How should I decode a UTF-8 string

Question

I have a string like:

About \\xee\\x80\\x80John F Kennedy\\xee\\x80\\x81\\xe2\\x80\\x99s Assassination . unsolved my         


        

Answer 1

Scan the input string char-by-char and convert values starting with \x (string to byte[] and back to string using UTF8 decoder), leaving all other characters unchanged:

static string Decode(string input)
{
    var sb = new StringBuilder();
    int position = 0;
    var bytes = new List();
    while(position < input.Length)
    {
        char c = input[position++];
        if(c == '\\')
        {
            if(position < input.Length)
            {
                c = input[position++];
                if(c == 'x' && position <= input.Length - 2)
                {
                    var b = Convert.ToByte(input.Substring(position, 2), 16);
                    position += 2;
                    bytes.Add(b);
                }
                else
                {
                    AppendBytes(sb, bytes);
                    sb.Append('\\');
                    sb.Append(c);
                }
                continue;
            }
        }
        AppendBytes(sb, bytes);
        sb.Append(c);
    }
    AppendBytes(sb, bytes);
    return sb.ToString();
}

private static void AppendBytes(StringBuilder sb, List bytes)
{
    if(bytes.Count != 0)
    {
        var str = System.Text.Encoding.UTF8.GetString(bytes.ToArray());
        sb.Append(str);
        bytes.Clear();
    }
}

Output:

About John F Kennedy’s Assassination . unsolved mystery – 45 years later. Over the last decade, a lot of individuals have speculated on conspiracy theories that ...