Best place to store configuration files and log files on Windows for my program?

Note: You can get the path to the LocalApplicationData folder in .NET by using the following function:

string strPath=System.Environment.GetFolderPath(System.Environment.SpecialFolder.LocalApplicationData);

If you're not using ConfigurationManager to manage your application and user settings, you should be. The configuration toolkit in the .NET Framework is remarkably well thought out, and the Visual Studio tools that interoperate with it are too.

The default behavior of ConfigurationManager puts both invariant (application) and modifiable (user) settings in the right places: the application settings go in the application folder, and the user settings go in System.Environment.SpecialFolder.LocalApplicationData. It works properly under all versions of Windows that support .NET.

As for log files, System.Environment.SpecialFolder.LocalApplicationData is generally the place that you want to put them, because it's guaranteed to be user-writeable.

There are certainly cases where you wouldn't - for instance, if you want to write files to a network share so that you easily can access them remotely. There's a pretty wide range of ways to implement that, but most of them start with creating an application setting that contains the path to the shared folder. All of them involve administration.

I have a couple of complaints about ConfigurationManager and the VS tools: there needs to be better high-level documentation than there is, and better documentation of the VS-generated Settings class. The mechanism by which the app.config file turns into the application configuration file in the target build directory is opaque (and the source of one of the most frequently asked questions of all: "what happened to my connection string?"). And if there's a way of creating settings that don't have default values, I haven't found it.