Data sent from CPP causes interface crash in QML

YigitCtnkaya

Hello, first of all, I have a problem like this. I want to transfer the data to the QML side with a signal from C ++, but after a while my interface crashes without giving any error. I can't find the reason for this, I can't see it even though I debug, is there any error in my code?
NOTE: I didn't add unnecessary parts of the code
NOTE2: QT 5.15.16

QML:
Window {
 QtObject {
    id: tcpVariables
    property real tcp_velocity_X_Angle: 0
}
   Connections {
            target: tcpClient
             function onVelocity_X_Changed() {
               var newVelocity = tcpClient.get_Velocity_X()

               if (!isNaN(newVelocity) && isFinite(newVelocity)) {

                       tcpVariables.tcp_velocity_X_Angle = newVelocity;
                         console.log("tcp_velocity_X_Angle signal triggered: " + tcpVariables.tcp_velocity_X_Angle);

               } else {
                    console.error("Invalid velocity value: " + newVelocity);
               }
           }
        }
}

tcpClient.h:

class TcpClient : public QObject
{
    Q_OBJECT
public:
    Q_PROPERTY(qreal float_X_velocity READ get_Velocity_X WRITE setVelocity_X NOTIFY velocity_X_Changed)
    QML_ELEMENT
public:
    Q_INVOKABLE qreal get_Velocity_X() const {return float_X_velocity; }
     void  setVelocity_X (qreal value);
    qreal float_X_velocity; /**/

signals:
    void velocity_X_Changed();

tcpClient.cpp ( CODE USAGE ):

 qint32 x_velocity_int = (static_cast<qint32>(data[29]) << 24) |
                                                (static_cast<qint32>(data[28]) << 16) |
                                                (static_cast<qint32>(data[27]) << 8) |
                                                (static_cast<qint32>(data[26]) & 0xff);
float float_X_velocity;
std::memcpy(&float_X_velocity, &x_velocity_int, sizeof(float));
   setVelocity_X(static_cast<qreal>(float_X_velocity));

tcpClient.cpp: (FUNCTION)
void TcpClient::setVelocity_X(qreal value) {
    if (!qFuzzyCompare(float_X_velocity, value)) {
        if (qIsNaN(value) || !qIsFinite(value)) {
            qWarning() << "Invalid velocity value: " << value;
            return; // Geçersiz değeri atama
        }
        float_X_velocity = value;
        emit velocity_X_Changed();
        qDebug() << "float_X_velocity signal emitted, new value: " << float_X_velocity;
    }
}

main.cpp:

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    // OpenGL USAGE
    QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);
  // TCP OBJECTS
    TcpClient tcpclient;

    // UI OBJECTS
    QQmlApplicationEngine engine;
 engine.rootContext()->setContextProperty("tcpClient", &tcpclient);
  const QUrl url(QStringLiteral("../qml/Screens/splashScreen.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
         if (!obj && url == objUrl)
             QCoreApplication::exit(-1);
     }, Qt::QueuedConnection);

    engine.load(url);

    videoStreamer.startCapture();

    return app.exec();
}

SGaist

Hi and welcome to devnet,

Do you have a stack trace of that crash ?
Why are you using a memcpy to assign an qint32 to a float and then static cast it to qreal ? There's no need for all of that. Also what makes you think that the size of a float is the same or smaller as the size of a qint32 ?
On a side note, please use coding tags next time you post code.

YigitCtnkaya

First of all, thank you,

Next time I will be careful to use code blocks.

What kind of correction do you suggest, I thought it would be correct this way?

What do you mean by stack trace of that crash?

SGaist

The correct way ? Just call setVelocity_X(x_velocity_int); directly.

Well, if your application is crashing, run it with the debugger until it crashes and there you'll have the stack trace of the crash which is the position of the crash and the functions call stack that lead to it.

YigitCtnkaya

@SGaist
I use it to correct the data, and if I do it the same way as you say, the result is the same.

When I analyze it with the debugger, my interface crashes after about 20 seconds, so it's hard to follow.

SGaist

Well, since it crashes quickly with the debugger, you should already have a stack trace at hand to share with us.