C# Signature:

[DllImport("user32.dll")]
static extern bool ExitWindowsEx(uint uFlags, uint dwReason);

User-Defined Types:

None.

Notes:

    uFlags
        4 = Force any applications to quit instead of prompting the user to close them.
        0 = Log off the network.
        8 = Shut down the system and, if possible, turn the computer off.
        2 = Perform a full reboot of the system.
1 = Shut down the system.

    dwReason
        Just set this = 0            

Tips & Tricks:

To shut down or restart the system on NT/2K/XP, the calling process must use the AdjustTokenPrivileges function to enable the SE_SHUTDOWN_NAME privilege.

Sample Code:

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

        [STAThread]
        static void Main(string[] args)
        {
            ExitWindowsEx(0, 0); //this will cause the computer to logoff.
        }
    }

Alternative Managed API:

Do you know one? Please contribute it!