VB File Processing

1
VB File Processing
2
The Process of Using a File

• The file must be opened.
• Data is either written to the file or read from
  the file.
• When the application is finished using the file,
  the file is closed.

3
Types of Text File

• Sequential text file
• HTML file, Email file, etc.
• Comma-Delimited file
• "s5","peter",3.5
• "s1","paul",3
• "s7","mary",2
• Random access file

4
x-sender me_at_dchaolaptop x-receiver
you_at_dchaolaptop Received from mail pickup
service by dchaolaptop with Microsoft SMTPSVC
Mon, 19 May 2003 112702 -0700 From ltmegt To
ltyou_at_dchaolaptopgt Subject testReply6 Date Mon,
19 May 2003 112701 -0700 Message-ID
lt008e01c31e343d9826600100007f_at_dchaolaptopgt MIME-
Version 1.0 Content-Type text/plain charset"is
o-8859-1" Content-Transfer-Encoding
7bit X-Mailer Microsoft CDO for Windows
2000 Thread-Index AcMeND2WJSRAs2TDR6WvOdKh/HDlHA
Content-Class urncontent-classesmessage X-Mim
eOLE Produced By Microsoft MimeOLE
V6.00.2600.0000 X-OriginalArrivalTime 19 May
2003 182702.0053 (UTC) FILETIME3DCDB55001C31E
34 testreplyreply6
5
System.IO Namespace

• Directory
• File
• StreamReader
• StreamWriter
• StringReader
• StringWriter

6
Stream

• A stream is an abstraction of a sequence of
  bytes, such as a file, an input/output device, an
  inter-process communication pipe, or a TCP/IP
  socket. The Stream class and its derived classes
  provide a generic view of these different types
  of input and output, isolating the programmer
  from the specific details of the operating system
  and the underlying devices.

7
Creating a Sequential Text File

• Declare a System.IO.StreamWriter writer object
• Dim myFile As System.IO.StreamWriter
• Create a file using System.IO.File.CreateText or
  AppendText method.
• myFilesystem.IO.File.CreateText(c\myTextFile.tx
  t)
• CreateText method returns a StreamWriter.
• If myTextFile.txt already exist, its contents
  will be erased
• myFilesystem.IO.File. AppendText(c\myTextFile.t
  xt)
• If myTextFile.txt already exist, data will be
  appended to the end.
• Note CreateText and AppendText return a
  StreamWriter object.
• Use writer objects WriteLine method to write
  data.
• myFile.WriteLine(test) create a new line
• myFile.Write(test) does not create a new
  line
• Use writer objects Close method to close the
  file.
• myFile.Close()

8
Creating a Text File
Imports System.IO Private Sub Button1_Click(ByVal
sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim myFile As System.IO.StreamWriter
myFile System.IO.File.CreateText("c\myTextFile.
txt") myFile.Write(TextBox1.Text)
myFile.Close() End Sub
9
Reading Files with StreamReader

• Declare a System.IO.StreamReader reader object
• Dim myFile As System.IO.StreamReader
• Open the file using System.IO.File.OpenText
  method.
• myFilesystem.IO.File.OpenText(c\myTextFile.txt
  )
• Use system.IO.File.Exists(FileName) to test if
  file exists.
• Read Data
• myFile.ReadLine() Read one line
• myFile.Read() Read one character code. Use
  Chr function to convert the code to character
  chr(myFile.Read())
• ReadLine and Read methods automatically move the
  pointer.
• To detect the end of a file MyFile.Peek-1
• myFile.ReadToEnd() read entire contents of a
  file.
• Use writer objects Close method to close the
  file.
• myFile.Close()

10
Reading a Text File
Private Sub Button2_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs)
Handles Button2.Click Dim myFile As
System.IO.StreamReader myFile
System.IO.File.OpenText("c\myTextFile.txt")
TextBox1.Text myFile.ReadToEnd()
myFile.Close() End Sub
11
OpenFileDialog

• Properties
• Filter descriptionfilter
• The description and the filter are separated with
  the pipe symbol.
• Text file (.txt) .txt
• All files (.) .
• Initial directory
• FileName
• Method
• ShowDialog

12
OpenFileDialog Example
If OpenFileDialog1.ShowDialog() DialogResult.OK
Then MessageBox.Show(OpenFileDialog1.F
ileName) myFile System.IO.File.OpenT
ext(OpenFileDialog1.FileName)
TextBox1.Text myFile.ReadToEnd Else
MsgBox("no file selected") End If
13
SaveFileDialog Example
Dim outFile As System.IO.StreamWriter If
documentName "" Then If
saveFileDialog1.ShowDialog DialogResult.OK
Then documentName
saveFileDialog1.FileName End If End
If outFile System.IO.File.CreateText(doc
umentName) outFile.Write(TextBox1.Text)
outFile.Close()
14
DrawString Print One Line of Text

• System.Drawing.Graphics
• DrawString method arguments
• String to print
• Font
• Brush
• X position
• Y position
• The X, Y coordinates must be declared as Single
  data type. X coordinate is the horizontal
  distance across a line from the left edge, Y
  coordinate is the distance from the top.

15
PrintDocument Control

• PrinterSetting property
• PrinterName
• PrintToFile
• MaximumPage
• MinimumPage
• PaperSize
• Method
• Print The Print method will trigger the
  PrintPage event

16
PrintDialog Control

• Use the PrintDialog to get the values for the
  PrinterSetting property of the PrintDocument
  control.
• PrintDialog1.Document PrintDocument1
• PrintDialog1.ShowDialog()
• With PrintDocument1.PrinterSettings
• .PrintToFile PrintDialog1.PrinterSettings.
  PrintToFile
• .MaximumPage PrintDialog1.PrinterSettings.
  MaximumPage
• .PrinterName PrintDialog1.PrinterSettings.
  PrinterName
• End With
• Note The PrintDialogs Document property gets or
  sets a value indicating the PrintDocument used to
  obtain PrinterSetting.

17
PrintDocument Example
PrintDocument1.Print()
Private Sub PrintDocument1_PrintPage(ByVal sender
As System.Object, ByVal e As System.Drawing.Printi
ng.PrintPageEventArgs) Handles PrintDocument1.Prin
tPage e.Graphics.DrawString(textbox1.text,
New Font("courier", 18, FontStyle.Bold),
Brushes.Black, 150, 80) End Sub
18
Print and PrintPage Event

• The Print method of the PrintDocument control
  will trigger the PrintPage event. This event is
  fired once for each page to be printed. After
  finishing printing one page, we can use the
  PrintPageEventArgs HasMorePage property to
  inform the PrintDocument whether there is more
  page to print.

19
PrintPreviewDialog Control

• PrintPreviewDialog1.Document PrintDocument1
• PrintPreviewDialog1.ShowDialog()

20
Print Multiple Lines

• Textboxs MultiLine property is true.
• Textboxs Lines property returns a string array
  with each line as an element.
• The Y position must be increased by the height of
  the font.

21
PrintPageEventArgs

• DrawString Send a line of text to the graphics
  page.
• Properties
• MarginBounds.Left, top, bottom, etc.
• HasMorePage

22
Private Sub PrintDocument1_PrintPage(ByVal sender
As System.Object, ByVal e As System.Drawing.Printi
ng.PrintPageEventArgs) Handles PrintDocument1.Prin
tPage Dim fntPrintFont As New
Font("Courier", 18) Dim sngLineHeight As
Single fntPrintFont.GetHeight 2 Dim
sngXPos As Single e.MarginBounds.Left
Dim sngYPos As Single e.MarginBounds.Top
Dim tempArray() As String tempArray
TextBox1.Lines Dim line As Integer
For line 0 To tempArray.GetUpperBound(0)
e.Graphics.DrawString(tempArray(line),
fntPrintFont, Brushes.Black, sngXPos, sngYPos)
sngYPos sngLineHeight Next
End Sub
23
Printing Multiple Pages
Private Sub PrintDocument1_PrintPage(ByVal sender
As System.Object, ByVal e As System.Drawing.Printi
ng.PrintPageEventArgs) Handles PrintDocument1.Prin
tPage Static pageCount As Integer 1
Static lineCount As Integer 0 Dim
fntPrintFont As New Font("Courier", 18)
Dim sngLineHeight As Single fntPrintFont.GetHeig
ht 2 Dim sngXPos As Single
e.MarginBounds.Left Dim sngYPos As Single
e.MarginBounds.Top Dim counter As
Integer Dim tempArray() As String
tempArray TextBox1.Lines
e.Graphics.DrawString("Page "
pageCount.ToString, fntPrintFont, Brushes.Black,
sngXPos, sngYPos) sngYPos
sngLineHeight For counter lineCount To
tempArray.GetUpperBound(0)
e.Graphics.DrawString(tempArray(counter),
fntPrintFont, Brushes.Black, sngXPos, sngYPos)
sngYPos sngLineHeight If
sngYPos gt e.MarginBounds.Bottom Then
pageCount pageCount 1
lineCount counter 1
e.HasMorePages True Exit For
End If Next End Sub
24
A Few Notes

• The X, Y coordinates must be declared as Single
  data type. X coordinate is the horizontal
  distance across a line from the left edge, Y
  coordinate is the distance from the top.
• Font object type and its properties and methods.
• Textboxs Lines property returns a string array
  with each line as an element.
• Why the pageCount and lineCount are declared as
  Static?

25
Comma-Delimited File

• It stores each data item with a comma separating
  each item and places double quotes around string
  fields.
• S5, Peter, 3.0
• S1, Paul, 2.5

26
Creating a Comma-Delimted File

• Imports System.IO
• Open the file for output
• fileNumber FreeFile()
• FileOpen(fileNumber, "c\stdata.txt",
  OpenMode.Output)
• Note FreeFile function returns a file number.
• Use WriteLine function to write a record to the
  file
• WriteLine(fileNumber, TextBox1.Text,
  TextBox2.Text, CDbl(TextBox3.Text))
• Note Assuming write a student record with CID,
  CNAme, and GPA fields.
• Use the FileCose function to close the file
• FileClose(fileNumber)
• Note OpenMode.Append

27
Reading a Comma-Delimted File

• Imports System.IO
• Open the file for input
• fileNumber FreeFile()
• FileOpen(fileNumber, "c\stdata.txt",
  OpenMode.Input)
• Use Input function to read a field from the file
• If Not EOF(fileNumber) Then
• Input(fileNumber, TextBox1.Text)
• Input(fileNumber, TextBox2.Text)
• Input(fileNumber, TextBox3.Text)
• Else
• MsgBox("Reach EOF")
• End If
• Note The Input function can read only one filed
  from the file at a time.
• Note The EOF function detects the End of File
  condition.
• Use the FileCose function to close the file
• FileClose(fileNumber)

28
Sequentialy Accessing the Student File to Compute
Average GPA
Dim fileNumber, stCounter As Integer Dim
temp1, temp2 As String Dim gpa, sumGpa As
Double fileNumber FreeFile()
FileOpen(fileNumber, "c\stdata.txt",
OpenMode.Input) Do While Not
EOF(fileNumber) Input(fileNumber,
temp1) Input(fileNumber, temp2)
Input(fileNumber, gpa) sumGpa
gpa stCounter 1 Loop
MessageBox.Show(sumGpa / stCounter.ToString)
29
Create a File Processing Application

• Use a form to display a customer record in
  textboxes. This form has a MoveNext button to
  show the next record.
• A form to enter new customer data.

30
Structures

• A user-defined data type to hold related fields.
• Structure emp
• Dim eid As String
• Dim ename As String
• Dim salary As Double
• End Structure
• Dim myEmp as emp
• myEmp.eide1
• myEmp.enamepeter
• myEmp.salary5000.00

31

• A structure may contain arrays as fields, but
  cannot be declared with an initial size. Must
  use a ReDim statement to declare the size.
  Structure emp
• Dim eid As String
• Dim ename As String
• Dim salary As Double
• Dim dependent() As String
• End Structure
• Dim myEmp as emp
• ReDim myEmp.dependent(3)

32

• A structure may also contain methods.
• Structure emp
• Dim eid As String
• Dim ename As String
• Dim salary As Double
• Dim dependent() As String
• Function tax(ByVal salary) As Double
• tax salary 0.15
• End Function
• End Structure
• Dim myEmp As emp
• myEmp.salary 1000
• myEmp.tax(myEmp.salary)

33
Random-Access File

• Records in a random-access file do not have to
  processed in sequence. A record can be retrieved
  selectively.
• A random-access file can be opened for both
  reading and writing.
• Each record in a random-a ccess file is
  identified by a unique integer, the first record
  is record 1.
• The records in a random-access file must be the
  same size.

34
Using a Structure to Create Record

• Structure emp
• ltVBFixedString(3)gt Dim eid As String
• ltVBFixedString(10)gt Dim ename As String
• Dim salary As Double
• Function tax(ByVal salary) As Double
• tax salary 0.15
• End Function
• End Structure
• Note Use ltVBFixedString(3)gt to control string
  size.

35
Opening a Random-Access File

• FileOpen(fileNumber, fileName,OpenMode,OpenAccess,
  OpenShare, RecordLength)
• OpenMode Random
• OpenAccessReadWrite
• OpenShare
• RecordLength
• Example
• Dim MyEmp as Emp
• fileNumber FreeFile()
• FileOpen(fileNumber, "c\empRnd.txt",
  OpenMode.Random, OpenAccess.ReadWrite,
  OpenShare.Default, Len(myEmp))

36
Writing a Record

• FilePut(FileNumber, Record, RecordNumber)
• myEmp.eid TextBox1.Text
• myEmp.ename TextBox2.Text
• myEmp.salary CDbl(TextBox3.Text)
• FilePut(fileNumber, myEmp,
  CInt(myEmp.eid.Substring(1)))
• Note Assuming EID is of this format XNN.

37
Reading a Record

• FileGet(FileNumber, Record, RecordNumber)
• Dim recNumber As Integer
• recNumber CInt(InputBox("Please enter empID
  ").Substring(1))
• FileGet(fileNumber, myEmp, recNumber)
• TextBox1.Text myEmp.eid
• TextBox2.Text myEmp.ename
• TextBox3.Text myEmp.salary.ToString

38
Random File Example
Dim fileNumber As Integer Structure emp
ltVBFixedString(3)gt Dim eid As String
ltVBFixedString(10)gt Dim ename As String
Dim salary As Double Function tax(ByVal
salary) As Double tax salary
0.15 End Function End Structure
Dim myEmp As emp Private Sub Form2_Load(ByVal
sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
fileNumber FreeFile()
FileOpen(fileNumber, "c\empRnd.txt",
OpenMode.Random, OpenAccess.ReadWrite,
OpenShare.Default, Len(myEmp))
39
Writing and Reading
Private Sub Button1_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs)
Handles Button1.Click myEmp.eid
TextBox1.Text myEmp.ename
TextBox2.Text myEmp.salary
CDbl(TextBox3.Text) FilePut(fileNumber,
myEmp, CInt(myEmp.eid.Substring(1))) End
Sub Private Sub Button2_Click(ByVal sender
As System.Object, ByVal e As System.EventArgs)
Handles Button2.Click Dim recNumber As
Integer recNumber CInt(InputBox("Please
enter empID ").Substring(1))
FileGet(fileNumber, myEmp, recNumber) If
myEmp.eid.Substring(0, 1) ltgt "e" Then
MsgBox("record not exist") Else
TextBox1.Text myEmp.eid
TextBox2.Text myEmp.ename
TextBox3.Text myEmp.salary.ToString End
If End Sub
40
Sequential Access to a Random-Access File
Dim outString As String Dim recNumber As
Integer 1 Do While Not EOF(fileNumber)
FileGet(fileNumber, myEmp, recNumber)
outString outString
recNumber.ToString myEmp.eid myEmp.ename
myEmp.salary.ToString vbCrLf
recNumber 1 Loop
MessageBox.Show(outString) Note Do While
recNumber lt NumberOfRecords
41
Hashing

• RecordAddress H(Key)
• H(Key)Key Mod M
• 0 lt Key Mod M lt M 1
• 1 lt 1 Key Mod M lt M

42
Hashing Example

• Key Mod 8
• H(1821) 5
• H(7115) 3
• H(2428) 4
• H(4750) 6
• H(1620) 4 Collision
• H(4692) 4
• H(4758) 6
• Collision resolution
• Linear probing

43
Inserting a Record

• H(Key)
• If space H(Key) available, insert into space
  K(Key)
• Else check subsequent space until a free space is
  found.
• How to detect the file is full?

44
Searching a Record

• Read record at H(Key)
• If no record at H(Key), then record not exist
• If record at H(Key) is the searched record, then
  Found
• Else Search the next space until reach an empty
  space.

45
Deleting a Record

• Search the record to be deleted.
• Change a field to a special deletion flag.
• Write it back to its original space with the
  deletion flag.

46
Serialization

• The act of saving (serializing) an object onto a
  storage medium and later deserializing it from
  the storage medium to recreate an object.
• BinaryFormatter
• Serialize
• Deserialize

47
Imports System.IO Imports System.Runtime.Serializa
tion.Formatters.Binary Private Sub
Form1_Load(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles MyBase.Load
Dim fs As New FileStream("c\testSerializing.dat",
FileMode.Create) Dim myArrayList As New
ArrayList myArrayList.Add("A")
myArrayList.Add("B") myArrayList.Add(5)
myArrayList.Add(10) Dim bf As New
BinaryFormatter bf.Serialize(fs,
myArrayList) fs.Close() End Sub
Private Sub Button1_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs)
Handles Button1.Click Dim fs As New
FileStream("c\testSerializing.dat",
FileMode.Open) Dim myArrayList As New
ArrayList Dim bf As New BinaryFormatter
myArrayList CType(bf.Deserialize(fs),
ArrayList) Dim obj As New Object
For Each obj In myArrayList
ListBox1.Items.Add(obj) Next End Sub