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BinaryWriter.Write Method (String)

Writes a length-prefixed string to this stream in the current encoding of the BinaryWriter, and advances the current position of the stream in accordance with the encoding used and the specific characters being written to the stream.

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Overridable Sub Write ( _
	value As String _
)

Parameters

value
Type: System.String
The value to write.

ExceptionCondition
IOException

An I/O error occurs.

ArgumentNullException

value is Nothing.

ObjectDisposedException

The stream is closed.

A length-prefixed string represents the string length by prefixing to the string a single byte or word that contains the length of that string. This method first writes the length of the string as a UTF-7 encoded unsigned integer, and then writes that many characters to the stream by using the BinaryWriter instance's current encoding.

For a list of common I/O tasks, see Common I/O Tasks.

This example demonstrates how Write adds the length prefix when it writes a string. The string data is first read as a sequence of raw bytes and its length is calculated. Next, a BinaryReader reads the string directly. The output from both string retrievals is displayed.


Imports System
Imports System.IO
Imports System.Text

Public Class BinReadWrite
    Public Shared Sub Main()
        Dim testfile As String = "C:\testfile.bin"

        ' create a test file using BinaryWriter
        Dim fs As FileStream = File.Create(testfile)
        Dim utf8 As New UTF8Encoding()

        Dim bw As New BinaryWriter(fs, utf8)
        Dim bstring As String

        bstring  = "This is line #1 of text written as a binary stream." + vbNewLine
        bstring = bstring + "This is line #2 of text written as a binary stream." + vbNewLine
        bstring = bstring + "This is line #3 of text written as a binary stream." + vbNewLine
        bw.Write(bstring)

        ' reset the stream position for reading
        fs.Seek(0, SeekOrigin.Begin)

        ' Read the string as raw bytes using FileStream...
        ' The first series of bytes is the UTF7 encoded length of the
        ' string. In this case, however, it is just the first two bytes.
        Dim len As Integer = fs.ReadByte() And 127
        len = len + fs.ReadByte() * 128
        ' read the string as bytes of length = len
        Dim rawbytes(len) As Byte
        fs.Read(rawbytes, 0, len)

        ' display the string
        Console.WriteLine("Read from FileStream:   " + vbNewLine + utf8.GetString(rawbytes))
        Console.WriteLine()

        ' Now, read the string using BinaryReader

        ' reset the stream position for reading again
        fs.Seek(0, SeekOrigin.Begin)

        Dim br As New BinaryReader(fs, utf8)
        ' ReadString will read the length prefix and return the string.
        bstring = br.ReadString()
        Console.WriteLine("Read from BinaryReader: "+ vbNewLine + bstring)
        fs.Close()
    End Sub
End Class

' The output from the program is this:
'
' Read from FileStream:
' This is line #1 of text written as a binary stream.
' This is line #2 of text written as a binary stream.
' This is line #3 of text written as a binary stream.
'
' Read from BinaryReader:
' This is line #1 of text written as a binary stream.
' This is line #2 of text written as a binary stream.
' This is line #3 of text written as a binary stream.


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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