Re: rtti in msvc
In article <f0lr3n$ism$1@news.Stanford.EDU>, Seungbeom Kim
<musiphil@bawi.org> wrote:
Carl Barron wrote:
Dynamic casts are ussually the most expensive C++ style cast and require
infromation about what classes a particular pointer to a given class
type is also a pointer to a different class type at run time and this
infromation is per object.
On a typical implementation, the class information is in the vtbl,
and what's included per object is only the vptr, isn't it?
Space overhead per object should be the same regardless of dynamic_cast,
as long as the class is polymorphic.
[example snipped]
now each Base * must contain infromation[ if it is also an A *, B *, or
C *] and this is per object.
That's what vptr does; vptr is already there if the class is polymorphic.
Not quite a vptr or a vtable entry only needs to hold where to jump
to. the virtual function itself is little more than the equivalent of
a function call thru a function pointer, but the syntax is nicer and
the user of virtual functions does not to need to program the details.
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