confused about QFileDialog in debug and release mode

I want to get file names in the function void QQTScene::dropEvent(QGraphicsSceneDragDropEvent *event),QQTScene is a class inherited from QGraphicsScene .Within the function,I write
fileName = QFileDialog::getOpenFileName(NULL, tr("打开图片"), "",tr("Image Files (*.png *.jpg *.bmp)"));
to get a file name.
However,this works perfectly in release mode,while in debug mode it crashes saying that the memory can't be "read".
What is wrong?Thanks!

You're accessing some invalid pointer?

Where exacly does it crash, before getting the name, after, in getOpenFileName().
Use debugger to pin-point offending line.

Now if I just declare a QFileDialog variable in the function dropEvent() (just add one sentence),it will crash.If not adding this,it works perfectly.What's more,even in the release mode,it also craches after I just set the icon size of the toolbar.Is that strange?

I don't know.

Can you paste some actual code, it's difficult to spot any problems when just working with my imagination.

Code:

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void QQTScene::dropEvent(QGraphicsSceneDragDropEvent *event)
{
    const QMimeData *mimeData = event->mimeData();
    QString text = mimeData->text();
 
    QGraphicsItem *item;
 
    if(text == tr("文本"))
    {
        item = new QQTText(text);
        connect(qgraphicsitem_cast<QQTText *>(item), SIGNAL(selectedChange(QGraphicsItem*)), this, SIGNAL(itemSelected(QGraphicsItem*)));
    }
    else if(text == tr("图像"))
    {
        QString fileName;
        fileName = QFileDialog::getOpenFileName(0, tr("打开图片"), "",
                                                tr("Image Files (*.png *.jpg *.bmp)"));
 
        if(!fileName.isEmpty()){
            QPixmap pixmap(fileName);
            item = new QQTImage(pixmap);
            QRectF r = item->boundingRect();
            if(r.width() > 800)
            {
                item->scale(0.5, 0.5);
            }
            //connect(qgraphicsitem_cast<QQTImage *>(item), SIGNAL(resize()), this, SLOT(resize()));
            /* 修改当前工作目录，使下次打开图片的时候可以减少重新选择目录的操作 */
            QDir::setCurrent(QFileInfo(fileName).absolutePath());
        }
        else
        {
            event->setDropAction(Qt::IgnoreAction);
            return;
        }
    }
    item->setPos(event->scenePos());
    addItem(item);
 
    event->setDropAction(Qt::CopyAction);
    event->accept();
}

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It crashes at

Code:

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fileName = QFileDialog::getOpenFileName(0, tr("打开图片"), "",
                                                tr("Image Files (*.png *.jpg *.bmp)"));

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I debug it to find that it crashes in system function

Code:

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void qt_blend_argb32_on_argb32_sse2(uchar *destPixels, int dbpl,
                                    const uchar *srcPixels, int sbpl,
                                    int w, int h,
                                    int const_alpha)

---

at line

Code:

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BLEND_SOURCE_OVER_ARGB32_SSE2(dst, src, w, nullVector, half, one, colorMask, alphaMask);

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