From: http://blog.csdn.net/zhoubl668/archive/2009/04/30/4139933.aspx
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()。
CoInitialize和CoUninitialize必须成对使用，后者不必。
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）。
////////////////////////////////////////
//以下是AfxOleInit的源码
--------------------------------------------------------------------------------
BOOL AFXAPI AfxOleInit()
{
_AFX_THREAD_STATE* pState = AfxGetThreadState();
ASSERT(!pState->m_bNeedTerm); // calling it twice?
// Special case DLL context to assume that the calling app initializes OLE.
// For DLLs where this is not the case, those DLLs will need to initialize
// OLE for themselves via OleInitialize. This is done since MFC cannot provide
// automatic uninitialize for DLLs because it is not valid to shutdown OLE
// during a DLL_PROCESS_DETACH.
if (afxContextIsDLL)
{
pState->m_bNeedTerm = -1; // -1 is a special flag
return TRUE;
}
// first, initialize OLE
SCODE sc = ::OleInitialize(NULL);
if (FAILED(sc))
{
// warn about non-NULL success codes
TRACE1("Warning: OleInitialize returned scode = %s.\n",
AfxGetFullScodeString(sc));
goto InitFailed;
}
// termination required when OleInitialize does not fail
pState->m_bNeedTerm = TRUE;
// hook idle time and exit time for required OLE cleanup
CWinThread* pThread; pThread = AfxGetThread();
pThread->m_lpfnOleTermOrFreeLib = AfxOleTermOrFreeLib;
// allocate and initialize default message filter
if (pThread->m_pMessageFilter == NULL)
{
pThread->m_pMessageFilter = new COleMessageFilter;
ASSERT(AfxOleGetMessageFilter() != NULL);
AfxOleGetMessageFilter()->Register();
}
return TRUE;
InitFailed:
AfxOleTerm();
return FALSE;
}
可见,AfxOleInit()主要是封装了OleInitialize(),而OleInitialize内部调用了ConInitialize
OleInitialize比ConInitialize多了以下支持:
Clipboard
Drag and drop
Object linking and embedding (OLE)
In-place activation
如果你不需要这些附加功能,就用CoInitialize或CoInitializeEx.
///////////////////////////////////////////////////////////////////////////////////////////
多线程问题的
AfxOleInit实际上调用了OleInitialize，虽然它在内部也调用了CoInitializeEx，但它只能处理单线程，这是AfxOleInit和CoInitialize 主要区别：
OleInitialize calls CoInitializeEx internally to initialize the COM library on the current apartment. Because OLE operations are not thread-safe, OleInitialize specifies the concurrency model as single-thread apartment.
Once the concurrency model for an apartment is set, it cannot be changed. A call to OleInitialize on an apartment that was previously initialized as multithreaded will fail and return RPC_E_CHANGED_MODE.
所以，你最初调用AfxOleInit()失败，就是因为你的程序在多线程的状态
