I'm having trouble understanding why the same code is producing different results between .NET 6 and .NET 8 environments.
Specifically, I'm trying to understand why 'end' is not equal to 'newEnd'.
Here you can see a screenshots of the result from each environment:
.NET 6 - the string representation of newEnd is '8/12/2025 11:59:59'.
.NET 8 - the string representation of newEnd is '8/12/2025 11:59:58'.
This is the code:
DateTime start = new DateTime(2025, 08, 10, 0, 0, 0);
DateTime end = new DateTime(2025, 08, 12, 23, 59, 59);
double hoursDiff = end.Subtract(start).TotalHours;
DateTime newEnd = start.AddHours(hoursDiff);
As Panagiotis Kanavos pointed out earlier (in the staging phase) - the hoursDiff value is the same between the two runtimes (it can be proved by printing the entire double using the 'N20' toString parameter).
Therefore, the issue must be related to differences in the DateTime object.
After further investigation of the NET DateTime documentation, I have found that there's been a change in the rounding behavior inside the DateTime.AddHours method which I believe is the source of the issue.
Source - https://learn.microsoft.com/en-us/dotnet/api/system.datetime.addhours?view=net-7.0