我第一次用VARIANT和CComVariant的时候全然不明确它是怎么回事，为它什么数据类型都能够存放。什么数据都能够被能够初始化？里面究竟是怎么实现的？感觉又奇妙又迷惑！我们在上一节中讲了union的使用方法之后你或许想到了大概是怎么回事了。没错。union能够帮我们实现这一个奇妙的功能。并且VARIANT定义中确实使用了union。假设你还不明确，那我们就自己来模拟实现一个相似于CComVariant功能的类把，废话不多说，看代码：
CVariate.h:
#ifndef CVARIATE_H
#define CVARIATE_H
#include <string.h>
//======================================================
const unsigned int DEFAULT_STRLEN = 256;
//=======================================================
//自定义一个类用于存放随意类型的数据，以模拟类型VARIANT的功能。
class CVariate
{
public:
CVariate() : type(INT), nVal(0){} //默认构造函数。初始化nVal，值为0
virtual ~CVariate(){}; //虚构函数，不做不论什么处理
CVariate(const CVariate& val) : type(val.type) //拷贝构造函数
{
CopyUnion(val);
}
CVariate &operator=(char c)
{
type = CHAR;
cVal = c;
return *this;
}
CVariate &operator=(short int sn)
{
type = SHORT;
snVal = sn;
return *this;
}
CVariate &operator=(int i)
{
type = INT;
nVal = i;
return *this;
}
CVariate &operator=(long l)
{
type = LONG;
lVal = l;
return *this;
}
CVariate &operator=(float f)
{
type = FLOAT;
fVal = f;
return *this;
}
CVariate &operator=(double d)
{
type = DOUBLE;
dVal = d;
return *this;
}
CVariate &operator=(const char* str);
void CopyUnion(const CVariate& val); //数据的拷贝
void DisplayValue();
private:
enum {CHAR, SHORT, INT, LONG, FLOAT, DOUBLE, STR}type; //为不同的数据类型定义一个枚举值
union //union，能够存入各种类型的数据
{
char cVal;
short snVal;
int nVal;
long lVal;
float fVal;
double dVal;
char strVal[DEFAULT_STRLEN];
};
};
#endif // CVARIATE_H
CVariate.cpp:Test.cpp:
int main() { CVariate cVal; cVal.DisplayValue(); cVal = 125; cVal.DisplayValue(); CVariate cVal2(cVal); cVal2.DisplayValue(); cVal2 = 188.598; cVal2.DisplayValue(); cVal2 = "Hello World."; cVal2.DisplayValue(); return 0; }结果例如以下：
VARIANT的结构能够參考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义例如以下：
struct tagVARIANT { union { struct __tagVARIANT { VARTYPE vt; WORD wReserved1; WORD wReserved2; WORD wReserved3; union { ULONGLONG ullVal; ---VT_UI8 LONGLONG llVal; ---VT_I8 LONG lVal; ---VT_I4 */ BYTE bVal; ---VT_UI1 */ SHORT iVal; ---VT_I2 */ FLOAT fltVal; ---VT_R4 */ DOUBLE dblVal; ---VT_R8 */ VARIANT_BOOL boolVal; ---VT_BOOL */ _VARIANT_BOOL bool; ---(obsolete) */ SCODE scode; ---VT_ERROR */ CY cyVal; ---VT_CY */ DATE date; ---VT_DATE */ BSTR bstrVal; ---VT_BSTR */ IUnknown * punkVal; ---VT_UNKNOWN */ IDispatch * pdispVal; ---VT_DISPATCH */ SAFEARRAY * parray; ---VT_ARRAY */ BYTE * pbVal; ---VT_BYREF|VT_UI1 */ SHORT * piVal; ---VT_BYREF|VT_I2 */ LONG * plVal; ---VT_BYREF|VT_I4 */ LONGLONG * pllVal; ---VT_BYREF|VT_I8 */ FLOAT * pfltVal; ---VT_BYREF|VT_R4 */ DOUBLE * pdblVal; ---VT_BYREF|VT_R8 */ VARIANT_BOOL *pboolVal; ---VT_BYREF|VT_BOOL */ _VARIANT_BOOL *pbool; ---(obsolete) */ SCODE * pscode; ---VT_BYREF|VT_ERROR */ CY * pcyVal; ---VT_BYREF|VT_CY */ DATE * pdate; ---VT_BYREF|VT_DATE */ BSTR * pbstrVal; ---VT_BYREF|VT_BSTR */ IUnknown ** ppunkValVARIANT的结构能够參考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义。struct tagVARIANT { union { struct __tagVARIANT { VARTYPE vt; WORD wReserved1; WORD wReserved2; WORD wReserved3; union { ULONGLONG ullVal; ---VT_UI8 LONGLONG llVal; ---VT_I8 LONG lVal; ---VT_I4 */ BYTE bVal; ---VT_UI1 */ SHORT iVal; ---VT_I2 */ FLOAT fltVal; ---VT_R4 */ DOUBLE dblVal; ---VT_R8 */ VARIANT_BOOL boolVal; ---VT_BOOL */ _VARIANT_BOOL bool; ---(obsolete) */ SCODE scode; ---VT_ERROR */ CY cyVal; ---VT_CY */ DATE date; ---VT_DATE */ BSTR bstrVal; ---VT_BSTR */ IUnknown * punkVal; ---VT_UNKNOWN */ IDispatch * pdispVal; ---VT_DISPATCH */ SAFEARRAY * parray; ---VT_ARRAY */ BYTE * pbVal; ---VT_BYREF|VT_UI1 */ SHORT * piVal; ---VT_BYREF|VT_I2 */ LONG * plVal; ---VT_BYREF|VT_I4 */ LONGLONG * pllVal; ---VT_BYREF|VT_I8 */ FLOAT * pfltVal; ---VT_BYREF|VT_R4 */ DOUBLE * pdblVal; ---VT_BYREF|VT_R8 */ VARIANT_BOOL *pboolVal; ---VT_BYREF|VT_BOOL */ _VARIANT_BOOL *pbool; ---(obsolete) */ SCODE * pscode; ---VT_BYREF|VT_ERROR */ CY * pcyVal; ---VT_BYREF|VT_CY */ DATE * pdate; ---VT_BYREF|VT_DATE */ BSTR * pbstrVal; ---VT_BYREF|VT_BSTR */ IUnknown ** ppunkVal; ---VT_BYREF|VT_UNKNOWN */ IDispatch ** ppdispVal; ---VT_BYREF|VT_DISPATCH */ SAFEARRAY ** pparray; ---VT_BYREF|VT_ARRAY */ VARIANT * pvarVal; ---VT_BYREF|VT_VARIANT */ PVOID byref; ---Generic ByRef */ CHAR cVal; ---VT_I1 */ USHORT uiVal; ---VT_UI2 */ ULONG ulVal; ---VT_UI4 */ INT intVal; ---VT_INT */ VARIANT的结构能够參考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义。 struct tagVARIANT { union { struct __tagVARIANT { VARTYPE vt; WORD wReserved1; WORD wReserved2; WORD wReserved3; union { ULONGLONG ullVal; ---VT_UI8 LONGLONG llVal; ---VT_I8 LONG lVal; ---VT_I4 */ BYTE bVal; ---VT_UI1 */ SHORT iVal; ---VT_I2 */ FLOAT fltVal; ---VT_R4 */ DOUBLE dblVal; ---VT_R8 */ VARIANT_BOOL boolVal; ---VT_BOOL */ _VARIANT_BOOL bool; ---(obsolete) */ SCODE scode; ---VT_ERROR */ CY cyVal; ---VT_CY */ DATE date; ---VT_DATE */ BSTR bstrVal; ---VT_BSTR */ IUnknown * punkVal; ---VT_UNKNOWN */ IDispatch * pdispVal; ---VT_DISPATCH */ SAFEARRAY * parray; ---VT_ARRAY */ BYTE * pbVal; ---VT_BYREF|VT_UI1 */ SHORT * piVal; ---VT_BYREF|VT_I2 */ LONG * plVal; ---VT_BYREF|VT_I4 */ LONGLONG * pllVal; ---VT_BYREF|VT_I8 */ FLOAT * pfltVal; ---VT_BYREF|VT_R4 */ DOUBLE * pdblVal; ---VT_BYREF|VT_R8 */ VARIANT_BOOL *pboolVal; ---VT_BYREF|VT_BOOL */ _VARIANT_BOOL *pbool; ---(obsolete) */ SCODE * pscode; ---VT_BYREF|VT_ERROR */ CY * pcyVal; ---VT_BYREF|VT_CY */ DATE * pdate; ---VT_BYREF|VT_DATE */ BSTR * pbstrVal; ---VT_VARIANT的结构能够參考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义。
struct tagVARIANT { union { struct __tagVARIANT { VARTYPE vt; WORD wReserved1; WORD wReserved2; WORD wReserved3; union { ULONGLONG ullVal; ---VT_UI8 LONGLONG llVal; ---VT_I8 LONG lVal; ---VT_I4 */ BYTE bVal; ---VT_UI1 */ SHORT iVal; ---VT_I2 */ FLOAT fltVal; ---VT_R4 */ DOUBLE dblVal; ---VT_R8 */ VARIANT_BOOL boolVal; ---VT_BOOL */ _VARIANT_BOOL bool; ---(obsolete) */ SCODE scode; ---VT_ERROR */ CY cyVal; ---VT_CY */ DATE date; ---VT_DATE */ BSTR bstrVal; ---VT_BSTR */ IUnknown * punkVal; ---VT_UNKNOWN */ IDispatch * pdispVal; ---VT_DISPATCH */ SAFEARRAY * parray; ---VT_ARRAY */ BYTE * pbVal; ---VT_BYREF|VT_UI1 */ SHORT * piVal; ---VT_BYREF|VT_I2 */ LONG * plVal; ---VT_BYREF|VT_I4 */ LONGLONG * pllVal; ---VT_BYREF|VT_I8 */ FLOAT * pfltVal; ---VT_BYREF|VT_R4 */ DOUBLE * pdblVal; ---VT_BYREF|VT_R8 */ VARIANT_BOOL *pboolVal; ---VT_BYREF|VT_BOOL */ _VARIANT_BOOL *pbool; ---(obsolete) */ SCODE * pscode; ---VT_BYREF|VT_ERROR */ CY * pcyVal; ---VT_BYREF|VT_CY */ DATE * pdate; ---VT_BYREF|VT_DATE */ BSTR * pbstrVal; ---VT_BYREF|VT_BSTR */ IUnknown ** ppunkVal; ---VT_BYREF|VT_UNKNOWN */ IDispatch ** ppdispVal; ---VT_BYREF|VT_DISPATCH */ SAFEARRAY ** pparray; ---VT_BYREF|VT_ARRAY */ VARIANT * pvarVal; ---VT_BYREF|VT_VARIANT */ PVOID byref; ---Generic ByRef */ CHAR cVal; ---VT_I1 */ USHORT uiVal; ---VT_UI2 */ ULONG ulVal; ---VT_UI4 */ INT intVal; ---VT_INT */ UINT uintVal; ---VT_UINT */ DECIMAL * pdecVal; ---VT_BYREF|VT_DECIMAL */ CHAR * pcVal; ---VT_BYREF|VT_I1 */ USHORT * puiVal; ---VT_BYREF|VT_UI2 */ ULONG * pulVal; ---VT_BYREF|VT_UI4 */ ULONGLONG * pullVal; --- VT_BYREF|VT_UI8 */ INT * pintVal; ---VT_BYREF|VT_INT */ UINT * puintVal; ---VT_BYREF|VT_UINT struct __tagBRECORD { PVOID pvRecord; IRecordInfo * pRecInfo; } __VARIANT_NAME_4; --- VT_RECORD } __VARIANT_NAME_3; } __VARIANT_NAME_2; DECIMAL decVal; } __VARIANT_NAME_1; };BYREF|VT_BSTR */ IUnknown ** ppunkVal; ---VT_BYREF|VT_UNKNOWN */ IDispatch ** ppdispVal; ---VT_BYREF|VT_DISPATCH */ SAFEARRAY ** pparray; ---VT_BYREF|VT_ARRAY */ VARIANT * pvarVal; ---VT_BYREF|VT_VARIANT */ PVOID byref; ---Generic ByRef */ CHAR cVal; ---VT_I1 */ USHORT uiVal; ---VT_UI2 */ ULONG ulVal; ---VT_UI4 */ INT intVal; ---VT_INT */ UINT uintVal; ---VT_UINT */ DECIMAL * pdecVal; ---VT_BYREF|VT_DECIMAL */ CHAR * pcVal; ---VT_BYREF|VT_I1 */ USHORT * puiVal; ---VT_BYREF|VT_UI2 */ ULONG * pulVal; ---VT_BYREF|VT_UI4 */ ULONGLONG * pullVal; --- VT_BYREF|VT_UI8 */ INT * pintVal; ---VT_BYREF|VT_INT */ UINT * puintVal; ---VT_BYREF|VT_UINT struct __tagBRECORD { PVOID pvRecord; IRecordInfo * pRecInfo; } __VARIANT_NAME_4; --- VT_RECORD } __VARIANT_NAME_3; } __VARIANT_NAME_2; DECIMAL decVal; } __VARIANT_NAME_1; }; UINT uintVal; ---VT_UINT */ DECIMAL * pdecVal; ---VT_BYREF|VT_DECIMAL */ CHAR * pcVal; ---VT_BYREF|VT_I1 */ USHORT * puiVal; ---VT_BYREF|VT_UI2 */ ULONG * pulVal; ---VT_BYREF|VT_UI4 */ ULONGLONG * pullVal; --- VT_BYREF|VT_UI8 */ INT * pintVal; ---VT_BYREF|VT_INT */ UINT * puintVal; ---VT_BYREF|VT_UINT struct __tagBRECORD { PVOID pvRecord; IRecordInfo * pRecInfo; } __VARIANT_NAME_4; --- VT_RECORD } __VARIANT_NAME_3; } __VARIANT_NAME_2; DECIMAL decVal; } __VARIANT_NAME_1; };; ---VT_BYREF|VT_UNKNOWN */ IDispatch ** ppdispVal; ---VT_BYREF|VT_DISPATCH */ SAFEARRAY ** pparray; ---VT_BYREF|VT_ARRAY */ VARIANT * pvarVal; ---VT_BYREF|VT_VARIANT */ PVOID byref; ---Generic ByRef */ CHAR cVal; ---VT_I1 */ USHORT uiVal; ---VT_UI2 */ ULONG ulVal; ---VT_UI4 */ INT intVal; ---VT_INT */ UINT uintVal; ---VT_UINT */ DECIMAL * pdecVal; ---VT_BYREF|VT_DECIMAL */ CHAR * pcVal; ---VT_BYREF|VT_I1 */ USHORT * puiVal; ---VT_BYREF|VT_UI2 */ ULONG * pulVal; ---VT_BYREF|VT_UI4 */ ULONGLONG * pullVal; --- VT_BYREF|VT_UI8 */ INT * pintVal; ---VT_BYREF|VT_INT */ UINT * puintVal; ---VT_BYREF|VT_UINT struct __tagBRECORD { PVOID pvRecord; IRecordInfo * pRecInfo; } __VARIANT_NAME_4; --- VT_RECORD } __VARIANT_NAME_3; } __VARIANT_NAME_2; DECIMAL decVal; } __VARIANT_NAME_1; };
相关说明參考文章：
http://blog.csdn.net/nppg2008/article/details/7885139
http://blog.csdn.net/china_chentao/article/details/4059698