使用ADO操作数据库时一个好用的VARIANT类！

inline CString VTOCSTR(VARIANT *v)
{
if(v->vt==VT_BSTR)
{
CString str((LPCWSTR)v->bstrVal);
return str;
}
else
{
return CString("");
}
}

#define VTOLONG(v)((v).vt==VT_I4 ? (LONG)(v).lVal:0L)
#define VTODATE(v)((v).vt==VT_DATE ? (CTime)(v).iVal:0L)

class CVar : public VARIANT
{
public:
CVar()
{
VariantInit(this);
}
CVar(VARTYPE vt, SCODE scode = 0)
{
VariantInit(this);
this->vt = vt;
this->scode = scode;
}
CVar(VARIANT var)
{
*this = var;
}
~CVar()
{
VariantClear(this);
}

// ASSIGNMENT OPS.
CVar & operator=(PCWSTR pcwstr)
{
VariantClear(this);
if (NULL == (this->bstrVal = SysAllocStringLen(pcwstr, wcslen(pcwstr))))
throw E_OUTOFMEMORY;
this->vt = VT_BSTR;
return *this;
}
CVar & operator=(VARIANT var)
{
HRESULT hr;

VariantClear(this);
if (FAILED(hr = VariantCopy(this, &var)))
throw hr;
return *this;
}

.
operator STR() const
{
if(VT_BSTR == this->vt)
return this->bstrVal;
else
return NULL;
}

operator LONG() const
{
if (VT_I4 == this->vt)
return this->lVal;
else
return NULL;
}
operator DATE() const
{
if (VT_DATE == this->vt)
return this->date;
else
return NULL;
}
operator CY() const
{
COleCurrency cyNULL;
cyNULL.SetCurrency(0,0);
if (VT_CY == this->vt)
return this->cyVal;
else
return cyNULL;
}
HRESULT Clear()
{
return VariantClear(this);
}
};

这是我在MSDN中整理并增强的一个类，希望对进行ADO操作数据库的伙计们有所帮助！