Count-Eigenschaft (Beispiel) (VC++)

In diesem Beispiel wird die eigenschaft Count mit zwei Auflistungen in der Datenbank Employee veranschaulicht. Die Eigenschaft ruft die Anzahl der Objekte in jeder Auflistung ab und legt die obere Grenze für Schleifen fest, die diese Auflistungen aufzählen.

// BeginCountCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <ole2.h>  
#include <stdio.h>  
#include<conio.h>  
  
// Function declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void CountX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
   CountX();  
   ::CoUninitialize();  
}  
  
void CountX() {  
   // Define ADO object pointers.  Initialize pointers on define.  
   // These are in the ADODB::  namespace  
   _RecordsetPtr pRstEmployee = NULL;  
  
   // Define Other Variables  
   _variant_t Index;  
   Index.vt = VT_I2;  
   int j = 0;  
  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
   try {  
      // Open recordset with data from Employee table.  
      TESTHR(pRstEmployee.CreateInstance(__uuidof(Recordset)));  
      pRstEmployee->Open("Employee", strCnn, adOpenForwardOnly, adLockReadOnly, adCmdTable);  
  
      // Print information about Fields collection.  
      printf("%d Fields in Employee\n", pRstEmployee->Fields->Count);  
      for (short int intLoop = 0 ; intLoop <= (pRstEmployee->Fields->Count-1) ; intLoop++) {  
         Index.iVal = intLoop;  
         printf(" %s\n", (LPSTR) pRstEmployee->Fields->GetItem(Index)->Name);  
      }  
  
      // Print information about Properties collection.  
      printf("\n%d Properties in Employee\n", pRstEmployee->Properties->Count);  
      for (short int intLoop = 0 ; intLoop <= (pRstEmployee->Properties->Count - 1) ; intLoop++) {  
         j++;  
         Index.iVal = intLoop;  
         printf(" %s\n" , (LPSTR)pRstEmployee->Properties->GetItem(Index)->Name);  
      }  
   }  
   catch(_com_error &e) {  
      // Display any errors that result from executing the query.  
      // Pass a connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstEmployee->GetActiveConnection();  
  
      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 (pRstEmployee)  
      if (pRstEmployee->State == adStateOpen)  
         pRstEmployee->Close();  
}  
  
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("Error number: %x\t%s\n", pErr->Number, 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);  
}  

Siehe auch

Count-Eigenschaft (ADO)