I have an embedded system that currently keeps track of seconds until an event is supposed to occur using a real-time clock driven by a watch crystal.
Now it needs to keep track of the actual date and time. So, I need to be able to calculate the day, month, year, hour, minute and second from a start date/time and offset in seconds.
Could anyone point me in the right direction for taking into account leap years, daylight savings time (DST) and other complications?
Hardware solutions are not an option as this feature is being added to an existing product. An RTC peripheral is integrated into the MCU chosen for the next generation device.
The C Snippets archive has some date and time functions. Update: unfortunately, the C snippets archive is now defunct. I have updated the link to point to the web archive of the page.
See also “Julian day“, Wikipedia, which includes formulas for Julian date calculation.
A “julian date calculation” Google search should uncover more if you want to search further.