Qt signal forwarding - what am I doing wrong? - c++

Question

I am writing a test Qt application in which everything works fine until I try to receive a signal by slot and then emit another signal (MyWidget::setValue doesn't cause an emission of MyWidget::valueChanged). What am I doing wrong?
#include <QApplication>
#include <QVBoxLayout>
#include <QSpinBox>
#include <QSlider>
class MyWidget: public QWidget {
Q_OBJECT
signals:
void valueChanged(int value);
public slots:
void setValue(int value){
emit valueChanged(value);
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MyWidget* win = new MyWidget;
QVBoxLayout* layout = new QVBoxLayout(win);
QSpinBox* spin =new QSpinBox();
QSlider* slider = new QSlider(Qt::Horizontal);
spin->setMinimum(-100);
spin->setMaximum(100);
slider->setMinimum(-100);
slider->setMaximum(100);
layout->addWidget(spin);
layout->addWidget(slider);
QObject::connect(spin, SIGNAL(valueChanged(int)), slider, SLOT(setValue(int)));
QObject::connect(slider, SIGNAL(valueChanged(int)), win, SLOT(setValue(int)));
QObject::connect(win, SIGNAL(valueChanged(int)), spin, SLOT(setValue(int)));
win->show();
return app.exec();
}

Answer 1

What am I doing wrong?
You've created a binding loop and would overflow the stack if Qt didn't protect you from yourself by forcibly breaking the loop. As this is only a protection mechanism, its only job is to prevent a freeze and a crash. It's not supposed to make your application functional.
You have to avoid creating the loop in the first place.
You could do so e.g. by not invoking the setValue slot of the originating widget - recall that your setValue slot is called from within the valueChanged signal's body.