Checking for no return data on query call

[entropy01]

Hey guys, long story short i'm querying an access database for a serial number by a given host name and it is failing to correctly identify when the query returns no match (when the host name is not in the database)

The following is an excerpt code block that executes the query and checks the returned data:

 // Prepare SQL query to grab serial number of host
//host variable is a _bstr_t that is given a value earlier

                _bstr_t query = "SELECT [SerialNumber] FROM [Computer Inventory] WHERE [ComputerName] = \"" + host + "\";";

                // Excecute the query
                DAO::RecordsetPtr pRS = NULL;
                pRS = pDbPtr->OpenRecordset(query, _variant_t(DAO::dbOpenDynaset));

                //create record set, check for bad set
                if (pRS && 0 < pRS->RecordCount)
                {
                    DAO::FieldsPtr pFields = NULL;
                    pFields = pRS->GetFields();
                    if (pFields && pFields->Count == 0)
                    {
                        cout<<DAM<<": Error: Number of fields in the result set is 0."<<endl;
						
                    }
                    // get actual data
                                        //check for VARIANT = VT_NULL and VARIANT = VT_EMPTY
					if ((pFields->GetItem(0)->GetValue().vt != 1) && (pFields->GetItem(0)->GetValue().vt != 0))
						serial = (_bstr_t)(pFields->GetItem(0)->GetValue());
					else{
						cout << "\nComputer has no record in database!";
						return "99/99/9999";//return no date identifier (ignore)
					}
				}

I checked for VT_NULL and VT_EMPTY, is their another value the VARIANT could be if the query finds no matches in the database?

[Pocoya]

if there is no data returned, it might be lost after casting

[entropy01]

Thanks it was a good though but I found the mistake...

This line "if (pRS && 0 < pRS->RecordCount)"

actually is the first check that concludes there was no data returned, and since there was no accompanying else for that if, there was no action being taken against no results!

The second check for no data:
if ((pFields->GetItem(0)->GetValue().vt != 1) && (pFields->GetItem(0)->GetValue().vt != 0))

Never got evaluated as essentially that case was already checked.

Thanks guys!

[VictorN]

I guess you have to do

pRS->MoveLast();

before getting pRS->RecordCount.