How to copy a data snippet from a string?

Question

I’m starting in the programming area and I’m developing a serial communication application, where, I receive data strings with some information in which I need to separate them by categories, for example:

A connection string : STX8abcdefETX<CRC>

A string of Parameters: STXNabcdefETX<CRC>

where, the CRC has two characters.

What I need to do is monitor the serial port and when the string arrives, identify the start (STX), continue reading the same until you find the (ETX), count two more characters and insert into one listbox, the content read.

Strings come all together, for example:

STX8abcdefETX<CRC>STXNabcdefETX<CRC>

Which method to use ? Because I have already used Substring, split, but as sizes may vary, sometimes I get the content wrong.

Follow modified code (SOLVED).

    while (true)
        {
            posicaoSTX = bufferRx.IndexOf("STX");

            if (posicaoSTX != -1)
            {
                posicaoETX = bufferRx.IndexOf("ETX");
                if (posicaoETX != -1 && (bufferRx.Length >= (posicaoETX + 5)))
                {
                    posicaoETX += 3;
                    stringFinal = bufferRx.Substring(posicaoSTX, (posicaoETX - posicaoSTX) + 2);
                    bufferRx = bufferRx.Remove(0, posicaoETX);
                    trataProtocolo(stringFinal);
                }
                else break;
            }
            else break;
        }

Answer 1

Surely there are several ways to do this, I tried to make a didactic code so you understand the logic, I hope I can help:

        //Exemplo da mensagem recebida
        string mensagem = "STXMEnsagem1ETXSTXMEnsagem2ETXSTXMEnsagem3ETXSTXMEnsagem4ETXSTXMEnsagem5ETXSTXMEnsagem6ETX";
        //Lista para armazenar as mensagens
        List<string> mensagens = new List<string>();


        while (mensagem.Length > 0)
        {
            //Encontra o próximo STX
            int i1 = mensagem.IndexOf("STX");
            //Encontra o próximo ETX a partir do STX anterior
            int i2 = mensagem.IndexOf("ETX",i1);


            //Pega a SubString
            string sub = mensagem.Substring(i1+3,i2-3);
            //Retira a parte já processada da mensagem
            mensagem = mensagem.Remove(0, sub.Length+6);
            //Adiciona a mensagem à lista de mensagens
            mensagens.Add(sub);
        }

        //Quantidade de mensagens recebidas
        int count = mensagens.Count;

        //Imprime as mensagens na tela
        foreach (string s in mensagens)
            Console.WriteLine(s);

ps. I have not made any error handling.

I repeat: I believe that the STX and ETX should be just a char, thus avoiding the calculations +3, -3, +6, etc.

Answer 2

I believe the best way to do that is with Regex, see how it would look:

string[] arr = Regex.Split(valores, @"(?=STX)");
arr =  arr.Where(x => !string.IsNullOrEmpty(x)).ToArray();
listBox1.Items.AddRange(arr);

Don’t forget to add the namespaces to the project:

using System.Linq;
using System.Text.RegularExpressions;

See working on Ideone.

See also the documentation of Regex to better understand how it works.

Answer 3

One more way to do it:

 public IEnumerable<string> ParseMessages( string messages )
 {
     //Separa o texto por STX....ETX
     var msgs = System.Text.RegularExpressions.Regex.Matches( messages, "STX.+?ETX" );

     foreach( var message in msgs ) 
         yield return message.Value;

     //Pega os dois ultimos digitos do crc
     yield return messages.Substring( messages.Length - 2 );
 }