On 3 Jan 2016, at 8:43 PM, Markus Mohrhard <markus.mohrhard@googlemail.com> wrote:
Hey
On Sun, Jan 3, 2016 at 9:20 AM, Chris Sherlock <chris.sherlock79@gmail.com> wrote:
Hi all,
I’ve been getting an OSL_ENSURE failure when I run LibreOffice on my Ubuntu Linux VM.
The error is:
warn:legacy.osl:25546:1:sw/source/core/attr/format.cxx:227: SwFormat::~SwFormat: Def dependents!
This appears to be occuring because the OSL_ENSURE is calling on DerivedFrom(), which actually
returns the following:
return const_cast<SwFormat*>(static_cast<const SwFormat*>(GetRegisteredIn()));
GetRegisteredIn() is just an event source of type SwModify, the odd thing is that it calls on
GetRegistedIn() which is NOT a member of SwModify (or any child classes).
In fact, I’m surprised that this even compiles, as I was under the impression that a static_cast
was a compile time check...
I can only help you with the C++ part but not explain why it makes sense to call that code.
The code calls SwFormat::GetRegisteredIn which is actually SwClient::GetRegisteredIn (through
the inheritance hierarchy SwFormat->SwModify->SwClient). SwClient::GetRegisteredIn returns a
pointer to a SwModify where the code actually assumes that it always returns a SwFormat.
Ah - I appear to have misread the inheritance on that class. Thanks :-)
http://opengrok.libreoffice.org/xref/core/sw/inc/format.hxx#110
Anyway, what *exactly* is this attempting to do? The name looks like it’s doing a debugging check
to ensure that the SwFormat class was registered in a derived class, but I can’t see how this
would ever work!
It looks a bit like it is using some generic writer code to store the inheritance of the styles.
In fact, wouldn’t a dynamic_cast be better, as this most specifically down or upcasts a pointer,
and returns NULL if it fails?
That depends on all the code around it. Here the code just assumes that all returned SwModify
objects are actually SwFormat objects.
I did some more reading of static_cast - my understanding is that static_cast will up-cast or
down-cast the object without any runtime safety checks. What isn’t clear is what happens when you
try to do a static_cast on two entirely unrelated classes. Would DerivedFrom() work by just doing a
static_cast?
Regardless, the OSL_ENSURE is expecting a true, but is getting a false so the original writers of
the code think that something is going wrong - I suppose that ultimately it matters more whether
there is an issue in the check, or literally something is going badly wrong in the code and the
object is *not* derived correctly and there’s a bug there somewhere…
Sorry, not experienced at all in this module, and casting in c++ with the different static, dynamic
and reinterpret casts has always been a bit tricky for me (well, not so much now that I’ve had a
good read).
If these questions are a bit obvious, please let me know and I’ll code up some scenarios to get a
better understanding of how casting objects in C++ works (in fact, I’ll probably do this anyway,
I’m knee-deep in refactoring VCL code).
Chris
Any advise on this would be greatly appreciated, got me thoroughly tricked...
Chris
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