关于VARIANT和VT_NULL

Question

我在调试程序的过程中，有一个VARIANT类型变量varStr的值为VT_NULL，可是当我在程序中写if(varStr!=VT_NULL)时总是报错，错误信息是：
error C2678: binary '!=' : no operator defined which takes a left-hand operand of type 'struct  tagVARIANT' (or there is no acceptable conversion)
VT_NULL是VC系统定义的结构体struct tagVARIANT中的一个变量，
请问如何能够通过程序表达varStr！=VT_NULL这个意思。

Answer 1

if(varStr.vt!= VT_NULL)这样试试。

Answer 2

VARIANT仅仅是一个结构而已，而VT_NULL是枚举变量VARENUM中的一个成员，一个结构怎么能跟一个枚举形的变量进行比较呢。就是COleVariant类也没有重载操作符'!='

Answer 3

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.
   };
};Agree with xuxutj(紫雨)

Answer 4

Agree with xuxutj(紫雨)