CreateInstance为什么会出错呢？谁帮我看看这段数据库连接的代码。先谢了.

Question

inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
_ConnectionPtr m_pConnection;
BSTR m_bstrCnn;
m_pConnection = NULL;
m_bstrCnn = SysAllocString(L"Provider=SQLOLEDB;User id=sa;Password=;DataSource=legendNT;Initial Catalog=macau_web");
try
{
TESTHR(m_pConnection.CreateInstance
(__uuidof(Connection)));
TESTHR(m_pConnection->Open(m_bstrCnn,"","",NULL));
}
catch(_com_error &error)
{
                    .....
         }
为什么执行 CreateInstance就出错了？ 先谢了

Answer 1

have you called CoInitialize(NULL)?

Answer 2

Throw Exception.How to called CoInitialize(NULL)?

Answer 3

我在CreatInstance前加了CoInitialize(NULL),CoInitialize(NULL)执行成功，
CreatInstance 还是 Throw Exception.
能否再帮我看一下?谢了.

Answer 4

各位朋友，能否帮帮我，给我一份ADO用创建好连接的代码范例。假设数据库SQL SERVER 机器名为LegendNT.
我很奇怪找不到ado Visual C++ MFC程序的范例，SDK范例搬到MFC就不行了，郁闷。
请发到:[email protected] 谢谢.刚才调试过程的错误信息是:expresion can not be evaluated

Answer 5

#import "C:\Program Files\Common Files\System\ADO\msado15.dll" \
    no_namespace rename("EOF", "EndOfFile")#include <oledb.h>
#include <stdio.h>
#include <conio.h>
#include "OpenX.h"// Function declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void OpenX(void);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);///////////////////////////////////////////////////////////
//                                                       //
//      Main Function                                    //
//                                                       //
///////////////////////////////////////////////////////////void main()
{
    if(FAILED(::CoInitialize(NULL)))
        return;    OpenX();    ::CoUninitialize();
}///////////////////////////////////////////////////////////
//                                                       //
//               OpenX Function                          //
//                                                       //
///////////////////////////////////////////////////////////void OpenX(void)
{
    // Define ADO object pointers.
    // Initialize pointers on define.
    // These are in the ADODB::  namespace
     _RecordsetPtr    pRstEmployees  = NULL;
     _ConnectionPtr pConnection    = NULL;    // Define string variables.
    _bstr_t strCnn("Provider=sqloledb;Data Source=srv;"
        "Initial Catalog=Pubs;User Id=sa;Password=;");    // Define Other Variables.
    HRESULT  hr = S_OK;
    IADORecordBinding   *picRs  = NULL;  // Interface Pointer declared.
    CEmployeesRs emprs;       // C++ Class object
    DBDATE varDate;    try
    {
        // open connection and record set
        TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
        pConnection->Open(strCnn,"","",NULL);        TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset)));
        pRstEmployees->Open("Employees", 
            _variant_t((IDispatch *)pConnection,true), adOpenKeyset,
            adLockOptimistic, adCmdTable);        // Open an IADORecordBinding interface pointer which we'll 
        // use for Binding Recordset to a class.
        TESTHR(pRstEmployees->QueryInterface(
            __uuidof(IADORecordBinding),(LPVOID*)&picRs));        //Bind the Recordset to a C++ Class here.
        TESTHR(picRs->BindToRecordset(&emprs));        // Assign the first employee record's hire date
        // to a variable, then change the hire date.
        varDate = emprs.m_sze_hiredate;
        printf("\nOriginal data\n");
        printf("\tName - Hire Date\n");
        printf("  %s  %s - %d/%d/%d\n\n",
            emprs.le_fnameStatus == adFldOK ? 
            emprs.m_sze_fname : "<NULL>",
            emprs.le_lnameStatus == adFldOK ? 
            emprs.m_sze_lname : "<NULL>",
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.month : 0,
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.day : 0,
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.year : 0);         emprs.m_sze_hiredate.year=1900;
        emprs.m_sze_hiredate.month=1;
        emprs.m_sze_hiredate.day=1;
        picRs->Update(&emprs);        printf("\nChanged data\n");
        printf("\tName - Hire Date\n");
        printf("  %s %s - %d/%d/%d\n\n",
            emprs.le_fnameStatus == adFldOK ? 
            emprs.m_sze_fname : "<NULL>",
            emprs.le_lnameStatus == adFldOK ? 
            emprs.m_sze_lname : "<NULL>",
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.month : 0,
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.day : 0,
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.year : 0);         // Requery Recordset and reset the hire date.
        pRstEmployees->Requery(adOptionUnspecified);
        // Open an IADORecordBinding interface pointer which we'll 
        // use for Binding Recordset to a class.
        TESTHR(pRstEmployees->QueryInterface(
            __uuidof(IADORecordBinding),(LPVOID*)&picRs));        // Rebind the Recordset to a C++ Class here.
        TESTHR(picRs->BindToRecordset(&emprs));
        emprs.m_sze_hiredate = varDate;
        picRs->Update(&emprs);
        printf("\nData after reset\n");
        printf("\tName - Hire Date\n");
        printf("  %s %s - %d/%d/%d",emprs.le_fnameStatus == adFldOK ? 
            emprs.m_sze_fname : "<NULL>",
            emprs.le_lnameStatus == adFldOK ? 
            emprs.m_sze_lname : "<NULL>",
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.month : 0,
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.day : 0,
            emprs.le_hiredateStatus == adFldOK ? 
            emprs.m_sze_hiredate.year : 0);         // Clean up objects before exit.
        pRstEmployees->Close();
        pConnection->Close();
    }    catch(_com_error &e)
    {
        // Notify the user of errors if any.
        // Pass a connection pointer accessed from the Connection.
        PrintProviderError(pConnection);
        PrintComError(e);
    }
}///////////////////////////////////////////////////////////
//                                                       //
//      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;    if( (pConnection->Errors->Count) > 0)
    {
        long nCount = pConnection->Errors->Count;
        // Collection ranges from 0 to nCount -1.
        for(long i = 0;i < nCount;i++)
        {
            pErr = pConnection->Errors->GetItem(i);
            printf("\t Error number: %x\t%s", pErr->Number,
                pErr->Description);
        }
    }
}///////////////////////////////////////////////////////////
//                                                       //
//      PrintComError Function                           //
//                                                       //
///////////////////////////////////////////////////////////void PrintComError(_com_error &e)
{
   _bstr_t bstrSource(e.Source());
   _bstr_t bstrDescription(e.Description());    // Print COM errors. 
   printf("Error\n");
   printf("\tCode = %08lx\n", e.Error());
   printf("\tCode meaning = %s\n", e.ErrorMessage());
   printf("\tSource = %s\n", (LPCSTR) bstrSource);
   printf("\tDescription = %s\n", (LPCSTR) bstrDescription);
}OpenX.h:#include "icrsint.h"// This Class extracts only fname,lastname and 
// hire_date from employee table
class CEmployeesRs : public CADORecordBinding
{BEGIN_ADO_BINDING(CEmployeesRs)
    
    // Column fname is the 2nd field in the table   
   ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_fname, 
         sizeof(m_sze_fname), le_fnameStatus, FALSE)
    
    // Column lname is the 4th field in the table.
   ADO_VARIABLE_LENGTH_ENTRY2(4, adVarChar, m_sze_lname, 
         sizeof(m_sze_lname), le_lnameStatus, FALSE)    // Column hiredate is the 8th field in the table.
   ADO_VARIABLE_LENGTH_ENTRY2(8, adDBDate,m_sze_hiredate, 
         sizeof(m_sze_hiredate), le_hiredateStatus, TRUE)
   
END_ADO_BINDING()public:
   CHAR        m_sze_fname[21];
   ULONG    le_fnameStatus;
   CHAR        m_sze_lname[31];
   ULONG    le_lnameStatus;
   DBDATE    m_sze_hiredate;
   ULONG    le_hiredateStatus;
};

Answer 6

在MSDN中有大量的ADO例子！
Platfrom SDK -> Data Services->Microsfot Data Access Components->
Microsoft ActiveX Data Object ->ADO->Sample
下面!上面的例子就是摘录自其中！！：）

Answer 7

force_eagle(战鹰) :你误会我的意思了，你提到的例子是SDK.该问题我终于弄明白的，初始化时候没有加: if (!AfxOleInit())
{
AfxMessageBox(_T("ole Initialize Fail"));
return FALSE;
}sign.无论如何，非常感谢各位朋友.