Re: Virtual destructors and vtable layout
On Oct 11, 4:21 am, "Ole Nielsby"
<ole.niel...@tekare-you-spamminglogisk.dk> wrote:
James Kanze <james.ka...@gmail.com> wrote:
The vtable layout used by the C++ compiler has nothing to do
with what the component model does. None of the component
models I'm familiar with even use a vtable, except insofar
as they map to C++ code, in which case, they're just normal
C++ code.
COM does rely on vtable layout. COM interfaces are declared
as pure virtual classes, all methods using stdcall convention, and
this works because most (if not all) C++ compilers for the MSW
use a very similar vtable layout.
In other words, COM is pretty much unusable.
Seriously, you've got to be kidding. How does it work when the
components are on different machines? Running different
binaries with the functions at different addresses?
Either it's not really a component model, but just a means of
supporting linking different languages (which, admittedly, all
systems should provide), or you've misunderstood something. And
of course, when you link different languages, you tell the
compiler (that's what ``extern "xxx"'' is for, but I believe
VC++ uses some proprietary syntax instead), you (obviously) obey
the restrictions of the common interface (no pass by value for
Fortran, nothing but POD's for C, etc.), and the compiler does
whatever is necessary. Or you write a wrapper; Java can only
call code adhering to the JNI interface, so you if you want your
code to be callable from Java, you implement a wrapper for it
which adheres to the JNI interface.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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