ADO 教程 (VC++)

本教程以新版 Microsoft Visual C++ Extensions 为特征。VC++ Extensions 删除了对繁琐的 VARIANT 数据类型的使用。

本教程还使用了 #import 伪指令，它将 ADO Typelib 转换到头文件中，这个头文件使一些 ADO 的功能在使用和外观上类似 Microsoft Visual Basic 中相应的用法。

注意   在该范例中发布和使用的绑定宏已经过更改，不再与原始文档相同。有关当前宏定义的详细信息，请参阅头文件 icrsint.h。

#define INITGUID
#import "c:\Program Files\Common Files\System\ADO\msado15.dll" \
   no_namespace rename("EOF", "EndOfFile")
#include <stdio.h>
#include <icrsint.h>

void dump_com_error(_com_error &e)
   {
   printf("Error\n");
   printf("\a\tCode = %08lx\n", e.Error());
   printf("\a\tCode meaning = %s", e.ErrorMessage());
   _bstr_t bstrSource(e.Source());
   _bstr_t bstrDescription(e.Description());
   printf("\a\tSource = %s\n", (LPCSTR) bstrSource);
   printf("\a\tDescription = %s\n", (LPCSTR) bstrDescription);
   }

class CCustomRs : 
   public CADORecordBinding
{
BEGIN_ADO_BINDING(CCustomRs)
   ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, m_szau_lname, 
         sizeof(m_szau_lname), lau_lnameStatus, false)
   ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_szau_fname, 
         sizeof(m_szau_fname), lau_fnameStatus, false)
   ADO_VARIABLE_LENGTH_ENTRY2(3, adVarChar, m_szphone,    
         sizeof(m_szphone),    lphoneStatus,    true)
END_ADO_BINDING()

public:
   CHAR   m_szau_lname[41];
   ULONG   lau_lnameStatus;
   CHAR   m_szau_fname[41];
   ULONG   lau_fnameStatus;
   CHAR   m_szphone[12];
   ULONG   lphoneStatus;
};

VOID   main()
   {
   HRESULT            hr;
   IADORecordBinding   *picRs = NULL;
   
   ::CoInitialize(NULL);

   try 
      {
      _ConnectionPtr pConn("ADODB.Connection.1.5");
      _RecordsetPtr pRs("ADODB.Recordset.1.5");
      CCustomRs rs;

// 步骤 1 — 打开连接

      pConn->Open("dsn=pubs;", "sa", "", adConnectUnspecified);

// 步骤 2 — 创建命令
// 步骤 3 — 执行命令

      pRs->Open("select * from authors", 
         _variant_t(pConn),
         adOpenDynamic, adLockOptimistic, adCmdText);
      
      if (FAILED(hr = pRs->QueryInterface(__uuidof(IADORecordBinding), 
            (LPVOID*)&picRs)))
         _com_issue_error(hr);
      
      if (FAILED(hr = picRs->BindToRecordset(&rs)))
         _com_issue_error(hr);

// 步骤 4 — 操作数据

      pRs->Fields->GetItem("au_lname")->Properties->GetItem("Optimize")->Value = true; 
      pRs->Sort = "au_lname ASC";
      pRs->Filter = "phone LIKE '415 5*'";

      pRs->MoveFirst();
      while (VARIANT_FALSE == pRs->EndOfFile)
         {
         printf("\a\tName: %s\t %s\tPhone: %s\n",  
            (rs.lau_fnameStatus == adFldOK ? rs.m_szau_fname : ""), 
            (rs.lau_lnameStatus == adFldOK ? rs.m_szau_lname : ""),
            (rs.lphoneStatus == adFldOK ? rs.m_szphone   : ""));

         if (rs.lphoneStatus == adFldOK)
            memcpy(rs.m_szphone, "777", 3);
            
         if (FAILED(hr = picRs->Update(&rs)))
            _com_issue_error(hr);

      // Change the current row of the Recordset. 
      // Recordset data for the new current row will automatically be 
      // extracted and placed in the CCustomRs C++ instance variables.
   
         pRs->MoveNext();
         }
      pRs->Filter = (long) adFilterNone;

// 步骤 5 — 更新数据

      pConn->BeginTrans();
      try 
         {
         pRs->UpdateBatch(adAffectAll);

         // 步骤 6-A — 结束更新 
         pConn->CommitTrans();
         }

      catch (_com_error)
         {
         // 步骤 6-B  — 结束更新
         pRs->Filter = (long) adFilterConflictingRecords;
         pRs->MoveFirst();
         while (VARIANT_FALSE == pRs->EndOfFile)
            {
            printf("\a\tConflict: Name = %s\t %s\n", 
               (rs.lau_fnameStatus == adFldOK ? rs.m_szau_fname : ""), 
               (rs.lau_lnameStatus == adFldOK ? rs.m_szau_lname : ""));
            pRs->MoveNext();
            }
         pConn->RollbackTrans();
         }
      }

   catch (_com_error &e)
      {
      dump_com_error(e);
      }

   CoUninitialize();
   }

VC++ 教程到此结束。