Visual C Sharp File IO 1

1
Visual C Sharp File I/O - 1

• Variables and arrays only temporary
• - lost when a program terminates
• Files used for long term storage
• (Data bases considered later in course)
• We will cover
• File types
• File and Directory classes
• File open and save dialogs
• Sequential-access files
• Random-access files
• Stream-input/output features

2
Visual C Sharp File I/O - 2

• File Types Text (ASCII) or Binary
• Text files - ASCII characters with CR and LF.
• Handled in a line-by-line, or sequential manner.
• Binary Files - Typed and Untyped files
• Binary files all values - cant be displayed -
  .EXE file.
• Typed files - known format using data types -
  database. Untyped files - no rigid structure,
  sizes can vary.
• E.g. EXE program files, BMP bitmap graphic files.
  
• - Program using it knows how to deal with it.

3
Visual C Sharp File I/O - 3

• Files and streams
• C views files as a sequential stream of bytes.
• File ends with EOF marker or after a byte count.
• You open the file, read and write to it, then
  close it.
• Uses StreamReader and StreamWriter Classes
• They implement methods to read and write files.
• Similar classes used to read/write to Internet or
  serial I/O

4
Visual C Sharp File I/O - 4

• File and Directory Classes (static classes)
• Can perform Directory or File handling
• Directory
• CreateDirectory, Delete, GetFiles, Exists
• File
• Exists does file exist?
• Create creates file
• CreateText creates a text file
• AppendText appends or creates
• Delete deletes the file
• Open opens with desired R / W attributes
• OpenRead opens for read-only
• OpenText returns StreamReader (later)
• OpenWrite returns FileStream (later)
• Need using System.IO

5
Visual C Sharp File I/O - 5

• First of all Menu and Dialog controls
• Text Editor example
• MenuStrip control used to create menus (File Edit
  Help)
• C has FileDialog controls open and save files
• OpenFileDialog SaveFileDialog
• Rich Text box control will display text files
• RT box has more functions than textbox cut,
  paste etc.

6
Visual C Sharp File I/O - 6

• File Dialog controls
• Open and Save dialogs
• non visual (not on form appear when program
  runs)
• ShowDialog displays the familiar open and save
  dialogs

7
Visual C Sharp File I/O - 7

• MenuStrip control
• Enter required main menu commands (File, Edit,
  Help)
• Add submenus FilegtOpen, Help gt About etc.
• To add code click File, double-click Open
• Add code
• if (openFileDialog1.ShowDialog( ) !
  DialogResult.Cancel)
• richTextBox1.LoadFile(openFileDialog1.FileName,
• RichTextBoxStreamType.PlainText)
• // more detail later
• ShowDialog method displays the familiar file
  handling dialog

8
Visual C Sharp File I/O - 8

• Code to display FileDialogs. Use
• openFileDialog1.ShowDialog( ) and
• saveFileDialog1.ShowDialog( )
• Need to check for OK or Cancel.
• if (openFileDialog1.ShowDialog( ) !
  DialogResult.Cancel)
• // filename is openFileDialog1.FileName
• N.b.
• File I/O needs namespace using System.IO

9
Visual C Sharp File I/O - 9

• Open/Save File dialog properties
• CheckFileExists, DefaultExt InitialDirectory
  etc.
• File filter. Can set in code
• openFileDialog1.Filter "All files
  (.).Text files(.TXT).txt"

10
Visual C Sharp File I/O - 10

• Rich Text Box file handling
• Easiest way to open and save text files is to use
  RTB
• Open file
• if (openFileDialog1.ShowDialog() !
  DialogResult.Cancel)
• richTextBox1.LoadFile(openFileDialog1.FileName,
  RichTextBoxStreamType.PlainText)
• RTB has methods, e.g
• RTB.Find method finds strings in RTB (Search)

11
Visual C Sharp File I/O - 11

• Rich Text Box file handling Save file
• For MenuStrip FilegtSave, add
• if (saveFileDialog1.ShowDialog( ) !
  DialogResult.Cancel)
• RichTextBox1.SaveFile(saveFileDialog1.FileNam
  e,
• RichTextBoxStreamType.PlainText)
• Text editor created in a few lines of code.

12
Visual C Sharp File I/O - 12

• Using StreamReader to read file into RichTextBox
• StreamReader streamRdr new
  StreamReader(openFileDialog1.FileName)
• richTextBox1.Text streamRdr.ReadToEnd( )
• streamRdr.Close( )
• Writing file using StreamWriter
• StreamWriter streamWr new
• StreamWriter(saveFileDialog1.FileName)
• streamWr.Write(richTextBox1.Text)
• streamWr.Close( )
• Why use? may not want to use RT box to read file

13
Visual C Sharp File I/O - 13

• Example code snippet read file
• string filename
• filename txtFilename.Text // read from textbox
• if ( File.Exists(filename) )
• string inputString File.ReadAllText(fileName)
• textBox1.Text inputString

14
Visual C Sharp File I/O - 14

• Example code snippet - write
• string filename
• filename txtFilename.Text // read from textbox
• if ( File.Exists(filename) )
• File.WriteAllText(filename, txtFileName.txt)
• textBox1.Text inputString

15
Visual C Sharp File I/O - 15

• Binary files
• // Read
• byte fileByteArray new byte1000
• fileByteArray File.ReadAllBytes("test.bin")
• // have to do something with the binary files to
  display them
• // could split into upper and lower nibbles and
  add 40hex
• // makes chars _at_ABC.. MNO
• // To Write
• File.WriteAllBytes("test.bin", fileByteArray)

16
Visual C Sharp File I/O - 16

• Sequential-Access File Handling
• Non-text files? E.g. Student record (integer,
  string, double)
• Could create our own Record, Class, or even
  object for this.
• Search - Start at beginning and read data until
  its found
• Maybe necessary to do this lots of times
• How do we save Objects?
• Tell compiler our Class can be saved as bytes
  Serializable attribute
• FileStream class used to writing of binary data
• (instead of StreamReader/Writer)

17
Visual C Sharp File I/O - 17

• Random Access File Handling
• Allows instant access to information
• - Individual records accessed without searching
  through file
• Easiest when all records are a fixed length
• Data can be inserted without destroying other
  data in file
• Records can be updated without rewriting the
  entire file
• Uses file-position pointer - points to next byte
  to be read or written - can be repositioned to
  any point in file
• Uses class BinaryWriter and BinaryReader instead
  of serialization
• By attaching a FileStream to it, bytes can be
  read/written directly to a file

18
Visual C Sharp File I/O - 18

• Exception handling
• Exceptions File may not exist, divide by zero,
  convert alpha string to number
• Use Try .. Catch code
• int number1123, zero 0
• try
• number1 number1 / zero
• catch (DivideByZeroException)
• MessageBox.Show("Something's
  wrong here")

19
Visual C Sharp File I/O - 19

• Summary
• File types
• File and Directory classes
• MenuStrip control
• Text Editor example RTBox
• Open / Save Dialogs
• Files and Streams
• Sequential-access files
• Random-access files