1. Chapter 6: FILE I/O and Serialize CFile class

2. 2 Introduction (1/2) How to read/write a file –Usual way of File I/O Use CFile class Use member functions: CFile::Read() and CFile::Write() Universal use. Low level file I/O –Serialize Use CArchive class Use operators: > Easy to use Limited functionality

3. 3 Introduction (2/2) MFC Class Hierarchy Basic File I/O Derived Classes for specific purposes

4. 4 CFile class Basic functionality  Open or create a file(Open).  Read data at the file pointer(Read).  Write data at the file pointer(Write).  Change the file pointer (Seek).  Close the file(Close).

5. CFile: Two ways to Open a file 1.Use CFile::Open member function 2.Use a constructor CFile file ( filename, mode ); CFile file; file.Open( filename, mode, error ); CFile file; file.Open( filename, mode, error );

6. 6 CFile class (1/6) Open and Create: Use CFile::Open(..) CFile file; if( file.Open("mytest.txt", CFile::modeRead) == false) AfxMessageBox(_T(“Error”)); CFile file; file.Open( filename, mode, error ); CFile file; file.Open( filename, mode, error );

7. 7 CFile class (1/6) Open and Create: Use CFile::Open(..) Get errors and related information CFile file; CFileException e; if(!file.Open("mytest.txt", CFile::modeReadWrite, &e)) e.ReportError(); CFile file; file.Open( filename, mode, error ); CFile file; file.Open( filename, mode, error );

8. CFile class (1/6) Open and Create : Use the constructor try { CFile file("mytest.txt", CFile::modeReadWrite); } catch (CFileException* e) { e->ReportError(); e->Delete(); } CFile file ( filename, mode );

9. 9 CFile class (2/6) Access modes of CFile flagsmeaning CFile::modeCreate Directs the constructor to create a new file. If the file exists already, it is truncated to 0 length CFile::modeNoTruncate Combine this value with modeCreate. If the file being created already exists, it is not truncated to 0 length. CFile::modeRead Requests read access only CFile::modeReadWrite Requests read and write access CFile::modeWrite Requests write access only CFile::shareDenyNone Opens the file nonexclusively CFile::shareDenyRead Denies read access to other parties. CFile::shareDenyWrite Denies write access to other parties. CFile:: shareDenyExclusive Denies both read and write access to other parties (default).

10. 10 CFile class(3/6) Close a file: Destructor closes it automatically void CExFileView::OnLButtonDblClk(UINT nFlags, CPoint point) { CFile file; CFileException e; if(!file.Open("mytest.txt", CFile::modeReadWrite|CFile::modeCreate, &e)) { e.ReportError(); return; } // skip... } // -> CFile::~CFile() is called and close the file automatically.

11. 11 CFile class (4/6) Close a file: CFile::Close member function –When opening a multiple files void CExFileView::OnLButtonDblClk(UINT nFlags, CPoint point) { CFile file; CFileException e; if(!file.Open("mytest.txt“, CFile::modeReadWrite|CFile::modeCreate| CFile::modeNoTruncate, &e)) { e.ReportError(); return; } file.Close(); }

12. 12 CFile class (5/6) Read and Write Change the file pointer UINT CFile::Read (void* lpBuf, UINT nCount) ; void CFile::Write (const void* lpBuf, UINT nCount) ; ULONGLONG CFile::Seek (LONGLONG lOff, UINT nFrom) ; nFrommeaning CFile::beginMove the file pointer by lOff bytes from the beginning CFile::current Move the file pointer by lOff bytes from the current position CFile::endMove the file pointer by lOff bytes from the end

13. 13 CFile class: Write Data CFile file(_T(“test.txt“), CFile::modeCreate|CFile::modeWrite ); int a = 30; int b = 20; file.Write(&a, sizeof(a)); file.Write(&b, sizeof(b)); void CFile::Write (const void* lpBuf, UINT nCount) ;

14. 14 CFile class: Read Data CFile file; CFileException e; if(!file.Open(_T("test.txt“), CFile::modeRead, &e)) { e.ReportError(); return; }; int a,b; file.Read(&a, sizeof(a)); file.Read(&b, sizeof(b)); UINT CFile::Read (void* lpBuf, UINT nCount) ;

15. 15 CFile class: Read Data CFile file; CFileException e; if(!file.Open(_T("test.txt“), CFile::modeRead, &e)){ e.ReportError(); return; }; int a,b; file.Read(&a, sizeof(a)); file.Read(&b, sizeof(b)); CString str; str.Format(_T("a=%d b=%d"), a, b); AfxMessageBox(str); UINT CFile::Read (void* lpBuf, UINT nCount) ;

16. Coding Practice 1.Create variables “a” and “b” 2.When clicking mouse left button, create “test.txt” file, and store the values of “a” and “b” variables 3.When clicking mouse right button, read “test.txt” file, and read the values of “a” and “b” variables 4.Show the data by using AfxMessageBox function

17. 17 CFile class (6/6) Miscellaneous functions –CFile::GetLength(), CFile::SetLength() Get or change the file size. –CFile::GetPosition() Get the file position. –CFile::LockRange(), CFile::UnlockRange() Lock or Unlock the file. If lock a file, other process can not access the file. –CFile::GetFilePath(), CFile::GetFileName() Get full path or file name as a CString

18. 18 CStdioFile Class (1/2) For read/write a text file –CStdioFile::ReadString : to read a text from a file –CStdioFile::WriteString : to write a text to a file CString str; file.ReadString(str); CString str; file.ReadString(str); CString str =_T(“Output”); file.WriteString(str); CString str =_T(“Output”); file.WriteString(str);

19. 19 CStdioFile Class (2/2) Coding example: Make lower characters into upper characters and save it. CStdioFile file1; file1.Open(_T("test1.txt"), CFile::modeRead); CStdioFile file2; file2.Open(_T("test2.txt"),CFile::modeWrite|CFile::modeCreate); CString str; while(file1.ReadString(str)) { str.MakeUpper(); file2.WriteString(str + _T("\n")); }

20. 20 Utility class: CFileFind Class To search a file in the local disk. –CFileFile::FindFile() function to search CFileFind finder; bool bExist = finder.FindFile(“MyText.txt”); CFileFind finder; bool bExist = finder.FindFile(“MyText.txt”);

21. 21 CFileFind Class (2/2) Coding Example: show every files in the current directory CFileFind finder; BOOL bWorking = finder.FindFile(_T("*.*")); while(bWorking) { bWorking = finder.FindNextFile(); if(finder.IsDirectory()) TRACE("[%s]\n", (LPCTSTR)finder.GetFileName()); else TRACE("%s\n", (LPCTSTR)finder.GetFileName()); } Asterisk: Wildcard symbol

22. FILE I/O Serialization and the CArchive Class

23. 23 Serialization basics (1/8) –serialization is … (from Wikipedia) the process of saving an object onto a storage medium (such as a file, or a memory buffer) to transmit it across a network connection link in binary form. The series of bytes or the format can be used to re-create an object that is identical in its internal state to the original object (actually, a clone).”

24. 24 Serialization basics (2/8) Read data by using CFile CFile file; CFileException e; if(!file.Open("mytest.dat", CFile::modeReadWrite|CFile::modeCreate, &e)) { e.ReportError(); return } int a = 100; int b = 200; file.Write(&a, sizeof(a)); file.Write(&b, sizeof(b));

25. 25 Serialization basics (3/8) Read data by serialization CFile file; CFileException e; if(!file.Open("mytest.dat", CFile::modeReadWrite|CFile::modeCreate, &e)) { e.ReportError(); return; } int a = 100; int b = 200; CArchive ar (&file, CArchive::store); ar << a << b;

26. 26 Serialization basics (4/8) Write data by using CFile CFile file; CFileException e; if(!file.Open("mytest.dat", CFile::modeRead, &e)) { e.ReportError(); return; } int a, b; file.Read(&a, sizeof(a)); file.Read(&b, sizeof(b)); TRACE("a = %d, b = %d\n", a, b);

27. 27 Serialization basics (5/8) Write data by serialization CFile file; CFileException e; if(!file.Open("mytest.dat", CFile::modeRead, &e)) { e.ReportError(); return; } int a, b; CArchive ar (&file, CArchive::load); ar >> a >> b; TRACE("a = %d, b = %d\n", a, b);

28. 28 Serialization (6/8) CArchive Class constructor: –pFile Pointer to CFile object –nMode CArchive::load or CArchive::store –nBufSize Buffer size (don’t need to change it) –lpBuf Buffer address (don’t need to change it) CArchive::CArchive (CFile* pFile, UINT nMode, int nBufSize = 4096, void* lpBuf = NULL) ;

29. 29 Serialization basics (7/8) Data types ready to the serialization Data types Basic data types BYTE, WORD, LONG, DWORD, float, double, int, short, char, wchar_t, unsigned, bool, ULONGLONG, LONGLONG MFC data types RECT, POINT, SIZE, CRect, CPoint, CSize, CString, CTime, CTimeSpan, COleVariant, COleCurrency, COleDateTime, COleDataTimeSpan

30. 30 Serialization basics (8/8) Concept of serialization CArchive ar(...); ar << a << b; CArchive ar(...); ar >> a >> b; CArchive ObjectCFile Object Local disk a, b

31. Coding practice Make a program for typing Mouse left click: Save the contents as “testString.dat” file Mouse right click: Load the contents from “testString.dat” file and show it.

32. 32 Serialization Implementation (1/5) How to make your own class to support the serialization? class CMyData { public: CString m_str; COLORREF m_color; public: CMyData(CString &str, COLORREF &color) { m_str = str; m_color = color; } virtual ~CMyData(); };

33. 33 Serialization Implementation (2/5) It will not support any serialization by default void CYourProgram::SaveOrLoad(CArchive& ar) { if (ar.IsStoring()) { ar << m_data; } else { ar >> m_data; } X

34. 34 Serialization Implementation (3/5) Change your class to support the serialization // in your header file class CMyData : public CObject ① { DECLARE_SERIAL(CMyData) ② public: CString m_str; COLORREF m_color; public: CMyData() { } ③ CMyData(CString &str, COLORREF &color) { m_str = str; m_color = color; } virtual ~CMyData(); void Serialize(CArchive& ar); ④ };

35. 35 Serialization Implementation (4/5) Change your class to support the serialization (cont'd) // In your cpp file CMyData::~CMyData() { } IMPLEMENT_SERIAL(CMyData, CObject, 1) ⑤ void CMyData::Serialize (CArchive& ar) ⑥ { CObject::Serialize(ar); if(ar.IsStoring()) ar << m_str << m_color; else ar >> m_str >> m_color; }

36. 36 Serialization Implementation (5/5) Now your own class support serialization void CYourProgram ::SaveOrLoad(CArchive& ar) { if (ar.IsStoring()) { m_data.Serialize(ar); } else { m_data.Serialize(ar); } O

37. Downside of the Serialize The whole file should be read The whole file should be written Extra information should be stored.

38. Coding Practices Draw many circles by using mouse left clicks. Add menu ‘Save’ and save the information of the circles as “circle.dat” file Add menu ‘Load’ and load the data from the file “circle.dat”.