The program crashes suddenly when working with a new feature

VRonin

@tomy said in The program crashes suddenly when working with a new feature:

where is the window called "stack trace window", please?

It's the one in the bottom right corner

tomy

I ran the program with Debugger (F5) and tested it for crash many a time, but thus far it's never crashed in this mode. But when I run it by crtl+R, it crashes at the second or third time I apply the sum action on the highlighted cells!
Why please? Does the debugger change the behavior of the program, please?

Here is the project spreadsheet.rar. Please if possible test it and let me know what makes the program crash, please?
I wanted to upload it here but faced a message saying I haven't that privilege! so posted that below:
https://www.dropbox.com/s/anuk091qr8tjeem/spreadsheet.rar?dl=0

SGaist

Hi,

Check for uninitialised pointers and/or variables. In debug mode, the pointers at least are initialised to zero but not in release mode (that's nothing Qt specific though)

tomy

I changed the initial value of some pointers from 0 to nullptr and also assigned 0 to some uninitialized variables too ( E.g., quint16) then reran the project and tested for the crash. This time I got this message at the time of crash:

12:53:28: Starting C:\Users\Abbasi\Desktop\Documents\Qt\qt-book\chap03\build-spreadsheet-Desktop_Qt_5_12_0_MinGW_64_bit-Debug\debug\spreadsheet.exe...
ASSERT: "size == 0 || offset < 0 || size_t(offset) >= sizeof(QArrayData)" in file..\..\include/QtCore/../../src/corelib/tools/qarraydata.h, line 67
12:53:50: The program has unexpectedly finished.
12:53:50: The process was ended forcefully.
12:53:51: C:/Users/Abbasi/Desktop/Documents/Qt/qt-book/chap03/build-spreadsheet-Desktop_Qt_5_12_0_MinGW_64_bit-Debug/debug/spreadsheet.exe crashed.

And when I clicked on that file I got this message:

By the way, I always run the programs in the Debug mode unless they're in their last state before creating an installer for them. So all crashes have happened in the Debug mode so far.

And still by the Debugger, I get no crashes!!

Christian Ehrlicher

You're hitting an assertion because you are accesing a QVector/QList with an index which is out-of-bounds. Take a look at the backtrace to see from where the call is coming.

So all crashes have happened in the Debug mode so far. And still by the Debugger, I get no crashes!!

This somehow makes no sense from me - either it crashes in debug or not.

J.Hilk

@Christian-Ehrlicher
as far as i unerstand it, it‘s always a debug build but only crashes, when rhe debugger is not attached.

which is unusual.

You could potentially try attaching the debugger after wards to the running process via VS.

Christian Ehrlicher

Since it's an assertion it will also happen when a debugger is attached. And that's also the reason why it does 'work' in release mode.

tomy

@Christian-Ehrlicher

Take a look at the backtrace to see from where the call is coming.

As I said, when run by the Debugger, the project never crashes, at least based on my many tests' result!

This somehow makes no sense from me - either it crashes in debug or not.

I don't use the Release mode, so please let's drop this word down for the time being.

I run the program only in the Debug mode, either by pressing F5 (which is the Debugger) or ctrl+R (which is a rormal run).

When run normally: Crash occurs.
when run by the Debugger: Crash doesn't occur.

Why don't you simply download and run the project, please?

Christian Ehrlicher

@tomy said in The program crashes suddenly when working with a new feature:

QTableWidgetItem* item = new QTableWidgetItem;

This is wrong, you have to use 'Cell' ...

Cell *Spreadsheet::cell(int row, int column) const
{
    return static_cast<Cell *>(item(row, column));
}

tomy

@Christian-Ehrlicher

Do you mean I use sum() this way:

void Spreadsheet::sum()
{
    double d = 0.0;

    QList<QTableWidgetItem *> items = selectedItems();

    if(add(items, d)) {
        int row = 0, column = 0;
        position(items, row, column);

        ++row;
        Cell *c = cell(row, column);
        c->setTextAlignment(Qt::AlignRight);
        c->setText((QString::number(d)));

        somethingChanged();
    }
}

It still crashes.

Christian Ehrlicher

@tomy said in The program crashes suddenly when working with a new feature:

It still crashes.

But this time your debugger will show you where...

tomy

@Christian-Ehrlicher
Right!

![0_1552139887443_5.PNG]

Christian Ehrlicher

So when you go up the backtrace you see that "Cell *c = cell(row, column);" returns a nullptr.

tomy

@Christian-Ehrlicher

So when you go up the backtrace you see that "Cell *c = cell(row, column);" returns a nullptr.

Since it's empty, yeah?

So how to get to the next row (which may or may not be empty) to set the result into it, please?

Christian Ehrlicher

When there is no object (yet) you should create one, or?

tomy

@Christian-Ehrlicher
I was doing it by:

QTableWidgetItem* item = new QTableWidgetItem;

I don't know why we need: Cell *c = cell(row, column); while it's the last filled cell and we can't increase its row number to get to the next cell to put the result of sum() into it!

Christian Ehrlicher

I already told you that you don't have to use QTableWidgetItem but Cell since the model is working with Cell objects (which derives from QTableWidgetItem) instead QTableWidgetItem and therefore the static cast does undefined stuff -> c++ basics...

tomy

@Christian-Ehrlicher

When there is no object (yet) you should create one, or?

Using this statement: Cell* c = cell(row, column); we can only have c as a pointer to a non-empty cell in the sheet. Moreover, we can't make it point to the next cell as our target cell for putting the result of our function, because the program crashes. So that c is useless.

What do you mean by creating an object? And object of what? A cell? If so, how? This way: Cell ce = *cell(row, column);?

I really don't understand what your intention is.
Isn't there any way to solve this issue?

Christian Ehrlicher

How to create a new object on the heap: http://www.cplusplus.com/reference/new/operator new/

tomy

@Christian-Ehrlicher

You mean new? I've tested it beforehand in this version of sum and already for QTableWidgetItem.

void Spreadsheet::sum()
{
    double d = 0.0;

    QList<QTableWidgetItem *> items = selectedItems();

    if(add(items, d)) {
        int row = 0, column = 0;
        position(items, row, column);

        row++;
        
        Cell* c = new cell(row, column);
        c->setTextAlignment(Qt::AlignRight);
        c->setText((QString::number(d)));
       
        somethingChanged();
    }
}

Neither Cell* c = new cell(row, column); nor Cell* c = new Cell(row, column); works.

Found it:

void Spreadsheet::sum()
{
    double d = 0.0;

    QList<QTableWidgetItem *> items = selectedItems();

    if(add(items, d)) {
        int row = 0, column = 0;
        position(items, row, column);

        row++;

        Cell* c = new Cell();
        c->setTextAlignment(Qt::AlignRight);
        c->setText((QString::number(d)));
        setItem(row, column, c);
        somethingChanged();
    }
}

And apparently works fine. :)