关于_variant_t变量

_variant_t类封闭了VARIANT数据类型,VARIANT是一个结构体类型,我们可以看一下它的定义

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用来存储存储变量的类型,联合体用来存储对用类型的值

对_variant_t变量初始化调用的是_variant_t的构造函数,我们一般习惯于用一个int型的变量对数字类的变量进行初始化,这对_variant_t变量是不允许的,原因很简单,_variant_t的构造函数中没用用整型对其初始化的构造函数,可先将整型转化成long对其进行初始化,赋值操作与构造函数类似.

_variant_t与CString之间的转化

CString--->_variant_t

CString   str;   

  _variant_t   str1=(LPCTSTR)str;

_variant_t--->CString

_variant_t vt;

   CString tempstr=(LPCSTR)_bstr_t(vt);