Problem pointing to a QStringList

[ljuhrich]

I wanted to make my application logging, so I added a "QStringList l" to my Mainwindow Class.
Because the Program has some sub-classes that also should be logging, I added Pointers to the mainwindow's QStringList into them.
The program executes the Pledge-Algorithm for a robot to leave a room full of blocks, so I created the Classes "CPledge", "CRob" and "CMap".

The problem: I get a SIGSEGV error when I reference the log-lists of CRob/CMap to the Mainwindow's logList.
CODE:
Mainwindow Class:

#include <QMainWindow>
 
namespace Ui {
class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
    // !The Log Object!
    QStringList l;
 
    void saveLog(QString file);
 
private:
    Ui::MainWindow *ui;
 
 
    QString i(int i);
    QString dt();
 
private slots:
    void on_btStartThread_clicked();
    // etc.
};
 
 
#endif // MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    // !The Log Object!
    QStringList l;

    void saveLog(QString file);

private:
    Ui::MainWindow *ui;


    QString i(int i);
    QString dt();

private slots:
    void on_btStartThread_clicked();
    // etc.
};


#endif // MAINWINDOW_H

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The CPledge Class (Gets the CRob out of a CMap):

class CPledge : public QObject
{
    Q_OBJECT
public:
    explicit CPledge(QObject *parent = 0);
 
    CMap *map;
    CRob *rob;
    void setBot(int x, int y);
    // Log list reference
    QStringList *l;
 
private:
    void followLeftWallTilTurnIsZero();
 
public slots:
    void solve(QString filePath);
 
signals:
    void finished();
};

class CPledge : public QObject
{
    Q_OBJECT
public:
    explicit CPledge(QObject *parent = 0);

    CMap *map;
    CRob *rob;
    void setBot(int x, int y);
    // Log list reference
    QStringList *l;

private:
    void followLeftWallTilTurnIsZero();

public slots:
    void solve(QString filePath);

signals:
    void finished();
};

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The CMap Class (The Labyrinth):

class CMap : public QObject
{
    Q_OBJECT
public:
    explicit CMap(QObject *parent = 0);
    // Log list reference
    QStringList *l;
 
    typedef QList<bool> StonesLine;
 
    void loadFromFile(QString FilePath);
 
    bool free(int x, int y);
    bool left(int x, int y, int turn);
    bool front(int x, int y, int turn);
    QPoint movedPos(int x, int y, int turn);
 
    int cleanTurning(int turn);
 
    QPoint *defaultRobPos;
 
private:
    // A 2D bool-list: 1->stone; 0-> No stone
    QList <StonesLine> stones;
    // The list of points where the rob is free
    QPoint freePoints[2];
 
    void insertBlock(int x1, int y1, int x2, int y2);
    void initBlocks(int width, int height);
 
    StonesLine horizontalStonesBorder(int width);
    StonesLine verticalStonesBorder(int width);
};

class CMap : public QObject
{
    Q_OBJECT
public:
    explicit CMap(QObject *parent = 0);
    // Log list reference
    QStringList *l;

    typedef QList<bool> StonesLine;

    void loadFromFile(QString FilePath);

    bool free(int x, int y);
    bool left(int x, int y, int turn);
    bool front(int x, int y, int turn);
    QPoint movedPos(int x, int y, int turn);

    int cleanTurning(int turn);

    QPoint *defaultRobPos;

private:
    // A 2D bool-list: 1->stone; 0-> No stone
    QList <StonesLine> stones;
    // The list of points where the rob is free
    QPoint freePoints[2];

    void insertBlock(int x1, int y1, int x2, int y2);
    void initBlocks(int width, int height);

    StonesLine horizontalStonesBorder(int width);
    StonesLine verticalStonesBorder(int width);
};

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The CRob Class (The Robot):

class CRob : public QObject
{
    Q_OBJECT
public:
    explicit CRob(QObject *parent = 0);
    // Log list reference
    QStringList *l;
 
    bool free();
 
    bool left();
    bool front();
 
    void turnR();
    void turnL();
 
    void move();
 
    void setPosition(int newx, int newy);
 
    int turning();
 
private:
    int x, y;
    CMap *map;
 
    int fturning;
};

class CRob : public QObject
{
    Q_OBJECT
public:
    explicit CRob(QObject *parent = 0);
    // Log list reference
    QStringList *l;

    bool free();

    bool left();
    bool front();

    void turnR();
    void turnL();

    void move();

    void setPosition(int newx, int newy);

    int turning();

private:
    int x, y;
    CMap *map;

    int fturning;
};

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The Error comes here at Mainwindow.cpp:

// etc.
void MainWindow::on_btStartThread_clicked()
{
    CPledge *pledge = new CPledge();
    pledge->l = &l;
    // #########FATAL SIGSEGV ERROR################
    pledge->rob->l = &l;
    pledge->map->l = &l;
 
 
    pledge->solve(ui->edMapPath->text());
}
// etc.

// etc.
void MainWindow::on_btStartThread_clicked()
{
    CPledge *pledge = new CPledge();
    pledge->l = &l;
    // #########FATAL SIGSEGV ERROR################
    pledge->rob->l = &l;
    pledge->map->l = &l;


    pledge->solve(ui->edMapPath->text());
}
// etc.

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