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 "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