CoInitialize()、CoInitializeEx()和AfxOleInit()区别联系

CoInitialize()和AfxOleInit()

都是初始化COM库，不同之处在与：

OLE是建立在COM之上的技术，层次比COM要高。AfxOleInit()调用的是OleInitialize()，而 OleInitialize()除了调用CoInitializeEx()来初始化COM库外，还进行一些其它的操作，这些操作对OLE应用来说是必须的，这些OLE应用包括：
    (1)Clipboard；
    (2)Drag   and   drop；
    (3)Object   linking   and   embedding（现在的OLE，已不再仅仅是Object   linking   and   embedding的概念）；
    (4)In-place   activation；
    与AfxOleInit()对应的是，AfxOleTerm()。

    AfxOleInit()和AfxOleTerm()其实也是需要成对的，但是，在你的程序中，AfxOleTerm()可以不出现，这是因为，MFC已经帮你做好了（有兴趣的话，你可以仔细研究一下CWinThread::m_lpfnOleTermOrFreeLib，而CWinApp是从CWinThread继承的）。

注:但是当你的函数出现了重复调用AfxOleInit()时间便不能依靠mfc自动调用了,需要显式的调用AfxOleTerm清理com库

CoInitialize与AfxOleInit

使用MFC的控制台主程序中如果用AfxOleInit()初始化com就会出现DLL中调用wordApp.CreateDispatch("Word.Application",NULL)失败，而改用用CoInitialize（）则会成功

在AfxOleInit()函数中设置断点调试之后可以知道:afxContextIsDLL这个标志的值为ture,因而它并不会去调用OleInitialize,进而不会调用CoInitialize.

MSDN(If AfxOleInit is called from an MFC DLL, the call will fail. The failure occurs because the function assumes that, if it is called from a DLL, the OLE system was previously initialized by the calling application.) 看来在这个函数中把当前项目当做DLL来处理了.^_^,不知是不是MFC本身的bug

 1 BOOL AFXAPI AfxOleInit()
 2 {
 3     _AFX_THREAD_STATE* pState = AfxGetThreadState();
 4     ASSERT(!pState->m_bNeedTerm);    // calling it twice?
 5 
 6     // Special case DLL context to assume that the calling app initializes OLE.
 7     // For DLLs where this is not the case, those DLLs will need to initialize
 8     // OLE for themselves via OleInitialize.  This is done since MFC cannot provide
 9     // automatic uninitialize for DLLs because it is not valid to shutdown OLE
10     // during a DLL_PROCESS_DETACH.
11     if (afxContextIsDLL)
12     {
13         pState->m_bNeedTerm = -1;  // -1 is a special flag
14         return TRUE;
15     }
16 
17     // first, initialize OLE
18     SCODE sc = ::OleInitialize(NULL);
19     if (FAILED(sc))
20     {
21         // warn about non-NULL success codes
22 #ifdef _DEBUG
23         TRACE(traceOle, 0, _T("Warning: OleInitialize returned scode = %s.\n"),
24             AfxGetFullScodeString(sc));
25 #endif
26         goto InitFailed;
27     }
28     // termination required when OleInitialize does not fail
29     pState->m_bNeedTerm = TRUE;
30 
31     // hook idle time and exit time for required OLE cleanup
32     CWinThread* pThread; pThread = AfxGetThread();
33     ASSERT(pThread);
34     pThread->m_lpfnOleTermOrFreeLib = AfxOleTermOrFreeLib;
35 
36     // allocate and initialize default message filter
37     if (pThread->m_pMessageFilter == NULL)
38     {
39         pThread->m_pMessageFilter = new COleMessageFilter;
40         ASSERT(AfxOleGetMessageFilter() != NULL);
41         AfxOleGetMessageFilter()->Register();
42     }
43     return TRUE;
44 
45 InitFailed:
46     AfxOleTerm();
47     return FALSE;
48 }

COM中CoInitializeEx 与CoInitialize的区别

CoInitialize、CoInitializeEx都是windows的API，主要是告诉windows以什么方式为程序创建COM对象，原因是程序调用com库函数（除CoGetMalloc和内存分配函数）之前必须初始化com库。
    CoInitialize指明以单线程方式创建。
    CoInitializeEx可以指定COINIT_MULTITHREADED以多线程方式创建。
    创建单线程方式的COM服务器时不用考虑串行化问题，多线程COM服务器就要考虑。

CoInitialize并不装载com库，这个函数只是用来初始化当前线程使用什么样的套间。当使用这个函数以后，线程就和一个套间建立了对应关系。
线程的套间模式决定了该线程如何调用com对象，是否需要列集等

套间是com中用来解决并发调用冲突的很有效的办法
Before calling any COM functions, a thread needs to call CoInitialize to load the COM infrastructure (and to enter an apartment). Once a thread calls CoInitialize, the thread is free to call COM APIs.

CoInitializeEx provides the same functionality as CoInitialize and also provides a parameter to explicitly specify the thread's concurrency model. The current implementation of CoInitialize calls CoInitializeEx and specifies the concurrency model as single-thread apartment. Applications developed today should call CoInitializeEx rather than CoInitialize.

注：新的应用程序应该调用CoInitializeEx而不是CoInitialize，否则就会有必要在之后每个调用Com的线程中调用CoInitialize来初始化出每个线程自己的套间。