在vc6中編譯一個MFC程序時其中有段代碼在創(chuàng)建數(shù)據(jù)庫連接報(bào)錯。
其源碼如下：
其中聲明
_ConectPtr m_pConn,在函數(shù)中
HRESULT hr = m_pConn.CreateInstance(__uuidof(Connection)); //_T("ADODB.Connection"));
if(FAILED(hr))
{
return false;
}
后來在檢查，發(fā)現(xiàn)需要調(diào)用AfxOleInit（）初始化組件即可解決。而我在文件中是加入了：：CoInitialize(),但是在實(shí)際運(yùn)行中該函數(shù)并沒有起到作用。
而在所宣言中，AfxOleInit包含了CoInitialize()。但是為啥AfxOleInit能解決數(shù)據(jù)連接的CreateInterface問題呢？觀察
AfxOleInit的源碼。
--------------------------------------------------------------------------------
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); //該句子做初始化ole
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;
}
可見,AfxOleInit()是封裝了OleInitialize()來初始化com組件；
查詢網(wǎng)上資料說：OleInitialize內(nèi)部調(diào)用了CoInitialize 。在OleInitialize比ConInitialize多了以下支持:
Clipboard
Drag and drop
Object linking and embedding (OLE)
In-place activation
如果你不需要這些附加功能,就用CoInitialize或CoInitializeEx。
但是在本人程序中調(diào)用CoInitialize不行而AfxOleInit可以，難道OleInitialize中創(chuàng)建的所附幾個在ADO com控件上用到，但是在寫了一個控制臺上的ado程序，調(diào)用CoInitialize卻是可行的。其中細(xì)節(jié)和玄妙打個標(biāo)記，容以后在研究吧，偷懶了，如果發(fā)現(xiàn)CoInitalize不行就用AfxOleInit吧。
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汗顏：因?yàn)樵赼pp的InitInstance中的粗心末尾加了一句：：UnCoInitialize（），造成coinitalize錯誤。實(shí)際上2個函數(shù)都可以初始化ado組件。mark。