求教Variant~~

Question

variant到底是个什么东西？
.vt属性可以改变存储的值？怎么存数组呢？
一个VARIANT对象可以存许多不同类型的数据吗？
为啥在VC6里，看不到给VARIANT赋值的结果呢..

Answer 1

你可以看出是模板类。支持类型有以下几种
Constructs a _variant_t object.
_variant_t( ) throw( );_variant_t(
   const VARIANT& varSrc 
);_variant_t(
   const VARIANT* pVarSrc 
);_variant_t(
   const _variant_t& var_t_Src 
);_variant_t(
   VARIANT& varSrc,
   bool fCopy 
);_variant_t(
   short sSrc,
   VARTYPE vtSrc = VT_I2 
);_variant_t(
   long lSrc,
   VARTYPE vtSrc = VT_I4 
);_variant_t(
   float fltSrc 
) throw( );_variant_t(
   double dblSrc,
   VARTYPE vtSrc = VT_R8 
);_variant_t(
   const CY& cySrc 
) throw( );_variant_t(
   const _bstr_t& bstrSrc 
);_variant_t(
   const wchar_t *wstrSrc 
);_variant_t(
   const char* strSrc 
);_variant_t(
   IDispatch* pDispSrc,
   bool fAddRef = true 
) throw( );_variant_t(
   bool bSrc 
) throw( );_variant_t(
   IUnknown* pIUknownSrc,
   bool fAddRef = true 
) throw( );_variant_t(
   const DECIMAL& decSrc 
) throw( );_variant_t(
   BYTE bSrc 
) throw( );variant_t(
   char cSrc
) throw();_variant_t(
   unsigned short usSrc
) throw();_variant_t(
   unsigned long ulSrc
) throw();_variant_t(
   int iSrc
) throw();_variant_t(
   unsigned int uiSrc
) throw();_variant_t(
   __int64 i8Src
) throw();_variant_t(
   unsigned __int64 ui8Src
) throw();

Answer 2

VARIANT 表示一个4字节长的整数
VARIANT v; v.vt=VT_I4; v.lVal=100; VARIANT 表示布尔值“真”
VARIANT v; v.vt=VT_BOOL; v.boolVal=VARIANT_TRUE;

Answer 3

VARIANT 其实就是一个结构体，你自己可以查下它的定义

Answer 4

typedef struct tagVARIANT VARIANT;struct tagVARIANT  { union  { struct __tagVARIANT {   VARTYPE vt;   // typedef unsigned short VARTYPE WORD wReserved1; WORD wReserved2; WORD wReserved3; union  { LONGLONG         llval;              // VT_I8.  LONG                     lVal;               // VT_I4. BYTE                     bVal;              // VT_UI1. SHORT                    iVal;               // VT_I2. FLOAT                    fltVal;             // VT_R4. DOUBLE                   dblVal;             // VT_R8. VARIANT_BOOL        boolVal;           // VT_BOOL. _VARIANT_BOOL      bool; SCODE                    scode;             // VT_ERROR. CY                       cyVal;             // VT_CY. DATE                     date;              // VT_DATE. BSTR                     bstrVal;           // VT_BSTR. IUnknown                * punkVal;         // VT_UNKNOWN. IDispatch                * pdispVal;        // VT_DISPATCH. SAFEARRAY               * parray;          // VT_ARRAY|*. BYTE                     * pbVal;           // VT_BYREF|VT_UI1. SHORT                    * piVal;           // VT_BYREF|VT_I2. LONG                     * plVal;           // VT_BYREF|VT_I4. LONGLONG              * pllVal;          // VT_BYREF|VT_I8. FLOAT                    * pfltVal;         // VT_BYREF|VT_R4. DOUBLE                   * pdblVal;         // VT_BYREF|VT_R8. VARIANT_BOOL        * pboolVal;        // VT_BYREF|VT_BOOL. _VARIANT_BOOL      * pbool; SCODE                     * pscode;          // VT_BYREF|VT_ERROR. CY                       * pcyVal;          // VT_BYREF|VT_CY. DATE                     * pdate;           // VT_BYREF|VT_DATE. BSTR                     * pbstrVal;        // VT_BYREF|VT_BSTR. IUnknown                ** ppunkVal;       // VT_BYREF|VT_UNKNOWN. IDispatch                ** ppdispVal;      // VT_BYREF|VT_DISPATCH. SAFEARRAY               ** pparray;        // VT_BYREF|VT_ARRAY. VARIANT                  * pvarVal;         // VT_BYREF|VT_VARIANT. PVOID                    * byref;           // Generic ByRef. CHAR                     cVal;              // VT_I1. USHORT                   uiVal;             // VT_UI2. ULONG                    ulVal;             // VT_UI4. ULONGLONG            ullVal;            // VT_UI8. INT                      intVal;            // VT_INT. UINT                     uintVal;           // VT_UINT. DECIMAL                 * pdecVal          // VT_BYREF|VT_DECIMAL. CHAR                      * pcVal;           // VT_BYREF|VT_I1. USHORT                  * puiVal;          // VT_BYREF|VT_UI2. ULONG                   * pulVal;          // VT_BYREF|VT_UI4. ULONGLONG           * pullVal;         // VT_BYREF|VT_UI8. INT                      * pintVal;         // VT_BYREF|VT_INT. UINT                     * puintVal;        // VT_BYREF|VT_UINT. struct __tagBRECORD { PVOID                   pvRecord; IRecordInfo             *pRecInfo; }    __VARIANT_NAME_4; }    __VARIANT_NAME_3; }    __VARIANT_NAME_2; DECIMAL decVal; }    __VARIANT_NAME_1;};
给VARIANT变量的赋值的时候，首先给vt成员赋值，指定类型，再对union中相同数据类型的变量赋值，VARIANT va;int a=2001;va.vt=VT_I4; //  指明整型数据va.lVal=a;     //  赋值