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How to check line state using WMI with C/C++
This article was contributed by Arkady Frenkel , Microsoft MVP [ Windows SDK /Networking ].
OverviewEnvironment: VS6 on W2K / XP NetConnect dll is ATL COM object which use WMI ( Windows Management Instrumentation ) to receive status of network connection and through connection point fire event into MFC client application - CheckNet.exe . NetConnect dll enumerate network adapters in the computer to work with . I set fix buffer of 5 adapters because I never used more than 2 , but it can be easy be change to free number by CSimpleArray of ATL or by API allocations . When StartPolling member function of main object ( CNetConnectobj ) called , It starts working thread which do polling of network connection for each adapter in the system and fire event to container ( CheckNet.exe ) through connection point interface ( Fire_Connection of Event class proxy CProxy_INetConnectobjEvents ) , After polling each adapter thread make a 1 sec sleep. So if higher precision needed change of sleep time to low value will make the deal. I choose connection point because I realized polling process inside in-process server where such communication is efficient enough ( "Effective Com" by Don Box, Keith Brown,Tim Ewalds and Chris Sells ) Because the process done on additional ( working ) thread and not on main thread of object I was need to use one of advices from http://www.mvps.org/vcfaq/com/1.htm. I used method 2 of Q196026 of KB MSDN "PRB: Firing Event in Second Thread Causes IPF or GPF" to fire event correctly for different containers , because the data I need to send is number of adapter and state , so it can easy be packet into wParam of message. As was asked on microsoft.public.win32.programmer.networks newsgroup about possibility to ask network state in using C programming language - CheckNetwork.c is source code to ask the state. CheckNetwork - is next member-function of CNetConnectobj which allow to ask connection state of needed adapter. I didn't derive the main class object from IProvideClassInfo2 , because I decided ( on create ) that it will be dual interface ( for VB and script languages using ), but if custom interface used , the object have to be derived from IProvideClassInfo2 to give needed information in run-time( "ATL internals" by Brent Rector and Chris Sells ) I choose to use dispinterface because opposite to of being slow ( in compare to VTBL (custom) interface ) it has option to work with VB and script languages ( VBA , VBscript , JScript ). Needed wbemcli.h and wbemuuid.lib taken from DDK Windows 2000. I did NetConnect.dll in debug mode but in the case of Release ( Mindependency or Min Size ) don't forget to remove ATL_CRT_MIN ( ) . Look at Q166480 "PRB: Link Error LNK2001: Unresolved External Symbol _main" of KB MSDN .
Code OverviewTo work with NetConnect.dll it have to registered so let's say directory where NetConnect.dll is C:\NetworkCheck the regsvr32 have to be called like this :
And to remove the registration of NetConnect.dll possible by :
Client ( container ) is MFC application CheckNet.exe which implement connection sync in it to receive event when cable plugged/unplugged on each of network adapters. Next steps done to dialog box application checknet to implement the sink ( receiver of event from ATL COM object ( NetConnect.dll ) : 1) First added line 23 to stdafx.h to generate object's smart pointer
2) Initialization of smart pointer m_pIM possible to see in line 123 of CheckNetDlg.cpp m_pIM = INetConnectobjPtr(CLSID_NetConnectobj); 3) After line 23 in stdafx.h added next lines :
4) AfxOleInit(); - Line 49 added to CCheckNetApp::InitInstance() in CheckNet.cpp 5) CComModule _Module ; - Line 15 added to CheckNet.cpp 6) _Module.Init(NULL , m_hInstance ) ; - Line 62 added to CheckNet.cpp 7) _Module.Term( ) ; - Line 76 added to CheckNet.cpp 8) Next lines added to CheckNetDlg.cpp from line 121 to CCheckNetDlg::OnInitDialog() try { m_pIM = INetConnectobjPtr(CLSID_NetConnectobj); // Create the sink object, and advise the server m_pHandler = new CEventHandler; IUnknownPtr pUnk = m_pIM; m_pHandler->DispEventAdvise(pUnk); } catch (_com_error &e) { MessageBox(e.ErrorMessage()); } to initialize smart pointer on ATL COM object as was written before ( point 2 ) , and creation and advising of sink to connection point of object 9) EventHandler.h & EventHandler.cpp realized sink class CEnentHandler 10) Added handler CCheckNetDlg::OnButton1( ) to CheckNetDlg.cpp where by line : m_pIM->StartPolling() ; Advice of sink done and from now all changes in line status ( plug/unplug ) received . 11) Added handler CCheckNetDlg::OnButton2( ) to CheckNetDlg.cpp where line : m_pIM->CheckNetwork(&i) ; responsible to checking connection of first ( usually single ) network adaptor 12) Next lines added to CCheckNetDlg::OnDestroy() IUnknownPtr pUnk = m_pIM; m_pHandler->DispEventUnadvise(pUnk); delete m_pHandler; to unadvise sink and delete CEventHandler class when client ( CheckNet ) closed. I believe that these are all steps before compiling/linking of CheckNet.exe , but if I forgot something the code with you :)
Using CheckNet ApplicationTo start receive notification events button "Start Check Net" have to be pressed . Button "Check Net" - to ask network state on first adapter on demand. Here is the CheckNet dialog when the first adapter cable is connected:
Here is the CheckNet dialog when the first adapter cable is disconnected:
Downloads
Download source code of ATL COM dll server- 821Kb
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