How can I change a Windows user's regional settings/date format?
c#, datetime, regional, registry, windows
Solution
This is specifically discouraged by Microsoft. Any solution you may come up with will be a filthy hack that will probably stop working soon.
Think of it this way: who are you to decide those settings? Don't you think that's the user's decision?
Back on topic: find an unambiguous format for the applications to communicate in, such as `YYYYMMDD`. The application that displays can then simply respect the actual user settings, as it should.
But, since you can't change it, just poke into the registry:
Current user:
HKEY_CURRENT_USER\Control Panel\International
Specific user:
HKEY_USERS\(user SID)\Control Panel\International
Default user:
HKEY_USERS\.DEFAULT\Control Panel\International
`sShortDate` is probably the value you want to change.
Problem
I use a VB6/COM+ application which outputs date/time values based on the short date settings in the Control Panel, Regional Settings, for the user that runs it. The program that then parses that output has a configurable setting for the date format it expects, and presents in the UI. e.g. If the regional setting for the user is set to mm/dd/yyyy, and it outputs 06/18/2009, the application expecting "18/06/2009" fails with "String was not recognized as a valid DateTime". As we usually run this application as a service account, which we have not logged in as interactively to create a profile, we generally set the correct date format and then tick the "Apply all settings to the current user account and the default user profile" option. I would like to be make the C# configuration utility I have written for this mess to be able to set the date format programmatically for a given user. Edit I would like nothing more than to change the code, but do not have the ability to do so at this time. I also know that what I am asking is a bad thing to do. With regards to "it should be the user's choice" - I am that user, as I create it explicitly for the task; I just want to set the date format by a scripted method, rather than having to do the clicking myself.