Question

How to accurately get difference(in years) between two DateTime objects in “Years”?

DateTime.Subtract() gives difference in TimeSpan and the maximum denomination is Days.

So, if I would want to get accurately, the difference between Today and a day in 1988(say 29th March 1988), is there an “easier” way to get the accurate age of this person?

What I’ve tried is:

DateTime March291988 = DateTime.Parse("29/03/1988");
TimeSpan ts = DateTime.Now.Subtract(March291988);
int years = (ts.Days/365);

More importantly, the question is: How to convert from TimeSpan to DateTime.

Answer 1

I’m biased, but I’d use Noda Time:

var date1 = new LocalDate(1988, 3, 29);
var date2 = new LocalDate(2013, 1, 23); // See note below
var years = Period.Between(date1, date2, PeriodUnits.Years).Years;

Basically the BCL doesn’t provide a hugely easy way of working with things like this – you really don’t want a TimeSpan, because it’s not anchored to a specific start/end point. You can subtract one Year value from another and then adjust if it does the wrong thing, but it’s a bit icky.

Now in your original code, you used DateTime.Now. In Noda Time, we treat a clock as a dependency, with SystemClock.Instance being the normal production implementation. An IClock doesn’t know about time zones – it just knows the current instant in time – so you have to say which time zone you’re interested in. For example:

var today = clock.Now.InZone(zone).LocalDateTime.Date;

I know this seems long-winded, but it’s isolating all the different conversions to make it all more explicit. (I may introduce a Date property on ZoneDateTime to reduce this slightly.)