[Solved] QSlider throws segmentation fault on create

eggmatters2

First off, I am brand new to Qt. It seems pretty slick but I can't wrap my head around this one.

I'm starting off trying to port some old Windows opengl code to Qt. I used a sample project "hellogl" to begin with. This project, as it stands works fine when I insert my OpenGl classes (well, not exactly but that's another thread.) The UI renders 3 sliders which rotate around respective axes. I wanted to add 3 more sliders to translate. I merely copied the original code and repurposed it for my needs.

When I launch, the program will create the original 3 sliders, one of the new ones and then throw a segmentation fault. Commenting out the original sliders and just calling my own will still do the same thing. Here is the code:

@
#include <QtGui>

#include "GLWidget.h"
#include "window.h"

Window::Window() {

glWidget = new GLWidget;    

xSlider = createSlider(1); //original 3 sliders
ySlider = createSlider(1);
zSlider = createSlider(1);

xTSlider = createSlider(2); //this call returns fine
yTSlider = createSlider(2); //segmentation fault
zTSlider = createSlider(2);

. . .
/*note: calling :
xTSlider = createSlider(1); //this call returns fine
yTSlider = createSlider(1); //segmentation fault
zTSlider = createSlider(1);
Does the same thing
*/
//The signals / slots and desktop and widget additions follow. The code never reaches this point though.
. . .
//The create method:
QSlider *Window::createSlider(int sliderType)
{
if (sliderType == 1) {
QSlider *slider = new QSlider(Qt::Vertical);
slider->setRange(0, 360 * 16);
slider->setSingleStep(16);
slider->setPageStep(15 * 16);
slider->setTickInterval(15 * 16);
slider->setTickPosition(QSlider::TicksRight);
return slider;
}
else {
QSlider *slider = new QSlider(Qt::Horizontal);
slider->setRange(0, 800);
slider->setSingleStep(8);
slider->setPageStep(8);
slider->setTickInterval(8);
slider->setTickPosition(QSlider::TicksBelow);
return slider;
}
}
@

If you notice, I pass in a flag which dictates which type of slider to create. To test this, I set the new sliders flag to "1" and the program still crashes.

Here is the header file contents:

@
#ifndef WINDOW_H
#define WINDOW_H

#include <QWidget>

QT_BEGIN_NAMESPACE
class QSlider;
QT_END_NAMESPACE

class GLWidget;

class Window : public QWidget
{
Q_OBJECT

public:
Window();

protected:
void keyPressEvent(QKeyEvent *event);

private:

GLWidget *glWidget;
QSlider *createSlider(int sliderType);
QSlider *xSlider;
QSlider *ySlider;
QSlider *zSlider;
QSlider *xTSlider;
QSlider *yTSlider;
QSlider *zTSlider;

};

#endif // WINDOW_H
@

The majority of this code was merely copied over from an existing project provided by Qt which works just fine. Here are the tests I ran:

Change the sliderType param to 1 for the new sliders - fails
Comment out the three existing sliders and attempt to create the new ones only for both sliderType params of 1 and 2 - fails.
(This is weird) Comment out the new sliders and change the names of the old ones to the new names - fails
Create only one new slider - fails

Unfortunately, I have core dumps turned off on my machine. I am running Debian under the Linux 2.6.32-5-686 kernel Developing on Qt(4.6.3)

Thanks!

lgeyer

Have you tried rebuilding your project?
Do you have a QApplication object at the time the sliders are created?
Did you try running your application in debug mode to find out where it actually crashes?

eggmatters2

Yes, it crashes when I try to rebuild it. Stepping through the debugger throws the error where commented in the code. I do have a QApplication object created: From main:
QApplication app(argc, argv);
Window window;

When I step through, it seems to generate infinitely recursive "this" objects.

eggmatters2

UPDATE: I can set one slider from my code without it throwing a seg fault.

eggmatters2

Looks like I fixed it. Apparently I had a typo in one of the functions I was registering with the signal / slots connection. That and Lukas comment about rebuilding. I was under the impression that the green "go" button rebuilt everything but, there were probably corrupt object files that got skipped. Please flag this post as solved. Thanks!

lgeyer

Rebuilding is almost always a good idea - solves strange problems from time immemorial. ;-)

You can flag this post as solved on your own. As there is no automatism for this (yet), just edit your inital post title and prepend it with [Solved].

eggmatters2

Thanks! Whew. A bit of a learning curve here but I think that the concept of signals and slots is ingenious. Who would have thought that registering event listeners in c++ can be done with under 10 lines of code!!!!