Esempio del metodo CompareBookmarks (VC++)

Questo esempio illustra il metodo CompareBookmarks. Il valore relativo dei segnalibri è raramente necessario, a meno che un particolare segnalibro non sia in qualche modo speciale.

Designare una riga casuale di un recordset derivato dalla tabella Authors come destinazione di una ricerca. Visualizzare quindi la posizione di ogni riga rispetto a tale destinazione.

// BeginCompareBookmarksCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <ole2.h>  
#include <stdio.h>  
#include <conio.h>  
#include <time.h>  
#include <stdlib.h>  
  
// Function declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void CompareBookMarksX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   CompareBookMarksX();  
   ::CoUninitialize();  
}  
  
void CompareBookMarksX() {  
   HRESULT hr = S_OK;  
  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
   // Initialize pointers on define. These are in the ADODB::  namespace.  
   _RecordsetPtr pRstAuthors = NULL;  
   _variant_t vTarget;  
   _bstr_t strAns;  
   _bstr_t strTitle;  
   strTitle = "CompareBookmarks Example";  
   try {      
      TESTHR(pRstAuthors.CreateInstance(__uuidof(Recordset)));  
  
      pRstAuthors->Open("SELECT * FROM authors ORDER BY au_id", strCnn, adOpenStatic, adLockReadOnly, adCmdText);  
  
      long count = pRstAuthors->RecordCount;  
      printf("Rows in the Recordset = %d\n", count);  
      if (count == 0)   
         exit(1);   // Exit if an empty recordset  
  
      srand( (unsigned)time( NULL ) );   // Randomize  
  
      count = int(rand() % (count-1));   // Get position between 1 and count-1  
      if (!count)   
         count++;  
  
      printf("Randomly chosen row position = %d\n", count);  
      _variant_t vtBookMark = (short)adBookmarkFirst;  
      pRstAuthors->Move(count,vtBookMark);   // Move row to random position  
  
      vTarget = pRstAuthors->Bookmark;   // Remember the mystery row.  
      count = 0;  
      pRstAuthors->MoveFirst();  
  
      while (!(pRstAuthors->EndOfFile)) {   // Loop through recordset  
         long result = pRstAuthors->CompareBookmarks(pRstAuthors->Bookmark, vTarget);  
  
         if (result == adCompareNotEqual)  
            printf("Row %d: Bookmarks are not equal. %d\n", count, result);  
         else if  (result == adCompareNotComparable)   
            printf("Row %d: Bookmarks are not comparable.\n", count);  
         else {  
            switch(result) {  
            case adCompareLessThan:  
               strAns = "less than";  
               break;  
            case adCompareEqual:  
               strAns = "equal to";  
               break;  
            case adCompareGreaterThan:  
               strAns = "greater than";  
               break;  
            default:  
               strAns = "in error comparing to";  
               break;  
            }  
            printf ("Row position  %d  is  %s  the target.\n",  
               count,(LPCSTR)strAns);  
         }  
         count++;  
         pRstAuthors->MoveNext();  
      }  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      // Pass a connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstAuthors->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 (pRstAuthors)  
      if (pRstAuthors->State == adStateOpen)  
         pRstAuthors->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);  
}  

Vedere anche

Metodo CompareBookmarks (ADO)
Oggetto Recordset (ADO)