Getting All Users In A Computer

First we'll create a class to process WinApi calls.

 

This Class has been written by Michael Bright in 2003.Since then i've been using this code and extending it for network related needs.

using System;
using System.Runtime.InteropServices;
namespace GettingAllUsers {
    public class NetworkAPI {
        // USER_INFO_1 - Strucutre to hold obtained user information
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        public struct USER_INFO_1 {
            public string usri1_name;
            public string usri1_password;
            public int usri1_password_age;
            public int usri1_priv;
            public string usri1_home_dir;
            public string comment;
            public int usri1_flags;
            public string usri1_script_path;
        }
        // USER_INFO_0 - Structure to hold Just Usernames
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        public struct USER_INFO_0 {
            public String Username;
        }
        // NetUserAdd - To Add Users to a local machine or Network
        [DllImport("Netapi32.dll")]
        public extern static int NetUserAdd([MarshalAs(UnmanagedType.LPWStr)] string servername, int level, ref USER_INFO_1 buf, int parm_err);
        // NetUserDel - To delete Users from a local machine or Network
        [DllImport("Netapi32.dll")]
        public extern static int NetUserDel([MarshalAs(UnmanagedType.LPWStr)] string servername, [MarshalAs(UnmanagedType.LPWStr)] string username);
        // NetUserGetInfo - Returns to a struct Information about the specified user
        [DllImport("Netapi32.dll")]
        public extern static int NetUserGetInfo([MarshalAs(UnmanagedType.LPWStr)] string servername, [MarshalAs(UnmanagedType.LPWStr)] string username, int level, out IntPtr bufptr);
        // NetUserSetInfo - Allows us to modify User information
        [DllImport("Netapi32.dll")]
        public extern static int NetUserSetInfo([MarshalAs(UnmanagedType.LPWStr)] string servername, [MarshalAs(UnmanagedType.LPWStr)] string username, int level, ref USER_INFO_1 buf, int error);
        // NetUserChangePassword - Allows us to change a users password providing we have it
        [DllImport("Netapi32.dll")]
        public extern static int NetUserChangePassword([MarshalAs(UnmanagedType.LPWStr)] string domainname, [MarshalAs(UnmanagedType.LPWStr)] string username, [MarshalAs(UnmanagedType.LPWStr)] string oldpassword, [MarshalAs(UnmanagedType.LPWStr)] string newpassword);
        // NetUserEnum - Obtains a list of all users on local machine or network
        [DllImport("Netapi32.dll")]
        public extern static int NetUserEnum(string servername, int level, int filter, out IntPtr bufptr, int prefmaxlen, out int entriesread, out int totalentries, out int resume_handle);
        // NetAPIBufferFree - Used to clear the Network buffer after NetUserEnum
        [DllImport("Netapi32.dll")]
        public extern static int NetApiBufferFree(IntPtr Buffer);
        public NetworkAPI() {
            //
            // TODO: Add constructor logic here
            //
        }
    }
}

Add a ListBox in your form and then,Later inside your main application create a function:

public void EnumerateUsers() {
    int EntriesRead;
    int TotalEntries;
    int Resume;
    listBox1.Items.Clear();
    IntPtr bufPtr;
    NetworkAPI.NetUserEnum(null, 0, 2, out bufPtr, -1, out EntriesRead, out TotalEntries, out Resume);
    if (EntriesRead > 0) {
        NetworkAPI.USER_INFO_0[] Users = new NetworkAPI.USER_INFO_0[EntriesRead];
        IntPtr iter = bufPtr;
        for (int i = 0; i < EntriesRead; i++) {
            Users[i] = (NetworkAPI.USER_INFO_0) Marshal.PtrToStructure(iter, typeof(NetworkAPI.USER_INFO_0));
            iter = (IntPtr)((int) iter + Marshal.SizeOf(typeof(NetworkAPI.USER_INFO_0)));
            listBox1.Items.Add(Users[i].Username);
        }
        NetworkAPI.NetApiBufferFree(bufPtr);
    }
    listBox1.SelectedIndex = 0;
}
Now just call EnumerateUsers inside Form_Load to populate them in your listbox at startup
private void Form1_Load(object sender, EventArgs e) {
    EnumerateUsers();
}

And run it!

 

 

 

Hope that helps!