Re: VPTR and VTABLE
On Dec 2, 5:25 am, Victor Bazarov <v.Abaza...@comAcast.net> wrote:
doublemaster...@gmail.com wrote:
[..]
As per my understanding vtbl is static array of function pointer
[static because its in class level]
vptr is non static pointer [since every object has its copy]
Well, this is basically correct. Except that neither vtbl,
nor vptr are visible to the user of the class (or even the
class itself) through the language means. There is no
portable way to say 'MyClass::__vtbl' and get the [pointer to
the] array, or 'MyClassInstance.__vptr' and get the local copy
of the actual virtual function table pointer. [Note: the
syntax is made up to illustrate the point]
More to the point, they may not have a type which can be
expressed in C or C++. All you can really say is that the vptr
points to some class specific meta information (called the
vtable or vtbl) and that this meta information includes all the
information necessary for virtual function calls and
RTTI---considerably more, in fact, than just pointers to
functions. (The names, and the idea that the vtbl is just a
table of pointers to functions, come from the earliest versions
of CFront: before multiple inheritance and RTTI were introduced
to the language, the vtbl was just a table of pointers to
functions, and CFront used C as its intermediate language, and
in this generated C, the names were __vptr and
__vtbl__classname, or something like that.)
--
James Kanze