Re: gmtime_r or strftime problem or just my code?????

I have this piece of code that takes a day of the year and converts it
to the month and day of month:

   char start_mon[40];
   char start_day[40];
   int s_day = 84;
   time_t daysecs = (s_day * 86400) - 1;
   struct tm tm_result;
   struct tm *tm_time = &tm_result;
   tm_time = gmtime_r(&daysecs,&tm_result);

   strftime(start_mon, sizeof(start_mon), (char*)"%m", tm_time);
   strftime(start_day, sizeof(start_day), (char*)"%d", tm_time);

I am just testing it with 84, but this is a parameter to the method.
Anyway, the month and day should be 03 24, but I am getting 03 25. It
seems like it is not taking into account leap year. Is it gmtime_r or
strftime or something else? Do I need to actually check the year and
figure out if it is a leap year? I was hoping there was something that
would do that automatically, but probably not. Thanks.