tagVARIANT、VARIANT、_variant

　　tagVARIANT是一个结构体struct：

C++ Code： tagVARIANT

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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;
    };

　　VARIANT是tagVARIANT的别名：

C++ Code：VARIANT

typedef /* [wire_marshal] */ struct tagVARIANT VARIANT;

　　_variant_t 是VARIANT的包装管理类：

　　A _variant_t object encapsulates the VARIANT data type.

　　The class manages resource allocation and deallocation and makes function calls to VariantInit and VariantClear as appropriate.

C++ Code： _variant_t类

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//////////////////////////////////////////////////////////////////////////////
//
// Wrapper class for VARIANT
//
//////////////////////////////////////////////////////////////////////////////

/*
* VARENUM usage key,
*
* * [V] - may appear in a VARIANT
* * [T] - may appear in a TYPEDESC
* * [P] - may appear in an OLE property set
* * [S] - may appear in a Safe Array
* * [C] - supported by class _variant_t
*
*
*  VT_EMPTY            [V]   [P]        nothing
*  VT_NULL             [V]   [P]        SQL style Null
*  VT_I2               [V][T][P][S][C]  2 byte signed int
*  VT_I4               [V][T][P][S][C]  4 byte signed int
*  VT_R4               [V][T][P][S][C]  4 byte real
*  VT_R8               [V][T][P][S][C]  8 byte real
*  VT_CY               [V][T][P][S][C]  currency
*  VT_DATE             [V][T][P][S][C]  date
*  VT_BSTR             [V][T][P][S][C]  OLE Automation string
*  VT_DISPATCH         [V][T][P][S][C]  IDispatch *
*  VT_ERROR            [V][T]   [S][C]  SCODE
*  VT_BOOL             [V][T][P][S][C]  True=-1, False=0
*  VT_VARIANT          [V][T][P][S]     VARIANT *
*  VT_UNKNOWN          [V][T]   [S][C]  IUnknown *
*  VT_DECIMAL          [V][T]   [S][C]  16 byte fixed point
*  VT_I1                  [T]           signed char
*  VT_UI1              [V][T][P][S][C]  unsigned char
*  VT_UI2                 [T][P]        unsigned short
*  VT_UI4                 [T][P]        unsigned short
*  VT_I8                  [T][P]        signed 64-bit int
*  VT_UI8                 [T][P]        unsigned 64-bit int
*  VT_INT                 [T]           signed machine int
*  VT_UINT                [T]           unsigned machine int
*  VT_VOID                [T]           C style void
*  VT_HRESULT             [T]           Standard return type
*  VT_PTR                 [T]           pointer type
*  VT_SAFEARRAY           [T]          (use VT_ARRAY in VARIANT)
*  VT_CARRAY              [T]           C style array
*  VT_USERDEFINED         [T]           user defined type
*  VT_LPSTR               [T][P]        null terminated string
*  VT_LPWSTR              [T][P]        wide null terminated string
*  VT_FILETIME               [P]        FILETIME
*  VT_BLOB                   [P]        Length prefixed bytes
*  VT_STREAM                 [P]        Name of the stream follows
*  VT_STORAGE                [P]        Name of the storage follows
*  VT_STREAMED_OBJECT        [P]        Stream contains an object
*  VT_STORED_OBJECT          [P]        Storage contains an object
*  VT_BLOB_OBJECT            [P]        Blob contains an object
*  VT_CF                     [P]        Clipboard format
*  VT_CLSID                  [P]        A Class ID
*  VT_VECTOR                 [P]        simple counted array
*  VT_ARRAY            [V]              SAFEARRAY*
*  VT_BYREF            [V]              void* for local use
*/

class _variant_t : public ::tagVARIANT {
public:
    // Constructors
    //
    _variant_t() throw();

_variant_t(const VARIANT& varSrc) throw(_com_error);
_variant_t(const VARIANT* pSrc) throw(_com_error);
_variant_t(const _variant_t& varSrc) throw(_com_error);

_variant_t(VARIANT& varSrc, bool fCopy) throw(_com_error); // Attach VARIANT if !fCopy

_variant_t(short sSrc, VARTYPE vtSrc = VT_I2) throw(_com_error);    // Creates a VT_I2, or a VT_BOOL
    _variant_t(long lSrc, VARTYPE vtSrc = VT_I4) throw(_com_error);     // Creates a VT_I4, a VT_ERROR, or a VT_BOOL
    _variant_t(float fltSrc) throw();                                   // Creates a VT_R4
    _variant_t(double dblSrc, VARTYPE vtSrc = VT_R8) throw(_com_error); // Creates a VT_R8, or a VT_DATE
    _variant_t(const CY& cySrc) throw();                                // Creates a VT_CY
    _variant_t(const _bstr_t& bstrSrc) throw(_com_error);               // Creates a VT_BSTR
    _variant_t(const wchar_t *pSrc) throw(_com_error);                  // Creates a VT_BSTR
    _variant_t(const char* pSrc) throw(_com_error);                     // Creates a VT_BSTR
    _variant_t(IDispatch* pSrc, bool fAddRef = true) throw();           // Creates a VT_DISPATCH
    _variant_t(bool bSrc) throw();                                      // Creates a VT_BOOL
    _variant_t(IUnknown* pSrc, bool fAddRef = true) throw();            // Creates a VT_UNKNOWN
    _variant_t(const DECIMAL& decSrc) throw();                          // Creates a VT_DECIMAL
    _variant_t(BYTE bSrc) throw();                                      // Creates a VT_UI1

// Destructor
//
~_variant_t() throw(_com_error);

// Extractors
    //
    operator short() const throw(_com_error);           // Extracts a short from a VT_I2
    operator long() const throw(_com_error);            // Extracts a long from a VT_I4
    operator float() const throw(_com_error);           // Extracts a float from a VT_R4
    operator double() const throw(_com_error);          // Extracts a double from a VT_R8
    operator CY() const throw(_com_error);              // Extracts a CY from a VT_CY
    operator _bstr_t() const throw(_com_error);         // Extracts a _bstr_t from a VT_BSTR
    operator IDispatch*() const throw(_com_error);      // Extracts a IDispatch* from a VT_DISPATCH
    operator bool() const throw(_com_error);            // Extracts a bool from a VT_BOOL
    operator IUnknown*() const throw(_com_error);       // Extracts a IUnknown* from a VT_UNKNOWN
    operator DECIMAL() const throw(_com_error);         // Extracts a DECIMAL from a VT_DECIMAL
    operator BYTE() const throw(_com_error);            // Extracts a BTYE (unsigned char) from a VT_UI1

    // Assignment operations
    //
    _variant_t& operator=(const VARIANT& varSrc) throw(_com_error);
    _variant_t& operator=(const VARIANT* pSrc) throw(_com_error);
    _variant_t& operator=(const _variant_t& varSrc) throw(_com_error);

_variant_t& operator=(short sSrc) throw(_com_error);                // Assign a VT_I2, or a VT_BOOL
    _variant_t& operator=(long lSrc) throw(_com_error);                 // Assign a VT_I4, a VT_ERROR or a VT_BOOL
    _variant_t& operator=(float fltSrc) throw(_com_error);              // Assign a VT_R4
    _variant_t& operator=(double dblSrc) throw(_com_error);             // Assign a VT_R8, or a VT_DATE
    _variant_t& operator=(const CY& cySrc) throw(_com_error);           // Assign a VT_CY
    _variant_t& operator=(const _bstr_t& bstrSrc) throw(_com_error);    // Assign a VT_BSTR
    _variant_t& operator=(const wchar_t* pSrc) throw(_com_error);       // Assign a VT_BSTR
    _variant_t& operator=(const char* pSrc) throw(_com_error);          // Assign a VT_BSTR
    _variant_t& operator=(IDispatch* pSrc) throw(_com_error);           // Assign a VT_DISPATCH
    _variant_t& operator=(bool bSrc) throw(_com_error);                 // Assign a VT_BOOL
    _variant_t& operator=(IUnknown* pSrc) throw(_com_error);            // Assign a VT_UNKNOWN
    _variant_t& operator=(const DECIMAL& decSrc) throw(_com_error);     // Assign a VT_DECIMAL
    _variant_t& operator=(BYTE bSrc) throw(_com_error);                 // Assign a VT_UI1

// Comparison operations
    //
    bool operator==(const VARIANT& varSrc) const throw(_com_error);
    bool operator==(const VARIANT* pSrc) const throw(_com_error);

bool operator!=(const VARIANT& varSrc) const throw(_com_error);
bool operator!=(const VARIANT* pSrc) const throw(_com_error);

// Low-level operations
//
void Clear() throw(_com_error);

void Attach(VARIANT& varSrc) throw(_com_error);
VARIANT Detach() throw(_com_error);

void ChangeType(VARTYPE vartype, const _variant_t* pSrc = NULL) throw(_com_error);

void SetString(const char* pSrc) throw(_com_error); // used to set ANSI string
};

　　COleVariant 也是对VARIANT的封装类：

C++ Code：COleVariant类

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class COleVariant : public tagVARIANT
{
// Constructors
public:
COleVariant();

COleVariant(const VARIANT& varSrc);
COleVariant(LPCVARIANT pSrc);
COleVariant(const COleVariant& varSrc);

COleVariant(LPCTSTR lpszSrc);
COleVariant(LPCTSTR lpszSrc, VARTYPE vtSrc); // used to set to ANSI string
COleVariant(CString& strSrc);

COleVariant(BYTE nSrc);
    COleVariant(short nSrc, VARTYPE vtSrc = VT_I2);
    COleVariant(long lSrc, VARTYPE vtSrc = VT_I4);
    COleVariant(const COleCurrency& curSrc);

COleVariant(float fltSrc);
COleVariant(double dblSrc);
COleVariant(const COleDateTime& timeSrc);

COleVariant(const CByteArray& arrSrc);
COleVariant(const CLongBinary& lbSrc);

COleVariant(LPCITEMIDLIST pidl);

// Operations
public:
    void Clear();
    void ChangeType(VARTYPE vartype, LPVARIANT pSrc = NULL);
    void Attach(VARIANT& varSrc);
    VARIANT Detach();

BOOL operator==(const VARIANT& varSrc) const;
BOOL operator==(LPCVARIANT pSrc) const;

const COleVariant& operator=(const VARIANT& varSrc);
const COleVariant& operator=(LPCVARIANT pSrc);
const COleVariant& operator=(const COleVariant& varSrc);

const COleVariant& operator=(const LPCTSTR lpszSrc);
const COleVariant& operator=(const CString& strSrc);

const COleVariant& operator=(BYTE nSrc);
    const COleVariant& operator=(short nSrc);
    const COleVariant& operator=(long lSrc);
    const COleVariant& operator=(const COleCurrency& curSrc);

const COleVariant& operator=(float fltSrc);
const COleVariant& operator=(double dblSrc);
const COleVariant& operator=(const COleDateTime& dateSrc);

const COleVariant& operator=(const CByteArray& arrSrc);
const COleVariant& operator=(const CLongBinary& lbSrc);

void SetString(LPCTSTR lpszSrc, VARTYPE vtSrc); // used to set ANSI string

operator LPVARIANT();
operator LPCVARIANT() const;

// Implementation
public:
~COleVariant();
void _ClearCompat();
};

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