C++ QT Memory Allocation

Question

Possible Duplicate:
Memory management in Qt?

I have been learning Qt and there was a discussion if the pointers to Q objects such as QLabel should be deleted. Does Qt have automatic memory management for pointers to Qt objects or must they be deleted manually?

ex)

#include <QApplication>
#include <QLabel>

int main(int argc, char *argv[])
{

 QApplication app(argc, argv);

 QLabel *label = new QLabel("Im Tough.");

 label->show();

 int result = app.exec();

 //would this be necessary or would QT handle this automatically?
 delete label;

 return result;
}

BЈовић · Accepted Answer · 2013-01-09T08:45:51.343

6

If the object has a parent, you don't need to release it - it will be done automatically by the QT memory management system.

In your specific example, you do need to delete your object, since it has no parent. Even if you do not do it, it will be done by your OS when app.exec(); returns.

From the documentation about the qt's object trees :

QObjects organize themselves in object trees. When you create a QObject with another object as parent, it's added to the parent's children() list, and is deleted when the parent is.

edited Jan 09 '13 at 08:45

answered Jan 09 '13 at 06:08

BЈовић

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Worth mentioning: Where the child is only deleted when the parent is deleted. – Frank Osterfeld Jan 09 '13 at 07:29

score 4 · Answer 2 · answered Jan 09 '13 at 06:01

4

If QLabel has parent it will be deleted on its parent deleting, otherwise you should do it on your own. More: http://doc.qt.digia.com/qt/objecttrees.html

answered Jan 09 '13 at 06:01

Arsenii Fomin

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so if i did this: Qlabel *label = new Qlabel("str"); would it be necessary to delete the pointer manually? – lambda Jan 09 '13 at 06:03
3

@Unit978, yes since `label` doesn't have a parent. – laurent Jan 09 '13 at 06:10

C++ QT Memory Allocation

2 Answers2