How do I create a 2 dimensional array of QGraphicsRectItems?

[Guillermo-Gatoto]

I need to display a dynamic amount of QGraphicsRectItems in a QGraphicsView in rows and columns, so I decided to create a 2D array, but I always get an error. This is my header:

#ifndef MAINWINDOW_H
    #define MAINWINDOW_H
 
    #include <QGraphicsRectItem>
    #include <QMainWindow>
    #include <QGraphicsScene>
 
    namespace Ui{
        class MainWindow;
    }
 
    class MainWindow : public QMainWindow{
        Q_OBJECT        
 
        public:
            explicit MainWindow(QWidget *parent = 0);
            ~MainWindow();
 
        private:
            Ui::MainWindow *ui;
            QGraphicsRectItem*** objRect; //This would be my 2D array
    };
 
    #endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
    #define MAINWINDOW_H
    
    #include <QGraphicsRectItem>
    #include <QMainWindow>
    #include <QGraphicsScene>
    
    namespace Ui{
        class MainWindow;
    }
    
    class MainWindow : public QMainWindow{
        Q_OBJECT        
    
        public:
            explicit MainWindow(QWidget *parent = 0);
            ~MainWindow();
    
        private:
            Ui::MainWindow *ui;
            QGraphicsRectItem*** objRect; //This would be my 2D array
    };
    
    #endif // MAINWINDOW_H

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This is how I instance it:

objRect = new QGraphicsRectItem**[x];
        for(int i = 0; i < x; i++){
            objRect[i] = new QGraphicsRectItem*[x];
        }

objRect = new QGraphicsRectItem**[x];
        for(int i = 0; i < x; i++){
            objRect[i] = new QGraphicsRectItem*[x];
        }

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The code above runs perfectly with no errors. But whenever I try to do something with it, like establishing the size of one of the rectangles, it throws me an error message:

objRect[0][0]->setRect(0,0,100,100);

objRect[0][0]->setRect(0,0,100,100);

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If I run the program normally, no error message appears, but the window doesn't even appear. I can only see the error message if I run the project in Debug mode.

This is the error message:

2017-08-11.jpg

"The inferior stopped because it received a message from the operating system"

Signal name: SIGSEGV

Signal meaning: Segmentation fault

I've tried a lot of different ways of instancing it, but nothing seems to work.

[Ginsengelf]

Hi, think it would be easier to use a standard container like QVector or QList instead of creating the array by yourself.

Ginsengelf

[Santosh Reddy]

So far good, but where are you allocating the object, that is only thing missing.

Here is a generic example

template <typename T>
T *** New2DArray(int rows, int cols)
{
    T *** array = new T**[rows];
 
    for(int r = 0; r < rows; ++r)
    {
        array[r] = new T*[cols];
 
        for(int c = 0; c < cols; ++c)
            array[r][c] = new T;
    }
 
    return array;
}
 
template <typename T>
void Delete2DArray(T *** array, int rows, int cols)
{
    for(int r = 0; r < rows; ++r)
    {
        for(int c = 0; c < cols; ++c)
            delete array[r][c];
 
        delete[] array[r];
    }
 
    delete[] array;
}
 
...
QGraphicsRectItem *** objRect = New2DArray<QGraphicsRectItem>(rows, cols);
...
Delete2DArray(array, rows, cols);
...

template <typename T>
T *** New2DArray(int rows, int cols)
{
    T *** array = new T**[rows];

    for(int r = 0; r < rows; ++r)
    {
        array[r] = new T*[cols];

        for(int c = 0; c < cols; ++c)
            array[r][c] = new T;
    }

    return array;
}

template <typename T>
void Delete2DArray(T *** array, int rows, int cols)
{
    for(int r = 0; r < rows; ++r)
    {
        for(int c = 0; c < cols; ++c)
            delete array[r][c];

        delete[] array[r];
    }

    delete[] array;
}

...
QGraphicsRectItem *** objRect = New2DArray<QGraphicsRectItem>(rows, cols);
...
Delete2DArray(array, rows, cols);
...

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