[solved] Qt4 - Program written in QtCreator segfaults

nexuiz

The following code is suppose to change a property of a progress bar when a button is clicked.
I tried to do the same in Qt3Designer and everything worked fine.
What happens is as soon as the button is clicked, the program crashes with the following message:

Starting /home/user/qt4/test1/test1...
The program has unexpectedly finished.
/home/user/qt4/test1/test1 exited with code 0

Here's mainwindow.cpp
@
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "kled.h"
#include <QLCDNumber>
#include <QProgressBar>

QProgressBar *qprogressbar;
QLCDNumber *lcdnumber;
KLed *kled;

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{

ui->setupUi(this);

}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::changeEvent(QEvent *e)
{

QMainWindow::changeEvent(e);
switch (e->type()) {
case QEvent::LanguageChange:
    ui->retranslateUi(this);
    break;
default:
    break;
}

}

void MainWindow::on_pushButton_clicked()
{
qprogressbar->setValue(30);
}

@

Thank you.

mlong

Where are you instantiating qprogressbar?

nexuiz

Thanks for your quick reply.
Disclaimer: I am not a C++ programmer. I just create frontends for my C based console programs that drive my instruments.

Back to my post now, I thought that QtCreator did it automatically (pretty much like in Qt3-Designer).
I mean since all widgets already were placed on the form, then they should already have been instantiated, right?

mlong

Based on your comments, I'm assuming you have a widget in the Ui named qprogressbar?

If so, you need to get rid of line 7 in your code above ( (It doesn't refer to the progressbar in your ui. It's just an unused global pointer) , and replace line 42 with
@
ui->qprogressbar->setValue(30)
@
as anything that is created in the Ui file will be available through that pointer. There's no need to redeclare pointers for the Ui widgets in your code.

nexuiz

That worked. Next stop: get the fundamentals of C++.

Thank you very much.