AppendChunk and GetChunk Methods Example (VC++)
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 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()
{
if(FAILED(::CoInitialize(NULL)))
return;
AppendChunkX();
::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
//Interface Pointer declared.(VC++ Extensions)
IADORecordBinding *picRs = NULL;
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(pConnection.CreateInstance(__uuidof(Connection)));
TESTHR(pConnection->Open(strCnn,"","",NULL));
TESTHR(hr= pRstPubInfo.CreateInstance(__uuidof(Recordset)));
pRstPubInfo->CursorType = adOpenKeyset;
pRstPubInfo->LockType = adLockOptimistic;
TESTHR(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 up to 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
TESTHR(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);
// Temporarily add new publisher to table to avoid error due
// to foreign key constraint.
pConnection->Execute("INSERT publishers(pub_id) VALUES('" +
strPubID + "')",NULL,adCmdText);
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;
//Show the newly added record.
printf("New Record : %s\nDescription : %s\nLogo Size : %s\n",
pubrs.m_sz_pubid,
pubrs.m_sz_prinfo,(LPCSTR)(_bstr_t)pRstPubInfo->Fields->
Item["logo"]->ActualSize);
//Delete new records because this is demonstration.
pConnection->Execute("DELETE FROM PUB_INFO WHERE pub_id = '"
+ strPubID +"'",NULL,adCmdText);
pConnection->Execute("DELETE FROM publishers 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);
}
}
}
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;
};