BinaryReader.Read Method (Byte(), Int32, Int32)


Reads the specified number of bytes from the stream, starting from a specified point in the byte array.

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

Public Overridable Function Read (
	buffer As Byte(),
	index As Integer,
	count As Integer
) As Integer


Type: System.Byte()

The buffer to read data into.

Type: System.Int32

The starting point in the buffer at which to begin reading into the buffer.

Type: System.Int32

The number of bytes to read.

Return Value

Type: System.Int32

The number of bytes read into buffer. This might be less than the number of bytes requested if that many bytes are not available, or it might be zero if the end of the stream is reached.

Exception Condition

The buffer length minus index is less than count.


The number of decoded characters to read is greater than count. This can happen if a Unicode decoder returns fallback characters or a surrogate pair.


buffer is null.


index or count is negative.


The stream is closed.


An I/O error occurs.

BinaryReader does not restore the file position after an unsuccessful read operation.

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

The following example shows how to write binary data by using memory as a backing store. It displays a message to the console that indicates whether the data was written correctly.

Imports System.IO

Module Module1

    Sub Main()
        Const upperBound As Integer = 1000
        Dim dataArray(upperBound) As Byte
        Dim verifyArray(upperBound) As Byte

        Dim randomGenerator As New Random

        Using binWriter As New BinaryWriter(New MemoryStream())
            Console.WriteLine("Writing the data.")
            binWriter.Write(dataArray, 0, dataArray.Length)

            Using binReader As New BinaryReader(binWriter.BaseStream)
                binReader.BaseStream.Position = 0

                If binReader.Read(verifyArray, 0, dataArray.Length) <> dataArray.Length Then
                    Console.WriteLine("Error writing the data.")
                End If
            End Using
        End Using

        For i As Integer = 0 To upperBound
            If verifyArray(i) <> dataArray(i) Then
                Console.WriteLine("Error writing the data.")
            End If
        Next i

        Console.WriteLine("The data was written and verified.")
    End Sub

End Module

This example reads the contents of a file and displays each byte's numeric value in 16-column format. The end of the file that is being read is detected when the Read method returns zero bytes.

Imports System
Imports System.IO
Imports System.Text

Module Module1
    Private ReadOnly CHUNK_SIZE As Integer = 1024
    Public Sub Main(args() As String)
        If ((args.Length = 0) OrElse Not File.Exists(args(0))) Then
            Console.WriteLine("Please provide an existing file name.")
            Using fs As FileStream = New FileStream(args(0), FileMode.Open, FileAccess.Read)
                Using br As New BinaryReader(fs, New ASCIIEncoding())
                    Dim chunk(CHUNK_SIZE) As Byte
                    chunk = br.ReadBytes(CHUNK_SIZE)

                    While chunk.Length > 0
                        DumpBytes(chunk, chunk.Length)
                        chunk = br.ReadBytes(CHUNK_SIZE)
                    End While
                End Using
            End Using
        End If
    End Sub

    Public Sub DumpBytes(bdata() As Byte, len As Integer)
        Dim i As Integer
        Dim j As Integer = 0
        Dim dchar As Char
        ' 3 * 16 chars for hex display, 16 chars for text and 8 chars
        ' for the 'gutter' int the middle.
        Dim dumptext As New StringBuilder("        ", 16 * 4 + 8)
        For i = 0 To len - 1
            dumptext.Insert(j * 3, String.Format("{0:X2} ", CType(bdata(i), Integer)))
            dchar = Convert.ToChar(bdata(i))
            ' replace 'non-printable' chars with a '.'.
            If Char.IsWhiteSpace(dchar) Or Char.IsControl(dchar) Then
                dchar = "."
            End If
            j += 1
            If j = 16 Then
                dumptext.Length = 0
                dumptext.Append("        ")
                j = 0
            End If
        Next i
        ' display the remaining line
        If j > 0 Then
            ' add blank hex spots to align the 'gutter'.
            For i = j To 15
                dumptext.Insert(j * 3, "   ")
            Next i
        End If
    End Sub

End Module

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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