Class

[privatepepper]

Hello,
why I can not add any more variables to my class? If I add a new variable to the class, my program crashes.

#ifndef GRAPH_H
#define GRAPH_H

#include <QtCore>
#include <QtGui>


class Graph
{
public:

    Graph();

    int width = 40;
    int height = 30;

    int Vertices;

    void initialize_matrix(int nodes){
        Vertices = nodes;
        matrix->clear();
        store_searching_path.clear();
        store_path.clear();
        matrix = new QVector <int> [nodes];
    }

    void addEdge(int vertice1, int vertice2){
        matrix[vertice1].push_back(vertice2);
    }

    QVector <int> store_searching_path;
    QVector <int> store_path;

    bool BFS(int start, int end);
    bool DFS(int start, int end);
    //void recursive_DFS(int source);
    void dijkstra_algorithm();

private:

    QVector <int> *matrix;
    //bool *visited;
    int blabla;

};

#endif // GRAPH_H

For example when I add blabla integer my program crashes, if I delete blabla integer then everything is fine

[Pl45m4]

@privatepepper

Your blabla int member itself is most likely not the reason for your crash. Where do you use it?

[privatepepper]

@Pl45m4
That's the point, I don't use it, I added blabla for the example

[Pl45m4]

Where exactly crashes your program? Any error message?

@privatepepper said in Class:

int width = 40;
int height = 30;

int Vertices;

What's the reason for them being public?

[privatepepper]

@Pl45m4

I get only one error - The program has unexpectedly finished.

I use width and height in the mainwindow class to draw grid of QGraphicsRectItems , and I just realized that Vertices should be private, because I use Vertices only in this class, but now when i add Vertices to private and delete blabla integer my program too crashes;/

[SGaist]

Hi,

Then use the debugger to see what is happening.

[Pl45m4]

@privatepepper said in Class:

I use width and height in the mainwindow class to draw grid of QGraphicsRectItems

There are fancy things called setters / getters :-)

[privatepepper]

@Pl45m4
what do you mean by that?

I found a way to fix my code. But I don't know why this thing works and what is that. When I started to use the debugger on my ide opened like another file, it looked like behind the scenes what qt is doing.
Little part of that code:

inline void QVector<T>::clear()
{
    //if (!d->size)
    //    return;
   // destruct(begin(), end());
   // d->size = 0;
}

And if i comment out these lines, my code works fine and i can add new variables to my class:). Could someone explain what is this and why my code didn't work before?

[SGaist]

As I already suggested, use the debugger.

[privatepepper]

@SGaist
Yeah I know, and thanks for the help:), I already fixed my code as I mentioned above, but I don't understand what I fixed:/

[SGaist]

If you are talking about the QVector snippet, you did not fix anything, you broke QVector.

[JonB]

@privatepepper
Your comment-out code prevents QVector<T>::clear() from actually clearing its elements, and then your code works. I would look at everywhere you use a QVector. You have matrix->clear();; just what do you do with your QVector <int> *matrix? It is a member variable right next to where you introduce a new variable and then it crashes....

        matrix->clear();
        ...
        matrix = new QVector <int> [nodes];

What about first time round? You do initialize matrix before this, don't you, else you're trying to clear() a random area of memory....

[privatepepper]

@JonB
@SGaist

Thanks for help very much :), like JonB said the problem was matrix->clear(), I feel so dumb right now:D, lets hope that I will learn from this mistake; but it is weird for me that this problem only occurred when I tried to add new variables to the header file.

[Christian Ehrlicher]

There is also no need to use a pointer here.

[privatepepper]

@Christian-Ehrlicher said in Class:

There is also no need to use a pointer here.

Do you mean QVector <int> *matrix ? I added this pointer because I want that this vector would be 2d

[SGaist]

Then use QVector<QVector<int>> matrix

[privatepepper]

@SGaist

Okay, I will use QVector<QVector<int>> matrix, but why I shouldn't use a pointer? Is there a big difference? Sorry for dumb questions...

[Christian Ehrlicher]

@privatepepper said in Class:

but why I shouldn't use a pointer?

Because it's not needed and when using an object you can't forget to initialize (and delete) it (as you did both)