Qt串行端口有时丢失最后一个字节

Question

I am making RPM counter GUI with Qt, and arduino, i am using cooling fun to get the RPM values. I am using the serial port to read the values from arduino, but sometimes i miss the last byte from the value that i print in Qt GUI, but i dont have the same problem in the arduino serial monitor. Here is the code from Qt :

void ArduinoRpm::serialReciver()
{

    QString input_converter;
    std::string to_file_string;

    int sizeFromInput = 0;
    char *dataBuffer;

    //get the port size depending on bytes available to read
    int bufferSize = serial->bytesAvailable();
    //int bufferSize = serial->bytesAvailable();

    //dataBuffer, get the data from serial port, bufferSize + 1 for the newline
    dataBuffer = new char[bufferSize + 2];

    //flush the port before read


    //This function reads a line of ASCII characters from the device, up to a maximum of
    //maxSize - 1 bytes, stores the characters in dataBuffer, and returns the number of bytes
    //read. if a line could not be read but no error ocurred, this function returns 0. if an
    //error occurs, this function returns the length of what could read or -1 if nothing was read.
    //bufferSize is the maxsize readline can read.

    sizeFromInput = serial->readLine(dataBuffer, bufferSize);

    //to_file_string, to write data in file
    to_file_string = dataBuffer;
    input_converter = QString::fromStdString(to_file_string);


    if ((sizeFromInput >= 1) && (input_converter.toInt() <= 9999)) {
        if(input_converter.toInt() > 10) {
            ui->lcdNumber->display(input_converter);
            rpmNeedle->setCurrentValue(input_converter.toInt());
            input_file << to_file_string << std::endl;
        }

    }

    delete dataBuffer;
    bufferSize = 0;
    serial->flush();

}

 void ArduinoRpm::SerialInitializer()
{
    serial = new QSerialPort(this);
    serial->setPortName(serialPortValue); //COM-port your Arduino is connected to
    serial->open(QIODevice::ReadWrite);
    serial->setBaudRate(QSerialPort::Baud9600); //must be the same as your arduino-baudrate
    serial->setDataBits(QSerialPort::Data8);
    serial->setParity(QSerialPort::NoParity);
    serial->setStopBits(QSerialPort::OneStop);
    serial->setFlowControl(QSerialPort::NoFlowControl);
}

for example

27
1621
1621
1627
1627
1627
1627
1627
1627
1627
1627
1627
1627
1627
1627
1627
1621
1616
1616
1605
1605
1599
1594
1588
158
1583
158
1578
1578
1572
1572
1572

it should read 4 digits all the time, but sometimes it losts the last digit.. Any solution for this ?

Answer 1

your function should be something like this:

void ArduinoRpm::serialReciver()
{
    char dataBuffer[6];

    if(!serial->canReadLine()) //if there isn't a whole line available
        return; //return from this call (wait for the next readyRead() signal)
    serial->readLine(dataBuffer, 6)

    /* do whatever you want with dataBuffer here */

    if(serial->bytesAvailable() > 0) //if there are still unread bytes
        QMetaObject::invokeMethod(this, "serialReciver", Qt::QueuedConnection); //call function again as if readyRead() signal was emitted
}

PS this answer assumes that the input is guaranteed to be always like this: 4 chars of digits then a newline then 4 chars of digits then a newline again, etc. . . So if it did not follow this pattern, then this will cause undefined behavior.

PS I did not fix your typo in serialReciver .