Standard conformant way of converting std::time_t to System::DateTime?

Question

I have already found several answers related to converting a std::time_t value to System::DateTime and back. However, almost all answers seem to ne

Answer 1

Here's the solution my team arrived at:

DateTime represents the number of mixed-fractional days since midnight December 30, 1899, expressed as a double. I believe that this epoch date was used to account for the fact that 1900 was not a leap year, and it allows for an extra two days (Why two and not one? - It is not clear to me why Dec 31, 1899 was not chosen as their epoch.)

So a DateTime of 2.50 would be equivalent to January 1, 1900 12:00:00 , (i.e. the fraction represents 1/2 the day - 12PM).

We calculated that Jan 1, 1970 - the Unix Epoch - is 25569 days after the DateTime Epoch.

So the equivalent formula would be:

#include 
System::DateTime toDateTime(time_t &t)
{
    return 25569.0 + t / 86400.0; // ensure you use floating point math or you will truncate the fractional portion
}