Re: Implicit cast from derived to base == static_cast
@Francis
Thanks for your inputs.
@Mathias
On Feb 22, 3:05 am, Mathias Gaunard <loufo...@gmail.com> wrote:
On 20 f?v, 20:10, abhay.bu...@gmail.com wrote:
Hello,
Question-1:
Recently i was asked a question on the following lines...
1. class A {};
2. class B : public A {};
3. A *anA = 0;
4. B *aB = new B;
5. anA = aB;
6. anA = dynamic_cast<A*>(aB);
What is the difference between lines 5 and 6? Are they both same
semantically?
They're the same, yes.
6 should be less efficient, but a good compiler should realize that
the dynamic cast is actually not needed.
AFAIK, implicit cast in C++ has semantics of a static_cast.
And that is completely false, thankfully.
Implicit conversions, explicit conversions and static_cast are all
different things. However, if you can convert implicitly, you can
convert explicitly, and if you can convert explicitly, you can cast
statically.
The same in the other direction is not true, however.
[...]
Thanks for the input. But if implicit cast is indeed same as
dynamic_cast, how would an implicit derived to base cast work, on non-
polymorphic classes and where we have a compiler that would allow us
to switch-off RTTI (Ex. MSVC++) ?
Question-2:
Can i vindicate my understanding of Question-1 above with the
following code as proof! [...]
12. anA = dynamic_cast<A*>(aB);
If this compiles, your compiler has a bug.
Its MS Visual Studio Team Edition 2005. I tried on comeau and it too
does not complain. I thought comeau was a reliable compiler :-)
Looks like there are no simple relationships between implicit, static
and dynamic casts.
Regards,
Abhay
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