[RQt-devel] another crash

[Michael Lawrence]

On Thu, Nov 19, 2009 at 4:15 AM, Deepayan Sarkar
<deepayan.sarkar at gmail.com>wrote:

> On Wed, Nov 18, 2009 at 2:49 PM, Deepayan Sarkar
> <deepayan.sarkar at gmail.com> wrote:
> > On Wed, Nov 18, 2009 at 1:46 PM, Deepayan Sarkar
> > <deepayan.sarkar at gmail.com> wrote:
> >> Any idea what's going wrong here?
> >>
> >> ### Just code:
> >>
> >> library(qtbase)
> >>
> >> gscene <- Qt$QGraphicsScene()
> >> rtxt <- gscene$addText("some text")
> >> rtxt
> >> (rtxt$toPlainText()) ## fine
> >
> > And as a confirmation that the <QList> thing is not a problem, I get:
> >
> >> item0 <- gscene$itemAt(0, 0)
> >> item0
> > <environment: 0x9e21428>
> > attr(,"class")
> > [1] "QGraphicsTextItem"   "QObject"             "QGraphicsItem"
> > [4] "UserDefinedDatabase" "environment"
> >> item0$toPlainText()
> >
> >  *** caught segfault ***
>
> Other QGraphicsItem-s seem fine, so it must be the multiple
> inheritance (QObject+QGraphicsItem) problem of  QGraphicsTextItem
> again. Given that rtxt works but item0 doesn't, maybe it's a coercion
> problem somewhere in the wrapping stage?
>
>
Everything method invocation fails with item0. The weird thing is that the
environments are different. Every C++ pointer should have the same
environment, and this holds true for the other QGraphicsItem types. This
indicates that the pointer being returned by itemAt() and items() is
incorrect.

Just checked it, and it looks like the pointer retrieved by e.g. itemAt()
points 8 bytes higher than the one from addText(). This happens at the Smoke
level, but looking at their wrappers reveals nothing. Yes, they are casting
to different types, (QGraphicsTextItem *) vs (QGraphicsItem *), but that
shouldn't change the value of the pointer, should it? The same error happens
for addWidget() and its QGraphicsProxyWidget return value. So yes it seems
like a multiple inheritance issue, but I don't understand how a simple cast
could cause this. Maybe it's just another C++ surprise?


> -Deepayan
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