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POHow does Qt delete objects ? And what is the best way to store QObjects?
 

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  1. POHow does Qt delete objects ? And what is the best way to store QObjects?
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    <p>I heard that objects in Qt will automatically delete their children, I want to know what will happen in those situations.</p> <pre><code>#include &lt;QApplication&gt; #include &lt;QLabel&gt; #include &lt;QHBoxLayout&gt; #include &lt;QWidget&gt; int main(int argc, char **argv) { QApplication app(argc, argv); /* QLabel label("label"); // Program will crash. Destruct order is 1. widget, 2. layout, 3. label QHBoxLayout layout; // But layout will be deleted twice QWidget widget; */ QWidget widget; // Program doesn't seem to crash but is it safe ? Does Qt use QHBoxLayout layout; // delete to operate on already destructed children ? QLabel label("label"); layout.addWidget(&amp;label); // layout is label's parent widget.setLayout(&amp;layout); // widget is layout's parent widget.show(); return app.exec(); } </code></pre> <p>Is this allowed in Qt? What does Qt do when destroying a child ?</p> <p>BTW, I considered using smart pointers such as shared_ptr. But I think Qt would also delete the object which had already been destroyed by smart pointer too.</p> <p>I know you would like to use new to allocate dynamic memory for objects. But I don't feel its reassuring, please tell me if there are any situations (e.g. exceptions) that will lead to memory leaks when relying on Qt's object tree to handle dynamic memory?</p> <p>If I use objects rather than pointers to dynamically allocate objects, I have to consider the order of destruction of objects as long as they have ownership, which is tedious. I don't know whether it is good practice to use dynamic memory in Qt. </p> <p>Do you have any suggestions or better solutions?</p>
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    1. COif the shared_ptr deletes the child, the parent is notified, so that's not a problem. The problem is the other way round, the shared_ptr won't notice when the parent deletes the child => double deletion.
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      1. USFrank Osterfeld
 

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