Visual C++ Extensions 範例

此程式會顯示如何從欄位擷取值，並轉換成 C/C++ 變數。

此範例也會利用「智慧指標」，自動處理 IADORecordBinding 介面呼叫 QueryInterface 與參考計數的 COM 特定詳細資料。

若沒有智慧指標，您可以透過以下方式撰寫程式碼：

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

有智慧指標時，您可以使用此陳述式從 IADORecordBinding 介面衍生 IADORecordBindingPtr 類型：

_COM_SMARTPTR_TYPEDEF(IADORecordBinding, __uuidof(IADORecordBinding));  

並具現化指標，如下所示：

IADORecordBindingPtr picRs(pRs);  

因為 Visual C++ 延伸模組是由 Recordset 物件實作，所以智慧指標 picRs 的建構函式會採用 _RecordsetPtr 指標 (pRs)。 建構函式會使用 pRs 呼叫 QueryInterface，以尋找 IADORecordBinding 介面。

// Visual_Cpp_Extensions_Example.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#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;  
};  
  
int main() {  
   ::CoInitialize(NULL);  
   try {  
      _RecordsetPtr pRs("ADODB.Recordset");  
      CCustomRs rs;  
      IADORecordBindingPtr picRs(pRs);  
  
      pRs->Open(L"SELECT * FROM Employee ORDER BY lname", L"dsn=DataPubs;Trusted_Connection=yes;", 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();  
}  

另請參閱

使用 Visual C++ Extensions
Visual C++ Extensions 標題