Memory-Management in Qt: AddressBook tutorial

Question

So, I've learned so far, that Qt releases the memory of all child objects when a parent object gets deleted. Also, one generally doesn't have to care about memory management for objects created on the stack (i.e. NOT as pointers).

Now, when I did the very good "AddressBook" tutorial, I found this in part 5:

AddressBook::AddressBook(QWidget *parent) : QWidget(parent)
{
    dialog = new FindDialog;
}

Complete source is available: addressbook.h addressbook.cpp finddialog.h

Here, dialog is a private member of AddressBook, and it is a pointer to a FindDialog. FindDialog inherits QDialog, but no this-Pointer is passed to the constructor (as seen above). No explicit destructor exists, there is no delete dialog-call...

Also, not passing this seems to be intentional:

[The FindDialog's] constructor is defined to accept a parent QWidget, even though the dialog will be opened as a separate window.

Wouldn't this cause a memory leak? Or is there some other mechanism that will silently delete dialog and free its memory?

Thanks in advance for any help!

Update: I posted this issue to the qt-project.org forums and it should get fixed soon.

Answer 1

There is no excuse for this, and it eventually has more issues than you just bring up, namely:

• It is not managed as you say.

• It does not use the conventional new Foo() syntax.

• It is not done in the constructor's initializer list.

The OS will probably free this up once the application quits, but still, I always speak up against such issues, anyhow, especially in example projects. The appropriate fix would be to use either a stack object instead of the heap object or QPointer in my opinion.

See the following post for details in case the latter:

How to crash (almost) every Qt/KDE Application and how to fix

This should be reported and fixed upstream; good catch!

I have just submitted a change to Gerrit about this in here.