Close an Input Sequential Access File

HOW TO: Close an Input Sequential Access File
Syntax
streamReaderVariableName.Close()

Example
inFile.Close()
closes the file associated with the inFile variable.

Use the Peek method of the StreamReader

HOW TO: Use the Peek method
Syntax
streamReaderVariableName.Peek

Example
Dim lineOfText As String
   Do Until inFile.Peek = -1
   lineOfText = inFile.ReadLine
   MessageBox.Show(lineOfText)
Loop
reads each line of the file associated with the inFile variable, line by line. Each line (excluding the newline character) is assigned to the lineOfText variable and is then displayed in a messagebox.

Determine whether a Sequential Access File Exists

HOW TO: Determine whether a Sequential Access File Exists
Syntax
IO.File.Exists(fileName)

Example
If IO.File.Exists(“report.txt”)  = True Then
determines whether the report.txt file exists in the current project’s bin\Debug folder.

Reading data from a Sequential Access File

HOW TO: Declare a StreamReader Variable
Syntax
{Dim | Private} streamReaderVariableName As IO.StreamReader

Example
Dim inFile As IO.StreamReader
declares a StreamReader variable named inFile.

HOW TO: Create a StreamReader Object
Syntax
IO.File.OpenText(fileName)

Example
inFile = IO.File.OpenText(“report.txt”)
opens the report.txt file for input, creates a StreamReader object and assigns it to the inFile variable.

HOW TO: Read data from a sequential access file
Syntax
streamReaderVariableName.ReadLine

Example
Dim message As String
message = inFile.ReadLine
reads a line of text from the file associated with the inFile variable and assigns the line, excluding the newline character, to the message variable.

Close an Output Sequential Access File

HOW TO: Close an Output Sequential Access File
Syntax
streamWriterVariableName.Close()

Example
outFile.Close()
closes the file associated with the outFile variable.

Write data to a sequential access file

HOW TO: Write data to a sequential access file using StreamWriter
Syntax
streamWriterVariableName.Write(data)
streamWriterVariableName.WriteLine(data)

Example 1
outFile.write(“Hello”)

Result
The string “Hello” is written to the file, the next character written to the file will appear immediatley after the letter “o”.

Example 2
outFile.WriteLine(“Hello”)

Result
The string “Hello” is written to the file. The next character written to the file will appear on the next line.

StreamWriter object

HOW TO: Declare a StreamWriter object
Syntax
{Dim | Private} streamWriterVariableName As IO.StreamWriter

Example
Dim outFile As IO.StreamWriter
declares a StreamWriter variable named outFile

HOW TO: Create a StreamWriter object
Syntax
IO.File.method(fileName)

Methods
CreateText: opens a file for output - creates a new empty file to which data can be written. If the file already exists, the data in the file is deleted before any new data is written to it.

AppendText: opens a file for append - the new data is written after any existing data in the file. If the file does not exist, the file is created for you.

Example 1
outFile = IO.File.CreateText(“mytextfile.txt”)
opens the mytextfile.txt file for output; creates a StreamWriter object and assigns it to the outFile variable. The file is open for output.

Example 2
outFile = IO.File.AppendText(“report.txt”)
opens the report.txt file for append; creates a StreamWriter object and assigns it to the outFile variable. The file is open for append.