CompareBookmarks Method Example (VC++)

This example demonstrates the CompareBookmarks method. The relative value of bookmarks is seldom needed unless a particular bookmark is somehow special.

Designate a random row of a Recordset derived from the Authors table as the target of a search. Then display the position of each row relative to that target.

// BeginCompareBookmarksCpp
#import "C:\Program Files\Common Files\System\ADO\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);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);

//////////////////////////////////////////////////////////
//                                                      //
//        Main Function                                 //
//                                                      //
//////////////////////////////////////////////////////////

void main()
{
    if(FAILED(::CoInitialize(NULL)))
        return;

    CompareBookMarksX();

    printf("Press any key to continue...");
    getch();
    ::CoUninitialize();
}

//////////////////////////////////////////////////////////
//                                                      //
//           CompareBookMarksX Function                 //
//                                                      //
//////////////////////////////////////////////////////////

void CompareBookMarksX(void) 
{
    HRESULT hr = S_OK;

    _bstr_t strCnn("Provider='sqloledb';Data Source='MySqlServer';"
        "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;
        long intLineCnt = 3;
        pRstAuthors->MoveFirst();

        while (!(pRstAuthors->EndOfFile))       //Loop through recordset
        {
            intLineCnt++;
            if (intLineCnt%20 == 0)
            {
                printf("\nPress any key to continue...\n");
                getch();
            }
            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();
}

//////////////////////////////////////////////////////////
//                                                      //
//            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("Error number: %x\t%s\n", pErr->Number, 
                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);
}
// EndCompareBookmarksCpp

See Also

CompareBookmarks Method | Recordset Object