John Labenski <jlaben...@...> writes:
>
> wxLua 2.8.10 introduced multiple inheritance in the C++ bindings which
> wxWidgets uses for the wxComboBox, wxChoice, and wxBitmapComboBox
> classes. However, I was not aware that C++ compilers shift the vtable
> of the second and higher base classes and therefore if you directly
> cast a void* pointer to an object to its second or higher base class
> you will segfault when you try to call one of its functions. I have
> finally come across a solution that does work for GCC and MSVC, but it
> is compiler implementation dependent. The only other compiler that I
> think we may care about is the Intel one, which I cannot test. The
> bottom line is that the code will probably not even compile or
> immediately segfault when called if GCC or MSVC change their code
> generation (unlikely), which is fine since we can fix it then, for the
> foreseeable future this will work even though it may upset C++
> purists.
Maybe I do not understand the problem but here is my suggestion.
Why not use dynamic cast since you seem to know which class.
C casting is a brute force method.
v-table are sometime incompatible from compiler to compiler and even across
compiler versions but using C-casting is not likely to improve portability.
// TestCasting->cpp
#include "stdafx.h"
class A { public: int x; };
class B { public: int y; };
class AB : public A, public B { public: int z; };
void f(void *p)
{
AB* ab = (AB *)p;
A* a = dynamic_cast<A*>(ab);
B* b = dynamic_cast<B*>(ab);
printf("%x\n", p); // 347e28
printf("%x\n", ab); // 347e28
printf("%x\n", a); // 347e28
printf("%x\n", b); // 347e2c
}
int _tmain(int argc, _TCHAR* argv[])
{
AB *ab = new AB() ;
f((void *)ab);
return 0;
}
I would expect dynamic_cast to be more portable then any explicit pointer
manipulation.
even better if you know that f expect AB * then code define f as:
void f(AB *p)
Andre
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