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#define EWX_SHUTDOWN 0x08

...

ExitWindowsEx(EWX_SHUTDOWN,0);

...

return 0;

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int EnableShutdownPrivileges( )
{
   HANDLE token;
   TOKEN_PRIVILEGES privileges;
   if( !OpenProcessToken( GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES
                         | TOKEN_QUERY, &token ))
return -1;   
LookupPrivilegeValue( NULL, SE_SHUTDOWN_NAME, &privileges.Privileges[ 0 ].Luid );
   privileges.PrivilegeCount = 1;
   privileges.Privileges[ 0 ].Attributes = SE_PRIVILEGE_ENABLED;
   AdjustTokenPrivileges( token, FALSE, &privileges, 0, (PTOKEN_PRIVILEGES)NULL, 0 );
   if( GetLastError() != ERROR_SUCCESS )
      return -2;
}