Qt串行端口无法正确读取字符串

Question

I use Qt 5.4 on Ubuntu Gnome 14.04 LTS to reads a string line from serial port. Everything was OK, but when I re-installed Ubuntu Gnome 14.04 and Qt 5.4, my code of serial port does not work well. When the Arduino send "0" the code of Qt reads it like this " " and the other numbers that sends over serial the Qt reads it as a letters and symbols. I think the problem with unicode of my Qt. The unicode of my ubuntu is en.US.UTF-8 and the QT unicode is setted to "system". Please help me :( This is my code that read the data from serial port:

    QByteArray input;    
if (serial->canReadLine())    //chect if data line is ready
     input.clear();
   input = serial->readLine(); //read data line from sreial port
   ui->label->setText(input);
   qDebug ()<<input<<endl;

this code of Arduino it is working fine with CuteCom and Arduino serial monitor

    const int analogInPin = A0; 


unsigned int sensorValue = 0;        // value read from the pot


void setup() {

  Serial.begin(19200);
}

void loop() {
  Serial.print("\n");
  Serial.print("#");
  for (int i=0; i < 5; i++) {
  // read the analog in value:
  sensorValue = analogRead(analogInPin);

  Serial.print(sensorValue);
  Serial.print("#");

};
  sensorValue = analogRead(analogInPin);
  Serial.print(sensorValue);
  Serial.print("# \n");  
}

Sorry for my English

Answer 1

If the parity or data/stop bit parameters are different you can still write and read, but you get "funny" output similar to the one you showed us above, and this is not a problem of the unicode setting (especially not with '0', which is a character of the ASCII set).

Try setting the same port parameters explicitly on both ends just before starting the communication.

Answer 2

There are several problems:

1. You didn't post enough code to know the context of how you use it. I'm assuming that you handle the data in a method attached to the readyRead signal.

2. You are only reading one line, where you should be reading lines until no more are available. The readyRead signal can be emitted with any number of bytes available for reading: these may make up no complete lines, or several complete lines! If you don't keep on reading lines until no more are available, you'll be severely lagging behind incoming data.

3. You are using implicit QByteArray to QString conversions. These are a bad code smell. Be explicit about it.

4. You have fairly verbose code. You don't need to clear a QByteArray before setting its value. You also should declare it at the point of use. Better yet, use type inference that C++11 brought.

Thus:

class MyWindow : public QDialog {
  QSerialPort m_port;
  void onData() {
    while (m_port->canReadLine())
      auto input = QString::fromLatin1(m_port->readLine());
      ui->label->setText(input);
      qDebug() << input;
    }
  }
  ...
public:
  MyWindow(QWidget * parent = 0) : QDialog(parent) {
    ...
    connect(&m_port, &QIODevice::readyRead, this, &MyWindow::onData);
  }
};