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Thread: QDrag : memory allocation

  1. #1
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    Default QDrag : memory allocation

    I'm using Instruments (on Mac) to track memory leaks in a QT app I wrote. I've gotten rid of the ones due to my code and am left with those it is not clear are really leaks and are from QT.

    1. QMessageBox - is it destroyed on close?
    2. QDrag - is it destroyed when the drag is complete?

    An example of the code that registers as a leak is:
    Qt Code:
    1. void about() {
    2. QMessageBox::information(this, "About X", "X is a program.\n")
    3. }
    To copy to clipboard, switch view to plain text mode 

    and,

    Qt Code:
    1. void PhotoMailer::mousePressEvent(QMouseEvent *event) {
    2. //http://doc.trolltech.com/4.2/dnd.html
    3. if (event->button() == Qt::LeftButton) {
    4. QDrag *drag = new QDrag((QWidget*)this);
    5. QMimeData *mimeData = new QMimeData;
    6. mimeData->setUrls(url);
    7. drag->setMimeData(mimeData);
    8. drag->start();
    9. }
    10. }
    To copy to clipboard, switch view to plain text mode 

    My question is, should I worry - they are created with new and then 'lost', i.e. the calling function returns without telling anyone of the pointer, so I understand that a profiler will flag this as a leak, but will QT take care of them? Or have I missed a programming paradigm here.

    Thanks!
    -K

  2. #2
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    Default Re: QDrag : memory allocation

    Quote Originally Posted by kghose View Post
    1. QMessageBox - is it destroyed on close?
    If used as a static call as in the code you presented then yes.
    2. QDrag - is it destroyed when the drag is complete?
    Yes.


    My question is, should I worry - they are created with new and then 'lost'
    The message box is not created with new, at least not explicitely. I'd say it's created on stack and goes out of scope when the function returns.

    , i.e. the calling function returns without telling anyone of the pointer, so I understand that a profiler will flag this as a leak, but will QT take care of them? Or have I missed a programming paradigm here.
    As far as I remember the docs say that Qt takes ownership of the drag object.

  3. The following 2 users say thank you to wysota for this useful post:

    D Cell (1st November 2010), kghose (15th August 2008)

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