标签：size   ber   ofo   object c   ongl   false   ring   rom   patch   

VARIANT and VARIANTARG

Use VARIANTARG to describe arguments passed within DISPPARAMS, and VARIANT to specify variant data that cannot be passed by reference. When a variant refers to another variant by using the VT_VARIANT | VT_BYREF vartype, the variant being referred to cannot also be of type VT_VARIANT | VT_BYREF. VARIANTs can be passed by value, even if VARIANTARGs cannot. The following definition of VARIANT is described in OAIDL.H automation header file:

typedef struct FARSTRUCT tagVARIANT VARIANT;
typedef struct FARSTRUCT tagVARIANT VARIANTARG;

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.
   };
};
 

To simplify extracting values from VARIANTARGs, Automation provides a set of functions for manipulating this type. Use of these functions is strongly recommended to ensure that applications apply consistent coercion rules.

The vt value governs the interpretation of the union as follows:

COM技术中的VARIANT and VARIANTARG

标签：size   ber   ofo   object c   ongl   false   ring   rom   patch   

原文地址：https://www.cnblogs.com/johnyang/p/12617881.html