Re: How to find out if a function is overridden
On May 24, 12:21 pm, Christopher Dearlove
But it's not
impossible in theory, even without any knowledge of any Derived.
Note that all I want to know is if the function has been overridden
in the specific object that a Base * points to. So for example with
a typical vptr/vtbl implementation I just need to know if the
appropriate entry in the vtbl that I get for this particular Base *
is the same as the corresponding entry in the vtbl I get for an
instance that really is a Base. That information is theoretically
available at runtime without knowing anything about any Derived
classes. But if C++ allows me a roundabout way of getting at that
information, I don't know it, hence the question.
That is even theoretically impossible. V-tables usually are set-up on
a per-class basis. Base class has one as well as derived class has
one. The object being pointed to by the base pointer should hold
information about the V-table to refer to. The base V-table holds info
about the base virtual function pointers, derived holds its own or the
base class' virtual function pointer if it not overridden. This is one
possible way of implementing the dynamic dispatch.
It is impossible to know which function is overriden since you have
put the restriction that you don't know anything about any derived
classes. How would you even know if a particular derived class' v-
table exists?
Now, unless there is an implementation that fattens the base V-table
with the derived class info, it's tough and I don't know if there is
such an implementation that would do this (?) and even if it does
this, it exposes interfaces to extract the info you require (?).
I think this is static information that you must feed in at compile
time.
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