Problem with serial port opening

[Will_Craig]

I've been trying to open a connection between my qt app and an Arduino uno via serial port connection. I have all the correct header files included, ive looked at multiple examples and done exactly as others have and i still get errors for no apparent reason my main problem is with the QIODevice::open() function it will always give an error and i can't quite figure out if i'm being stupid or if i've missed something. Main file cpp, header file, and header files #included are shown in the screenshots:

[jsulm]

@will_craig You should check the return value of open().
Also, what does https://doc.qt.io/qt-5/qserialport.html#error-prop tell you?

[sierdzio]

@jsulm said in Problem with serial port opening:

@will_craig You should check the return value of open().
Also, what does https://doc.qt.io/qt-5/qserialport.html#error-prop tell you?

Won't tell him a thing if it does not compile ;-)

@Will_Craig not sure but try importing QIODevice. Or use QSerialPort::ReadOnly instead of QIODevice::ReadOnly.

[jsulm]

@sierdzio said in Problem with serial port opening:

Won't tell him a thing if it does not compile ;-)

It does - see the application output in the screen-shots. The error comes from QtCreators code model...

[Will_Craig]

@sierdzio same error when including QIODevice and if i use QSerialPort::ReadOnly instead
thanks for replying quick :)

[jsulm]

@will_craig What does https://doc.qt.io/qt-5/qserialport.html#error-prop tell you?

[Will_Craig]

@jsulm how do i implement that function? not too familiar with it
thank you

[jsulm]

@will_craig You call it

qDebug() << arduino->error();

after calling open()

[Will_Craig]

@jsulm sorry it was coming up with an error when i first tried entering that heres the screenshot of after running the applicaiton it gives no error? real wierd

[aha_1980]

@will_craig Please post code as text, not as picture. That makes it easier for us to copy parts of the code for commenting.

What do you think should QSerialPort::OpenMode() return? It is not even related to your arduino variable.

The correct way is:

if (!arduino->open(QIODevice::ReadWrite)) {
  // error handling
} else {
  // port successfully opened
}

As a side note: What should ReadOnly do with a serial port? I'm not even sure that is supported on all platforms. Better use ReadWrite (you don't need to write if you don't want to).

Regards

[Will_Craig]

@aha_1980 Sorry haven't used forums that much before but heres the code with the fix you told me. The output reaches the successful section of the if statement and i'm still getting the "No viable conversion" error on line 70 (above) and as noted in code below. The port still recognises that it is "NotOpen" which confuses me.

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->TempSensor->display("----");
    ui->PHSensor->display("----");
    ui->MoistureSensor->display("----");

    arduino = new QSerialPort(this);
    arduinoPortName = "cu.usbmodem14201";
    openSerial();
    //readSerial();
}

MainWindow::~MainWindow()
{
    if(arduino->isOpen()){arduino->close();}
    delete ui;
}

void MainWindow::openSerial()
{
            arduinoIsAvailable = true;
            // open and configure the serialport
            qDebug() << "Found the arduino port...\n" << "Port name used: " << arduinoPortName << "\n";
            arduino->setPortName(arduinoPortName);
            arduino->setBaudRate(QSerialPort::Baud9600, QSerialPort::Directions());
            arduino->setDataBits(QSerialPort::Data8);
            arduino->setFlowControl(QSerialPort::NoFlowControl);
            arduino->setParity(QSerialPort::NoParity);
            arduino->setStopBits(QSerialPort::OneStop);
            connect(arduino, SIGNAL(readyRead()), this, SLOT(readSerial()));

            if(!arduino->open(QIODevice::ReadWrite)){               //error is here
                qDebug() << "Error Handling Section Reached";
            }else{
                qDebug() << "Port opened succesfully...\n";
            }
            qDebug() << arduino->error();
            qDebug() << QSerialPort::OpenMode();
            /*
            // give error message if not available
            QMessageBox MsgBx;
            MsgBx.setText("Error: Null Connection");
            MsgBx.exec();
            */
}

output:

Found the arduino port...
 Port name used:  "cu.usbmodem14201" 

Port opened succesfully...

QSerialPort::NoError
OpenMode( "NotOpen" )

thankyou for you help

[aha_1980]

Hi @will_craig,

No problem. We all started some day :)

f statement and im still getting the "No viable conversion" error on line 70 (above) and as noted in code below.

That is a Code Model Error, please ignore it in the first place. If your code compiles, all is fine. Have you included <QIODevice> ?

if(arduino->open(QIODevice::ReadWrite)){  
    qDebug() << "Error Handling Section Reached";
}else{
    qDebug() << "Port opened succesfully...\n";
}

You didn't carefully copy my code!

I wrote ! in the if condition, you completely inverted the branches so it will not work.

And please put your code in code tags, I'll add them for you now.

Regards

Edit: and once again: qDebug() << QSerialPort::OpenMode(); is completely pointless. Remove that line!

[Will_Craig]

@aha_1980 I've added the ! and the code goes to the correct section of the successful opening, i have used the header <QIODevice>, <QSerialPort> and <QSerialPortInfo>.
So you're saying that even though it gives me the error before compiling as long as it still compiles there is no problem? cause i have been assuming that if that error has come up then the code will not work properly. thanks again and sorry about not using code tags.
My code now looks like this:

 if(!arduino->open(QIODevice::ReadWrite)){
                qDebug() << "Error Handling Section Reached";
            }else{
                qDebug() << "Port opened succesfully...\n";
            }
            qDebug() << arduino->error();

and this is my debug output:

Found the arduino port...
 Port name used:  "cu.usbmodem14201" 

Port opened succesfully...
QSerialPort::NoError

Is this correct?, thanks again :)

[aha_1980]

Hi @will_craig,

looks good now and should work!

So you're saying that even though it gives me the error before compiling as long as it still compiles there is no problem?

Yeah, the Clang Code Model is nice, but sometimes it goes crazy. If it annoys you very much, you can deactivate it by Help > About Plugins > Clang Code Model and restart Creator. Then you use the "old" code model, which has fewer features but works more solid.

Regards

[Will_Craig]

@aha_1980 thank you so much for the help you're a lagend

[aha_1980]

@will_craig You're welcome :)

[Pablo J. Rogina]

@will_craig is your issue solved? Then please don't forget to mark your post as such. Thanks.

[Will_Craig]

@Pablo-J-Rogina how do i do that?

[aha_1980]

Hi @Will_Craig,

with the Topic Tools button, but it seems you already found that.

Greetings