,
          tmtstart.tm_year + 1900);
   start_date.tm_mday += 30;
   tmtstart = mktime(&start_date);
}

And that's fine. But it's a lot of code for such a simple task (and, to 
my eyes at least, it's ugly code). Now consider this:

long start = tojul(2016, 11, 15);
long end = tojul(2021, 1, 17);
int d = 0;
int m = 0;
int y = 0;
while(start < end)
{
   fromjul(&y, &m, &d, start);
   printf("%02d/%02d/%04d\n", d, m, y);
   start += 30;
}

(I note in passing that the Julian version uses two function calls per 
loop iteration rather than three.)

Okay, some people might prefer the former code, but I'm not one of them.

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within

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What about my last date functions? there are some error? Rosario19 <Ros@invalid.invalid> - 2016-11-08 11:28 +0100
  Re: What about my last date functions? there are some error? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-08 10:55 +0000
    Re: What about my last date functions? there are some error? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-08 19:00 +0800
    Re: What about my last date functions? there are some error? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-08 11:04 +0000
      Re: What about my last date functions? there are some error? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-08 19:22 +0800
    Re: What about my last date functions? there are some error? Richard Heathfield <rjh@cpax.org.uk> - 2016-11-08 11:35 +0000
      Re: What about my last date functions? there are some error? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-08 15:46 +0000
        Re: What about my last date functions? there are some error? Richard Heathfield <rjh@cpax.org.uk> - 2016-11-08 16:20 +0000
          Re: What about my last date functions? there are some error? Rosario19 <Ros@invalid.invalid> - 2016-11-08 17:44 +0100
            Re: What about my last date functions? there are some error? Richard Heathfield <rjh@cpax.org.uk> - 2016-11-08 16:51 +0000
              Re: What about my last date functions? there are some error? Jerry Stuckle <jstucklex@attglobal.net> - 2016-11-08 13:21 -0500
          Re: What about my last date functions? there are some error? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-08 18:06 +0000
            Re: What about my last date functions? there are some error? Richard Heathfield <rjh@cpax.org.uk> - 2016-11-08 18:56 +0000
              Re: What about my last date functions? there are some error? Keith Thompson <kst-u@mib.org> - 2016-11-08 12:05 -0800
              Re: What about my last date functions? there are some error? David Brown <david.brown@hesbynett.no> - 2016-11-08 21:10 +0100
                Re: What about my last date functions? there are some error? Richard Heathfield <rjh@cpax.org.uk> - 2016-11-08 20:16 +0000
          Re: What about my last date functions? there are some error? jadill33@gmail.com - 2016-11-08 11:16 -0800
            Re: What about my last date functions? there are some error? Richard Heathfield <rjh@cpax.org.uk> - 2016-11-08 20:08 +0000
            Re: What about my last date functions? there are some error? Keith Thompson <kst-u@mib.org> - 2016-11-08 12:11 -0800
              Re: What about my last date functions? there are some error? Keith Thompson <kst-u@mib.org> - 2016-11-08 12:29 -0800
      Re: What about my last date functions? there are some error? Rosario19 <Ros@invalid.invalid> - 2016-11-08 17:41 +0100
        Re: What about my last date functions? there are some error? asetofsymbols@gmail.com - 2016-11-08 11:26 -0800
          Re: What about my last date functions? there are some error? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-08 19:38 +0000
  Re: What about my last date functions? there are some error? Keith Thompson <kst-u@mib.org> - 2016-11-08 08:19 -0800

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