Esempio del metodo Clone (VC++)

In questo esempio si usa il metodo Clone per creare copie di un oggetto Recordset e quindi consente all'utente di posizionare in modo indipendente il puntatore a record di ogni copia.

// BeginCloneCpp.cpp  
// compile with: /EHsc /c  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <stdio.h>  
#include <ole2.h>  
#include <conio.h>  
#include "icrsint.h"  
  
// class extracts only store name  from "stores" table.  
class CStores : public CADORecordBinding {  
   BEGIN_ADO_BINDING(CStores)  
  
   // Column stor_name is the 1st field in the recordset    
   ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, m_szS_stor_name, sizeof(m_szS_stor_name),   
                              lS_stor_nameStatus, FALSE)  
  
   END_ADO_BINDING()  
  
public:  
   CHAR m_szS_stor_name[150];  
   ULONG lS_stor_nameStatus;  
};  
  
// Function Declarations.  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void CloneX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
inline char* mygets(char* strDest, int n) {  
   char strExBuff[10];  
   char* pstrRet = fgets(strDest, n, stdin);  
  
   if (pstrRet == NULL)  
      return NULL;  
  
   if (!strrchr(strDest, '\n'))  
      // Exhaust the input buffer.  
      do {  
         fgets(strExBuff, sizeof(strExBuff), stdin);  
      } while (!strrchr(strExBuff, '\n'));  
   else  
      // Replace '\n' with '\0'  
      strDest[strrchr(strDest, '\n') - strDest] = '\0';  
  
   return pstrRet;  
}  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   CloneX();  
   ::CoUninitialize();  
}  
  
void CloneX() {  
   // Define ADO object pointers, initialize pointers on define.  These are in the ADODB::  namespace.  
   _RecordsetPtr  arstStores[3];  
  
   // Define Other Variables  
   HRESULT hr = S_OK;  
   int intLoop = 0;  
   _bstr_t strSQL;  
   _bstr_t strMessage;  
   _bstr_t strFind;  
   int intLoop1 = 0;  
   char *tempStr;  
   bool boolFlag = TRUE;  
   char m_szS_stor_name[150];  
   char * token1;  
  
   // Assign SQL statement and connection string to variables.  
   strSQL = "SELECT stor_name FROM Stores ORDER BY stor_name";  
  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
   try  {  
      // Open recordset as a static cursor type recordset.  
      arstStores[0].CreateInstance(__uuidof(Recordset));  
      arstStores[0]->CursorType = adOpenStatic;  
      arstStores[0]->LockType = adLockBatchOptimistic;  
  
      TESTHR(arstStores[0]->Open(strSQL,strCnn, adOpenStatic,  
         adLockBatchOptimistic, adCmdText));  
  
      // Create two clones of the original Recordset.  
      arstStores[1] = arstStores[0]->Clone(adLockUnspecified);  
      arstStores[2] = arstStores[0]->Clone(adLockUnspecified);  
  
      while (boolFlag) {  
         // Loop through the array so that on each pass, the user is searching a   
         // different copy of the same Recordset.  
         for (intLoop = 1; intLoop <= 3 ; intLoop++) {  
            // Ask for search string while showing where  
            // the current record pointer is for each Recordset.  
            printf("Recordsets from stores table:\n");   
  
            _bstr_t str1 = arstStores[0]->Fields->GetItem("stor_name")->Value;  
            printf("\t1 - Original - Record pointer at %s", (LPCSTR)str1);  
  
            _bstr_t str2 = arstStores[1]->Fields->GetItem("stor_name")->Value;  
            printf("\n\t2 - Clone - Record pointer at %s", (LPCSTR)str2);  
  
            _bstr_t str3 = arstStores[2]->Fields->GetItem("stor_name")->Value;  
            printf("\n\t3 - Clone - Record pointer at %s", (LPCSTR)str3);   
  
            printf("\n\nEnter search string for # %d, or press Enter to quit.\n", intLoop);  
            mygets(m_szS_stor_name, 150);  
  
            // Trim the String.  
            tempStr = strtok_s(m_szS_stor_name, "  \t", &token1);  
            strMessage = tempStr;  
            if (tempStr == NULL) {  
               boolFlag = FALSE;  
               break;  
            }  
  
            // Find the search string; if there's no  
            // match, jump to the last record.  
            intLoop1 = intLoop - 1;  
  
            arstStores[intLoop1]->Filter = "stor_name >= '" +   
               strMessage + "'";  
  
            if (arstStores[intLoop1]->EndOfFile) {  
               arstStores[intLoop1]->Filter = (long)adFilterNone;  
               arstStores[intLoop1]->MoveLast();  
            }  
         }  
      } // End of While Loop  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      _variant_t vtConnect;  
  
      vtConnect = arstStores[0]->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 (arstStores[0])  
      if (arstStores[0]->State == adStateOpen)  
         arstStores[0]->Close();  
   if (arstStores[1])  
      if (arstStores[1]->State == adStateOpen)  
         arstStores[1]->Close();  
   if (arstStores[2])  
      if (arstStores[2]->State == adStateOpen)  
         arstStores[2]->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,  
            (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);  
}  

Vedere anche

Oggetto Recordset (ADO)