转：MFC之COleVariant[通俗易懂]

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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

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

例子

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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

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1. class COleVariant : public tagVARIANT
2. {
3. COleVariant(LPCTSTR lpszSrc);
4. COleVariant(LPCTSTR lpszSrc, VARTYPE vtSrc); // used to set to ANSI string
5. COleVariant(CString& strSrc);
7. COleVariant(BYTE nSrc);
8. COleVariant(short nSrc, VARTYPE vtSrc = VT_I2);
9. COleVariant(long lSrc, VARTYPE vtSrc = VT_I4);
10. COleVariant(const COleCurrency& curSrc);
12. COleVariant(float fltSrc);
13. COleVariant(double dblSrc);
14. COleVariant(const COleDateTime& timeSrc);
15. ………………………………
16. const COleVariant& operator=(float fltSrc);
17. const COleVariant& operator=(double dblSrc);
18. const COleVariant& operator=(const COleDateTime& dateSrc);
20. const COleVariant& operator=(const CByteArray& arrSrc);
21. const COleVariant& operator=(const CLongBinary& lbSrc);
22. };
24. void Clear();
25. void ChangeType(VARTYPE vartype, LPVARIANT pSrc = NULL);
26. void Attach(VARIANT& varSrc);
27. VARIANT Detach();
28. void GetByteArrayFromVariantArray(CByteArray& bytes);
29. void SetString(LPCTSTR lpszSrc, VARTYPE vtSrc); // used to set ANSI string
30. operator LPVARIANT();
31. operator LPCVARIANT() const
32. /
33. struct tagVARIANT
34. { union
35. {
36. struct __tagVARIANT
37. {
38. VARTYPE vt;
39. …………………..
40. union
41. {
42. LONGLONG llVal;
43. LONG lVal;
44. BYTE bVal;
45. SHORT iVal;
46. FLOAT fltVal;
47. DOUBLE dblVal;
48. ………..
49. DATE date;
50. BSTR bstrVal;
51. IUnknown *punkVal;
52. IDispatch *pdispVal;
53. …………..
54. }
56. COleVariant::COleVariant(float fltSrc)
57. { vt = VT_R4; fltVal = fltSrc; }
58. _AFXDISP_INLINE COleVariant::COleVariant(CString& strSrc)
59. { vt = VT_EMPTY; *this = strSrc; }
61. const COleVariant& COleVariant::operator=(const CString& strSrc)
62. {
63. // Free up previous VARIANT
64. Clear();
66. vt = VT_BSTR;
67. bstrVal = strSrc.AllocSysString();
69. return *this;
70. }
72. typedef unsigned short VARTYPE;
74. /*
75. * VARENUM usage key,
76. *
77. * * [V] – may appear in a VARIANT
78. * * [T] – may appear in a TYPEDESC
79. * * [P] – may appear in an OLE property set
80. * * [S] – may appear in a Safe Array
81. *
82. *
83. * VT_EMPTY [V] [P] nothing
84. * VT_NULL [V] [P] SQL style Null
85. * VT_I2 [V][T][P][S] 2 byte signed int
86. * VT_I4 [V][T][P][S] 4 byte signed int
87. * VT_R4 [V][T][P][S] 4 byte real
88. * VT_R8 [V][T][P][S] 8 byte real
89. * VT_CY [V][T][P][S] currency
90. * VT_DATE [V][T][P][S] date
91. * VT_BSTR [V][T][P][S] OLE Automation string
92. * VT_DISPATCH [V][T] [S] IDispatch *
93. * VT_ERROR [V][T][P][S] SCODE
94. * VT_BOOL [V][T][P][S] True=-1, False=0
95. * VT_VARIANT [V][T][P][S] VARIANT *
96. * VT_UNKNOWN [V][T] [S] IUnknown *
97. * VT_DECIMAL [V][T] [S] 16 byte fixed point
98. …………………………………
100. enum VARENUM
101. { VT_EMPTY = 0,
102. VT_NULL = 1,
103. VT_I2 = 2,
104. VT_I4 = 3,
105. VT_R4 = 4,
106. VT_R8 = 5,
107. VT_CY = 6,
108. VT_DATE = 7,
109. VT_BSTR = 8,
110. …………………………………..
111. } ;