用ADO的rs->GetFields()->GetItem("content")->GetChunk(lDataSize)读取大文本的问题

Question

SAFEARRAY FAR *psa;
    SAFEARRAYBOUND rgsabound[1];
//Create a safe array to store the array of BYTES  
lngLogoSize = pRstPubInfo->Fields->Item["logo"]->ActualSize;        rgsabound[0].cElements = lngLogoSize;
        psa = SafeArrayCreate(VT_UI1,1,rgsabound);        long index1 = 0;
        while(lngOffSet < lngLogoSize)
        {
            varChunk = pRstPubInfo->Fields->
                        Item["logo"]->GetChunk(ChunkSize);            //Copy the data only upto the Actual Size of Field.  
            for(long index=0;index<=(ChunkSize-1);index++)
            {
                hr= SafeArrayGetElement(varChunk.parray,&index,&chData);
                if(SUCCEEDED(hr))
                {
                    //Take BYTE by BYTE and advance Memory Location
                    hr = SafeArrayPutElement(psa,&index1,&chData); 
                    index1++;
                }
                else
                    break;
            }
            lngOffSet = lngOffSet + ChunkSize;
        }
        lngOffSet = 0;

Answer 1

你可以学习一下这个例子，from msdn--------------------
AppendChunk and GetChunk Methods Example (VC++)
[This is preliminary documentation and subject to change.] 
This example uses the AppendChunk and GetChunk methods to fill an image field with data from another record.// BeginAppendChunkCpp
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" \
    no_namespace rename("EOF", "EndOfFile")#define ChunkSize   100#include <ole2.h>
#include <stdio.h>
#include "conio.h"
#include "malloc.h"
#include "AppendChunkX.h"//Function declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void AppendChunkX(VOID);
void PrintProviderError(_ConnectionPtr pConnection);///////////////////////////////////////////////////////////
//                                                       //
//      Main Function                                    //
//                                                       //
///////////////////////////////////////////////////////////
void main()
{
   HRESULT  hr = S_OK;   if(FAILED(::CoInitialize(NULL)))
      return;
   
   AppendChunkX();
      
   //Wait here for the user to see the output
   printf("\n\nPress any key to continue..");
   getch();
   ::CoUninitialize();
}
///////////////////////////////////////////////////////////
//                                                       //
//      AppendChunkX Function                            //
//                                                       //
///////////////////////////////////////////////////////////
VOID  AppendChunkX(VOID)
{
   // Define ADO object pointers.
    // Initialize pointers on define.
    // These are in the ADODB::  namespace.
    _RecordsetPtr pRstPubInfo = NULL;
    _ConnectionPtr pConnection = NULL;
   
     //Define other variables
     IADORecordBinding   *picRs = NULL;  //Interface Pointer declared.(VC++ Extensions)   
     CPubInfoRs pubrs;          //C++ class object        HRESULT hr = S_OK;
    _bstr_t strCnn("Provider=sqloledb;Data Source=MyServer;"
         "Initial Catalog=pubs;User Id=sa;Password=;");
    
    _bstr_t strMessage,strPubID,strPRInfo;
    _variant_t varChunk;
    long lngOffSet,lngLogoSize;
     char pubId[50];
    lngOffSet = 0;    
      
    UCHAR chData;
    CHAR ch;
    SAFEARRAY FAR *psa;
    SAFEARRAYBOUND rgsabound[1];
    rgsabound[0].lLbound = 0;
    rgsabound[0].cElements = ChunkSize;    try
    {
        //Open a Connection.
        TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
        hr = pConnection->Open(strCnn,"","",adConnectUnspecified);        TESTHR(hr= pRstPubInfo.CreateInstance(__uuidof(Recordset)));          pRstPubInfo->CursorType = adOpenKeyset;
        pRstPubInfo->LockType = adLockOptimistic;        hr = pRstPubInfo->Open("pub_info",
            _variant_t((IDispatch*)pConnection,true),
            adOpenKeyset,adLockOptimistic,adCmdTable);        //Open an IADORecordBinding interface pointer which we'll use 
        //for Binding Recordset to a class    
        TESTHR(pRstPubInfo->QueryInterface(
            __uuidof(IADORecordBinding),(LPVOID*)&picRs));        //Bind the Recordset to a C++ Class here    
        TESTHR(picRs->BindToRecordset(&pubrs));        //Display the available logos here
        strMessage = "Available logos are: " + (_bstr_t)"\n\n";
        printf(strMessage);
        int Counter = 0;
        while(!(pRstPubInfo->EndOfFile))
        { 
            printf("\n%s",pubrs.m_sz_pubid);
            printf("\n%s",strtok(pubrs.m_sz_prinfo,","));            //Display 5 records at a time and wait for user to continue..
            if (++Counter >= 5)
            {
                Counter = 0;
                printf("\nPress any key to continue...");
                getch();
            }
            pRstPubInfo->MoveNext(); 
        }        //Prompt For a Logo to Copy
        printf("\nEnter the ID of a logo to copy: ");
        scanf("%s",pubId);
        strPubID = pubId;        //Copy the logo to a variable in chunks        pRstPubInfo->Filter = "pub_id = '"  + strPubID + "'";
        lngLogoSize = pRstPubInfo->Fields->Item["logo"]->ActualSize;        //Create a safe array to store the array of BYTES  
        rgsabound[0].cElements = lngLogoSize;
        psa = SafeArrayCreate(VT_UI1,1,rgsabound);        long index1 = 0;
        while(lngOffSet < lngLogoSize)
        {
            varChunk = pRstPubInfo->Fields->
                        Item["logo"]->GetChunk(ChunkSize);            //Copy the data only upto the Actual Size of Field.  
            for(long index=0;index<=(ChunkSize-1);index++)
            {
                hr= SafeArrayGetElement(varChunk.parray,&index,&chData);
                if(SUCCEEDED(hr))
                {
                    //Take BYTE by BYTE and advance Memory Location
                    hr = SafeArrayPutElement(psa,&index1,&chData); 
                    index1++;
                }
                else
                    break;
            }
            lngOffSet = lngOffSet + ChunkSize;
        }
        lngOffSet = 0;        printf("Enter a new Pub Id: ");
        scanf("%s",pubrs.m_sz_pubid);
        strPubID = pubrs.m_sz_pubid;
        printf("Enter descriptive text: " );
        scanf("%c",&ch);
        gets(pubrs.m_sz_prinfo);
        
        pRstPubInfo->AddNew();
        pRstPubInfo->Fields->GetItem("pub_id")->PutValue(strPubID);
        pRstPubInfo->Fields->GetItem("pr_info")->
            PutValue(pubrs.m_sz_prinfo);        //Assign the Safe array  to a variant. 
        varChunk.vt = VT_ARRAY|VT_UI1;
        varChunk.parray = psa;
        hr = pRstPubInfo->Fields->GetItem("logo")->
                AppendChunk(varChunk);         //Update the table 
        pRstPubInfo->Update();        lngLogoSize = pRstPubInfo->Fields->Item["logo"]->ActualSize;

Answer 2

        //Show the newly added record.
        printf("New Record : %s\n Description : %s\n Logo Size : %s",
            pubrs.m_sz_pubid,
            pubrs.m_sz_prinfo,(LPCSTR)(_bstr_t)pRstPubInfo->Fields->
            Item["logo"]->ActualSize);        //Delete new record because this is demonstration.
        pConnection->Execute("DELETE FROM PUB_INFO WHERE pub_id = '"
                        + strPubID +"'",NULL,adCmdText);        pRstPubInfo->Close();
        pConnection->Close();
    }    catch(_com_error &e)
   {
       // Notify the user of errors if any.
      _bstr_t bstrSource(e.Source());
      _bstr_t bstrDescription(e.Description());      PrintProviderError(pConnection);
      printf("Source : %s \n Description : %s\n",(LPCSTR)bstrSource,(LPCSTR)bstrDescription);   }
}
///////////////////////////////////////////////////////////
//                                                       //
//      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;
   long      nCount   = 0;    
   long      i     = 0;   if( (pConnection->Errors->Count) > 0)
   {
      nCount = pConnection->Errors->Count;
      // Collection ranges from 0 to nCount -1.
      for(i = 0; i < nCount; i++)
      {
         pErr = pConnection->Errors->GetItem(i);
         printf("\t Error number: %x\t%s", pErr->Number,(LPCSTR) pErr->Description);
      }
   }
}// EndAppendChunkCppAppendChunkX.h:// BeginAppendChunkH
#include "icrsint.h"//This Class extracts pubid,prinfo.class CPubInfoRs : public CADORecordBinding
{
   BEGIN_ADO_BINDING(CPubInfoRs)
      
      ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, m_sz_pubid, 
         sizeof(m_sz_pubid), l_pubid, TRUE)
      
      ADO_VARIABLE_LENGTH_ENTRY2(3, adVarChar, m_sz_prinfo, 
         sizeof(m_sz_prinfo), l_prinfo, TRUE)
   
   END_ADO_BINDING()public:
   CHAR   m_sz_pubid[10];
   ULONG  l_pubid;
   CHAR   m_sz_prinfo[200];
   ULONG l_prinfo;    
};
// EndAppendChunkH

Answer 3

主要代码就在下面了，帮我看看，98下正常，2000第一次没错，后面就出错了long lDataSize=0;
 lDataSize=rs->GetFields()->GetItem("内容")->ActualSize; 
     char *pBuf = NULL; 
        pBuf = new char[lDataSize] ; if(lDataSize > 0) 
{ 
  _variant_t  varBLOB; 
  varBLOB=rs->GetFields()->GetItem("内容")->GetChunk(lDataSize); 
 
SafeArrayAccessData(varBLOB.parray,(void **)&pBuf);  SafeArrayUnaccessData (varBLOB.parray); 
pBuf[lDataSize-2]=NULL;
pEdit->SetWindowText((LPCSTR)pBuf);//显示内容     for( int i=0;i<lDataSize;i++) 
{ 
pBuf[i]=NULL; 
} 
        GlobalFree(pBuf);        rs->Close(); return TRUE;
} else { rs->Close();    return FALSE;}}catch (...) 
{ 
rs->Close();
TRACE0("CAdo::WriteFileToDb Unknow Exception * * *\n");
}