Extracting a double value from an ADODB recordset

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I'm having trouble extracting the value of a double-precision floating point number from an ADODB recordset. I want to assign the value to a local variable in my C++ routine. I've tried as follows.

C++

double dblTemp = rst->Fields->GetItem("DoubleValue")->Value;

and I've also tried:

C++

double dblTemp = rst->Fields->Item("DoubleValue")->Value;

But neither works. Does anyone know how to do this and can share a code example? I've tried looking at the article by Amit Dey entitled "ATL COM and ADO," but I need an example with a double type variable.

Please let me know.

Thanks,
Carl Olen

Posted 14-Sep-11 3:33am

CarlOlen

Updated 19-Sep-11 11:29am

Chris Maunder773.6K

v3

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Comments

Richard MacCutchan 14-Sep-11 10:00am

But it doesn't work
This is probably the most useless problem description ever invented. Please, explain what you expect to see returned and what you actually see. Are you sure all the pointers in your expression point to a valid record, etc.

3 solutions

Solution 1

Try Item instead.

C++

rst->Fields->Item["DoubleValue"]->Value

Posted 14-Sep-11 17:58pm

Prerak Patel

Solution 2

I post this code but i cannot test it, because i cant establish an ADODB connection on my laptop. Its a long time ago i wrote this. This code makes a snapshot of a recordset.

C++

RecordSetSnapshot::RecordSetSnapshot(ADODB::_RecordsetPtr* rset)
{
  long          count;
  unsigned int  ix,iy;
  long          colrow[2];

  _rows = 0;
  _cols = (*rset)->Fields->Count;

  try
  {

    _variant_t  fields = vtMissing;
    _variant_t  data   = (*rset)->GetRows(ADODB::adGetRowsRest,(long)ADODB::adBookmarkCurrent,fields);
    _variant_t  value;

    if( (VT_EMPTY!=data.vt) && (S_OK==::SafeArrayGetUBound(data.parray,2,&count)) )
    {
      _rows = 1 + count;

      for(ix=0;ix<_cols;ix++)
      {
        ADODB::Field*    field = 0;

        (*rset)->Fields->get_Item(_variant_t((long)ix),&field);
        // store the field name here: field->Name;

        field->Release();
      }

      for(ix=0;ix<_cols;ix++)
      {
        colrow[0] = ix;
        for(iy=0;iy<_rows;iy++)
        {
          colrow[1] = iy;
          if(S_OK==::SafeArrayGetElement(data.parray,colrow,&value))
          {
            // BSTR or something else. VT_R4 (is double)
            VariantChangeType(&value,&value,0,VT_BSTR);
            // store the value
            VariantClear(&value);
          }
        }
      }
    }

    VariantClear(&data);
    VariantClear(&fields);

  }
  catch(_com_error e)
  {
    TRACE(_S("Error: %s\r\n"),(TCHAR*)e.Description());
    Clear();
  }
  catch(...)
  {
    Clear();
  }

}

Hope this helps.
Regards.

Posted 19-Sep-11 10:08am

mbue

Updated 19-Sep-11 10:10am

v2

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CarlOlen · Accepted Answer · 2011-09-20T08:35:00

Here's one solution that worked and I'm continuing to develop with other ideas I've received. Thanks!

double dblTemp;
FieldsPtr fields;
FieldPtr field;
VARIANT D_Value;
VariantInit(&D_Value);
D_Value.vt = VT_R8;
VARIANT Index;
VariantInit(&Index);
Index.vt = VT_I4;
Index.lVal = 1; // index of the field with the double value to be retreived.

HRESULT hr=rst->get_Fields(&fields);
if(SUCCEEDED(hr)) {
hr=fields->get_Item(Index, &field);
}
if(SUCCEEDED(hr)) {
hr=field->get_Value(&D_Value);
}
dblTemp = D_Value.dblVal;