DateTime.Parse not reversing month and day based on thread culture

Question

I'm parsing a date string from a database so that I can display it in the current culture of the UI thread. For some reason, the date is not parsing with respect to the culture - specifically, I'm parsing a en-US date to switch to a es-ES date and the month/day positions are not switching.

According to this MSDN article I should just be able to use Parse with only the date string as a parameter. I should also be able to explicitly provide a culture object. Neither works and my date remains as mm/dd instead of dd/mm. I've verified that both the thread's CurrentCulture and CurrentUICulture are set properly and if I do a new DateTime, that outputs correctly.

Am I missing something?

EDIT: Nothing fancy in the code, just the .NET API.

CultureInfo culture = CultureInfo.CreateSpecificCulture(cultureName);
Thread.CurrentThread.CurrentCulture = culture;
Thread.CurrentThread.CurrentUICulture = culture;
DateTime formattedDate = DateTime.Parse("5/9/2014");
formattedDate.ToShortDateString(); //this returns 5/9/2014
DateTime.Today.ToShortDateString(); //this returns 9/5/2014

Answer 1

The problem you are having is that 5/9/2014 is a perfectly valid month string in either dd/mm/yyyy or mm/dd/yyyy format so when you do DateTime.Parse("5/9/2014") it will successfully parse it as 5th September 2014 (since the es-es date format is dd/mm/yyyy).

This then explains why when you output you get something different to DateTime.Today (which is obviously 9th May).

A working version of your program would be:

var outputCulture = CultureInfo.CreateSpecificCulture("es-es");
var inputCulture = CultureInfo.CreateSpecificCulture("en-us");
Thread.CurrentThread.CurrentCulture = outputCulture;
Thread.CurrentThread.CurrentUICulture = outputCulture;
DateTime formattedDate = DateTime.Parse("5/9/2014", inputCulture);
Console.WriteLine(formattedDate.ToShortDateString()); //this returns 09/05/2014
Console.WriteLine(DateTime.Today.ToShortDateString()); //this returns 09/05/2014

As you see I am specifying the culture for input so that it knows to use the en-us culture rather than the explicitly set es-es culture for parsing.

Answer 2

Since you are parsing a string from a database, the only way to do this correctly is to persist the string in a standard format that does not depend on any culture specific data. ISO 8601 defines formats appropriate for this and you can use a custom format string to achieve this. You can also use .Net's 'o' format specifier for round trip. See How to: Round-trip Date and Time Values for more information.

Culture specific settings do change and cause items that used to parse, to no longer be able to parse even if you know the culture that was used to format the value with to start with.

Culture specific formatting and parsing is meant to be ephemeral and to be used to interact with the user only.