[SOLVED] How to compare two dates in C# on just year, month, day, hour, minute, second?

Issue

I have two dates and I only want to make sure they match on these 6 fields:
year, month, day, hour, minute and second.

I have noticed that if I perform a simple equality == comparison if(d1 == d2) that match on these fields, I still get ‘false’. I’m assuming this has to do with other fields under the hood that relate to ticks, milliseconds etc. How can I ignore everything and just make sure they match on the 6 fields above?

I have created the prototype function below but to me this feels amateurish and inefficient for production-level code. Furthermore, date1 has to be a nullable datetime.

Does anyone else have any better suggestions?

    private static bool DatesAreEqual(DateTime date1, DateTime date2)
    {

        var d1 = new DateTime(date1.Year, date1.Month, date1.Day,
                    date1.Hour, date1.Minute, date1.Second);

        var d2 = new DateTime(date2.Year, date2.Month, date2.Day,
                    date2.Hour, date2.Minute, date2.Second);

        return d1 == d2;
    }

Solution

You can remove fractional part of the dates (please, note, that fractional part is longer then just milliseconds):

DateTime date = DateTime.Now;

// 28 02 2022 22:19:56.3704625 
Console.WriteLine($"{date:dd MM yyyy HH:mm:ss.fffffff}"); 

date -= TimeSpan.FromTicks(date.Ticks % 10_000_000);

// 28 02 2022 22:19:56.0000000
Console.WriteLine($"{date:dd MM yyyy HH:mm:ss.fffffff}");

Code:

DateTime date1 = ...
DateTime date2 = ...

...

if (date1 - TimeSpan.FromTicks(date1.Ticks % 10_000_000) == 
    date2 - TimeSpan.FromTicks(date2.Ticks % 10_000_000)) {
  //TODO: Relevant code here
}

You can implement extension class to keep main code shorter and more readable:

public partial static class DateTimeExtensions {
  public static DateTime TrimToSeconds(this DateTime value) => 
    value - TimeSpan.FromTicks(value.Ticks % 10_000_000)
}

And then

DateTime date1 = ...
DateTime date2 = ...

...

if (date1.TrimToSeconds() == date2.TrimToSeconds()) {
  //TODO: Relevant code here
}

Answered By – Dmitry Bychenko

Answer Checked By – Willingham (BugsFixing Volunteer)