_variant_t類封閉了VARIANT資料類型,VARIANT是一個結構體類型,我們可以看一下它的定義
typedef struct tagVARIANT {
VARTYPE vt;
unsigned short wReserved1;
unsigned short wReserved2;
unsigned short wReserved3;
union {
Byte bVal; // VT_UI1.
Short iVal; // VT_I2.
long lVal; // VT_I4.
float fltVal; // VT_R4.
double dblVal; // VT_R8.
VARIANT_BOOL boolVal; // VT_BOOL.
SCODE scode; // VT_ERROR.
CY cyVal; // VT_CY.
DATE date; // VT_DATE.
BSTR bstrVal; // VT_BSTR.
DECIMAL FAR* pdecVal // VT_BYREF|VT_DECIMAL.
IUnknown FAR* punkVal; // VT_UNKNOWN.
IDispatch FAR* pdispVal; // VT_DISPATCH.
SAFEARRAY FAR* parray; // VT_ARRAY|*.
Byte FAR* pbVal; // VT_BYREF|VT_UI1.
short FAR* piVal; // VT_BYREF|VT_I2.
long FAR* plVal; // VT_BYREF|VT_I4.
float FAR* pfltVal; // VT_BYREF|VT_R4.
double FAR* pdblVal; // VT_BYREF|VT_R8.
VARIANT_BOOL FAR* pboolVal; // VT_BYREF|VT_BOOL.
SCODE FAR* pscode; // VT_BYREF|VT_ERROR.
CY FAR* pcyVal; // VT_BYREF|VT_CY.
DATE FAR* pdate; // VT_BYREF|VT_DATE.
BSTR FAR* pbstrVal; // VT_BYREF|VT_BSTR.
IUnknown FAR* FAR* ppunkVal; // VT_BYREF|VT_UNKNOWN.
IDispatch FAR* FAR* ppdispVal; // VT_BYREF|VT_DISPATCH.
SAFEARRAY FAR* FAR* pparray; // VT_ARRAY|*.
VARIANT FAR* pvarVal; // VT_BYREF|VT_VARIANT.
void FAR* byref; // Generic ByRef.
char cVal; // VT_I1.
unsigned short uiVal; // VT_UI2.
unsigned long ulVal; // VT_UI4.
int intVal; // VT_INT.
unsigned int uintVal; // VT_UINT.
char FAR * pcVal; // VT_BYREF|VT_I1.
unsigned short FAR * puiVal; // VT_BYREF|VT_UI2.
unsigned long FAR * pulVal; // VT_BYREF|VT_UI4.
int FAR * pintVal; // VT_BYREF|VT_INT.
unsigned int FAR * puintVal; //VT_BYREF|VT_UINT.
};
};
vt用來存儲存儲變量的類型,聯合體用來存儲對用類型的值
對_variant_t變量初始化調用的是_variant_t的構造函數,我們一般習慣于用一個int型的變量對數字類的變量進行初始化,這對_variant_t變量是不允許的,原因很簡單,_variant_t的構造函數中沒用用整型對其初始化的構造函數,可先将整型轉化成long對其進行初始化,指派操作與構造函數類似.
_variant_t與CString之間的轉化
CString--->_variant_t
CString str;
_variant_t str1=(LPCTSTR)str;
_variant_t--->CString
_variant_t vt;
CString tempstr=(LPCSTR)_bstr_t(vt);