Visual programming

DYNAMIC LINK LIBRARY(DLL)  To write modular software.  Classes are Build-Time Modular, DLLs are Runtime Modular.  Build smaller DLL modules and test them individually.  For example, put a c++ class in DLL, which might be as small as 12kb after compiling and linking. Client prg can load and link your DLL very quickly when they run.  Microsoft Windows itself uses DLLs for its major function.

How Import Are Matched to Export  A DLL contains a table of exported function.  The function table also contains the addresses of the functions within the DLL.  One EXE file an import functions from one or more DLLs.  DLLs call inside other DLLs.  DLL can have both import and export.  In the DLL code, explicitly declare the exported functions like this:  _declspec(dllexport)int MyFunction(int n);  On client side, declare the corresponding imports like this:  _declspec(dllimport)int MyFunction(int n);

How the Client program finds a DLL  If linked explicitly with LoadLibrary(), the DLLs can be specified in full pathname. If not, or if linked implicitly, windows follows this search sequence to locate your DLL.  1.The directory containing the EXE file.  2. The process’s current directory.  3. The Windows system directory.  4. The Windows directory.  5. The directories listed in the path environment variable.  Built a DLL, and run DLL from client program.

MFC DLLs  AppWizard allows building two kinds of DLLs with MFC library support.  Extension DLLs.  Regular DLLs.

Extension DLL  It supports a C++ interface.  The DLL can export whole classes, hence the client can construct objects of those classes or derive classes from them.  It dynamically links to the code in the DLL version of the MFC library. Hence it requires that the client program be dynamically linked to MFC library.  Both the client program and the extension DLL be synchronized to the same version of the MFC DLLs.  This type of DLLs are quite small, size 10kb, which loads quickly.

Regular DLL  If there is a need for DLL that can be loaded bt any win32 programming environment, use a regular DLL.  A big restriction here is that the regular DLL can export only C-style functions.  It can’t export C++ classes, member function, or overloaded functions because every C++ compiler has its own method of decorating names.  Use C++ classes inside the regular DLL.  To build this type of DLL, it can choose to statically link or dynamically link to the MFC

Example for creating a regular DLL for calculating the square root and use it in the project  Create a new application by selecting file- >new->project  Select MFC Appwizard(dll).  Project name: ex1  Press ok button.  In AppWizard  Application type: Regular DLL using Shared MFC.  Select finished button.  The form screen will appear.

 Add the code for the square root function in the ex1.cpp file. Extern “C” _declspec(dllexport)double squareroot(double d) { If (d>=0.0) return sqrt(d); AfxMessageBox(“can not square root”); return 0.0 } include math.h in the file containing this code. Built the project.

Testing DLL: Client Program  Create a new application by selecting file- >new->project  Select MFC Appwizard(exe).  Project name: ex2  Press ok button.  In AppWizard  Application type: Dialog based  Select finished button.  The Dialog window will appear.

 Add 2 static boxes, 2 Edit box and 1 button to form window.  Code the OnCompute function to call the DLL’s exported function Void Cex2Dialog::OnCompute() { UpdateDate(true); m_dOutput=squareroot(m_dInput); UpdateData(false); }  Declare this squareroot function as an imported function.  Add the following line to ex2Dialog.h file  .extern “C” _declspec(dllimport)double squareroot(double d);

 Select project->setting from vc++ and copy the link where u saved dll file (i.e) ex1.lib file.  E:mcavc++Debugex1.lib  Paste the above link to Object/Library  Build and test the application.

Introduction  Database is used to store data abd provide access to manipulate the data.  Use of standard file format.  Provides multiple user interaction.

VC++ Support for Database Access  ODBC- set of DLLs, Based on SQL, independent of any DB protocol.  DAO- Based on COM interfaces.  OLE DB- based on COM interfaces.

Advantages of Database Management  Use of standard file format.  Indexed file access.  Data integrity.  Multi- user access control.

ODBC ARCHITECTURE  Use the ODBC API to access data from a variety of different data sources.  Contains Driver manger for performing the database activities.  It supports various database drivers  Microsoft SQL server.  Oracle.  Microsoft Access.  Microsoft FoxPro.  Implemented by C native API.

MFC CLASSES FOR ODBC  There are 3 different Built in classes provided by MFC  CDatabase  CRecordSet  CRecordView

CRecordSet Functions  There are several functions are available. They are,  CRecordSet::GetSQL()  GetTableName()  GetODBCFieldCount()  Close()  Open()  Navigating the data in recordset  MoveNext()  MovePrev()  MoveLast()  MoveFirst()  CanScroll()

 To Manipulating the data’s in record set  Delete()  AddNew()  CanAppend()  Edit()  Update()

Recordset Selection  Visual C++ provides 3 types of Recordser. They are differ in speed versus features,  Snapshot Record set.  Dynaset Record set.  Table Record set.

One Simple Example program  Create a database and give the ODBC connectivity.  Database: student  DNS source name: student  Start VC++  Create a new application by selecting file- >new.  Project type: MFC AppWizard(exe).  Project name: recvew  Press ok button

 In AppWizard,  Choose single Document  Select the option “Database view without File support” And click on the Database source button-> select the table create previously in the database and set the Dynaset property.  Select the CrecordView as the view Class’s Base Class.  Select finish button.  Now a dialog will apper.

 Place two edit and two static control.  View-> class wizard -> member variables tab- > select the variables as following.  IDC_EDIT1 m_pSet->m_rollno  IDC_EDIT2 m_pSet->m_name.  Resource view-> Add four more manus to the record menu as follows  Add record, Delete Record, Update Record, Clear

 View-> class wizard-> message maps tab->  ID_RECORD_ADDRECORD OnRecordAddrecord()  ID_RECORD_DELETEREORD OnRecordDeleterecord()  ID_RECORD_UPDATERECORD OnRecordUpdaterecord()  ID_REORD_CLEAR OnRecordClear()

Type the coding as follows.  Void CRecvewView::OnRecordAddrecord()  {  m_pSet->AddNew();  UpdateData(true);  m_pSet->Update();  UpdateData(false);  }  Void CRecvewView::OnRecordUpdaterecord()  {  m_pSet->Edit();  UpdateData(true);  m_pSet->Update();  }

 Void CRecvewView::OnRecordDeleterecord()  {  try  {  m_pSet->Delete();  }  catch(CDBException *e)  {  AfxMessageBox(e->m_strError);  e->Delete();  m_pSet->MoveFirst();  UpdateData(false);  return;  }  UpdateData(false);  }

 Void CRecvewView::OnRecordClear()  {  m_pSet->SetFieldNull(NULL);  UpdateData(false);  } Build the program and Run.

Visual programming

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