Hello, I make a qt application for Embedded Custom Board and when i run the Application it gives segmentation fault. The application give segmentation fault due to following line. mosq->subscribe(mosq->getMID(), topic.data(), 1); where mosq is define and declare as follow. class MainWindow : public QMainWindow { Q_OBJECT public: explicit MainWindow(QWidget *parent = 0); ~MainWindow(); private: qtmosq* mosq = NULL; QStringList subed; QString currentTopic; Ui::MainWindow *ui; -------- -------- -------- }; where qtmosq is define as follow.. #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++; } .......... .......... .......... signals: void connected(); void messageSent(bool); void messageReceived(QString); void connectEnable(); void subscribed(); }; so what is the reason behind for this fault. The same application are successfully run on Host Linux PC. I have use same mosquitto library in both the test. please help me to sort out this problem. I have send the reference link at where i used above program. Link :- Ref. Link Thank you Milav Soni

@Milav said in segmentation fault : you tell me mosq is bad pointer, so what is best way to make it good pointer. Create an instance and assign the pointer: mosq = new qtmosq();

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segmentation fault

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M Milav
16 Oct 2019, 04:59

@Pablo-J-Rogina said in segmentation fault:

In addition, is there any compelling reason not to use the Qt MQTT module?
Have you try any of the Qt MQTT examples?

I use actually qt4.8.7 source for development so QMqtt is not build for this qt version, so that i do not use qmqtt class.

if you have any idea how to run QMqtt in qt 4.8.7 source than please tell me it is so helpful to me.

@Pablo-J-Rogina said in segmentation fault:

Could it be possible that you run such example AS IS, I mean just download/clone the code and try such example without any change.
If you manage to make it work, then you'll have the foundation to start adapting it to whatever you need/desire.

i actually tried same as is code for pc development and that is work fine.

but when i cross compiling the code for embedded target board than it gives segmentation error,

the difference between host pc and Embedded target board is only QT source.

Host pc => qmake (qt version 5.4.0 )
Embedded target => qmake (qt version 4.8.7)

hope you got my point.

if you have any query please tell me.

and please guys help me to sort out the problem.

i am also try another code for the same , but in that i have also suffer same problem.

Another code link :- link text
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Pablo J. Rogina

wrote on 16 Oct 2019, 12:35 last edited by

#61

@Milav said in segmentation fault:

the difference between host pc and Embedded target board is only QT source.
Host pc => qmake (qt version 5.4.0 )
Embedded target => qmake (qt version 4.8.7)

You should have stated these settings from the very beginning... :-)

Anyway, could it be possible that you build Qt 4.8.7 for PC (host) and build your example again with that Qt version and run in PC to see what happens.
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16 Oct 2019, 12:35