How to compare two datetimes

Question

I wonder how to compare two DateTime objects in .NET using DateTime methods Compare, CompareTo or Equals without comparing ticks.

I only need a tolerance level of milliseconds or seconds.

How can this be done?

Answer 1

You can subtract one DateTime from another to produce a TimeSpan that represents the time-difference between them. You can then test if the absolute value of this span is within your desired tolerance.

bool dtsWithinASecOfEachOther = d1.Subtract(d2).Duration() <= TimeSpan.FromSeconds(1);

The call to TimeSpan.Duration() can be omitted if you know that the first DateTime cannot represent an earlier point in time than the other, i.e. d1 >= d2.

To answer your query about the comparison methods, DateTime.Compare(d1, d2) produces the same result as d1.CompareTo(d2):

• 0 if they represent the same point in time (d1.Equals(d2) , d1 == d2). Do note though, that the resolution of DateTime is 1 tick = 100 nanoseconds = 10 ^ -7 seconds.
• 1 if d1 is chronologically after d2 (d1 > d2)
• -1 if d1 is chronologically before d2 (d1 < d2)

Answer 2

Use TimeSpan for your tolerance check - TimeSpan is the type returned from subtracting DateTimes:

TimeSpan tolerance = new TimeSpan(0,0,1);
return (date1 - date2) <= tolerance;

Compare, CompareTo and Equals will not take a tolerance for the comparison, so cannot used this way.

Other options are to create new DateTimes from the existing ones, discarding the unwanted accuracy and comparing the new ones:

DateTime noSeconds1 = new DateTime(d1.Year, d1.Month, d1.Day, d1.Hour, d1.Minute, 0);
DateTime noSeconds2 = new DateTime(d2.Year, d2.Month, d2.Day, d2.Hour, d2.Minute, 0);

noSeconds1.Equals(noSeconds2);
DateTime.Compare(noSeconds1, noSeconds2);
noSeconds1.CompareTo(noSeconds2);

Answer 3

Generally, if you want a single compare to tell you which date is less, equal to or greater, use DateTime.Compare(). Otherwise, you can use DateTime.Equals(). To add a tolerance value, subtract one from the other and compare result to be less than some TimeSpan:

// For seconds
if (laterDate-earlierDate<=TimeSpan.FromSeconds(1))
  ...

// For milliseconds
if (laterDate-earlierDate<=TimeSpan.FromMilliseconds(1))
  ...

Answer 4

You could convert both DateTimes to string and compare the resulting strings. Make sure you define the string format to avoid problems on machines with different regional settings than yours.