Here are easy answers to Paul Hill's date-calculation challenges using libtai's date functions. caldate_mjd() converts from a calendar date to the traditional MJD number, and caldate_frommjd() converts back. Paul Hill writes:
the beginning next week,
day = caldate_mjd(&cd); do caldate_frommjd(&cd,++day,&weekday,0); while (weekday != 0); /* there are faster ways to do this, of course */
the first day of this year,
cd.month = 1; cd.day = 1;
start of next month,
++cd.month; cd.day = 1; caldate_normalize(&cd); /* same as caldate_frommjd(&cd,caldate_mjd(&cd),0,0); */
two days before the beginning of the last month of the year,
cd.month = 12; cd.day = -1; caldate_normalize(&cd);
the last Thursday in November,
cd.month = 12; cd.day = 1; day = caldate_mjd(&cd); do caldate_frommjd(&cd,--day,&weekday,0); while (weekday != 4);
exactly 60 days from now,
caldate_frommjd(&cd,caldate_mjd(&cd) + 60,0,0);
exactly two months before now,
In my experience, as illustrated previously on this mailing list, people who use that phrase don't know what they're talking about. Try this: d = cd.day; cd.month -= 1; cd.day = 0; caldate_normalize(&cd); if (cd.day > d) cd.day = d; ---Dan