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Create a DLL with database classes (ODBC)


Dip. Ing. Fabio Saponaro - C.S.G. -- fabio@csg.it
Thursday, January 23, 1997

Enviroment: MSVC++ 1.52, Win 3.1

Hi,

I have a problem with use of ODBC class, incapsulated in a DLL.

I am creating a DLL that use database classes (ODBC) to connect with my
database, building with MS Access 2.0.

With Class Wizard I create the classes for connection with database.
The source file of this class (.h and .cpp) I removed from DLL project files.

I had seen example DLLTRACE, contained in MSVC++ 1.52, for setting compiler
e linker option and building my DLL.

Without including files of database classes, DLL works fine.

When I introduce database classes (including files .h) and use it, the
compiler give 0 errors, but linker says that was found an 'unresolved
external' errors.

This error occours for each database class that I use.

So, the question is:
How can I insert my database classe without problem ? And there's particular
settings for compiler and linker before building a DLL with MFC class ?

Thnks in advantage !!

Here's a part of code that produce a link error:

//
//
//

#include 
#include 
#include 

#include "dblistco.h"
#include "dblistit.h"
#include "dblistle.h"
#include "dblistqu.h"
#include "dblistse.h"
#include "dblistte.h"
#include "CMentore.h"
#include "agmentsa.h"

//	Public C interface
//

extern "C" BOOL FAR PASCAL __export GetCourseware(LPCSTR PathScriptDB,
CDBCourseware& Courseware)
{
	......              
}


extern "C" BOOL FAR PASCAL __export GetStringCourseware(LPCSTR PathScriptDB,
LPSTR StringCourseware)
{
        //Only for example .....

        CDatabase* m_database=NULL;
	CDBListCourseware* OneDBCourseware(m_database); <-- THIS DECLARATION
PRODUCE A LINK ERROR
                                                            WHEN I REMOVE
THIS                                                              ROW, NO
ERROR
OCCOURS WITH LINKER   
        ...
}

...

where class CDBListCourseware is:


// dblistco.h : header file
//

/////////////////////////////////////////////////////////////////////////////
// CDBListCourseware recordset

class CDBListCourseware : public CRecordset
{
public:
	CDBListCourseware(CDatabase* pDatabase = NULL);

// Field/Param Data
	//{{AFX_FIELD(CDBListCourseware, CRecordset)
	CString	m_Courseware_Name;
	CString	m_Password;
	CString	m_Title;
	CString	m_Language;
	int		m_TotLessons;
	int		m_TotLessonsEnable;
	int		m_TotSection;
	int		m_TotSectionEnable;
	double	m_Trigger;
	//}}AFX_FIELD


// Implementation
protected:
	virtual CString GetDefaultConnect();	// Default connection string
	virtual CString GetDefaultSQL(); 	// Default SQL for Recordset
	virtual void DoFieldExchange(CFieldExchange* pFX);	// RFX support
	DECLARE_DYNAMIC(CDBListCourseware)
};

// dblistco.cpp : implementation file
//

//#include "stdafx.h"
#include "dblistco.h"

#ifdef _DEBUG
#undef THIS_FILE
static char BASED_CODE THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CDBListCourseware

IMPLEMENT_DYNAMIC(CDBListCourseware, CRecordset)

CDBListCourseware::CDBListCourseware(CDatabase* pdb)
	: CRecordset(pdb)
{
	//{{AFX_FIELD_INIT(CDBListCourseware)
	m_Courseware_Name = "";
	m_Password = "";
	m_Title = "";
	m_Language = "";
	m_TotLessons = 0;
	m_TotLessonsEnable = 0;
	m_TotSection = 0;
	m_TotSectionEnable = 0;
	m_Trigger = 0;
	m_nFields = 9;
	//}}AFX_FIELD_INIT
}


CString CDBListCourseware::GetDefaultConnect()
{
	return "ODBC;DSN=Script;";
}

CString CDBListCourseware::GetDefaultSQL()
{
	return "ListCourseware";
}

void CDBListCourseware::DoFieldExchange(CFieldExchange* pFX)
{
	//{{AFX_FIELD_MAP(CDBListCourseware)
	pFX->SetFieldType(CFieldExchange::outputColumn);
	RFX_Text(pFX, "Courseware_Name", m_Courseware_Name);
	RFX_Text(pFX, "Password", m_Password);
	RFX_Text(pFX, "Title", m_Title);
	RFX_Text(pFX, "Language", m_Language);
	RFX_Int(pFX, "TotLessons", m_TotLessons);
	RFX_Int(pFX, "TotLessonsEnable", m_TotLessonsEnable);
	RFX_Int(pFX, "TotSection", m_TotSection);
	RFX_Int(pFX, "TotSectionEnable", m_TotSectionEnable);
	RFX_Double(pFX, "Trigger", m_Trigger);
	//}}AFX_FIELD_MAP
}

Dip. Ing. Fabio Saponaro
Email:  fabio@csg.it

Context Systems Group - Italian branch:
P.za Liberazione 25
20013 Magenta (MI)
Italia
Tel. ++39-2-97298145
Fax. ++39-2-97298225


Kenneth A. Argo -- argo@rias.COM
Friday, January 24, 1997

Change your include to use:

#include 

Removing the other DB class includes at the same time.

There are a number of libraries which are required which is why you are =
getting the unresolved.  This header properly adds the .LIBs to the link =
process while including the ODBC class headers.

Ken



----------
From:  Dip. Ing. Fabio Saponaro - C.S.G.[SMTP:fabio@csg.it]
Sent:  Thursday, January 23, 1997 12:06 PM
To:  mfc-l@netcom.com
Subject:  Create a DLL with database classes (ODBC)

Enviroment: MSVC++ 1.52, Win 3.1

Hi,

I have a problem with use of ODBC class, incapsulated in a DLL.

I am creating a DLL that use database classes (ODBC) to connect with my
database, building with MS Access 2.0.

With Class Wizard I create the classes for connection with database.
The source file of this class (.h and .cpp) I removed from DLL project =
files.

I had seen example DLLTRACE, contained in MSVC++ 1.52, for setting =
compiler
e linker option and building my DLL.

Without including files of database classes, DLL works fine.

When I introduce database classes (including files .h) and use it, the
compiler give 0 errors, but linker says that was found an 'unresolved
external' errors.

This error occours for each database class that I use.

So, the question is:
How can I insert my database classe without problem ? And there's =
particular
settings for compiler and linker before building a DLL with MFC class ?

Thnks in advantage !!

Here's a part of code that produce a link error:

//
//
//

#include 
#include 
#include 

#include "dblistco.h"
#include "dblistit.h"
#include "dblistle.h"
#include "dblistqu.h"
#include "dblistse.h"
#include "dblistte.h"
#include "CMentore.h"
#include "agmentsa.h"

//	Public C interface
//

extern "C" BOOL FAR PASCAL __export GetCourseware(LPCSTR PathScriptDB,
CDBCourseware& Courseware)
{
	......             =20
}


extern "C" BOOL FAR PASCAL __export GetStringCourseware(LPCSTR =
PathScriptDB,
LPSTR StringCourseware)
{
        //Only for example .....

        CDatabase* m_database=3DNULL;
	CDBListCourseware* OneDBCourseware(m_database); <-- THIS DECLARATION
PRODUCE A LINK ERROR
                                                            WHEN I =
REMOVE
THIS                                                              ROW, =
NO
ERROR
OCCOURS WITH LINKER  =20
        ...
}

..

where class CDBListCourseware is:


// dblistco.h : header file
//

/////////////////////////////////////////////////////////////////////////=
////
// CDBListCourseware recordset

class CDBListCourseware : public CRecordset
{
public:
	CDBListCourseware(CDatabase* pDatabase =3D NULL);

// Field/Param Data
	//{{AFX_FIELD(CDBListCourseware, CRecordset)
	CString	m_Courseware_Name;
	CString	m_Password;
	CString	m_Title;
	CString	m_Language;
	int		m_TotLessons;
	int		m_TotLessonsEnable;
	int		m_TotSection;
	int		m_TotSectionEnable;
	double	m_Trigger;
	//}}AFX_FIELD


// Implementation
protected:
	virtual CString GetDefaultConnect();	// Default connection string
	virtual CString GetDefaultSQL(); 	// Default SQL for Recordset
	virtual void DoFieldExchange(CFieldExchange* pFX);	// RFX support
	DECLARE_DYNAMIC(CDBListCourseware)
};

// dblistco.cpp : implementation file
//

//#include "stdafx.h"
#include "dblistco.h"

#ifdef _DEBUG
#undef THIS_FILE
static char BASED_CODE THIS_FILE[] =3D __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////=
////
// CDBListCourseware

IMPLEMENT_DYNAMIC(CDBListCourseware, CRecordset)

CDBListCourseware::CDBListCourseware(CDatabase* pdb)
	: CRecordset(pdb)
{
	//{{AFX_FIELD_INIT(CDBListCourseware)
	m_Courseware_Name =3D "";
	m_Password =3D "";
	m_Title =3D "";
	m_Language =3D "";
	m_TotLessons =3D 0;
	m_TotLessonsEnable =3D 0;
	m_TotSection =3D 0;
	m_TotSectionEnable =3D 0;
	m_Trigger =3D 0;
	m_nFields =3D 9;
	//}}AFX_FIELD_INIT
}


CString CDBListCourseware::GetDefaultConnect()
{
	return "ODBC;DSN=3DScript;";
}

CString CDBListCourseware::GetDefaultSQL()
{
	return "ListCourseware";
}

void CDBListCourseware::DoFieldExchange(CFieldExchange* pFX)
{
	//{{AFX_FIELD_MAP(CDBListCourseware)
	pFX->SetFieldType(CFieldExchange::outputColumn);
	RFX_Text(pFX, "Courseware_Name", m_Courseware_Name);
	RFX_Text(pFX, "Password", m_Password);
	RFX_Text(pFX, "Title", m_Title);
	RFX_Text(pFX, "Language", m_Language);
	RFX_Int(pFX, "TotLessons", m_TotLessons);
	RFX_Int(pFX, "TotLessonsEnable", m_TotLessonsEnable);
	RFX_Int(pFX, "TotSection", m_TotSection);
	RFX_Int(pFX, "TotSectionEnable", m_TotSectionEnable);
	RFX_Double(pFX, "Trigger", m_Trigger);
	//}}AFX_FIELD_MAP
}

Dip. Ing. Fabio Saponaro
Email:  fabio@csg.it

Context Systems Group - Italian branch:
P.za Liberazione 25
20013 Magenta (MI)
Italia
Tel. ++39-2-97298145
Fax. ++39-2-97298225


Ian Pepper -- Ian@flexicom.ie
Monday, January 27, 1997

Hi Fabio,

If I understand you correctly it appears that you are not including the
.cpp files as part of the DLL project.

Ian
ian@flexicom.ie


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