VB File Processing. 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.
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VB File Processing
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.
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
x-sender: me@dchaolaptop
x-receiver: you@dchaolaptop
Received: from mail pickup service by dchaolaptop with Microsoft SMTPSVC;
Mon, 19 May 2003 11:27:02 -0700
From: <me>
To: <you@dchaolaptop>
Subject: testReply6
Date: Mon, 19 May 2003 11:27:01 -0700
Message-ID: <008e01c31e34$3d982660$0100007f@dchaolaptop>
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
X-Mailer: Microsoft CDO for Windows 2000
Thread-Index: AcMeND2WJSRAs2TDR6WvOdKh/HDlHA==
Content-Class: urn:content-classes:message
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000
X-OriginalArrivalTime: 19 May 2003 18:27:02.0053 (UTC) FILETIME=[3DCDB550:01C31E34]
testreplyreply6
System.IO Namespace
• Directory
• File
• StreamReader
• StreamWriter
• StringReader
• StringWriter
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.
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.– myFile=system.IO.File.CreateText(“c:\myTextFile.txt”)
• CreateText method returns a StreamWriter.• If myTextFile.txt already exist, its contents will be erased
– myFile=system.IO.File. AppendText(“c:\myTextFile.txt”)• If myTextFile.txt already exist, data will be appended to the end. • Note: CreateText and AppendText return a StreamWriter object.
• Use writer object’s WriteLine method to write data.– myFile.WriteLine(“test”) ***create a new line– myFile.Write(“test”) ***does not create a new line
• Use writer object’s Close method to close the file.– myFile.Close()
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
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.– myFile=system.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 object’s Close method to close the file.– myFile.Close()
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
OpenFileDialog
• Properties– Filter: description|filter
• The description and the filter are separated with the pipe | symbol.
– Text file (*.txt) | *.txt
– All files (*.*) | *.*
– Initial directory
– FileName
• Method:– ShowDialog
OpenFileDialog Example
If OpenFileDialog1.ShowDialog() = DialogResult.OK Then
MessageBox.Show(OpenFileDialog1.FileName)
myFile = System.IO.File.OpenText(OpenFileDialog1.FileName)
TextBox1.Text = myFile.ReadToEnd
Else
MsgBox("no file selected")
End If
SaveFileDialog ExampleDim 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(documentName)
outFile.Write(TextBox1.Text)
outFile.Close()
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.
PrintDocument Control
• PrinterSetting property:– PrinterName
– PrintToFile
– MaximumPage
– MinimumPage
– PaperSize
• Method:– Print *** The Print method will trigger the PrintPage
event
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 PrintDialog’s Document property gets or sets a value indicating the PrintDocument used to obtain PrinterSetting.
PrintDocument Example
PrintDocument1.Print()
Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage
e.Graphics.DrawString(textbox1.text, New Font("courier", 18, FontStyle.Bold), Brushes.Black, 150, 80)
End Sub
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.
PrintPreviewDialog Control
• PrintPreviewDialog1.Document = PrintDocument1
• PrintPreviewDialog1.ShowDialog()
Print Multiple Lines
• Textbox’s MultiLine property is true.
• Textbox’s Lines property returns a string array with each line as an element.
• The Y position must be increased by the height of the font.
PrintPageEventArgs
• DrawString: Send a line of text to the graphics page.
• Properties:– MarginBounds.Left, top, bottom, etc.– HasMorePage
Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage
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
Printing Multiple PagesPrivate Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage
Static pageCount As Integer = 1
Static lineCount As Integer = 0
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 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 >= e.MarginBounds.Bottom Then
pageCount = pageCount + 1
lineCount = counter + 1
e.HasMorePages = True
Exit For
End If
Next
End Sub
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.• Textbox’s Lines property returns a string array
with each line as an element.• Why the pageCount and lineCount are declared as
Static?
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
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
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)
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)
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.
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.eid=“e1”– myEmp.ename=“peter”– myEmp.salary=5000.00
• 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)
• 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)
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.
Using a Structure to Create Record
• Structure emp• <VBFixedString(3)> Dim eid As String• <VBFixedString(10)> Dim ename As String• Dim salary As Double• Function tax(ByVal salary) As Double• tax = salary * 0.15• End Function• End Structure
• Note: Use <VBFixedString(3)> to control string size.
Opening a Random-Access File
• FileOpen(fileNumber, fileName,OpenMode,OpenAccess, OpenShare, RecordLength)
• OpenMode: Random
• OpenAccess:ReadWrite
• OpenShare
• RecordLength
• Example:– Dim MyEmp as Emp
– fileNumber = FreeFile()
– FileOpen(fileNumber, "c:\empRnd.txt", OpenMode.Random, OpenAccess.ReadWrite, OpenShare.Default, Len(myEmp))
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.
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
–
Random File ExampleDim fileNumber As Integer
Structure emp
<VBFixedString(3)> Dim eid As String
<VBFixedString(10)> 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))
Writing and ReadingPrivate 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) <> "e" Then
MsgBox("record not exist")
Else
TextBox1.Text = myEmp.eid
TextBox2.Text = myEmp.ename
TextBox3.Text = myEmp.salary.ToString
End If
End Sub
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 <= NumberOfRecords
Hashing
• RecordAddress = H(Key)
• H(Key)=Key Mod M0 <= Key Mod M <= M – 1
1 <= 1 + Key Mod M <= M
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
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?
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.
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.
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
Imports System.IOImports System.Runtime.Serialization.Formatters.BinaryPrivate 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
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