C#

[DllImport("test.dll", CharSet=CharSet.Auto)]
private static extern dont-forget-the-return-value Set(string str);

[DllImport("NetApi32.dll")] private static extern int NetUseGetInfo(string SrvrName,string MappedDrive,int Level,ref structUSE_INFO_2 MapInfo);
[DllImport("NetApi32.dll")] private static extern int NetApiBufferFree(ref structUSE_INFO_2 MapInfo);


[StructLayout(LayoutKind.Sequential)]
private struct structUSE_INFO_2
{
	public string sLocal;
	public string sRemote;
	public string sPassword;
	public int iType;
	public int iRefCount;
	public int iUseCount;
	public string sUsername;
	public string sDomain;
}

...
....
...
static public string GetMappedDriveUsername(string DriveLetter)
{	
	string Username=null;
	try
	{
		structUSE_INFO_2 MappInfo = new structUSE_INFO_2();
		int Err=NetUseGetInfo(null,DriveLetter.Replace(":",""),2,ref MappInfo);
                Username=MappInfo.sUsername;
		NetApiBufferFree(ref MappInfo);
	}
	catch(Exception Err)
	{
		throw new Exception("GetMappedDriveUsername Error: "+Err.Message);
	}
	return Username;
}

[DllImport("NetApi32.dll",CharSet=CharSet.Unicode)] private static extern int NetUseGetInfo(string SrvrName,string MappedDrive,int Level,ref structUSE_INFO_2 MapInfo);
[DllImport("NetApi32.dll",CharSet=CharSet.Unicode)] private static extern int NetApiBufferFree(ref structUSE_INFO_2 MapInfo);


[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Unicode)]
private struct structUSE_INFO_2
{
	public string sLocal;
	public string sRemote;
	public string sPassword;
	public int iType;
	public int iRefCount;
	public int iUseCount;
	public string sUsername;
	public string sDomain;
}
...
...
...

structUSE_INFO_2 MappInfo = new structUSE_INFO_2();
int Err=NetUseGetInfo(null,DriveLetter,2,ref MappInfo);
Username=MappInfo.sUsername;
Err=NetApiBufferFree(ref MappInfo);

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;

internal class GetInfo
{
  static void Main(string[] args)
  {
    if (args.Length != 1)
    {
      Console.Error.WriteLine("You must specify a drive letter.");
      Environment.Exit(1);
    }

    if (Environment.OSVersion.Platform != PlatformID.Win32NT)
    {
      Console.Error.WriteLine("Supported only on Windows NT.");
      Environment.Exit(2);
    }
 
    // Pay attention here
    IntPtr ptr = IntPtr.Zero;
    if (0 == NetUseGetInfo(null, args[0], 2, out ptr))
    {
      UseInfo2 info = (UseInfo2)Marshal.PtrToStructure(ptr,
        typeof(UseInfo2));

      Console.WriteLine("Username: " + info.username);
      Console.WriteLine("Domain: " + info.domainname);

      NetApiBufferFree(ptr);
    }
 
    else
    {
      int error = Marshal.GetLastWin32Error();
      Console.Error.WriteLine("Error " + error);
      Environment.Exit(error);
    }
  }

  [DllImport("netapi32.dll", CharSet=CharSet.Unicode, SetLastError=true)]
  public static extern uint NetUseGetInfo
  (
    string server,
    string drive,
    uint level,
    out IntPtr info
  );

  [DllImport("netapi32.dll")]
  public static extern uint NetApiBufferFree(IntPtr ptr);
}

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
internal struct UseInfo2
{
  public string local;
  public string remote;
  public string password;
  public uint status;
  public uint type;
  public uint refcount;
  public uint usecount;
  public string username;
  public string domainname;
}