Program is crashing

thomasGl

hey guys. What am i doing wrong. the Program starts only when i delete "beendeButton -> setGeometry(30,30,30,30);".

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <qlabel.h>
#include <QPushButton>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0, QLabel *const helloWorldLabel = nullptr, QPushButton *const beendeButton = nullptr);
    ~MainWindow();

private:
    QLabel *const helloWorldLabel;
    QPushButton *const beendeButton;


};




#endif // MAINWINDOW_H

#include "mainwindow.h"


MainWindow::MainWindow(QWidget *parent, QLabel *const helloWorldLabel, QPushButton *const beendeButton):QMainWindow(parent),helloWorldLabel(new QLabel("Hello World", this)), beendeButton(new QPushButton("Beenden", this))

{

  beendeButton -> setGeometry(30,30,30,30);

   //Verbindung des Beenden-Buttons mit der close()-Methode des MainWindow
   connect(beendeButton, &QPushButton::clicked, this, &MainWindow::close);

}

MainWindow::~MainWindow()
{
    delete helloWorldLabel;
    delete beendeButton;
}

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);



  MainWindow mainWindow;
  mainWindow.show();

  return a.exec();
}

JonB

@thomasGl ...because you never actually set beendeButton to anything (other than its default value nullptr)...?

Pl45m4

@thomasGl said in Program is crashing:

QLabel *const helloWorldLabel;
QPushButton *const beendeButton;

What's the reason for const? Remove the const

@thomasGl said in Program is crashing:

delete helloWorldLabel;
delete beendeButton;

also this can be removed... (child QObjects are deleted with their parent)

and it should work.

Edit:

@JonB

Initialized here:

MainWindow::MainWindow(QWidget *parent, QLabel *const helloWorldLabel, QPushButton *const beendeButton)
: QMainWindow(parent)
, helloWorldLabel(new QLabel("Hello World", this))
  beendeButton(new QPushButton("Beenden", this))

JonB

@Pl45m4 said in Program is crashing:

Initialized here:

OMG, I hate that syntax and it's scrolled off the screen anyway... :( :) At minimum I wish people put newlines in like you show.

Pl45m4

@JonB said in Program is crashing:

OMG, I hate that syntax and it's scrolled off the screen anyway... :( :)

Yup, reformatted it to make it somewhat readable.

What was the rule of thumb for maximum line length again? Until you get beaten as a programmer? :DD
Like 60-70 characters or so? ;-)

thomasGl

Starting P:\Qt training\build-AktuellAktiv-Desktop_Qt_5_9_0_MinGW_32bit-Debug\debug\AktuellAktiv.exe...
Warning: QT_DEVICE_PIXEL_RATIO is deprecated. Instead use:
QT_AUTO_SCREEN_SCALE_FACTOR to enable platform plugin controlled per-screen factors.
QT_SCREEN_SCALE_FACTORS to set per-screen factors.
QT_SCALE_FACTOR to set the application global scale factor.
The program has unexpectedly finished.
P:\Qt training\build-AktuellAktiv-Desktop_Qt_5_9_0_MinGW_32bit-Debug\debug\AktuellAktiv.exe crashed. I am still getting that error

SGaist

Hi,

Please post the stack trace of the crash.

thomasGl

Axel Spoerl

 beendeButton -> setGeometry(30,30,30,30);

will call setGeometry() on the constructor argument beendeButton, which defaults to nullptr, because no argument is passed to the c'tor in main.cpp.

I don't see, why this argument is necessary at all. Probably you get a compiler warning about an unused argument. Probably you expect setGeometryto be called on the member which you correctly initialize.

=> remove the unneeded arguments from the c'tor. They are the reason for the crash.

thomasGl

@Axel-Spoerl thx it works now.

Axel Spoerl

Remains the (unrelated) question, why you use Qt 5.9.0.
That ship has sailed long ago. Better use 6.5 or even 6.7.

Pl45m4

@Axel-Spoerl said in Program is crashing:

will call setGeometry() on the constructor argument beendeButton, which defaults to nullptr, because no argument is passed to the c'tor in main.cpp.

Oh gosh.... haven't even seen that the argument is named exactly the same as the private member.
Thought there is something else going on, beside the const which is weird in this case, because the code didn't looked that wrong.

@JonB Two blind people trying to help :D
Next time I scroll horizontally for you and you check the spelling for me :P

JonB

@Pl45m4
I saw the formal parameters were the same names as the member variables, which made me wonder how that works. But I said I never use that syntax and thought I could trust you on this one ;-)

Pl45m4

@JonB said in Program is crashing:

I saw the formal parameters were the same names as the member variables, which made me wonder how that works. But I said I never use that syntax and thought I could trust you on this one ;-)

It would have, if only the names were different :'-)
In a regular function you would use this->beendeButton(beendeButton), then the same names are not a problem anymore, but it does not work in initializer lists.

Axel Spoerl

m_beendeButton

…. and you’re set!