Question

I have a class ClientWindow. I have created several instances of it and appended the their pointers to a a list. If i try to show any of the windows however, I get “Segmentation fault (core dumped)” I keep the list of windows in a class called controller.

Here is my controller header file:

#ifndef CONTROLLER_H
#define CONTROLLER_H

#include "clientwindow.h"

class Controller
{
public:
    Controller();
    void createClients(int num);
    void showWindows();

private:
    QList<ClientWindow*> clWList;
    int size;
};

#endif // CONTROLLER_H

this is the cpp file:

#include "controller.h"

Controller::Controller()
{
}

void Controller::createClients(int num)
{
    size = num;
    for(int i = 0; i < size; i++)
    {
        ClientWindow cw;
        clWList.append(&cw);
    }
}

void Controller::showWindows()
{
    for(int i = 0; i < size; i++)
    {
        ClientWindow* cw = clWList.at(0);
        cw->show();
    }
}

this is my main:

#include <QtGui/QApplication>
#include "clientwindow.h"
#include "controller.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
   // ClientWindow w;
  // w.show();

    QString temp = argv[1];
    bool ok;
    int tempI = temp.toInt(&ok, 10);
    Controller c;
    c.createClients(tempI);
    c.showWindows();



    return a.exec();
}

Answer 1

This is where it goes wrong:

for(int i = 0; i < size; i++)
{
    ClientWindow cw;
    clWList.append(&cw);
}

A local variable cw is created on the stack in each iteration. It is deallocated at the end of each iteration. Meaning the data is gone. So you end up storing pointers pointing to junk.

Calling a member function of a junk typically results in crash. 🙂 Do this instead:

for(int i = 0; i < size; i++)
{
    ClientWindow * cw = new ClientWindow();
    clWList.append(cw);
}

You’ll have to go through the list and delete the objects after you are done with them.