如何用ADO从DATABASE中读二进制数据.

[davids]

以下是部分代码. SQL用 SELECT * FROM MYDATABASE

其他的数据都能读出,但二进制的数据不能.
FieldPtr pHEADER;
_variant_t vHEADER;

pHEADER =m_pRecordset->Fields->GetItem("kiji_header"); 二进制的数据

vHEADER.Clear ();
vHEADER=pHEADER ->GetChunk (1024);

请求援助.

[DOU]

MSDN里的一段例子，我也没使用过这种方式，sorry不能提供具体帮助

Microsoft Data Access Components 2.5 SDK Beta - ADO

AppendChunk and GetChunk Methods Example (Visual C++)


This example uses the AppendChunk and GetChunk methods to fill an image field with data from another record.

#import "C:\Program Files\Common Files\System\ADO\msado15.dll" \
no_namespace rename("EOF", "EndOfFile")

#define TESTHR(x) if FAILED(x) _com_issue_error(hr)
#define ChunkSize 100

#include <ole2.h>
#include <stdio.h>
#include "conio.h"
#include "malloc.h"
#include "AppendChunkX.h"

//Function declarations
void AppendChunkX(VOID);
void PrintProviderError(_ConnectionPtr pCnn1);

///////////////////////////////////////////////////////////
// //
// Main Function //
// //
///////////////////////////////////////////////////////////
void main()
{
HRESULT hr = S_OK;

hr = ::CoInitialize(NULL);
if (SUCCEEDED(hr))
{

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 pCnn1 = 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=SRV;"
"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(hr = pCnn1.CreateInstance(__uuidof(Connection)));
hr = pCnn1->Open(strCnn,"","",NULL);

TESTHR(hr= pRstPubInfo.CreateInstance(__uuidof(Recordset)));

pRstPubInfo->CursorType = adOpenKeyset;
pRstPubInfo->LockType = adLockOptimistic;


hr = pRstPubInfo->Open("pub_info",_variant_t((IDispatch*)pCnn1,true),adOpenKeyset,adLockOptimistic,adCmdTable);

//Open an IADORecordBinding interface pointer which we'll use for Binding Recordset to a class
if (FAILED(hr = pRstPubInfo->QueryInterface(__uuidof(IADORecordBinding),(LPVOID*)&picRs)))
_com_issue_error(hr);

//Bind the Recordset to a C++ Class here
if (FAILED(hr = picRs->BindToRecordset(&pubrs)))
_com_issue_error(hr);

//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))
{
// *pLogo++ = chData;
hr= SafeArrayPutElement(psa,&index1,&chData); //Take BYTE by BYTE and advance Memory Location
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 and VT_UI1;
varChunk.parray = psa;
hr = pRstPubInfo->Fields->GetItem("logo")->AppendChunk(varChunk);
lngOffSet = lngOffSet + ChunkSize;

//Update the table
pRstPubInfo->Update();



lngLogoSize = pRstPubInfo->Fields->Item["logo"]->ActualSize;
//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.
pRstPubInfo->Requery(0);

pCnn1->Execute("DELETE FROM PUB_INFO WHERE pub_id = '"+ strPubID +"'",NULL,adCmdText);

//
pRstPubInfo->Close();
pCnn1->Close();



}
catch(_com_error &e)
{
// Notify the user of errors if any.
_bstr_t bstrSource(e.Source());
_bstr_t bstrDescription(e.Description());

PrintProviderError(pRstPubInfo->GetActiveConnection());
printf("Source : %s \n Description : %s\n",(LPCSTR)bstrSource,(LPCSTR)bstrDescription);

}


}


///////////////////////////////////////////////////////////
// //
// PrintProviderError Function //
// //
///////////////////////////////////////////////////////////

VOID PrintProviderError(_ConnectionPtr pCnn1)
{
// 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( (pCnn1->Errors->Count) > 0)
{
nCount = pCnn1->Errors->Count;
// Collection ranges from 0 to nCount -1.
for(i = 0; i < nCount; i++)
{
pErr = pCnn1->Errors->GetItem(i);
printf("\t Error number: %x\t%s", pErr->Number,(LPCSTR) pErr->Description);
}
}
}

AppendChunkX.h:

#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;

};

[littletao]

试试vHEADER=pHEARDER->GetChunk(pHEADER ->ActualSize)？

[davids]

不是大小的问题,pHEADER ->ActualSize而是如何得到数据.
谢谢你!

DAVIDS