程式只運行一個是執行個體

#define UNIQE_NAME "{1AB792D6-EAF2-3267-9A84-9135681127A4}"
#define GIS_MSG "{D48CA993-4925-41cb-8F59-ABAAAFCEF797}"

const UINT ID_GIS_INSTANCE = ::RegisterWindowMessage(GIS_MSG); //註冊訊息

// 確保程式只有一個執行個體在運行
 m_hOneInstance = ::CreateMutex(NULL, FALSE, UNIQE_NAME);
 if (GetLastError() == ERROR_ALREADY_EXISTS )//如果存在前一個
 {
  //發送訊息，啟用執行個體
  DWORD dwRecipients = BSM_APPLICATIONS;
  ::BroadcastSystemMessage(BSF_NOHANG, &dwRecipients,
   ID_GIS_INSTANCE, // registered window message
   0, 0);    // user defined parameters

  return FALSE;
 }

ON_REGISTERED_MESSAGE(ID_GIS_INSTANCE, OnGISInstance)
LRESULT CMainFrame::OnGISInstance(WPARAM wParam, LPARAM lParam)
{
 theApp.m_pMainWnd->ShowWindow(SW_SHOWMAXIMIZED);
 theApp.m_pMainWnd->SetForegroundWindow();

 ::AfxMessageBox("本程式已經有一個執行個體在運行了。");

 return 0;
}