segmentation fault

[Milav]

@jsulm

i call it in mainwindow.cpp file.

here i have send the code snip for that portion.

mainwindow.cpp

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->send->setDisabled(true);
    ui->message->setDisabled(true);
    ui->subscribe->setDisabled(true);
    ui->topic->setDisabled(true);

    ui->lineIP->setText(QString("a3jkuztr3frwt4-ats.iot.ap-south-1.amazonaws.com"));
    ui->linePort->setText(QString("8883"));

    lib_init();

    connect (ui->connect, SIGNAL(clicked()), this, SLOT(connectPressed()));
    connect (ui->send, SIGNAL(clicked()), this, SLOT(sendPressed()));
    connect (ui->subscribe, SIGNAL(clicked()), this, SLOT(subscribePressed()));
}

void MainWindow::connectPressed()
{
    QByteArray host = ui->lineIP->text().toLocal8Bit();
    QByteArray id = ui->lineID->text().toLocal8Bit();

    int port = 0;
    port = ui->linePort->text().toInt();
    if (!port)
    {
        ui->linePort->clear();
        return ;
    }
    ui->connect->setDisabled(true);


    mosq = new qtmosq(id, true);
    int size = sizeof(*mosq);
    qDebug() << size;
    connect (mosq, SIGNAL(connectEnable()), this, SLOT(connectEnabled()));
    connect (mosq, SIGNAL(subscribed()), this ,SLOT(subscribed()));
    connect (mosq, SIGNAL(connected()), this, SLOT(connected()));
    connect (mosq, SIGNAL(messageSent(bool)), this, SLOT(setMessageStatus(bool)));
    connect (mosq, SIGNAL(messageReceived(QString)), this, SLOT(showMessage(QString)));
    mosq->connect_async(host.data(), port);
    mosq->loop_start();

}

mainwindow.h

#include <QMainWindow>
#include "qtmosq.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    qtmosq* mosq;
    QStringList subed;
    QString currentTopic;
    Ui::MainWindow *ui;

private slots:
    void setMessageStatus(bool);
    void connectPressed();
    void sendPressed();
    void connectEnabled();
    void subscribePressed();
    void subscribed();
    void connected();
    void showMessage(QString);
};

qtmosq.h

#ifndef QTMOSQ_H
#define QTMOSQ_H

#include "QObject"
#include "mosquittopp.h"

using namespace mosqpp;

class qtmosq : public QObject, public mosquittopp
{
    Q_OBJECT

public:
    qtmosq(const char *id = NULL, bool clean_session = true) : mosquittopp (id, clean_session) {MID = 0;}
    ~qtmosq() {}

    void on_connect(int result)
    {
        if (!result)
        {
            //subscribe(NULL, "$SYS/#", 2);
            emit connected();
        }
        else
            emit connectEnable();
    }
    void on_publish(int id)
    {
        MID++;
        emit messageSent(true);
    }
    void on_subscribe(int mid, int qos_count, const int *granted_qos)
    {
        if (MID != 0)
            emit subscribed();
        MID++;
    }
    void on_message(const mosquitto_message *message)
    {
        if (message->payloadlen)
        {
            QString s(message->topic);
            s += '>';
            s += (char*) message->payload;
            emit messageReceived(s);
        }
    }

    int* getMID() {return ∣}

private:
    int MID;

signals:
    void connected();
    void messageSent(bool);
    void messageReceived(QString);
    void connectEnable();
    void subscribed();
};

#endif // QTMOSQ_H

here above i send the code for the same.

if you get more please tell me.

[jsulm]

@Milav So, you get that error here in MainWindow:

ui->connect->setDisabled(true); 
mosq = new qtmosq(id, true); // Is it here?
int size = sizeof(*mosq);

?
It should work.
Are there any other warnings or errors?
Try to do a complete rebuild: delete build directory, run qmake and build.

[Milav]

@jsulm

when i build the project it give me only warning like follow.

/home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/qtmosq.h:14: warning: 'mosqpp::mosquittopp::mosquittopp(const char*, bool)' is deprecated (declared at ../../../../CC_Lib/mosquitto/phytec_wega_build_websockets/usr/local/include/mosquittopp.h:94) [-Wdeprecated-declarations]

/home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:57: warning: 'int mosqpp::mosquittopp::connect_async(const char*, int, int)' is deprecated (declared at ../../../../CC_Lib/mosquitto/phytec_wega_build_websockets/usr/local/include/mosquittopp.h:103) [-Wdeprecated-declarations]

/home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:80: warning: 'int mosqpp::mosquittopp::subscribe(int*, const char*, int)' is deprecated (declared at ../../../../CC_Lib/mosquitto/phytec_wega_build_websockets/usr/local/include/mosquittopp.h:110) [-Wdeprecated-declarations]

but i face segmentation fault error when i run that project, an i found the line at where i face segmentation fault.

it is ...

mosq->subscribe(NULL, "sensors/temprature", 1); // Segmentation falut

[Milav]

@jsulm

Hello

Here i have send the link at where i download the example.

Reference link

[jsulm]

@Milav That example does exactly what I suggested you to do:

ui->connect->setDisabled(true);

mosq = new qtmosq(id, false); // HERE
connect (mosq, SIGNAL(connectEnable()), this, SLOT(connectEnabled()));

Did you try to build and run this example? If so - does it work?

[Milav]

@jsulm

Yes i delete the build directory and again i rebuild the whole project but i couldn't run the example. it is not work.

[jsulm]

@Milav said in segmentation fault:

it is not work

What exactly does this mean? Doesn't build? Crashes? Does not do what it should? ...?

[Milav]

@jsulm

it means build successful.

but it is not run, it is crashes application.

means while running the application, the application are crash.

with following error.

"segmentation fault"

and i debug the application via qDebug(), the application are crash on following line of code.

mosq->subscribe(NULL, "sensors/temprature", 1); // Segmentation falut

[J.Hilk]

@Milav well, did you press connect before you pressed subscribe?

If not it will crash...

[Milav]

@J-Hilk

I press first Connect button and than after i press subscribed button.

but it is crash...

[mvuori]

If temprature is supposed to be temperature, this is a bug:
mosq->subscribe(NULL, "sensors/temprature", 1);

[jsulm]

@Milav Did you debug to see whether mosq is not a nullptr? If it's not please provide stack trace after crash.
Also, in connectPressed it does a return if port is not set - is it set if you press connect?
You should really run through debugger...

[Milav]

@jsulm

i debug the size of mosq pointer through following code.

 int size = sizeof(*mosq);
    qDebug() << size;

and output is 20;

and in connectpressed button slot are run succesfully.

port value are shown correctly.

when i run debugger it shows following error.

The inferior stopped because it received a signal from the Operating System.

Signal name : 
SIGILL
Signal meaning : 
Illegal instruction

hope you got my point.

[Milav]

@mvuori

no it is supposed to be sensors/temprature.

[jsulm]

@Milav said in segmentation fault:

i debug the size of mosq pointer through following code.

The size of a pointer is fixed, it doesn't matter whether it contains nullptr or something else.
Do

qDebug() << mosq;

instead to see the value of the pointer.
Without stack trace I can't tell you what is going on...

[Milav]

@jsulm

when i execute "qDebug() << mosq;" it gives following output.

qtmosq(0xac50b0)

how i see stack trace in qt?

can you please explore me more about stack trace?

[JonB]

@Milav

int size = sizeof(*mosq);

@jsulm

The size of a pointer is fixed,

A slight slip of the tongue there. I think what my colleague @jsulm meant to clarify is: sizeof(...) is a compile-time calculation, it does not matter what the value of mosq is or what it points at run-time, rather this statement just assigns sizeof(qtmosq) regardless. As he says, show us what is in the mosq.

[Milav]

@JonB

when i execute "qDebug() << mosq;" it gives following output.

qtmosq(0xac50b0)

[JonB]

@Milav

when i execute "qDebug() << mosq;" it gives following output.
qtmosq(0xac50b0)

I'm not sure this is actually trying to deference the pointer, it may just print its value. I would try something likeqDebug() << mosq->something;, where something is some field you know is supposed to exist & be valid in a qtmosq. Or try qDebug() << *mosq (note the *)?

how i see stack trace in qt?
can you please explore me more about stack trace?

I don't know how you run in your "Embedded Custom Board", but can you run the app from inside a debugger? then when it seg faults you will see a "stack trace" in the debugger showing the call stack when the fault occurred.

[jsulm]

@JonB said in segmentation fault:

I'm not sure this is actually trying to deference the pointer

It does not, but I wanted to see its value :-)
Looks like it's not NULL.