关于_bstr_t和 _variant_t

先看看代码：

class _bstr_t {public:// Constructors//_bstr_t() throw();                    //Default constructor_bstr_t(const _bstr_t& s) throw();    // Copy constructor_bstr_t(const char* s) throw(_com_error);          // Construct a _bstr_t from a const char*_bstr_t(const wchar_t* s) throw(_com_error);       // Construct a _bstr_t from a const whar_t*_bstr_t(const _variant_t& var) throw(_com_error);  _bstr_t(BSTR bstr, bool fCopy) throw(_com_error);  // Construct a _bstr_t from a BSTR.  If fCopy is FALSE, give control of// data to the _bstr_t without making a new copy// Destructor//~_bstr_t() throw();// Assignment operators//_bstr_t& operator=(const _bstr_t& s) throw();                 // Default assign operator_bstr_t& operator=(const char* s) throw(_com_error);          // Assign a const char* to a _bstr_t _bstr_t& operator=(const wchar_t* s) throw(_com_error);       // Assign a const wchar_t* to a _bstr_t_bstr_t& operator=(const _variant_t& var) throw(_com_error);  // Operators//_bstr_t& operator+=(const _bstr_t& s) throw(_com_error);     // Concatenate a _bstr_t onto this _bstr_t_bstr_t operator+(const _bstr_t& s) const throw(_com_error);  // Return the concatenation of this _bstr_t with another _bstr_t// Friend operators//friend _bstr_t operator+(const char* s1, const _bstr_t& s2) throw(_com_error);   // Return the concatenation of a const char* with a _bstr_tfriend _bstr_t operator+(const wchar_t* s1, const _bstr_t& s2) throw(_com_error);  // Return the concatenation of a const char* with a _bstr_t// Extractors//operator const wchar_t*() const throw();        // Extract a const wchar_t*operator wchar_t*() const throw();              // Extract a wchar_t*operator const char*() const throw(_com_error); // Extract a const char_t*operator char*() const throw(_com_error);       // Extract a char_t*// Comparison operators//bool operator!() const throw();                       bool operator==(const _bstr_t& str) const throw();bool operator!=(const _bstr_t& str) const throw();bool operator<(const _bstr_t& str) const throw();bool operator>(const _bstr_t& str) const throw();bool operator<=(const _bstr_t& str) const throw();bool operator>=(const _bstr_t& str) const throw();// Low-level helper functions//BSTR copy() const throw(_com_error);         // Extract a copy of the wrapped BSTRunsigned int length() const throw();         // Return the length of the wrapped BSTR// Binary string assign//void Assign(BSTR s) throw(_com_error);        // Binary string assignprivate:// Referenced counted wrapper//class Data_t {public:// Constructors//Data_t(const char* s) throw(_com_error);Data_t(const wchar_t* s) throw(_com_error);Data_t(BSTR bstr, bool fCopy) throw(_com_error);Data_t(const _bstr_t& s1, const _bstr_t& s2) throw(_com_error);// Reference counting routines//unsigned long AddRef() throw();unsigned long Release() throw();// Extractors//operator const wchar_t*() const throw();operator const char*() const throw(_com_error);// Low-level helper functions//const wchar_t* GetWString() const throw();const char* GetString() const throw(_com_error);BSTR Copy() const throw(_com_error);void Assign(BSTR s) throw(_com_error);unsigned int Length() const throw();int Compare(const Data_t& str) const throw();private:wchar_t*m_wstr;mutable char*m_str;unsigned longm_RefCount;// Never allow default construction//Data_t() throw();// Never allow copy//Data_t(const Data_t& s) throw();// Prevent deletes from outside. Release() must be used.//~Data_t() throw();void _Free() throw();};private:// Reference counted representation//Data_t* m_Data;private:// Low-level utilities//void _AddRef() throw();void _Free() throw();int _Compare(const _bstr_t& str) const throw();};

 

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_I2operator long() const throw(_com_error);// Extracts a long from a VT_I4operator float() const throw(_com_error);// Extracts a float from a VT_R4operator double() const throw(_com_error);// Extracts a double from a VT_R8operator CY() const throw(_com_error);// Extracts a CY from a VT_CYoperator _bstr_t() const throw(_com_error);// Extracts a _bstr_t from a VT_BSTRoperator IDispatch*() const throw(_com_error);// Extracts a IDispatch* from a VT_DISPATCHoperator bool() const throw(_com_error);// Extracts a bool from a VT_BOOLoperator IUnknown*() const throw(_com_error);// Extracts a IUnknown* from a VT_UNKNOWNoperator DECIMAL() const throw(_com_error);// Extracts a DECIMAL from a VT_DECIMALoperator 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};

 

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_t和_bstr_t这两个类分别封装并管理VARIANT和BSTR这两种数据类型，VARIANT和BSTR这两种类型是COM中使用的数据类型。为了C++中的变量应用到ADO编程中，只能进行数据类型的转换。_variant_t和_bstr_t这两个类，就可以方便的把C++类型变量转换成COM中的变量了。

//_variant_t转WORD类型BOOL AfxVariantConvert(WORD& val, const _variant_t& vt){if (vt.vt == VT_UI2){val = (WORD)vt.uiVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转DWORD类型BOOL AfxVariantConvert(DWORD& val, const _variant_t& vt){if (vt.vt == VT_UI4 ){val = (DWORD)vt.ulVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转DWORD64类型BOOL AfxVariantConvert(DWORD64& val, const _variant_t& vt){if (vt.vt != VT_UI8 ){val = (DWORD64)vt.ullVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转CString类型BOOL AfxVariantConvert(CString& val, const _variant_t& vt){if (vt.vt == VT_BSTR){val = (LPCTSTR)vt.bstrVal;//val=(LPCTSTR)(_bstr_t)vt;return TRUE;}else{val = _T("");return FALSE;}}//_variant_t转BOOL类型BOOL AfxVariantConvert(BOOL& val, const _variant_t& vt){if (vt.vt == VT_BOOL){val = vt.boolVal;return TRUE;}else{val = FALSE;return FALSE;}}//_variant_t转CTime类型（精度变短，可能丢失数据）BOOL AfxVariantConvert(CTime& val, const _variant_t& vt){if (vt.vt == VT_DATE){val = vt.date;return TRUE;}else{val = NULL;return FALSE;}}//_variant_t转double类型BOOL AfxVariantConvert(DOUBLE& val, const _variant_t& vt){if (vt.vt == VT_R8){val = vt.dblVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转byte类型BOOL AfxVariantConvert(BYTE& val, const _variant_t& vt){if (vt.vt == VT_UI1 || vt.vt == VT_I1){val = vt.bVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转float类型BOOL AfxVariantConvert( FLOAT& val, const _variant_t& vt ){if (vt.vt == VT_R4){val = vt.fltVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转long类型BOOL AfxVariantConvert( long& val,const _variant_t& vt ){if (vt.vt == VT_I4){val = vt.lVal;return TRUE;}else{val = 0;return FALSE;}}//_variant_t转INT64类型BOOL AfxVariantConvert( INT64& val,const _variant_t& vt ){if (vt.vt == VT_I8){val = vt.llVal;return TRUE;}else{val = 0;return FALSE;}}