VB.Net - Binary Files

The BinaryReader and BinaryWriter classes are used for reading from and writing to a binary file.

The BinaryReader Class

The BinaryReader class is used to read binary data from a file. A BinaryReader object is created by passing a FileStream object to its constructor.

The following table shows some of the commonly used methods of the BinaryReader class.

Sr.No.	Method Name & Purpose
1	Public Overridable Sub Close It closes the BinaryReader object and the underlying stream.
2	Public Overridable Function Read As Integer Reads the characters from the underlying stream and advances the current position of the stream.
3	Public Overridable Function ReadBoolean As Boolean Reads a Boolean value from the current stream and advances the current position of the stream by one byte.
4	Public Overridable Function ReadByte As Byte Reads the next byte from the current stream and advances the current position of the stream by one byte.
5	Public Overridable Function ReadBytes (count As Integer) As Byte() Reads the specified number of bytes from the current stream into a byte array and advances the current position by that number of bytes.
6	Public Overridable Function ReadChar As Char Reads the next character from the current stream and advances the current position of the stream in accordance with the Encoding used and the specific character being read from the stream.
7	Public Overridable Function ReadChars (count As Integer) As Char() Reads the specified number of characters from the current stream, returns the data in a character array, and advances the current position in accordance with the Encoding used and the specific character being read from the stream.
8	Public Overridable Function ReadDouble As Double Reads an 8-byte floating point value from the current stream and advances the current position of the stream by eight bytes.
9	Public Overridable Function ReadInt32 As Integer Reads a 4-byte signed integer from the current stream and advances the current position of the stream by four bytes.
10	Public Overridable Function ReadString As String Reads a string from the current stream. The string is prefixed with the length, encoded as an integer seven bits at a time.

The BinaryWriter Class

The BinaryWriter class is used to write binary data to a stream. A BinaryWriter object is created by passing a FileStream object to its constructor.

The following table shows some of the commonly used methods of the BinaryWriter class.

Sr.No.	Function Name & Description
1	Public Overridable Sub Close It closes the BinaryWriter object and the underlying stream.
2	Public Overridable Sub Flush Clears all buffers for the current writer and causes any buffered data to be written to the underlying device.
3	Public Overridable Function Seek (offset As Integer, origin As SeekOrigin ) As Long Sets the position within the current stream.
4	Public Overridable Sub Write (value As Boolean) Writes a one-byte Boolean value to the current stream, with 0 representing false and 1 representing true.
5	Public Overridable Sub Write (value As Byte) Writes an unsigned byte to the current stream and advances the stream position by one byte.
6	Public Overridable Sub Write (buffer As Byte()) Writes a byte array to the underlying stream.
7	Public Overridable Sub Write (ch As Char ) Writes a Unicode character to the current stream and advances the current position of the stream in accordance with the Encoding used and the specific characters being written to the stream.
8	Public Overridable Sub Write (chars As Char()) Writes a character array to the current stream and advances the current position of the stream in accordance with the Encoding used and the specific characters being written to the stream.
9	Public Overridable Sub Write (value As Double ) Writes an eight-byte floating-point value to the current stream and advances the stream position by eight bytes.
10	Public Overridable Sub Write (value As Integer ) Writes a four-byte signed integer to the current stream and advances the stream position by four bytes.
11	Public Overridable Sub Write (value As 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.

For complete list of methods, please visit Microsoft's documentation.

Example

The following example demonstrates reading and writing binary data −

Live Demo

Imports System.IO
Module fileProg
   Sub Main()
      Dim bw As BinaryWriter
      Dim br As BinaryReader
      Dim i As Integer = 25
      Dim d As Double = 3.14157
      Dim b As Boolean = True
      Dim s As String = "I am happy"
      'create the file
      
      Try
         bw = New BinaryWriter(New FileStream("mydata", FileMode.Create))
      Catch e As IOException
         Console.WriteLine(e.Message + "\n Cannot create file.")
         Return
      End Try
      'writing into the file
      
      Try
         bw.Write(i)
         bw.Write(d)
         bw.Write(b)
         bw.Write(s)
      Catch e As IOException
         Console.WriteLine(e.Message + "\n Cannot write to file.")
         Return
      End Try
      bw.Close()
      'reading from the file
      
      Try
         br = New BinaryReader(New FileStream("mydata", FileMode.Open))
      Catch e As IOException
         Console.WriteLine(e.Message + "\n Cannot open file.")
         Return
      End Try
      
      Try
         i = br.ReadInt32()
         Console.WriteLine("Integer data: {0}", i)
         d = br.ReadDouble()
         Console.WriteLine("Double data: {0}", d)
         b = br.ReadBoolean()
         Console.WriteLine("Boolean data: {0}", b)
         s = br.ReadString()
         Console.WriteLine("String data: {0}", s)
      Catch e As IOException
         Console.WriteLine(e.Message + "\n Cannot read from file.")
         Return
      End Try
      br.Close()
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Integer data: 25
Double data: 3.14157
Boolean data: True
String data: I am happy

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