How do you read the user's display (first and last) name on all versions of Windows reliably?

Question

I have found that on Windows 7 64 bit, on a machine with a domain name, GetUserNameEx( 3, .... ) which should get the extended name format DisplayName (==3), into a buffer,

Answer 1

Here is Warren's solution ported to C#. I added retrieval of a domain controller's IP from the domain name because at least on my domain, just using \\ as the server name didn't work.

using System;
using System.Text;
using System.Net;
using System.Runtime.InteropServices;
using System.DirectoryServices.ActiveDirectory;

[DllImport("secur32.dll", CharSet = CharSet.Auto)]
private static extern int GetUserNameEx (int nameFormat, StringBuilder userName, ref uint userNameSize);

[DllImport("netapi32.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
private static extern int NetUserGetInfo ([MarshalAs(UnmanagedType.LPWStr)] string serverName,
                                          [MarshalAs(UnmanagedType.LPWStr)] string userName,
                                          int level, out IntPtr bufPtr);

[DllImport("netapi32.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
private static extern long NetApiBufferFree (out IntPtr bufPtr);

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct USER_INFO_10
{
    [MarshalAs(UnmanagedType.LPWStr)] public string usri10_name;
    [MarshalAs(UnmanagedType.LPWStr)] public string usri10_comment;
    [MarshalAs(UnmanagedType.LPWStr)] public string usri10_usr_comment;
    [MarshalAs(UnmanagedType.LPWStr)] public string usri10_full_name;
}

private string getUserDisplayName ()
{
    var username = new StringBuilder(1024);
    uint userNameSize = (uint) username.Capacity;

    // try to get display name and convert from "Last, First" to "First Last" if necessary
    if (0 != GetUserNameEx(3, username, ref userNameSize))
        return Regex.Replace(username.ToString(), @"(\S+), (\S+)", "$2 $1");

    // get SAM compatible name \\
    if (0 != GetUserNameEx(2, username, ref userNameSize))
    {
        IntPtr bufPtr;
        try
        {
            string domain = Regex.Replace(username.ToString(), @"(.+)\\.+", @"$1");
            DirectoryContext context = new DirectoryContext(DirectoryContextType.Domain, domain);
            DomainController dc = DomainController.FindOne(context);

            if (0 == NetUserGetInfo(dc.IPAddress,
                                    Regex.Replace(username.ToString(), @".+\\(.+)", "$1"),
                                    10, out bufPtr))
            {
                var userInfo = (USER_INFO_10) Marshal.PtrToStructure(bufPtr, typeof (USER_INFO_10));
                return Regex.Replace(userInfo.usri10_full_name, @"(\S+), (\S+)", "$2 $1");
            }
        }
        finally
        {
            NetApiBufferFree(out bufPtr);
        }
    }

    return String.Empty;
}