_variant_t与其他数据类型的转换.doc

_variant_t与其他数据类型的转换 我们先看看COM所支持的一些类型的基本类：（微软提供，在comdef.h中定义）在COM中使用的标准类Class如下所示：_bstr_t：对BSTR类型进行打包，并提供有用的操作和方法；_com_error：定义抛出的error对象；_com_ptr_t：封装COM接口指针_variant_t：对VARIANT类型进行打包，并提供有用的操作和方法；一、_variant_t类的简单介绍：_variant_t对象封装了VARIANT数据类型。The class manages resource allocation and deallocation and makes function calls to VariantInit and VariantClear as appropriate.(1) _variant类提供的方法：1 构造函数_variant_t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 的构造函数中没有用整型( Int )对其初始化的构造函数可先将整型转化成long，然后再对其进行初始化2 Attach()Attaches a VARIANT object into the _variant_t object.3 Clear()Clears the encapsulated VARIANT object.4 ChangeTypeChanges the type of the _variant_t object to the indicated VARTYPE.5 DetachDetaches the encapsulated VARIANT object from this _variant_t object.6SetString将一个string赋值给_variant_t对象；7 Operators赋值操作，给现有的_variant_t对象赋一个新值；8 operator =, !=对比两个 _variant_t 对象是否相等；9 ExtractorsExtract data from the encapsulated VARIANT object.(2) _variant_t的定义：_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cpp view plaincopyprint?typedefstructtagVARIANTVARTYPEvt;/存储数据类型unsignedshortwReserved1;unsignedshortwReserved2;unsignedshortwReserved3;unionBytebVal;/VT_UI1.ShortiVal;/VT_I2.longlVal;/VT_I4.floatfltVal;/VT_R4.doubledblVal;/VT_R8.VARIANT_BOOLboolVal;/VT_BOOL.SCODEscode;/VT_ERROR.CYcyVal;/VT_CY.DATEdate;/VT_DATE.BSTRbstrVal;/VT_BSTR.DECIMALFAR*pdecVal/VT_BYREF|VT_DECIMAL.IUnknownFAR*punkVal;/VT_UNKNOWN.IDispatchFAR*pdispVal;/VT_DISPATCH.SAFEARRAYFAR*parray;/VT_ARRAY|*.ByteFAR*pbVal;/VT_BYREF|VT_UI1.shortFAR*piVal;/VT_BYREF|VT_I2.longFAR*plVal;/VT_BYREF|VT_I4.floatFAR*pfltVal;/VT_BYREF|VT_R4.doubleFAR*pdblVal;/VT_BYREF|VT_R8.VARIANT_BOOLFAR*pboolVal;/VT_BYREF|VT_BOOL.SCODEFAR*pscode;/VT_BYREF|VT_ERROR.CYFAR*pcyVal;/VT_BYREF|VT_CY.DATEFAR*pdate;/VT_BYREF|VT_DATE.BSTRFAR*pbstrVal;/VT_BYREF|VT_BSTR.IUnknownFAR*FAR*ppunkVal;/VT_BYREF|VT_UNKNOWN.IDispatchFAR*FAR*ppdispVal;/VT_BYREF|VT_DISPATCH.SAFEARRAYFAR*FAR*pparray;/VT_ARRAY|*.VARIANTFAR*pvarVal;/VT_BYREF|VT_VARIANT.voidFAR*byref;/GenericByRef.charcVal;/VT_I1.unsignedshortuiVal;/VT_UI2.unsignedlongulVal;/VT_UI4.intintVal;/VT_INT.unsignedintuintVal;/VT_UINT.charFAR*pcVal;/VT_BYREF|VT_I1.unsignedshortFAR*puiVal;/VT_BYREF|VT_UI2.unsignedlongFAR*pulVal;/VT_BYREF|VT_UI4.intFAR*pintVal;/VT_BYREF|VT_INT.unsignedintFAR*puintVal;/VT_BYREF|VT_UINT.;cpp view plain copy print?typedefstructtagVARIANTVARTYPEvt;/存储数据类型 unsignedshortwReserved1;unsignedshortwReserved2;unsignedshortwReserved3;unionBytebVal;/VT_UI1. ShortiVal;/VT_I2. longlVal;/VT_I4. floatfltVal;/VT_R4. doubledblVal;/VT_R8. VARIANT_BOOLboolVal;/VT_BOOL. SCODEscode;/VT_ERROR. CYcyVal;/VT_CY. DATEdate;/VT_DATE. BSTRbstrVal;/VT_BSTR. DECIMALFAR*pdecVal/VT_BYREF|VT_DECIMAL. IUnknownFAR*punkVal;/VT_UNKNOWN. IDispatchFAR*pdispVal;/VT_DISPATCH. SAFEARRAYFAR*parray;/VT_ARRAY|*. ByteFAR*pbVal;/VT_BYREF|VT_UI1. shortFAR*piVal;/VT_BYREF|VT_I2. longFAR*plVal;/VT_BYREF|VT_I4. floatFAR*pfltVal;/VT_BYREF|VT_R4. doubleFAR*pdblVal;/VT_BYREF|VT_R8. VARIANT_BOOLFAR*pboolVal;/VT_BYREF|VT_BOOL. SCODEFAR*pscode;/VT_BYREF|VT_ERROR. CYFAR*pcyVal;/VT_BYREF|VT_CY. DATEFAR*pdate;/VT_BYREF|VT_DATE. BSTRFAR*pbstrVal;/VT_BYREF|VT_BSTR. IUnknownFAR*FAR*ppunkVal;/VT_BYREF|VT_UNKNOWN. IDispatchFAR*FAR*ppdispVal;/VT_BYREF|VT_DISPATCH. SAFEARRAYFAR*FAR*pparray;/VT_ARRAY|*. VARIANTFAR*pvarVal;/VT_BYREF|VT_VARIANT. voidFAR*byref;/GenericByRef. charcVal;/VT_I1. unsignedshortuiVal;/VT_UI2. unsignedlongulVal;/VT_UI4. intintVal;/VT_INT. unsignedintuintVal;/VT_UINT. charFAR*pcVal;/VT_BYREF|VT_I1. unsignedshortFAR*puiVal;/VT_BYREF|VT_UI2. unsignedlongFAR*pulVal;/VT_BYREF|VT_UI4. intFAR*pintVal;/VT_BYREF|VT_INT. unsignedintFAR*puintVal;/VT_BYREF|VT_UINT. ;typedef struct tagVARIANT VARTYPE vt;/存储数据类型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.;注意：vt用来存储内部变量（联合体中保存的变量）的类型，联合体用来存储对应类型的值二、数据类型转换_bstr_t类可以作为_variant_t类与基本数据类型转换的中介(1) _variant_t与CString之间的转化1 CString转换为_variant_t：cpp view plaincopyprint?CStringstr;_variant_tstr1=(LPCTSTR)str;cpp view plain copy print?CStringstr;_variant_tstr1=(LPCTSTR)str;CString str;_variant_t str1=(LPCTSTR)str; 使用_variant_t的成员函数SetString来对_variant_t的对象赋值会更好；2 _variant_t转换为CString：cpp view plaincopyprint?_variant_tvt;CStringtempstr=(LPCSTR)_bstr_t(vt);/_bstr_t的构造函数有对_variant_t类型的处理cpp view plain copy print?_variant_tvt;CStringtempstr=(LPCSTR)_bstr_t(vt);/_bstr_t的构造函数有对_variant_t类型的处理_variant_t vt;CString tempstr=(LPCSTR)_bstr_t(vt); /_bstr_t的构造函数有对_variant_t类型的处理(2) _variant_t与char *之间的转换1 char * 转换为_variant_t方法与CString转换为_variant_t的方法类似：cpp view plaincopyprint?char*cValue;_variant_tvValue=(LPSTR)cValue;cpp view plain copy print?char*cValue;_variant_tvValue=(LPSTR)cValue;char * cValue;_variant_t vValue=(LPSTR)cValue;2 _variant_t转换为char *： 错误方法：cpp view plaincopyprint?_variant_tvValue;char*value=(LPSTR)(LPCSTR)_bstr_t(vValue)cpp view plain copy print?_variant_tvValue;char*value=(LPSTR)(LPCSTR)_bstr_t(vValue)_variant_t vValue;char * value=(LPSTR)(LPCSTR)_bstr_t(vValue)value指向一堆乱码.原因：不能用char *直接指向(LPSTR)(LPCSTR)_bstr_t( _variant_t )，因为这样转换之后实际上是一个string，而非一个char *正确方法：进行转换时，只能用strcpy()，将LPSTR指向的字符复制到char * 所指向的内存中；如下例：cpp view plaincopyprint?_variant_tvValue;charcValue16=0;strcpy(cValue,(LPCSTR)_bstr_t(vValue);cpp view plain copy print?_variant_tvValue;charcValue16=0;strcpy(cValue,(LPCSTR)_bstr_t(vValue);_variant_t vValue;char cValue1