How do I get the time difference between two DateTime objects using C#?

The following example demonstrates how to do this:

DateTime a = new DateTime(2010, 05, 12, 13, 15, 00);
DateTime b = new DateTime(2010, 05, 12, 13, 45, 00);
Console.WriteLine(b.Subtract(a).TotalMinutes);

When executed this prints "30" since there is a 30 minute difference between the date/times.

The result of DateTime.Subtract(DateTime x) is a TimeSpan Object which gives other useful properties.

What you need is to use the DateTime classs Subtract method, which returns a TimeSpan.

var dateOne = DateTime.Now;
var dateTwo = DateTime.Now.AddMinutes(-5);
var diff = dateTwo.Subtract(dateOne);
var res = String.Format("{0}:{1}:{2}", diff.Hours,diff.Minutes,diff.Seconds));

You want the TimeSpan struct:

TimeSpan diff = dateTime1 - dateTime2;

A TimeSpan object represents a time interval (duration of time or elapsed time) that is measured as a positive or negative number of days, hours, minutes, seconds, and fractions of a second. The TimeSpan structure can also be used to represent the time of day, but only if the time is unrelated to a particular date.

There are various methods for getting the days, hours, minutes, seconds and milliseconds back from this structure.

If you are just interested in the difference then:

TimeSpan diff = Math.Abs(dateTime1 - dateTime2);

will give you the positive difference between the times regardless of the order.

If you have just got the time component but the times could be split by midnight then you need to add 24 hours to the span to get the actual difference:

TimeSpan diff = dateTime1 - dateTime2;
if (diff < 0)
{
    diff = diff + TimeSpan.FromDays(1);
}