Visual C++ Extensions example

Applies to: Access 2013, Office 2013

This program shows how values are retrieved from fields and converted to C/C++ variables.

This example also takes advantage of "smart pointers," which automatically handle the COM-specific details of calling and reference counting for the IADORecordBinding interface.

Without smart pointers, you would code:

 
IADORecordBinding *picRs = NULL; 
... 
TESTHR(pRs->QueryInterface( 
 __uuidof(IADORecordBinding), (LPVOID*)&picRs)); 
... 
if (picRs) picRs->Release(); 

With smart pointers, you derive the IADORecordBindingPtr type from the type from the IADORecordBinding interface with this statement:

 
_COM_SMARTPTR_TYPEDEF(IADORecordBinding, __uuidof(IADORecordBinding)); 

And instantiate the pointer like this:

 
IADORecordBindingPtr picRs(pRs); 

Because the Visual C++ Extensions are implemented by the Recordset object, the constructor for the smart pointer, picRs , takes the _RecordsetPtr pointer, pRs . The constructor calls QueryInterface using pRs to find the , takes the _RecordsetPtr pointer, pRs . The constructor calls QueryInterface using pRs to find the IADORecordBinding interface.

 
// Visual C++ Extensions Example 
#import "c:\Program Files\Common Files\System\ADO\msado15.dll" no_namespace rename("EOF", "EndOfFile") 
 
#include <stdio.h> 
#include <icrsint.h> 
_COM_SMARTPTR_TYPEDEF(IADORecordBinding, __uuidof(IADORecordBinding)); 
 
inline void TESTHR(HRESULT _hr) { if FAILED(_hr) _com_issue_error(_hr); } 
 
class CCustomRs : public CADORecordBinding 
{ 
BEGIN_ADO_BINDING(CCustomRs) 
 ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_ch_fname, 
 sizeof(m_ch_fname), m_ul_fnameStatus, false) 
 ADO_VARIABLE_LENGTH_ENTRY2(4, adVarChar, m_ch_lname, 
 sizeof(m_ch_lname), m_ul_lnameStatus, false) 
END_ADO_BINDING() 
public: 
 CHAR m_ch_fname[22]; 
 CHAR m_ch_lname[32]; 
 ULONG m_ul_fnameStatus; 
 ULONG m_ul_lnameStatus; 
}; 
 
void main(void) 
{ 
 ::CoInitialize(NULL); 
 try 
 { 
 _RecordsetPtr pRs("ADODB.Recordset"); 
 CCustomRs rs; 
 IADORecordBindingPtr picRs(pRs); 
 
 pRs->Open("SELECT * FROM Employee ORDER BY lname", 
 "dsn=pubs;uid=sa;pwd=;", 
 adOpenStatic, adLockOptimistic, adCmdText); 
 
 TESTHR(picRs->BindToRecordset(&rs)); 
 
 while (!pRs->EndOfFile) 
 { 
 // Process data in the CCustomRs C++ instance variables. 
 printf("Name = %s %s\n", 
 (rs.m_ul_fnameStatus == adFldOK ? rs.m_ch_fname: "<Error>"), 
 (rs.m_ul_lnameStatus == adFldOK ? rs.m_ch_lname: "<Error>")); 
 
 // Move to the next row of the Recordset. 
 // Fields in the new row will automatically be 
 // placed in the CCustomRs C++ instance variables. 
 
 pRs->MoveNext(); 
 } 
 } 
 catch (_com_error &e ) 
 { 
 printf("Error:\n"); 
 printf("Code = %08lx\n", e.Error()); 
 printf("Meaning = %s\n", e.ErrorMessage()); 
 printf("Source = %s\n", (LPCSTR) e.Source()); 
 printf("Description = %s\n", (LPCSTR) e.Description()); 
 } 
 ::CoUninitialize(); 
}