MFC之COleVariant

colevariant

COleVariant 本质上是一个枚举，用同一种类型来表达不同的子类型。如同boost中的variant。

例子

COleVariant var(3.6f);
float v = var.fltVal;
CString str("testCOleVariant");
COleVariant var2(str);
CString cpStr(var2.bstrVal);

例子

CString CMFCPropertyGridProperty::m_strFormatChar = _T("%c");
CString CMFCPropertyGridProperty::m_strFormatShort = _T("%d");
CString CMFCPropertyGridProperty::m_strFormatLong = _T("%ld");
CString CMFCPropertyGridProperty::m_strFormatUShort = _T("%u");
CString CMFCPropertyGridProperty::m_strFormatULong = _T("%u");
CString CMFCPropertyGridProperty::m_strFormatFloat = _T("%f");
CString CMFCPropertyGridProperty::m_strFormatDouble = _T("%lf");

CString CMFCPropertyGridProperty::FormatProperty()
{
	ASSERT_VALID(this);
	ASSERT_VALID(m_pWndList);

	COleVariant& var = m_varValue;

	CString strVal;

	.............

	switch (var.vt)
	{
	case VT_BSTR:
		strVal = var.bstrVal;
		break;

	case VT_I2:
		strVal.Format(m_strFormatShort, (short)var.iVal);
		break;

	case VT_I4:
	case VT_INT:
		strVal.Format(m_strFormatLong, (long)var.lVal);
		break;

	case VT_UI1:
		if ((BYTE)var.bVal != 0)
		{
			strVal.Format(m_strFormatChar, (TCHAR)(BYTE)var.bVal);
		}
		break;

	case VT_UI2:
		strVal.Format( m_strFormatUShort, var.uiVal);
		break;

	case VT_UINT:
	case VT_UI4:
		strVal.Format(m_strFormatULong, var.ulVal);
		break;

	case VT_R4:
		strVal.Format(m_strFormatFloat, (float)var.fltVal);
		break;

	case VT_R8:
		strVal.Format(m_strFormatDouble, (double)var.dblVal);
		break;

	case VT_BOOL:
		strVal = var.boolVal == VARIANT_TRUE ? m_pWndList->m_strTrue : m_pWndList->m_strFalse;
		break;

	default:
		// Unsupported type
		strVal = _T("*** error ***");
	}

	return strVal;
}

COleVariant框架内容

class COleVariant : public tagVARIANT
{
	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);
....................................
	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 Clear();
	void ChangeType(VARTYPE vartype, LPVARIANT pSrc = NULL);
	void Attach(VARIANT& varSrc);
	VARIANT Detach();
   void GetByteArrayFromVariantArray(CByteArray& bytes);
void SetString(LPCTSTR lpszSrc, VARTYPE vtSrc); // used to set ANSI string
	operator LPVARIANT();
	operator LPCVARIANT() const
/////////////////////////////////////////////////////////////////////////////////
struct tagVARIANT
    {    union 
        {
        struct __tagVARIANT
            {
	VARTYPE vt;
	.......................
            union 
                {
                LONGLONG llVal;
                LONG lVal;
                BYTE bVal;
                SHORT iVal;
                FLOAT fltVal;
                DOUBLE dblVal;
                ...........
                DATE date;
                BSTR bstrVal;
                IUnknown *punkVal;
	 IDispatch *pdispVal;
	..............
	}
	
COleVariant::COleVariant(float fltSrc)
		{ vt = VT_R4; fltVal = fltSrc; }
_AFXDISP_INLINE COleVariant::COleVariant(CString& strSrc)
		{ vt = VT_EMPTY; *this = strSrc; }
	
const COleVariant& COleVariant::operator=(const CString& strSrc)
{
	// Free up previous VARIANT
	Clear();

	vt = VT_BSTR;
	bstrVal = strSrc.AllocSysString();

	return *this;
	}
	
typedef unsigned short VARTYPE;

/*
 * 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
 *
 *
 *  VT_EMPTY            [V]   [P]     nothing
 *  VT_NULL             [V]   [P]     SQL style Null
 *  VT_I2               [V][T][P][S]  2 byte signed int
 *  VT_I4               [V][T][P][S]  4 byte signed int
 *  VT_R4               [V][T][P][S]  4 byte real
 *  VT_R8               [V][T][P][S]  8 byte real
 *  VT_CY               [V][T][P][S]  currency
 *  VT_DATE             [V][T][P][S]  date
 *  VT_BSTR             [V][T][P][S]  OLE Automation string
 *  VT_DISPATCH         [V][T]   [S]  IDispatch *
 *  VT_ERROR            [V][T][P][S]  SCODE
 *  VT_BOOL             [V][T][P][S]  True=-1, False=0
 *  VT_VARIANT          [V][T][P][S]  VARIANT *
 *  VT_UNKNOWN          [V][T]   [S]  IUnknown *
 *  VT_DECIMAL          [V][T]   [S]  16 byte fixed point
 .......................................

enum VARENUM
    {	VT_EMPTY	= 0,
	VT_NULL	= 1,
	VT_I2	= 2,
	VT_I4	= 3,
	VT_R4	= 4,
	VT_R8	= 5,
	VT_CY	= 6,
	VT_DATE	= 7,
	VT_BSTR	= 8,
	.........................................
	    } ;

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COleVariant与常用基本数据类型之间的转换

COleVariant是数据库常用到的数据类型。它可以是字串，整型值，日期等。知道怎样将它转换为CString很有用处。设有CString A; COleVar