Imput & Output.docx - Input & output last modified July 6,...

Input & output
last modified July 6, 2020
This chapter is dedicated to input & output in Visual Basic. The
input & output in Visual Basic is based on streams.
Streams are objects to work with input & output. 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.
In Visual Basic, we have a
Stream
class that is an abstract class for
all streams. There are additional classes that derive from the
Stream class and make the programming a lot easier.
MemoryStream
A
MemoryStream
is a stream which works with data in a computer
memory.
Option Strict On
Imports System.IO
Module Example
Sub Main()
Dim ms As Stream = New MemoryStream(6)
ms.WriteByte(9)
ms.WriteByte(11)
ms.WriteByte(6)
ms.WriteByte(8)
ms.WriteByte(3)
ms.WriteByte(7)
ms.Position = 0
Dim rs As Integer
rs = ms.ReadByte()
Do While rs <> -1
Console.WriteLine(rs)
rs = ms.ReadByte()
Loop

ms.Close()
End Sub
End Module
We write six numbers to a memory with a
MemoryStream
. Then we
read those numbers and print them to the console.
Dim ms As Stream = New MemoryStream(6)
The line creates and initializes a
MemoryStream
object with a capacity
of six bytes.
ms.Position = 0
We set the position of the cursor in the stream to the beginning
using the
Position
property.
ms.WriteByte(9)
ms.WriteByte(11)
ms.WriteByte(6)
...
The
WriteByte()
method writes a byte to the current stream at the
current position.
Do While rs <> -1
Console.WriteLine(rs)
rs = ms.ReadByte()
Loop
Here we read all bytes from the stream and print them to the
console.
ms.Close()
Finally, we close the stream.
$ ./memory.exe
9
11
6
8
3
7
Output of the example.

StreamReader & StreamWriter
StreamReader
reads characters from a byte stream. It defaults to
UTF-8 encoding.
StreamWriter
writes characters to a stream in a
particular encoding.
Option Strict On
Imports System.IO
Module Example
Sub Main()
Dim file As String
file = "languages"
Try
Dim stream As StreamReader
stream = New StreamReader(file)
Console.WriteLine(stream.ReadToEnd())
Catch e As IOException
Console.WriteLine("Cannot read file.")
End Try
End Sub
End Module
We have a file called languages. We read characters from that file
and print them to the console.
Dim stream As StreamReader
stream = New StreamReader(file)
The
StreamReader
takes a file name as a parameter.
Console.WriteLine(stream.ReadToEnd())
The
ReadToEnd()
method reads all characters to the end of the
stream.