Question

I’m just starting out with Qt on a Mac and working through:

http://doc.qt.nokia.com/4.7/gettingstartedqt.html

When I run the second example which has the following code:

#include <QtGui>

int main(int argv, char **args)
{
    QApplication app(argv, args);

    QTextEdit textEdit;
    QPushButton quitButton("Quit");

    QObject::connect(&quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));

    QVBoxLayout layout;
    layout.addWidget(&textEdit);
    layout.addWidget(&quitButton);

    QWidget window;
    window.setLayout(&layout);

    window.show();

    return app.exec();
}

The application starts up fine and works fine. The only issue occurs when I click the “Quit” button. When I do that the crash reporter is invoked and osx says the app quit unexpectedly.

Anything obvious I’m doing wrong?

Thanks

Answer 1

The problem is the order of the delete if you declare variables on the stack. The best it to give your object parents so that they can destroy the children.

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

    QWidget window;

    // If window get's destroyed, it will destroy it's children...
    QTextEdit textEdit(&window);
    QPushButton quitButton("Quit",&window);

    QObject::connect(&quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));

    QVBoxLayout layout;
    layout.addWidget(&textEdit);
    layout.addWidget(&quitButton);

    window.setLayout(&layout);

    window.show();

    return app.exec();
}

PS: Did you actually try a debugger to see where it crashes? It will give you an idea 😉 My suggestion is to take a working Qt example and play with it.

PS2: The order I created the widgets also prevents the crash…