转：MFC之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,
    .........................................
        } ;