Re: Frasncis Glassboro wrote.
On Jan 8, 5:39 pm, "Paul" <pchris...@yahoo.co.uk> wrote:
"Leigh Johnston" <le...@i42.co.uk> wrote in message
news:v_KdnTNgnatkErXQnZ2dnUVZ8lGdnZ2d@giganews.com...
[...]
It is important to note however that the use of vtables is
an implementaiton specific way of doing things (vtables are
not mentioned by the standard AFAIK). I do not know of any
implementations that do not use vtables however; this is
down to the fact that the vtable solution to the problem of
dynamic dispatch is efficient and not memory intensive
(requiring only a single pointer in an object when using
single inheritance).
The function calling mechanisms for any given implementation
is *obviously* not defined in the standards.
The point here is that you seen to have eaten a book that
contains the word 'vtable' and now you are an expert on the
function calling mechanism for all implemenmtations. Most of
your babblings about your idea of how things work on some
implementation of yours, is pretty irrellevant.
But there is one important point, that the object contains a
pointer to the function, whether it be a direct or indirect.
Bullshit.
Leigh speaks about what is certainly the most common
implementation technique; I don't know of a C++ compiler which
uses anything else (and I've actually spoken with most of the
people who've actually written C++ compilers). Within the
standards committee, however, the possibility of other
implementations was discussed, and the typical alterative to a
vptr was to use a map, mapping object address to function
address.
All of which is completely irrelevant. Classes have members,
and objects have subobjects. At least according to the
standard.
The important point here is that an OBJECT contains the
pointer, not a CLASS.
Obviously, an object doesn't contain a class, since classes are
a compile time concept, and objects a runtime concept.
--
James Kanze