I found a leak in a small Qt 3.3 dialog and responded by deleting every child widget in the destructor. Then I noticed that the widgets already had the dialog as their parent. My heroic cleanup was redundant; the actual leak was an object with no parent at all.

Qt’s object trees are straightforward once I stop pretending they are magic. A QObject with a parent joins that parent’s child list. Destroying the parent destroys its children. Top-level objects and objects without parents remain my responsibility.

My useful check is now mechanical. At construction, I ask who owns each allocation. If the answer is a parent object, I do not delete it separately. If there is no parent, I give the lifetime an explicit home in C++ code. Layouts arrange widgets; they do not replace ownership reasoning.

QLabel *label = new QLabel(tr("Status"), this);

Here this is the relevant part, not new. The parent makes the intended lifetime visible and ties cleanup to the dialog.

This is not garbage collection. Qt does not discover arbitrary unreachable C++ objects, and a parent cannot rescue a dangling pointer used after destruction. It is a disciplined ownership convention layered over C++.

The conclusion is pleasantly small: establish one owner and make it obvious at construction. My destructor became shorter, which is about the nicest possible result of debugging C++ memory management.