GetRows Method Example (VC++)

This example uses the GetRows method to retrieve a specified number of rows from a Recordset and to fill an array with the resulting data. The GetRows method will return less than the desired number of rows in two cases: either if EOF has been reached, or if GetRows tried to retrieve a record that was deleted by another user. The function returns False only if the second case occurs. The GetRowsOK function is required for this procedure to run.

// BeginGetRowsCpp
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" \
    no_namespace rename("EOF", "EndOfFile")

#include <stdio.h>
#include <ole2.h>
#include <conio.h>

// Function Declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void GetRowsX(void);
bool GetRowsOK(_RecordsetPtr pRstTemp,int intNumber,
        _variant_t& avarData);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);

void main()
{
    if(FAILED(::CoInitialize(NULL)))
        return;

     GetRowsX();

    ::CoUninitialize();
}

///////////////////////////////////////////////////////////
//                                                       //
//      GetRowsX Function                                //
//                                                       //
///////////////////////////////////////////////////////////

void GetRowsX(void)
{
    HRESULT hr = S_OK;

    // Define string variables.
    _bstr_t strCnn("Provider='sqloledb';Data Source='MySqlServer';"
            "Initial Catalog='pubs';Integrated Security='SSPI';");

    // Define ADO object pointers.
    // Initialize pointers on define.
    // These are in the ADODB::  namespace.
    _RecordsetPtr pRstEmployees = NULL;
    
    try 
    {
        // Open recordset with names and hire dates from employee table.
        TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset)));

        pRstEmployees->Open("SELECT fName, lName, hire_date "
            "FROM Employee ORDER BY lName",strCnn, 
            adOpenStatic, adLockReadOnly,adCmdText);


        while (true) //continuous loop
        {
            int intLines = 0;

            // Get user input for number of rows.
            printf("\nEnter number of rows to retrieve (0 to exit): ");
            int intRows;
            scanf("%d", &intRows);

            if (intRows <= 0)
                break;

            //Clear the screen for the next display
            system("cls");


            // If GetRowsOK is successful, print the results,
            // noting if the end of the file was reached.
            _variant_t avarRecords;

            if (GetRowsOK(pRstEmployees, intRows, avarRecords))
            {
                long lUbound;
                HRESULT hr = SafeArrayGetUBound(avarRecords.parray, 
                    2,&lUbound);

                if (hr == 0)
                {
                    if (intRows > lUbound + 1)
                    {
                        printf("\n(Not enough records in Recordset to "
                            "retrieve %d rows)\n", intRows);
                    }
                }
                printf("%d records found.", lUbound+1);

                // Print the retrieved data.
                for (int intRecords = 0;intRecords < lUbound+1;
                     intRecords++)
                {
                    printf("\n ");

                    long rgIndices[2];
                    rgIndices[0] = 0; 
                    rgIndices[1] = intRecords;
                    _variant_t result;
                    result.vt = VT_BSTR;

                    hr= SafeArrayGetElement(avarRecords.parray, 
                        rgIndices, &result);

                    if (hr == 0){printf("%s ",(LPCSTR)(_bstr_t)result);}

                    rgIndices[0] = 1;

                    hr= SafeArrayGetElement(avarRecords.parray, 
                        rgIndices, &result);

                    if (hr == 0){printf("%s, ",(LPCSTR)(_bstr_t)result);}

                    rgIndices[0] = 2;

                    hr= SafeArrayGetElement(avarRecords.parray, 
                        rgIndices, &result);

                    if (hr == 0){printf("%s",(LPCSTR)(_bstr_t)result);}

                    intLines ++;

                    if (intLines % 10 == 0)
                    {
                        printf("\nPress any key to continue...");
                        getch();

                        intLines = 0;

                        //Clear the screen for the next display
                        system("cls");
                    }
                }
            }
            else
            {
                // Assuming the GetRows error was due to data
                // changes by another user, use Requery to
                // refresh the Recordset and start over.
                printf("GetRows failed--retry?\n");
                char chKey;
                do
                {
                    chKey = getch();
                }while(toupper(chKey) != 'Y'  && toupper(chKey) != 'N');
                
                if(toupper(chKey) == 'Y')
                {
                    pRstEmployees->Requery(adOptionUnspecified);
                }
                else
                {
                    printf("GetRows failed!\n");
                    break;
                }
            }

            // Because using GetRows leaves the current
            // record pointer at the last record accessed,
            // move the pointer back to the beginning of the
            // Recordset before looping back for another search.
            pRstEmployees->MoveFirst();
        }
    }  
    catch(_com_error &e)
    {
       // Notify the user of errors if any.
       // Pass a connection pointer accessed from the Recordset.
        _variant_t vtConnect = pRstEmployees->GetActiveConnection();

        // GetActiveConnection returns connect string if connection
        // is not open, else returns Connection object.
        switch(vtConnect.vt)
        {
            case VT_BSTR:
                PrintComError(e);
                break;
            case VT_DISPATCH:
                PrintProviderError(vtConnect);
                break;
            default:
                printf("Errors occured.");
                break;
        }
    }
        
    //Clean up objects before exit.
    if (pRstEmployees)
        if (pRstEmployees->State == adStateOpen)
            pRstEmployees->Close();
}

bool GetRowsOK(_RecordsetPtr pRstTemp,int intNumber,
        _variant_t& avarData)
{
    // Store results of GetRows method in array.
    avarData = pRstTemp->GetRows(intNumber);
    
    // Return False only if fewer than the desired
    // number of rows were returned, but not because the
    // end of the Recordset was reached.
    long lUbound;
    HRESULT hr = SafeArrayGetUBound(avarData.parray,2,&lUbound);   
    if (hr == 0)
    {
        if ((intNumber > lUbound + 1) && (!(pRstTemp->EndOfFile)))
            return false;
        else
            return true;   
    }
    else 
    {
        printf ("\nUnable to Get the Array's Upper Bound\n");
        return false;
    }
}

///////////////////////////////////////////////////////////
//                                                       //
//      PrintProviderError Function                      //
//                                                       //
///////////////////////////////////////////////////////////

void PrintProviderError(_ConnectionPtr pConnection)
{
    // Print Provider Errors from Connection object.
    // pErr is a record object in the Connection's Error collection.
    ErrorPtr  pErr  = NULL;

    if( (pConnection->Errors->Count) > 0)
    {
        long nCount = pConnection->Errors->Count;
        // Collection ranges from 0 to nCount -1.
        for(long i = 0; i < nCount; i++)
        {
            pErr = pConnection->Errors->GetItem(i);
            printf("\t Error number: %x\t%s", pErr->Number,
                (LPCSTR) pErr->Description);
        }
    }
}

///////////////////////////////////////////////////////////
//                                                       //
//      PrintComError Function                           //
//                                                       //
///////////////////////////////////////////////////////////

void PrintComError(_com_error &e)
{
   _bstr_t bstrSource(e.Source());
   _bstr_t bstrDescription(e.Description());

    // Print Com errors.
   printf("Error\n");
   printf("\tCode = %08lx\n", e.Error());
   printf("\tCode meaning = %s\n", e.ErrorMessage());
   printf("\tSource = %s\n", (LPCSTR) bstrSource);
   printf("\tDescription = %s\n", (LPCSTR) bstrDescription);
}
// EndGetRowsCpp

See Also

BOF, EOF Properties | GetRows Method | Recordset Object