InsertWidget on a layout results in a segfault if index is too big. Minimal example:

#include <QtWidgets>

class MyDialog : public QDialog {
public:
    MyDialog(QWidget *parent = nullptr) : QDialog(parent) {
        QVBoxLayout *layout_1 = new QVBoxLayout(this);
        layout_1->insertWidget(1, new QLabel("aaa", this));
    }
};

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

    MyDialog window;
    window.show();

    return qt_app.exec();
}

It works correctly if index is 0. This is confusing, as documentation says: "Inserts widget at position index, with stretch factor stretch and alignment alignment. If index is negative, the widget is added at the end." , which does not suggest any restrictions on index. I think a segfault is a very ugly way of handling it, some sort of more descriptive error would make debugging much easier.