Question

I was creating a very simple class as part of a much larger project. The class was as simple as:

class Login : public QDialog
{
    Q_OBJECT
    private:
        QLineEdit* txtUser;
        QLineEdit* txtPass;
        void setupUI();
    public:
        Login(QWidget* parent = 0);
};

When attempting to create the setupUI() function the line txtUser = new QLineEdit; would crash. I tried changing a lot of things and nothing would help. I took the project, copied it, and removed everything except this class and a main.cpp and there was no error. I returned to my original project (reloading Qt Creator) and it continued to fail. I began commenting out random self-written header files from the main in case of some sort of conflict. After commenting out each one, I would re-compile and run. Each time it would continue to fail. After the last one, it worked. Then, I re-enabled everything and it ran great once again.

So, my question is, what could cause a segfault of this type with such simple code? In addition what might my changes have done to fix it if no code was changed? Basically, if I get this problem to ever occur again and I’m sure there are no errors, what steps should I take?

Please keep in mind I am using Qt and Qt Creator within Windows.

Finally, for the sake of completion, here is the code within setupUI():

void Login::setupUI()
{
    QVBoxLayout* main = new QVBoxLayout;
    QHBoxLayout* userBox = new QHBoxLayout;
    QHBoxLayout* passBox = new QHBoxLayout;
    txtUser = new QLineEdit;
    txtPass = new QLineEdit;
    userBox->addWidget(new QLabel("User Name:"));
    userBox->addWidget(txtUser);
    passBox->addWidget(new QLabel("Password:"));
    txtPass->setEchoMode(QLineEdit::Password);
    passBox->addWidget(txtPass);
    main->addLayout(userBox);
    main->addLayout(passBox);
    setLayout(main);
}

Answer 1

Sometimes you need to run qmake to make it work. You can do that right from QtCreator.