1. Introduction to Programming Lecture 6
Msury Mahunnah,
Department of Informatics,
Tallinn University of Technology

2. “Operations With Text Files”

3. Text Files Text files have an extension that ends with .txt
It is called a Sequential File

4. Working with files
File handling in Visual Basic is based on System.IO namespace with a class library that supports string, character and file manipulation. These classes contain properties, methods and events for creating, copying, moving, and deleting files.
The most commonly used classes are FileStream, BinaryReader, BinaryWriter, StreamReader and StreamWriter.

5. You can open a Text File for ...
Reading
Writing
Appending

6. Opening a Text File for Reading
Const fname$ = “C:\Users\Owner\Documents\test.txt“
Dim objReader As New System.IO.StreamReader(fname)
After this sentence the file is not opened yet
“As New” – This means “Create a New Object”. The type of the object is a StreamReader: System.IO.StreamReader

7. Opening a Text File for Reading
One of the StreamReader methods available for reading is “ReadToEnd” (reading whole file at once)
This method read the whole text, right to the end.
i.e. TextBox1.Text = objReader.ReadToEnd
(After this sentence the file is opened and the text is read)
It is imporant to close the StreamReader after reading (otherwise you’ll get error messages)
objReader.Close()

8. ReadToEnd example
Const fname$ = “C:\Users\Owner\Documents\test.txt" If System.IO.File.Exists(fname) = True Then Dim objReader As New System.IO.StreamReader(fname) richtextbox1.AppendText(objReader.ReadToEnd) objReader.Close() Else MsgBox(“File Does Not Exist”) End If

9. Reading Line by Line
Method ReadToEnd is used for reading the whole file at once
Method ReadLine for reading one line at a time
To go through the whole file, use Do ... Loop statement with Peek method
Peek signifies the end of the text file. Returns the next available character but does not consume it.
If Peek returns -1 the reading sequence (process) is at the end of the file.

10. ReadLine example
Const fname$ = “C:\Users\Owner\Documents\test.txt“ If System.IO.File.Exists(fname) = True Then Dim objReader As New System.IO.StreamReader(fname) Dim TextLine As String = “” Do While objReader.Peek() <> -1 TextLine = TextLine & objReader.ReadLine() & vbNewLine Loop richtextbox1.AppendText(TextLine) objReader.Close() Else MsgBox(“File Does Not Exist”) End If

11. Opening a Text File for Writing
Const fname$ = “C:\Users\Owner\Documents\test2.txt"
Dim objWriter As New System.IO.StreamWriter(fname)
After this sentence the file is not opened yet
The type of the object is a StreamWriter: System.IO.StreamWriter

12. Writing into Text File Method Write add text into Text File.
VB insists that the file must exist before it can actually do something with it!
objWriter.Write(“Hello world”) or
objWriter.WriteLine(“Hello world”)
- This sentence writes “Hello word” into file and goes to new line

13. Write example
Const fname$ = “C:\Users\Owner\Documents\test.txt“ If System.IO.File.Exists(fname) = True Then Dim objWriter As New System.IO.StreamWriter(fname) objWriter.Write(“Hello world!”) objWriter.Close() MsgBox(“Text written to file!”) Else MsgBox(“File Does Not Exist”) End If

14. Creating a file if it doesn’t exist
Const fname$ = “C:\Users\Owner\Documents\test.txt“
Dim objWriter As New System.IO.StreamWriter(fname, False)
objWriter.Write(“Hello world!”)
objWriter.Close()
MsgBox(“Text written to file!”)
(Add a comma and False)

15. Opening a Text File for Appending
Const fname$ = “C:\Users\Owner\Documents\test.txt" If System.IO.File.Exists(fname) = True Then Dim objWriter As New System.IO.StreamWriter(fname, True) objWriter.Write(“Hello world!”) objWriter.Close() MsgBox(“Text written to file!”) Else MsgBox(“File Does Not Exist”) End If
(Add a comma and True)

16. Reading from a file and writing into an array
Dim TextLine$ Dim seq As Object Dim t&=-1 Dim i&, V$() .... TextLine = objReader.ReadLine() seq = Strings.Split(TextLine, “ “) For i = Lbound(seq) To Ubound(seq) t+=1 Redim Preserve V(t) V(t) = seq(i) Next ...

17. All txt-files in certain folder
Dim files() As String
files = System.IO.Directory.GetFiles(path, pattern)
files = System.IO.Directory.GetFiles(“C:\Users\John\", "*.txt")
MsgBox("Found " & files.Length & " txt-files")
Dim file As String
For Each file In files
RTB.AppendText(file & vbNewLine)
Next
RTB - RichTextBox

18. Create and delete a directory
System.IO.Directory.CreateDirectory(path)
System.IO.Directory.CreateDirectory(“C:\Users\John\folder1\folder2\”)
Possibility to add so many subfolder as needed!
System.IO.Directory.Delete(path)
System.IO.Directory.Delete(“C:\Users\John\folder1\folder2\”)

19. Delete all txt-files in folder
Dim files() As String files = System.IO.Directory.GetFiles(“C:\Users\John", "*.txt") MsgBox("Found " & files.Length & " txt-files") Dim file As String For Each file In files System.IO.File.Delete(file) Next

20. Retrieving the Names of All Drives in the Computer
Dim drives() As String
drives = System.IO.Directory.GetLogicalDrives
Dim drive As String
For Each drive In drives
RTB.AppendText(drive & vbNewLine)
Next
RTB - RichTextBox