VARIANT类型的用法

VARIANT的结构可以参考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义。
struct  tagVARIANT
    {
    union
        {
        struct  __tagVARIANT
            {
            VARTYPE vt;
            WORD wReserved1;
            WORD wReserved2;
            WORD wReserved3;
            union
                {
                LONG lVal;
                BYTE bVal;
                SHORT iVal;
                FLOAT fltVal;
                DOUBLE dblVal;
                VARIANT_BOOL boolVal;
                _VARIANT_BOOL bool;
                SCODE scode;
                CY cyVal;
                DATE date;
                BSTR bstrVal;
                IUnknown __RPC_FAR *punkVal;
                IDispatch __RPC_FAR *pdispVal;
                SAFEARRAY __RPC_FAR *parray;
                BYTE __RPC_FAR *pbVal;
                SHORT __RPC_FAR *piVal;
                LONG __RPC_FAR *plVal;
                FLOAT __RPC_FAR *pfltVal;
                DOUBLE __RPC_FAR *pdblVal;
                VARIANT_BOOL __RPC_FAR *pboolVal;
                _VARIANT_BOOL __RPC_FAR *pbool;
                SCODE __RPC_FAR *pscode;
                CY __RPC_FAR *pcyVal;
                DATE __RPC_FAR *pdate;
                BSTR __RPC_FAR *pbstrVal;
                IUnknown __RPC_FAR *__RPC_FAR *ppunkVal;
                IDispatch __RPC_FAR *__RPC_FAR *ppdispVal;
                SAFEARRAY __RPC_FAR *__RPC_FAR *pparray;
                VARIANT __RPC_FAR *pvarVal;
                PVOID byref;
                CHAR cVal;
                USHORT uiVal;
                ULONG ulVal;
                INT intVal;
                UINT uintVal;
                DECIMAL __RPC_FAR *pdecVal;
                CHAR __RPC_FAR *pcVal;
                USHORT __RPC_FAR *puiVal;
                ULONG __RPC_FAR *pulVal;
                INT __RPC_FAR *pintVal;
                UINT __RPC_FAR *puintVal;
                struct  __tagBRECORD
                    {
                    PVOID pvRecord;
                    IRecordInfo __RPC_FAR *pRecInfo;
                    } __VARIANT_NAME_4;
                } __VARIANT_NAME_3;
            } __VARIANT_NAME_2;
        DECIMAL decVal;
        } __VARIANT_NAME_1;
    };
　　对于VARIANT变量的赋值：首先给vt成员赋值，指明数据类型，再对联合结构中相同数据类型的变量赋值，举个例子：

VARIANT va;
int a=2001;
va.vt=VT_I4;///指明整型数据
va.lVal=a; ///赋值

　　对于不马上赋值的VARIANT，最好先用Void VariantInit（VARIANTARG FAR* pvarg）;进行初始化,其本质是将vt设置为VT_EMPTY,下表我们列举vt与常用数据的对应关系:

unsigned char 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
IUnknown FAR* punkVal; VT_UNKNOWN
IDispatch FAR* pdispVal; VT_DISPATCH
SAFEARRAY FAR* parray; VT_ARRAY|*
unsigned char 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; VT_BYREF

　　 _variant_t是VARIANT的封装类，其赋值可以使用强制类型转换，其构造函数会自动处理这些数据类型。

　　例如：

long l=222;
ing i=100;
_variant_t lVal（l）;
lVal = （long）i;

　　COleVariant的使用与_variant_t的方法基本一样，请参考如下例子：

COleVariant v3 = ＂字符串＂, v4 = （long）1999;
CString str =（BSTR）v3.pbstrVal;
long i = v4.lVal;

http://www.cnblogs.com/strinkbug/archive/2007/03/22/683473.html