I am a newbie with a question regarding reading specific bytes out of an array in C#. I received an array response that is 128 bytes long and I am looking to read and store the first 4 bytes of the array. How do I do so?
I've read a number of posts about shifting bytes but was a bit confused and I am looking to get going in the right direction.
Use one of the Array.Copy overloads:
byte[] bytes = new byte[4];
Array.Copy(originalArray, bytes, bytes.Length);
Use Array.Copy method:
// your original array
var sourceArray = new byte[128];
// create a new one with the size you need
var firstBytes = new byte[4];
// copy the required number of bytes.
Array.Copy(sourceArray, 0, firstBytes, 0, firstBytes.Length);
If you do not need the rest of the data in the original array, you can also resize it, truncating everything after the first 4 bytes:
Array.Resize(ref sourceArray, 4);
Read the first 4 bytes in 4 different variables:
byte first = array[0],
second = array[1],
third = array[2],
forth = array[4];
Read them as one 32-bit long integer:
int result =
first << 24 ||
second << 16 ||
third << 8 ||
forth;
The x << n operator shifts the bits of number x, n times to the left. You are effectively moving the bytes of first 24 positions to the left, thus first will be stored in bits with indices 24 to 31 like that:
first 00000000 00000000 00000000
Next, move second 16 positions to the left, thus storing it in bits 16 to 23 and so on:
first second 00000000 00000000
Wikipedia provides a good summary of bitwise operations if you need more details.
You could use the Take method. Although, this is only available if you are using .NET 3.5 or later. You will need to have using System.Linq; at the top of the .cs file.
var bytes = originalArray.Take(4).ToArray();
Example from a network stream.
byte[] bytesRead = 0;
using (NetworkStream stream = client.GetStream())
{
byte[] length = new byte[4];
bytesRead = stream.Read(length, 0, 4);
}
bytesRead contains the first 4 bytes stored in the networkstream.
