'CoInitializeEx' : undeclared identifier 錯誤

從MSDN中知道了要include objbase.h標頭檔

　#include ＜objbase.h＞

　void main()

　{

　　int hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED); 

　}

奇怪怎麼發生錯誤? Google了一下原來在 ColnitializeEx在objbase.h中的定義如下：

　#if (_WIN32_WINNT ＞＝ 0x0400 ) || defined(_WIN32_DCOM) // DCOM

　WINOLEAPI  CoInitializeEx(LPVOID pvReserved, DWORD dwCoInit);

　#endif // DCOM

這表示使用前必須先加入：#define   _WIN32_DCOM

重點是此行必須加在 #include ＜objbase.h＞ 之前，改成如下即可執行。

　#define   _WIN32_DCOM

　#include ＜objbase.h＞

　void main()

　{

　　int hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED); 

　}

IDL的型態 和C++、Visual Basic及JAVA 型態之間的轉換

IDL Type	C++	Visual Basic	Java
signed char	signed char		byte
unsigned char	unsigned char	Byte
wchar_t	wchar_t	Integer	char
signed short	short	Integer	short
unsigned short	unsigned short
signed int	int	Long	int
unsigned int	unsigned int
signed hyper	__int64		long
float	float	Single	float
double	double	Double	double
BSTR	BSTR	String	java.lang.String
boolean	bool	Boolean	boolean
VARIANT	VARIANT	Variant	com.ms.com.Variant
DATE	DATE	Date	double
CY	CY	Currency	long
SAFEARRAY	SAFEARRAY	[] (a standard Visual Basic array)	com.ms.com.SafeArray
IUnknown*	IUnknown*	IUnknown	com.ms.com.IUnknown
IDispatch*	IDispatch*	Object	java.lang.Objec

建立一個COM物件時，需要2個ID

1. 類別ID ( CLSID )：用來表示COM元件 ( DDL 或 EXE 檔案 ) 的ID

2. 介面ID ( IID )：用來表示要建立的物件的類別ID