Transform a string into an array of bytes

Question

I found this little snippet to to transform a string into an array of bytes:

    public byte[] GetBytes(string str)
    {
        byte[] bytes = new byte[str.Length * sizeof(char)];
        System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
        return bytes;
    }

And this one to transform an array of bytes into a string:

    public string GetString(byte[] bytes)
    {
        char[] chars = new char[bytes.Length / sizeof(char)];
        System.Buffer.BlockCopy(bytes, 0, chars, 0, bytes.Length);
        return new string(chars);
    }

But I notice that the first one returns an array twice as big as the initial string (because sizeof(char) = 2) and every other slot in my array is a 0.

Example:

string = TEST
bytes[] = { 84, 0, 69, 0, 83, 0, 84, 0 };

I'm using this function to send packets in UDP, so I need my packets to be the smallest possible.

Why is the array twice bigger? How do I fix it?

Answer 1

.NET actually uses UTF-16 encoding to store string's and char's, which means each character is actually encoded with 2 bytes. This is detailed in Character Encoding in the .NET Framework:

UTF-16 encoding is used by the common language runtime to represent Char and String values, and it is used by the Windows operating system to represent WCHAR values.

So you should expect to get 2 bytes for every character in your string.

If you want to only get 1 byte for per character you have to use a different encoding. For this input, ASCII encoding will work:

public byte[] GetBytes(string str)
{
    return System.Text.Encoding.ASCII.GetBytes(str);
}

Calling this with the input "TEST" will return { 84, 69, 83, 84 }

Answer 2

To get bytes for a string use:

Encoding.Utf8.GetBytes()

http://msdn.microsoft.com/en-us/library/system.text.encoding.getbytes(v=vs.110).aspx

To go back to string use:

Encoding.Utf8.GetString()

http://msdn.microsoft.com/en-us/library/744y86tc(v=vs.110).aspx