Ejemplo del método GetRows (VC ++)

En este ejemplo se usa el método GetRows para recuperar un número especificado de filas de un objeto Recordset y para rellenar una matriz con los datos resultantes. El método GetRows devolverá menos del número deseado de filas en dos casos: si se ha alcanzado EOF o si GetRows intentó recuperar un registro eliminado por otro usuario. La función devuelve False solo si se produce el segundo caso. La función GetRowsOK es necesaria para que se ejecute este procedimiento.

Ejemplo

// BeginGetRowsCpp.cpp  
// compile with: /EHsc  
#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();  
bool GetRowsOK(_RecordsetPtr pRstTemp, int intNumber, _variant_t& avarData);  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if (FAILED(::CoInitialize(NULL)))  
      return -1;  
  
   GetRowsX();  
   ::CoUninitialize();  
}  
  
void GetRowsX() {  
   HRESULT hr = S_OK;  
  
   // Define string variables.  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; 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("Enter number of rows to retrieve (0 to exit): ");  
         int intRows;  
         scanf_s("%d", &intRows);  
  
         if (intRows <= 0)  
            break;  
  
         // 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 record(s) found.\n", lUbound + 1);  
  
            // Print the retrieved data.  
            for (int intRecords = 0 ; intRecords < lUbound+1 ; intRecords++) {  
               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\n", (LPCSTR)(_bstr_t)result);  
  
               intLines ++;  
  
               if (intLines % 10 == 0) {  
                  printf("\nPress any key to continue...");  
                  _getch();  
                  intLines = 0;  
                  system("cls");  
               }  
            }  
            printf("\n");  
         }  
         else {  
            // Assume GetRows error caused by another user's data changes,   
            // 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 occurred.");  
            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;  
   }  
}  
  
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);  
      }  
   }  
}  
  
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);  
}  

Entrada

2  
0  

Salida de ejemplo

2 record(s) found.  
Paolo Accorti, 8/27/1992  
Pedro Afonso, 12/24/1990  

Consulte también

BOF, EOF (propiedades) (ADO)
Método GetRows (ADO)
Objeto de conjunto de registros (ADO)