Code Snippet
// 引入必要的命名空间

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;    // 提供DllImport等特性，是P/Invoke的关键


namespace test
{
      public partial class Form1 : Form
      {
          public Form1()
          {
              InitializeComponent();
          }


          // 这个结构体将会传递给API。使用StructLayout(...特性，确保其中的成员是按顺序排列的，C#编译器不会对其进行调整。

          [StructLayout(LayoutKind.Sequential, Pack = 1)]
          internal struct TokPriv1Luid
          {
              public int Count;
              public long Luid;
              public int Attr;
          }


          // 以下使用DllImport特性导入了所需的Windows API。

          // 导入的方法必须是static extern的，并且没有方法体。调用这些方法就相当于调用Windows API。

          [DllImport("kernel32.dll", ExactSpelling = true)]
          internal static extern IntPtr GetCurrentProcess();

          [DllImport("advapi32.dll", ExactSpelling = true, SetLastError = true)]
          internal static extern bool OpenProcessToken(IntPtr h, int acc, ref IntPtr phtok);

          [DllImport("advapi32.dll", SetLastError = true)]
          internal static extern bool LookupPrivilegeValue(string host, string name, ref long pluid);

          [DllImport("advapi32.dll", ExactSpelling = true, SetLastError = true)]
          internal static extern bool AdjustTokenPrivileges(IntPtr htok, bool disall,
          ref TokPriv1Luid newst, int len, IntPtr prev, IntPtr relen);

          [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
          internal static extern bool ExitWindowsEx(int flg, int rea);


          // 以下定义了在调用WinAPI时需要的常数。这些常数通常可以从Platform SDK的包含文件（头文件）中找到

          internal const int SE_PRIVILEGE_ENABLED = 0x00000002;
          internal const int TOKEN_QUERY = 0x00000008;
          internal const int TOKEN_ADJUST_PRIVILEGES = 0x00000020;
          internal const string SE_SHUTDOWN_NAME = "SeShutdownPrivilege";
          internal const int EWX_LOGOFF = 0x00000000;
          internal const int EWX_SHUTDOWN = 0x00000001;
          internal const int EWX_REBOOT = 0x00000002;
          internal const int EWX_FORCE = 0x00000004;
          internal const int EWX_POWEROFF = 0x00000008;
          internal const int EWX_FORCEIFHUNG = 0x00000010;


          // 通过调用WinAPI实现关机，主要代码再最后一行ExitWindowsEx，这调用了同名的WinAPI，正好是关机用的。

          private static void DoExitWin(int flg)
          {
              bool ok;
              TokPriv1Luid tp;
              IntPtr hproc = GetCurrentProcess();
              IntPtr htok = IntPtr.Zero;
              ok = OpenProcessToken(hproc, TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, ref htok);
              tp.Count = 1;
              tp.Luid = 0;
              tp.Attr = SE_PRIVILEGE_ENABLED;
              ok = LookupPrivilegeValue(null, SE_SHUTDOWN_NAME, ref tp.Luid);
              ok = AdjustTokenPrivileges(htok, false, ref tp, 0, IntPtr.Zero, IntPtr.Zero);
              ok = ExitWindowsEx(flg, 0);
          } 


          private void button1_Click(object sender, EventArgs e)
          {
              if (radioButton1.Checked == true)
              {
                  DoExitWin(EWX_SHUTDOWN); 
              }
              else
              {
                  Application.Exit(); 
              }
              //MessageBox.Show("2");
          }
      }
}