Smart Pointer Design

[lexfridman]

I've looked around on this forum and the web in general and have not found a clear discussion of using smart pointers with Qt objects. I am surprised to see most Qt examples using standard pointers. Does Qt perform some garbage collection?

Example:

QWidget * foo;
foo = new QWidget();
foo = new QWidget();

QWidget * foo;
foo = new QWidget();
foo = new QWidget();

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Will the first object float around in memory or be cleaned up?

If it's a leak, should I instead use something like Boost's shared_ptr:

shared_ptr<QWidget> foo;
foo = shared_ptr<QWidget>(new QWidget());
foo = shared_ptr<QWidget>(new QWidget());

shared_ptr<QWidget> foo;
foo = shared_ptr<QWidget>(new QWidget());
foo = shared_ptr<QWidget>(new QWidget());

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I apologize if this question is ignorant of the underlying Qt design and/or has been answered thoroughly elsewhere on the forum.

[ChrisW67]

Your example would cause a leak, but then you won't see that in any of the Qt examples. Either each new QWidget/QObject will be created with a parent QWidget/QObject (which is typically an optional argument to the constructor) or be immediately given to something that takes ownership (like a layout). Typically the application's main window is allocated on the stack and becomes the ultimate owner of most widgets. Have a look at the detailed description of the QObject docs.

Qt also has its own range of smart pointers: QPointer, QSharedPointer etc.