OLEDB接口读取各数据类型的转换方式(代码节录)

DBSTATUS dbStatus;
DBTYPE dbType;
CString str;
double dValue; long lValue;

// pAccessor 是一个指向CDynamicAccessor对象的指针
// nCol是读取的列下标
pAccessor->GetStatus(nCol, &dbStatus);

if(dbStatus != DBSTATUS_S_ISNULL && pAccessor->GetColumnType(nCol, &dbType))
{
switch (dbType)
{
case DBTYPE_VARIANT:
vt = COleVariant((LPCVARIANT)pAccessor->GetValue(nCol));
break;
case DBTYPE_STR:
str = (LPCSTR)pAccessor->GetValue(nCol);
break;
case DBTYPE_WSTR:
case DBTYPE_BSTR:
str = (LPCWSTR)pAccessor->GetValue(nCol);
break;
case DBTYPE_I1:
case DBTYPE_UI1:
lValue = (long)(*((BYTE*)pAccessor->GetValue(nCol)));
break;
case DBTYPE_I2:
case DBTYPE_UI2:
lValue = (long)(*((short*)pAccessor->GetValue(nCol)));
break;
case DBTYPE_I4:
case DBTYPE_UI4:
lValue = (long)(*((long*)pAccessor->GetValue(nCol)));
break;
case DBTYPE_R4:
dValue = (double)(*((float*)pAccessor->GetValue(nCol)));
break;
case DBTYPE_R8:
dValue = *((double*)pAccessor->GetValue(nCol));
break;
case DBTYPE_NUMERIC:
{
DB_NUMERIC num;
if(pAccessor->GetValue(nCol, &num))
{
dValue = (double)*((__int64*)num.val);
while(num.scale-- > 0)
dValue /= 10;
if(num.sign == 0)
dValue = -dValue;
}
}
break;
case DBTYPE_VARNUMERIC:
{
// MSDN中有这部分的代码，不过有错误，这儿做了修正
dValue = 0;
unsigned long nColumn = nCol;
DB_VARNUMERIC* pnum;
pAccessor->TranslateColumnNo(nColumn);
pnum = (DB_VARNUMERIC*)pAccessor->_GetDataPtr(nColumn);

ULONG uLength = 0;
pAccessor->GetLength(nCol, &uLength);

int prec = ( int )pnum->precision;
int scale = ( int )pnum->scale;
int sign = ( int ) ( pnum->sign > 0 ) ? 1 : -1;

BYTE hi, lo;
double multiplier = 1;
double adjust = 1;

uLength -= (sizeof(DBTYPE_VARNUMERIC) - 1);
for( ULONG i = 0, j = 0 ; i < uLength ; i++, j+=2 )
{
hi = lo = pnum->val[ i ];
lo <<= 4;
lo >>= 4;
dValue += ( ( ( ULONG ) lo ) * multiplier );
multiplier *= 16;
hi >>= 4;
dValue += ( ( ( ULONG ) hi ) * multiplier );
multiplier *= 16;
}
adjust *= pow(10, scale) * sign;
dValue /= adjust;
}
break;
case DBTYPE_DBDATE:
{
DBDATE dbDate;
if (pAccessor->GetValue(nCol, &dbDate))
{
CTime tm(dbDate.year, dbDate.month, dbDate.day, 0, 0, 0);
}
}
break;
case DBTYPE_DBTIMESTAMP:
{
DBTIMESTAMP dbTimeStamp;

if(pAccessor->GetValue(nCol, &dbTimeStamp))
{
CTime tm(dbTimeStamp.year, dbTimeStamp.month, dbTimeStamp.day,
dbTimeStamp.hour, dbTimeStamp.minute, dbTimeStamp.second);
lValue = tm.GetTime();
}
}
break;
case DBTYPE_DATE:
{
COleDateTime dt(*((DATE*)pAccessor->GetValue(nCol)));
lValue = dt.GetYear() * 10000 + dt.GetMonth() * 10000 + dt.GetDay();
}
break;
case DBTYPE_DBTIME:
{
DBTIME dbTime;
if(pAccessor->GetValue(nCol, &dbTime))
{
dt.SetTime(dbTime.hour, dbTime.minute, dbTime.second);
vt = COleVariant(dt);
}
}
break;
case DBTYPE_CY:
{
COleCurrency cy(*((CURRENCY*)pAccessor->GetValue(nCol)));
vt = COleVariant(cy);
}
break;
case DBTYPE_IUNKNOWN:
{
ISequentialStream* pStream = *(ISequentialStream**)pAccessor->GetValue(nCol);
if (pStream != NULL )
{
CString str;
unsigned long lRead = 0;
unsigned long lReadThis = 0;
CByteArray ayBytes;
BYTE szBuffer[4096];
BYTE* pByte = NULL;
do
{

pStream->Read(szBuffer, 4096, &lReadThis);
if (lReadThis > 0)
{
ayBytes.SetSize(lRead + lReadThis);
pByte = ayBytes.GetData();
memcpy(pByte + lRead, szBuffer, lReadThis);
lRead += lReadThis;
}
} while (lReadThis == 4096);
ayBytes.SetSize(lRead);
vt = ayBytes;

}
}
break;
case DBTYPE_NULL:
case DBTYPE_EMPTY:
default:
break;
}
}