Question

I’ve created a class and I would like to add this class in an other one (both are layouts) but the only error message that I get is that the program crashed.

I feel like there is some obvious logic flaw but I don’t find it, I can show both of them separately but when I try to add one to the other the program crashes. Here is the code:

Mesure.h:

class Mesure : public QWidget
{
    public:
    Mesure(QString angle);

    private:
    QToolButton *m_buttonClose;
    QHBoxLayout *m_hlayoutMesure;
    QCheckBox *m_checkboxMesure;
    QLabel *m_labelAngle;
};

Mesure.cpp:

Mesure::Mesure(QString angle) : QWidget()
{
    QHBoxLayout *m_hlayoutMesure = new QHBoxLayout;
    QCheckBox *m_checkboxMesure = new QCheckBox(this);
    QToolButton *m_buttonClose = new QToolButton(this);
    QLabel *m_labelAngle = new QLabel(angle, this);

    m_buttonClose->setText("X");

    m_hlayoutMesure->addWidget(m_checkboxMesure);
    m_hlayoutMesure->addWidget(m_labelAngle);
    m_hlayoutMesure->addWidget(m_buttonClose);

    setLayout(m_hlayoutMesure);
}

PanneauMesure.h:

class PanneauMesure : public QWidget
{
    public:
    PanneauMesure();
    void add(Mesure *mesure);

    private:
    QVBoxLayout *m_vlayoutMesures;
};

PanneauMesure.cpp:

PanneauMesure::PanneauMesure() : QWidget()
{
    QVBoxLayout *m_vlayoutMesures = new QVBoxLayout;
    setLayout(m_vlayoutMesures);
}

void PanneauMesure::add(Mesure *mesure)
{
    m_vlayoutMesures->addWidget(mesure);
    setLayout(m_vlayoutMesures);
}

main.cpp:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    PanneauMesure panneau;
    Mesure mesure("14°");
    panneau.add(&mesure);

    return app.exec();
}

Edit:
Problem solved, I just had to modify the files like this:

Mesure.cpp:

Mesure::Mesure(QString angle) : QWidget(),
    m_hlayoutMesure(new QHBoxLayout(this)),
    m_checkboxMesure(new QCheckBox(this)),
    m_buttonClose(new QToolButton(this)),
    m_labelAngle(new QLabel(angle, this))
{
    m_buttonClose->setText("X");

    m_hlayoutMesure->addWidget(m_checkboxMesure);
    m_hlayoutMesure->addWidget(m_labelAngle);
    m_hlayoutMesure->addWidget(m_buttonClose);

    setLayout(m_hlayoutMesure);
}

PanneauMesure.cpp:

PanneauMesure::PanneauMesure() : QWidget(),
    m_vlayoutMesures( new QVBoxLayout(this))
{
    setLayout(m_vlayoutMesures);
}

void PanneauMesure::add(Mesure *mesure)
{
    m_vlayoutMesures->addWidget(mesure);
    setLayout(m_vlayoutMesures);
}

Answer 1

In your constructors, you create local variables that hide your class members. You store the pointers to allocated elements in these local variables, but your actual class variables are left default-initialized (i.e. they contain garbage).

When accessing these garbage values (as you do in PanneauMesure::add) you end up having undefined behaviour, this time a crash (lucky you!)

As a sidenote, you should probably use initializer lists to initialize your class variables, like this:

Mesure::Mesure(QString angle):
    QWidget(),
    m_hlayoutMesure(new QHBoxLayout(this)), // always use parented constructor
                                            // when available in Qt
    // ...
{
    // logic
}

Also, you don’t need to call setLayout repeatedly.