Re: sizeof (size_t) and sizeof (pointer)
On Nov 15, 1:54 pm, Ron Natalie <r...@spamcop.net> wrote:
Joel Yliluoma wrote:
Are the pointers stored in ptrtable virtual or not? You
don't know. You don't even know whether A has virtual
functions or not, and thus whether there is need to express
virtual functions. So you need to be able.
Further, in the case of virtual/multiple inheritance it needs
to be able to have the offset to adjust the "this" pointer as
well.
If your compiler is ABSOLUTELY standards compliant, all
pointers to member functions need to be the same size
(regardless of whether there are virtual / multiple
inheritance). This is because there is no "void*" like super
poitner for pointer-to-member and someone made the
stupid-assed decision that you should thus be able to cast
between pointer-to-member types and back without losing
information.
I don't think that that's the only reason. You can have a
pointer to a member of an incomplete type, so the compiler
cannot possibly know whether there are virtual functions,
mulitple inheritance, etc. or not. VC++ does the optimizations
you refer to, unless you specify otherwise. With the result
that you cannot reliably pass pointer to member functions as
arguments: something like:
class Toto ;
void
f( Toto* p, void (Toto::*f)() )
{
p->*f() ;
}
will not work.
Because you can have pointers to member of an incomplete type,
all pointers to member functions must have the same
representation.
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