C# convert hexadecimal value in to UTF8 and ASCII

Question

I am trying to convert a hexadecimal values in a string in to both ASCII value and UTF8 value. But when I execute the following code, it prints out the same hex value I give as input

string hexString = "68656c6c6f2c206d79206e616d6520697320796f752e";
System.Text.UTF8Encoding  encoding=new System.Text.UTF8Encoding();
byte[] dBytes = encoding.GetBytes(hexString);

//To get ASCII value of the hex string.
string ASCIIresult = System.Text.Encoding.ASCII.GetString(dBytes);
MessageBox.Show(ASCIIresult, "Showing value in ASCII");

//To get the UTF8 value of the hex string
string utf8result = System.Text.Encoding.UTF8.GetString(dBytes);
MessageBox.Show(utf8result, "Showing value in UTF8");

Answer 1

Since you are naming a variable hexString , I assume that the value is already encoded into a hex format.

This means the following will not work:

string hexString = "68656c6c6f2c206d79206e616d6520697320796f752e";
System.Text.UTF8Encoding  encoding=new System.Text.UTF8Encoding();
byte[] dBytes = encoding.GetBytes(hexString);

This is because you are treating the already encoded string as plain UTF8 text.

You are probably missing a step to convert the hex encoded string into a byte array.

You can do this using this SO post which shows this function:

public static byte[] StringToByteArray(String hex)
{
  int NumberChars = hex.Length/2;
  byte[] bytes = new byte[NumberChars];
  using (var sr = new StringReader(hex))
  {
    for (int i = 0; i < NumberChars; i++)
      bytes[i] = 
        Convert.ToByte(new string(new char[2]{(char)sr.Read(), (char)sr.Read()}), 16);
  }
  return bytes;
}

So, the end result would be this:

byte[] dBytes = StringToByteArray(hexString);

//To get ASCII value of the hex string.
string ASCIIresult = System.Text.Encoding.ASCII.GetString(dBytes);
MessageBox.Show(ASCIIresult, "Showing value in ASCII");

//To get the UTF8 value of the hex string
string utf8result = System.Text.Encoding.UTF8.GetString(dBytes);
MessageBox.Show(utf8result, "Showing value in UTF8");

Answer 2

You should first convert the hex string to a byte array:

byte[] dBytes = Enumerable.Range(0, hexString.Length)
                 .Where(x => x % 2 == 0)
                 .Select(x => Convert.ToByte(hexString.Substring(x, 2), 16))
                 .ToArray();

Answer 3

I've used this method to convert any

public static string FromHex (string h) //Put your sequence of hex to convert to string.
{
    if (h.Length % 2 != 0) 
        throw new ArgumentException("The string " + nameof(h) + " is not a valid Hex.", nameof(h));
    char[] CharFromHex = new char[h.Length / 2];
    int j = 0;
    for (int i = 0; i < h.Length; i += 2)
    {
        string hexSubStr = h.Substring(i, 2);
        CharFromHex[j] = (char)Convert.ToInt32(hexSubStr, 16);
        j += 1;
    }
    StringBuilder str = new StringBuilder();
    str.Append(CharFromHex);
    return str.ToString();
}