AppendChunk and GetChunk Methods Example (VC++)
This example uses the AppendChunk and GetChunk methods to fill an image field with data from another record.
// BeginAppendChunkCpp.cpp
// compile with: /EHsc /c
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")
#define ChunkSize 100
#include <ole2.h>
#include <stdio.h>
#include "conio.h"
#include "malloc.h"
#include "icrsint.h"
// 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;
};
//Function declarations
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };
void AppendChunkX();
void PrintProviderError(_ConnectionPtr pConnection);
inline int myscanf(char* strDest, int n) {
char strExBuff[10];
char* pstrRet = fgets(strDest, n, stdin);
if (pstrRet == NULL)
return 0;
if (!strrchr(strDest, '\n'))
// Exhaust the input buffer.
do {
fgets(strExBuff, sizeof(strExBuff), stdin);
} while (!strrchr(strExBuff, '\n'));
else
// Replace '\n' with '\0'
strDest[strrchr(strDest, '\n') - strDest] = '\0';
return strlen(strDest);
}
inline char* mygets(char* strDest, int n) {
char strExBuff[10];
char* pstrRet = fgets(strDest, n, stdin);
if (pstrRet == NULL)
return NULL;
if (!strrchr(strDest, '\n'))
// Exhaust the input buffer.
do {
fgets(strExBuff, sizeof(strExBuff), stdin);
} while (!strrchr(strExBuff, '\n'));
else
// Replace '\n' with '\0'
strDest[strrchr(strDest, '\n') - strDest] = '\0';
return pstrRet;
}
int main() {
HRESULT hr = S_OK;
if (FAILED(::CoInitialize(NULL)))
return -1;
AppendChunkX();
::CoUninitialize();
}
void AppendChunkX() {
// Define ADO object pointers, initialize pointers on define. These are in the ADODB:: namespace.
_RecordsetPtr pRstPubInfo = NULL;
_ConnectionPtr pConnection = NULL;
char * token1;
// 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='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");
_bstr_t strMessage,strPubID,strPRInfo;
_variant_t varChunk;
long lngOffSet,lngLogoSize;
char pubId[50];
lngOffSet = 0;
UCHAR chData;
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 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_s(pubrs.m_sz_prinfo, ",", &token1));
// 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: ");
myscanf(pubId, sizeof(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
hr = SafeArrayPutElement(psa, &index1, &chData);
index1++;
}
else
break;
}
lngOffSet = lngOffSet + ChunkSize;
}
lngOffSet = 0;
printf("Enter a new Pub Id: ");
myscanf(pubrs.m_sz_pubid, sizeof(pubrs.m_sz_pubid));
strPubID = pubrs.m_sz_pubid;
printf("Enter descriptive text: " );
mygets(pubrs.m_sz_prinfo, sizeof(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;
// 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);
}
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);
}
// Clean up objects before exit.
if (pRstPubInfo)
if (pRstPubInfo->State == adStateOpen)
pRstPubInfo->Close();
if (pConnection)
if (pConnection->State == adStateOpen)
pConnection->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;
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);
}
}
}
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