File Processing and the Document

The MFC library provides a more advanced and elaborate system of file processing in the internals of the document/view architecture through the CDocument class. Although this system is not the easiest and is not shared by other programming environments, once you are familiar with it, you may like.

In the Document/View architecture world, a file or its content is displayed in the view while its real estate is managed by the frame. Therefore, while using a document, the user typically uses the view to manipulate the file. The trick for you is when it becomes time to save the file. Since you shouldn't manipulate the document in the document class (?), when it is time to save it, you must "transfer" the values to be saved from the view to the document class. then let the document class handle the processing of the file. This is valid both for saving and opening the file.

1. Start a new application as Single Document and name it LoanEval
2. Base its view class on CFormView
3. Design the form as follows:
    

   Control ID Caption Additional Properties Group Box   Loan Preparation   Static Text   Prepared By:   Edit Box IDC_PREPARED_BY     Static Text   Prepared For:   Edit Box IDC_PREPARED_FOR     Group Box   Values   Static Text   Principal: Edit Box IDC_PRINCIPAL   Align Text: Right Static Text   Interest: Edit Box IDC_INTEREST_RATE   Align Text: Right Static Text   %   Static Text   Periods:   Edit Box IDC_PERIODS   Align Text: Center Number: True Static Text   Years   Group Box   Compound Frequency   Radio Button IDC_COMPOUND Monthly Group: True Left Text: True Radio Button   Quarterly Left Text: True Radio Button   Semiannually Left Text: True Radio Button   Annually Left Text: True Group Box       Static Text   Interest Earned   Edit Box IDC_INTEREST_TOEARN   Align Text: Right Static Text   Amount Earned   Edit Box IDC_FUTURE_VALUE   Align Text: Right Button IDC_CALCULATE_BTN Calculate Default Button: True Button IDC_RESET_BTN Reset

4. Using either the ClassWizard or the Add Member Variable Wizard, add the following member variables to the controls:
    

   Identifier	Type	Value Variable
   IDC_PREPARED_BY	CString	m_PreparedBy
   IDC_PREPARED_FOR	CString	m_PreparedFor
   IDC_PRINCIPAL	double	m_Principal
   IDC_INTEREST_RATE	double	m_InterestRate
   IDC_PERIODS	UINT	m_Periods
   IDC_COMPOUND	int	m_Compound
   IDC_INTEREST_TOEARN	double	m_InterestToEarn
   IDC_FUTURE_VALUE	double	m_FutureValue

5. Change the design of the IDR_MAINFRAME icon as follows:
    
6. In the header file of the document class, declare a variable for each value that will be used in file processing:
    

   // LoanEvalDoc.h : interface of the CLoanEvalDoc class // ///////////////////////////////////////////////////////////////////////////// . . . class CLoanEvalDoc : public CDocument { protected: // create from serialization only CLoanEvalDoc(); DECLARE_DYNCREATE(CLoanEvalDoc) // Attributes public: CString strEmployee; CString strCustomer; double Principal; double InterestRate; UINT Periods; int Compound; // Operations public: . . . }; . . .

7. To prepare the file for processing, access the Serialize() event of the document and change it as follows:
    

   void CLoanEvalDoc::Serialize(CArchive& ar) { if (ar.IsStoring()) { ar << strEmployee << strCustomer << Principal << InterestRate << Periods << Compound; } else { ar >> strEmployee >> strCustomer >> Principal >> InterestRate >> Periods >> Compound; } }

8. Access the StdAfx.h header file and include the math.h header file:
    

   . . . #define VC_EXTRALEAN // Exclude rarely-used stuff from Windows headers #include <afxwin.h> // MFC core and standard components #include <afxext.h> // MFC extensions #include <afxdisp.h> // MFC Automation classes #include <afxdtctl.h> // MFC support for Internet Explorer 4 Common Controls #ifndef _AFX_NO_AFXCMN_SUPPORT #include <afxcmn.h> // MFC support for Windows Common Controls #endif // _AFX_NO_AFXCMN_SUPPORT #include <math.h> . . .

9. Generate a BN_CLICKED message for the the IDC_CALCULATE_BTN control associated with the view class and accept the suggested name of the function
10. Implement it as follows:
     

    void CLoanEvalView::OnCalculateBtn() { // TODO: Add your control notification handler code here UpdateData(); double InterestToEarn; double FutureValue; int CompoundType; switch( m_Compound ) { case 0: CompoundType = 12; break; case 1: CompoundType = 4; break; case 2: CompoundType = 2; break; case 3: CompoundType = 1; break; } double i = (m_InterestRate / 100) / CompoundType; int n = CompoundType * m_Periods; FutureValue = m_Principal * pow(1 + i, n); InterestToEarn = FutureValue - m_Principal; CWnd *edtInterestToEarn = reinterpret_cast<CEdit *>( GetDlgItem(IDC_INTEREST_TOEARN)); CWnd *edtFutureValue = reinterpret_cast<CEdit *>( GetDlgItem(IDC_FUTURE_VALUE)); char InterestAmount[20], FValue[20]; sprintf(InterestAmount, "%.2f", InterestToEarn); sprintf(FValue, "%.2f", FutureValue); edtInterestToEarn->SetWindowText(InterestAmount); edtFutureValue->SetWindowText(FValue); }

11. Generate a message for the ID_FILE_SAVE menu item associated with the view class and accept the suggested name of the function
12. Implement it as follows:
     

    void CLoanEvalView::OnFileSave() { // TODO: Add your command handler code here this->UpdateData(); CLoanEvalDoc *pDoc = GetDocument(); pDoc->strEmployee = this->m_PreparedBy; pDoc->strCustomer = this->m_PreparedFor; pDoc->Principal = this->m_Principal; pDoc->InterestRate = this->m_InterestRate; pDoc->Periods = this->m_Periods; pDoc->Compound = this->m_Compound; CFile flLoan; char strFilter[] = { "Loan Files (*.onf)|*.onf|Text Files (*.txt)|*.txt|All Files (*.*)|*.*||" }; CFileDialog FileDlg(FALSE, ".bcr", NULL, 0, strFilter); if( FileDlg.DoModal() == IDOK ) { flLoan.Open(FileDlg.GetFileName(), CFile::modeCreate | CFile::modeWrite); CArchive ar(&flLoan, CArchive::store); pDoc->Serialize(ar); ar.Close(); } else return; flLoan.Close(); }

13. Generate a message for the ID_FILE_OPEN menu item associated with the view class and accept the suggested name of the function
14. Implement it as follows:
     

    void CLoanEvalView::OnFileOpen() { // TODO: Add your command handler code here UpdateData(); CLoanEvalDoc *pDoc = GetDocument(); CFile flLoan; char strFilter[] = { "BCR Files (*.onf)|*.onf|Text Files (*.txt)|*.txt|All Files (*.*)|*.*||" }; CFileDialog FileDlg(FALSE, ".bcr", NULL, 0, strFilter); if( FileDlg.DoModal() == IDOK ) { if( flLoan.Open(FileDlg.GetFileName(), CFile::modeRead) == FALSE ) return; CArchive ar(&flLoan, CArchive::load); pDoc->Serialize(ar); m_PreparedBy.Format("%s", pDoc->strEmployee); m_PreparedFor.Format("%s", pDoc->strCustomer); m_Principal = pDoc->Principal; m_InterestRate = pDoc->InterestRate; m_Periods = pDoc->Periods; m_Compound = pDoc->Compound; ar.Close(); } else return; flLoan.Close(); UpdateData(FALSE); }

15. Access the frame's source file to remove the default title and set your own as follows:
     

    // MainFrm.cpp : implementation of the CMainFrame class // . . . ///////////////////////////////////////////////////////////////////////////// // CMainFrame construction/destruction . . . int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct) { if (CFrameWnd::OnCreate(lpCreateStruct) == -1) return -1; . . . this->SetWindowText("Loan Evaluation"); this->CenterWindow(); return 0; } BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs) { if( !CFrameWnd::PreCreateWindow(cs) ) return FALSE; cs.style &= ~FWS_ADDTOTITLE; return TRUE; } ///////////////////////////////////////////////////////////////////////////// // CMainFrame diagnostics . . .

16. Execute the application then create and save a record
     
    

MFC File Processing Options

In the above example, we used the CFile class to discuss file processing. MFC provides more extended file processing support than that. In reality, file processing is one of the strengths of MFC. It excels in it by providing the following classes:

FILE: FILE is a C structure used to perform file processing for that language. You can also use it in your MFC applications.

CStdioFile: MFC provides the same file processing support as the C language through the CStdioFile class.

Win32: The Win32 library provides its own mechanism of file processing through its HANDLE concept. A file is created using the CreateFile() function.