Decoding data from serial port (string with integers)

Question

I'm sending string from Arduino to PC using serial communication. Format of message includes char, value and space (separating data). Example message: "H123 V2 L63 V2413 I23 CRC2a". I have problem with decoding this message in Qt because when I use for example Utf-8 decoding it casting integers to chars (in a simplified way) and I receiving something like that: "H&?? j\u0002I&\u001AICL?H". Message length is not constant (different size for ex. H12 and H123) so I can't use predetermined position to casting. Do you have any idea how to decode message correctly?

Arduino code:

uint8_t H = 0, V = 0, L = 0, I = 0, CRC = 0;
String data;
void loop() {
  ++H; ++V; ++L; ++I;
  data = String("H");
  data += String(H, DEC);
  data += String(" V");
  data += String(V, DEC);
  data += String(" L");
  data += String(L, DEC);
  data += String(" I");
  data += String(I, DEC);
  CRC = CRC8(data.c_str(), strlen(data.c_str()));
  data += String(" CRC");
  data += String(CRC, HEX);
  Serial.println(data);
  delay(1000);
}

Qt code:


while(serial.isOpen())
{
  QByteArray data;

  if (serial.waitForReadyRead(1000))
  {
    data = serial.readLine();
    while (serial.waitForReadyRead(100))
    {
        data += serial.readAll();
    }
    QString response = QString::fromUtf8(data);
    qDebug() << "Data " << response << endl;
  }
  else
    qDebug() << "Timeout";
}

Why do you think you need utf-8 here? Use for example `QString::fromAscii(data.data())` — Michael, May 11 '19 at 16:36
There's not method called `QString::fromAscii()`. QString Class documentation: [link](https://doc.qt.io/qt-5/qstring.html) — albert828, May 11 '19 at 17:05
Baud rate ? Same on both sides ? Which Arduino? String::operator+ is one of the most difficult operations on an avr Arduino. ( And completey unnecessary here) — datafiddler, May 11 '19 at 17:11
Ok solved I've set in Qt Even Parity but default for Arduino is No Parity. Second thing encoding should be `QString::fromLocal8Bit(data)`. What is strange for `Serial.println("Test")` it worked correctly. Thank you datafiddler and Michael O. — albert828, May 11 '19 at 17:48

score 0 · Accepted Answer · answered Jul 25 '20 at 20:41

The problem is that you use UTF-8 decoding, while Arduino send just 1-byte ASCII chars. So use fromLocal8Bit as said albert828

Like this:

while(serial.isOpen())
{
  QByteArray data;

  if (serial.waitForReadyRead(1000))
  {
    data = serial.readLine();
    while (serial.waitForReadyRead(100))
    {
        data += serial.readAll();
    }
    QString response = QString::fromLocal8Bit(data);
    qDebug() << "Data " << response << endl;
  }
  else
    qDebug() << "Timeout";
}

Decoding data from serial port (string with integers)

1 Answers1