Re: compare two objects, if they have the same vtable
On 2008-10-03 18:41, Albert Zeyer wrote:
Mathias Gaunard schrieb:
On 1 oct, 20:38, Albert Zeyer <albert.z...@rwth-aachen.de> wrote:
I thought RTTI adds runtime type information to each class and typeid is
based on these additional information.
RTTI adds information in the vtable. It not only contains function
pointers, but also a name and information to tell whether the object
derives from some classes efficiently or not (which is required for
dynamic_cast).
I don't need the overhead of runtime type information just to compare
the vtable which is there anyway.
There is no overhead with typical implementations.
Since there is more data, however, it takes a bit more space in your
data segment.
Wouldn't it add the vtable pointer to each class/struct, also to those
which had no virtual functions before? In our game, we have a *lot* of
small structs containing only some little information and it would be
total overkill to add a vtable-pointer to each instance.
No, if the class has no virtual functions (and thus no vtable) it is not
polymorphic, and if it is not polymorphic its type is know at compile-
time and RTTI is not necessary.
--
Erik Wikstr??m
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