c# how to add byte to byte array

Question

How to add a byte to the beginning of an existing byte array? My goal is to make array what's 3 bytes long to 4 bytes. So that's why I need to add 00 padding in the beginning of it.

Answer 1

You can't do that. It's not possible to resize an array. You have to create a new array and copy the data to it:

bArray = AddByteToArray(bArray,  newByte);

code:

public byte[] AddByteToArray(byte[] bArray, byte newByte)
{
    byte[] newArray = new byte[bArray.Length + 1];
    bArray.CopyTo(newArray, 1);
    newArray[0] = newByte;
    return newArray;
}

Answer 2

As many people here have pointed out, arrays in C#, as well as in most other common languages, are statically sized. If you're looking for something more like PHP's arrays, which I'm just going to guess you are, since it's a popular language with dynamically sized (and typed,) arrays: you should use an ArrayList:

var mahByteArray = new ArrayList<byte>();

If you have a byte array from elsewhere, you can use the AddRange function.

mahByteArray.AddRange(mahOldByteArray);

Then you can use Add() and Insert() to add elements.

mahByteArray.Add(0x00); // Adds 0x00 to the end.
mahByteArray.Insert(0, 0xCA) // Adds 0xCA to the beginning.

Need it back in an array? .ToArray() has you covered!

mahOldByteArray = mahByteArray.ToArray();

Answer 3

Arrays can't be resized, so you need to allocte a new array that is larger, write the new byte at the beginning of it, and use Buffer.BlockCopy to transfer the contents of the old array across.

Answer 4

To prevent recopy the array every time which isn't efficient

What about using Stack

csharp> var i = new Stack<byte>();
csharp> i.Push(1);
csharp> i.Push(2); 
csharp> i.Push(3); 
csharp> i; { 3, 2, 1 }

csharp> foreach(var x in i) {
  >       Console.WriteLine(x);
  >     }

3 2 1

Answer 5

Although internally it creates a new array and copies values into it, you can use Array.Resize<byte>() for more readable code. Also you might want to consider checking the MemoryStream class depending on what you're trying to achieve.

Answer 6

Simple, just use the code below, as I do:

        public void AppendSpecifiedBytes(ref byte[] dst, byte[] src)
    {
        // Get the starting length of dst
        int i = dst.Length;
        // Resize dst so it can hold the bytes in src
        Array.Resize(ref dst, dst.Length + src.Length);
        // For each element in src
        for (int j = 0; j < src.Length; j++)
        {
            // Add the element to dst
            dst[i] = src[j];
            // Increment dst index
            i++;
        }
    }

    // Appends src byte to the dst array
    public void AppendSpecifiedByte(ref byte[] dst, byte src)
    {
        // Resize dst so that it can hold src
        Array.Resize(ref dst, dst.Length + 1);
        // Add src to dst
        dst[dst.Length - 1] = src;
    }

Answer 7

I think it is a more complete function

/// <summary>
/// add a new byte to end or start of a byte array
/// </summary>
/// <param name="_input_bArray"></param>
/// <param name="_newByte"></param>
/// <param name="_add_to_start_of_array">if this parameter is True then the byte will be added to the beginning of array otherwise
/// to the end of the array</param>
/// <returns>result byte array</returns>
        public byte[] addByteToArray(byte[] _input_bArray, byte _newByte, Boolean _add_to_start_of_array)
        {
            byte[] newArray;
            if (_add_to_start_of_array)
            {
                newArray = new byte[_input_bArray.Length + 1];
                _input_bArray.CopyTo(newArray, 1);
                newArray[0] = _newByte;
            }
            else
            {
                newArray = new byte[_input_bArray.Length + 1];
                _input_bArray.CopyTo(newArray, 0);
                newArray[_input_bArray.Length] = _newByte;
            }
            return newArray;
        }