Segfault when initializing pointer array of QPushButton

ryannasaurus

When I try to initialize an array of QPushButton, I get a segfault error.

Here, I declare the QPushButton variables in a header file.

QPushButton *num[12];

In a source file, I initialize the array and add it to a layout, which is added to a larger layout:

for (int i = 0; i < 12; i++)
    {
        //initializes and sets labels to numbers 1-12
        num[i] = new QPushButton(QString::number(i+1));

        //*QHBoxLayout
        selectLayout->addWidget(num[i]);
    }

    //*QGridLayout
    layout->addLayout(selectLayout, 2, 0, 2, 12, Qt::AlignCenter);

    setLayout(layout);

I have also tried initializing and then setting the text:

for (int i = 0; i < 12; i++)
    {
        //initializes and sets labels to numbers 1-12
        num[i] = new QPushButton();
        num[i]->setText(QString::number(i+1));

        //*QHBoxLayout
        selectLayout->addWidget(num[i]);
    }

When executing code, I get Segmentation Fault (Signal SIGSEGV) no matter how I write the code. I've also tried the 2nd variation with this pointers and initializing outside of the loop, but none of these have worked.

I'm fairly new to Qt and do not how to fix the error. Can anybody help?

aha_1980

@ryannasaurus

Are you sure the crash is within the loop? Where are selectLayout and num declared?

Why do you need num at all, i.e. are you accessing your buttons from some other place?

ryannasaurus

@aha_1980
selectLayout and num are declared in this class:

#ifndef UI_H
#define UI_H

#include <QWidget>

class QLabel;
class QPushButton;
class QGridLayout;
class QHBoxLayout;
class QVBoxLayout;

class ui : public QWidget
{
    Q_OBJECT
public:
    explicit ui(QWidget *parent = nullptr);

private:
    //layouts
    QGridLayout *layout;
    QHBoxLayout *selectLayout;
    QGridLayout *titleWidget;

    //fonts
    QFont *fTitle;
    QFont *fTitleMini;
    QFont *fInfo;

    //labels
    QLabel *title;
    QLabel *titleMini;
    QLabel *info;

    //buttons
    QPushButton *num[12];
    QPushButton *rollButton;

signals:

public slots:
};

#endif // UI_H

The buttons are not being accessed anywhere. They are just being initialized and displayed.

Christian Ehrlicher

@ryannasaurus said in Segfault when initializing pointer array of QPushButton:

QPushButton *num[12];

This is a pointer to an array (whyever) and the pointer is not initialized...

ryannasaurus

@Christian-Ehrlicher
I have it set to initialize in this for-loop here:

for (int i = 0; i < 12; i++)
    {
        //initializes and sets labels to numbers 1-12
        num[i] = new QPushButton(QString::number(i+1));
    }

I tried to add a constructor to initialize in the header file itself but it kept returning errors. It is ok to initialize it in the respective source file like I have done here?

Christian Ehrlicher

Sorry I misread the C declaration. I would use QVector <QPushButton*> num; instead. And there is no need to hold the font as pointer - QFont fTitle; etc is perefectl valid.
The crash must be somewhere else - I would suggest using a Debugger to take a look where it really crashes.

J.Hilk

hi @ryannasaurus said in Segfault when initializing pointer array of QPushButton:

is selectLayout defined? From what you pasted, I only see the pointer declaration and addWidget calls on it. Did you new
anywhere ?

ryannasaurus

This post is deleted!

ryannasaurus

@J.Hilk
Yep, this did it. I forgot to initialize one of the widgets. Thanks.