Re: [Cppunit-devel] Explanation of ExceptionTest.testAssignment failure under VisualC++

[Baptiste L. <bl...@cl...>]

Thanks.

I came to similar conclusion a few weeks ago. See
http://www.geocrawler.com/lists/3/SourceForge/6780/0/6778865/ for my
comments on that bug.

Baptiste.

----- Original Message -----
From: "Niel Clausen" <nr...@tr...>
To: <cpp...@li...>
Sent: Monday, October 22, 2001 9:56 AM
Subject: [Cppunit-devel] Explanation of ExceptionTest.testAssignment failure
under VisualC++


> Hi,
> The cause of the failure isn't too hard to figure. To keep the description
> simple, imagine that the vtable for an object is implemented by the _vtbl
> data member. _vtbl points to the class specific vtable, which I'll call
> Class::class_vtbl.
>
> 1. the line "other = e;" causes the other._vtbl to be overwritten with
> exception::class_vtbl.
>
> 2. Hence when "other.what()" is called from within "checkIsSame", the
> routine exception::what() is run, not CppUnit::Exception::what() as
> expected.
>
> The problem seems to lie in the call to the compiler generated assignment
> operator for exception (exception::operator =). Ignoring self assignment,
> this routine first calls exception::~exception (destructor) followed by
the
> compiler generated constructor (I can't tell if this is a default
> constructor or a copy constructor, only the latter really makes sense).
The
> constructor writes this->_vtbl (which of course, it should). In principle,
> this algorithm for generating the assignment operator seems reasonable,
> although not really what I'd expect.
>
> Note that the implementation of CppUnit::Exception::operator = is not
needed
> for this program, as C++ will do the "right thing" when assigning data
> members (it calls each member's assignment operator). Interestingly,
> commenting out CppUnit::Exception::operator = results in the same problem.
> The compiler generated assignment operator for CppUnit::Exception first
> calls exception::operator = (exactly the same as your original
> implementation), and then performs the assignments for each data member.
> Applying the same logic to CppUnit::Exception's copy constructor and
> commenting that out also still gives the same result. For some reason, the
> compiler generated exception::operator = is generated in a fundamentally
> different way to the CppUnit::Exception derived class.
>
> Obviously there's something very odd going on here.
>
>
> best regards,
>
> Niel Clausen.
>
>
>    /\                      Manor Court Yard, High Wycombe
>   /  \    /\  TRANSTECH    Bucks, HP13 5RE, UK
> -/    \  /  \^---------    Voice +44 1494 464432
>        \/     D   S   P    Fax   +44 1494 464472
>
> nr...@tr...        http://www.transtech-dsp.com
>
>
>
> _______________________________________________
> Cppunit-devel mailing list
> Cpp...@li...
> https://lists.sourceforge.net/lists/listinfo/cppunit-devel
>