Log off user from Win XP programmatically in C#

How do I initiate a Windows XP user Log Off from a C# app? The action of my app should produce the same result as clicking "Log Off" in XP start menu -- it's fine if the system asks for a confirmation.

Is there a .Net or an unmanaged API for this?

You could P/Invoke ExitWindowsEx:

http://www.pinvoke.net/default.aspx/user32/ExitWindowsEx.html

Pulling it all together:

using System.Runtime.InteropServices;
class Class1
{
    [DllImport("user32.dll")]
    static extern bool ExitWindowsEx(uint uFlags, uint dwReason);

    [STAThread]
    static void Main(string[] args)
    {
        ExitWindowsEx(ExitWindows.LogOff, ShutdownReason.MajorOther | ShutdownReason.MinorOther); 
    }
}

[Flags]
public enum ExitWindows : uint
{
   // ONE of the following five:
   LogOff = 0x00,
   ShutDown = 0x01,
   Reboot = 0x02,
   PowerOff = 0x08,
   RestartApps = 0x40,
   // plus AT MOST ONE of the following two:
   Force = 0x04,
   ForceIfHung = 0x10,
}

[Flags]
enum ShutdownReason : uint
{
    MajorApplication = 0x00040000,
    MajorHardware = 0x00010000,
    MajorLegacyApi = 0x00070000,
    MajorOperatingSystem = 0x00020000,
    MajorOther = 0x00000000,
    MajorPower = 0x00060000,
    MajorSoftware = 0x00030000,
    MajorSystem = 0x00050000,

    MinorBlueScreen = 0x0000000F,
    MinorCordUnplugged = 0x0000000b,
    MinorDisk = 0x00000007,
    MinorEnvironment = 0x0000000c,
    MinorHardwareDriver = 0x0000000d,
    MinorHotfix = 0x00000011,
    MinorHung = 0x00000005,
    MinorInstallation = 0x00000002,
    MinorMaintenance = 0x00000001,
    MinorMMC = 0x00000019,
    MinorNetworkConnectivity = 0x00000014,
    MinorNetworkCard = 0x00000009,
    MinorOther = 0x00000000,
    MinorOtherDriver = 0x0000000e,
    MinorPowerSupply = 0x0000000a,
    MinorProcessor = 0x00000008,
    MinorReconfig = 0x00000004,
    MinorSecurity = 0x00000013,
    MinorSecurityFix = 0x00000012,
    MinorSecurityFixUninstall = 0x00000018,
    MinorServicePack = 0x00000010,
    MinorServicePackUninstall = 0x00000016,
    MinorTermSrv = 0x00000020,
    MinorUnstable = 0x00000006,
    MinorUpgrade = 0x00000003,
    MinorWMI = 0x00000015,

    FlagUserDefined = 0x40000000,
    FlagPlanned = 0x80000000
}

Try calling the "ExitWindowsEx" API function with the constant "EWX_LOGOFF" or 0. API Guide tells me that the second parameter is ignored. For instance,

//The import
using System.Runtime.InteropServices;

// The declaration
[DllImport("user32.dll")]
public static extern int ExitWindowsEx(int uFlags, int dwReserved);

// The call
 ExitWindowsEx(0, 0);

For completeness, the simplest way I found is to call Shutdown.exe (included with Windows).

Process.Start("shutdown.exe", "-l -t 0");

This is the answer Cerebrus suggested, just in C# form.