Reading from and Writing to Text Files

The StreamReader and StreamWriter classes are used for reading from and writing data to text files. These classes inherit from the abstract base class Stream, which supports reading and writing bytes into a file stream.

The StreamReader Class

The StreamReader class also inherits from the abstract base class TextReader that represents a reader for reading series of characters. The following table describes some of the commonly used methods of the StreamReader class −

Sr.No. Method Name & Purpose
1

Public Overrides Sub Close

It closes the StreamReader object and the underlying stream and releases any system resources associated with the reader.
2

Public Overrides Function Peek As Integer

Returns the next available character but does not consume it.
3

Public Overrides Function Read As Integer

Reads the next character from the input stream and advances the character position by one character.

Example

The following example demonstrates reading a text file named Jamaica.txt. The file reads −

Down the way where the nights are gay
And the sun shines daily on the mountain top
I took a trip on a sailing ship
And when I reached Jamaica
I made a stop

Imports System.IO
Module fileProg
   Sub Main()
      Try
         ' Create an instance of StreamReader to read from a file. 
         ' The using statement also closes the StreamReader. 
         Using sr As StreamReader = New StreamReader("e:/jamaica.txt")
            Dim line As String
            ' Read and display lines from the file until the end of  
            ' the file is reached. 
            line = sr.ReadLine()
            While (line <> Nothing)
               Console.WriteLine(line)
               line = sr.ReadLine()
            End While
         End Using
      Catch e As Exception
         ' Let the user know what went wrong.
         Console.WriteLine("The file could not be read:")
         Console.WriteLine(e.Message)
      End Try
      Console.ReadKey()
   End Sub
End Module

Guess what it displays when you compile and run the program!

The StreamWriter Class

The StreamWriter class inherits from the abstract class TextWriter that represents a writer, which can write a series of character.

The following table shows some of the most commonly used methods of this class −

Sr.No. Method Name & Purpose
1

Public Overrides Sub Close

Closes the current StreamWriter object and the underlying stream.
2

Public Overrides Sub Flush

Clears all buffers for the current writer and causes any buffered data to be written to the underlying stream.
3

Public Overridable Sub Write (value As Boolean)

Writes the text representation of a Boolean value to the text string or stream. (Inherited from TextWriter.)
4

Public Overrides Sub Write (value As Char)

Writes a character to the stream.
5

Public Overridable Sub Write (value As Decimal)

Writes the text representation of a decimal value to the text string or stream.
6

Public Overridable Sub Write (value As Double)

Writes the text representation of an 8-byte floating-point value to the text string or stream.
7

Public Overridable Sub Write (value As Integer)

Writes the text representation of a 4-byte signed integer to the text string or stream.
8

Public Overrides Sub Write (value As String)

Writes a string to the stream.
9

Public Overridable Sub WriteLine

Writes a line terminator to the text string or stream.

The above list is not exhaustive. For complete list of methods please visit Microsoft's documentation

Example

The following example demonstrates writing text data into a file using the StreamWriter class −

Live Demo 
Imports System.IO
Module fileProg
   Sub Main()
      Dim names As String() = New String() {"Zara Ali", _
         "Nuha Ali", "Amir Sohel", "M Amlan"}
      Dim s As String
      Using sw As StreamWriter = New StreamWriter("names.txt")
         For Each s In names
            sw.WriteLine(s)
         Next s
      End Using
      ' Read and show each line from the file. 
      Dim line As String
      Using sr As StreamReader = New StreamReader("names.txt")
         line = sr.ReadLine()
         While (line <> Nothing)
            Console.WriteLine(line)
            line = sr.ReadLine()
         End While
      End Using
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Zara Ali
Nuha Ali
Amir Sohel
M Amlan
vb.net_file_handling.htm
Advertisements