`StreamWriter`

This writes data to a text file. It can write lines of text or strings to the file. It is easy to use, and one of the most common classes in VB.NET programs.

Ideal usage

Ideally StreamWriter should be used inside a VB.NET Using statement. This ensures the correct disposal of its resources. The syntax is clear and simple.

Example

Here we use StreamWriter to create a new file, and then write 2 lines of text to it along with 2 newlines. Note how the System.IO namespace is imported at the top.

Start The StreamWriter is instantiated and the file "myfile.txt" is opened for writing. You can change the path to another location.

Next The Write call and the two WriteLine calls write the three Strings to the file. The file's contents are listed in the comment.

Imports System.IO

Module Module1
    Sub Main()
        Using writer As StreamWriter =
            New StreamWriter("myfile.txt")

            writer.Write("One ")
            writer.WriteLine("two 2")
            writer.WriteLine("Three")
        End Using
    End Sub
End ModuleOne two 2
Three

`Append` text

Here we use StreamWriter to append lines of text to a file. This is more efficient than reading in the entire file—only the last part of the file needs to be accessed.

Argument 1 The first part of the example opens the file at the absolute path "C:\append.txt".

Argument 2 The second argument to the StreamWriter constructor is the Boolean True. This specifies the append overload.

Then The file is opened again, and a second line is appended to it. The text file contents are shown in the final comment.

Imports System.IO

Module Module1
    Sub Main()
        ' Append the first line of text to a new file.
        Using writer As StreamWriter =
            New StreamWriter("C:\append.txt", True)

            writer.WriteLine("First line appended; 1")
        End Using

        ' Append the second line.
        Using writer As StreamWriter =
            New StreamWriter("C:\append.txt", True)

            writer.WriteLine("Second line appended; 2")
        End Using
    End Sub
End ModuleFirst line appended; 1
Second line appended; 2

`For`-loop

Here we use a For-loop with StreamWriter. When you have to loop and add text to a file, you should reuse a single StreamWriter—this improves performance.

Start The file is opened, and one Windows file handle is created. Then, that same system resource is used to write ten numbers to the file.

Next The Write call in the For-loop specifies a format string. The format string prints the Integer with one decimal place.

Imports System.IO

Module Module1
    Sub Main()
        ' Create new file.
        Using writer As StreamWriter =
            New StreamWriter("loop.txt")

            ' Loop through ten numbers.
            Dim i As Integer
            For i = 0 To 10 - 1
                ' Write number with format string.
                writer.Write("{0:0.0} ", i)
            Next i
        End Using
    End Sub
End Module
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

Summary

Here we saw examples of using StreamWriter in VB.NET. This is an easy way to write to files in the .NET platform. The Using statement is an essential part of the type.

StreamWriter