Getting / setting file owner in C#

No need to P/Invoke. System.IO.File.GetAccessControl will return a FileSecurity object, which has a GetOwner method.

Edit: Reading the owner is pretty simple, though it's a bit of a cumbersome API:

const string FILE = @"C:\test.txt";

var fs = File.GetAccessControl(FILE);

var sid = fs.GetOwner(typeof(SecurityIdentifier));
Console.WriteLine(sid); // SID

var ntAccount = sid.Translate(typeof(NTAccount));
Console.WriteLine(ntAccount); // DOMAIN\username

Setting the owner requires a call to SetAccessControl to save the changes. Also, you're still bound by the Windows rules of ownership - you can't assign ownership to another account. You can give take ownership perms, and they have to take ownership.

var ntAccount = new NTAccount("DOMAIN", "username");
fs.SetOwner(ntAccount);

try {
   File.SetAccessControl(FILE, fs);
} catch (InvalidOperationException ex) {
   Console.WriteLine("You cannot assign ownership to that user." +
    "Either you don't have TakeOwnership permissions, or it is not your user account."
   );
   throw;
}