Byte array

Byte arrays hold data in an efficient way. Any file can be read in, or downloaded, into a Byte array. Often this is much more efficient than other representations.

Notes, handling

Data in a Byte array is sometimes harder to manipulate and read. Often strings or string arrays are a better storage format.

First example

We measure byte array memory use. We allocate a Byte array. The reference to the Byte array requires 4 or 8 bytes on the stack.

And The 3 million elements, bytes, of the array require a bit less than 3 megabytes of memory.

Important In an array, each byte element requires exactly 1 byte. But there are additional costs involved.

Detail This example uses a Byte array but not in a useful way. Byte arrays are useful as storage regions for images or binary data.

Module Module1
    Sub Main()
        'Get memory.
        Dim value1 As Long = GC.GetTotalMemory(False)

        ' Create an array of 3 million bytes.
        ' ... We specify the last index to create an array.
        Dim bytes(1000 * 1000 * 3 - 1) As Byte
        bytes(0) = 0

        ' Get memory and print the change.
        Dim value2 As Long = GC.GetTotalMemory(False)
        Console.WriteLine(value2 - value1)

        ' Ensure we have exactly 3 million bytes.
        Console.WriteLine(bytes.Length)
    End Sub
End Module3000032
3000000

Example 2

The BinaryReader and BinaryWriter types are often used with Byte arrays. It is possible to use a Byte array, wrapped in a MemoryStream, with these types as a backing store.

Info This is an efficient approach to reading bytes, as it does not access the hard disk more than once.

Here We use the File.ReadAllBytes Function. Then we wrap the Byte array in a MemoryStream.

And We pass that MemoryStream to a BinaryReader. We can use the Byte array, which stores a JPG image now, in the same way as a file.

Imports System.IO

Module Module1
    Sub Main()
        ' Byte array stores a JPG.
        Dim array() As Byte = File.ReadAllBytes("C:\athlete.jpg")

        Using memory As MemoryStream = New MemoryStream(array)
            Using reader As BinaryReader = New BinaryReader(memory)

                ' Display values of first two bytes of JPG in memory.
                Console.WriteLine(reader.ReadByte())
                Console.WriteLine(reader.ReadByte())

            End Using
        End Using
    End Sub
End Module255
216

Note, size

To create an array of 3 million elements, we must specify the last required element index, which is 3 million minus one. This is a key difference between VB.NET and C#.

A summary

A Byte array is a versatile type. It stores a direct, accurate representation of binary data. This includes images (JPG, PNG) as well as many different file formats.