RE: [Dev-C++] Strange effect

[Ioannis V. <no...@ya...>]

At first, this result comes from both dev-c++ and bcc32. We should not
see "C!" even if the member functions were virtual since we have an
object A, not C assigned to A * (that's why a dynamic_cast would fail).
Also every object has (must have) its own member function so there is
not "only one method in memory" as you mention. Yours is the case of
*static* member functions. Probably we have here some compiler
optimization being confused by casting. This is definately a compiler
defect(for both of them).
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Ioannis
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* Ioannis Vranos
* Programming pages: http://www.noicys.f2s.com
<http://www.noicys.f2s.com/>=20
* Alternative URL: http://run.to/noicys

-----Original Message-----
From: dev...@li...
[mailto:dev...@li...] On Behalf Of Jason
Hardman
Sent: Saturday, October 20, 2001 6:49 PM
To: Dev-C++
Subject: Re: [Dev-C++] Strange effect


AFAICT a static_cast will always be able to cast a pointer from a base
into a derived type without checking if it's OK to do so as dynamic_cast
would.
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Also of note is that the methods are not virtual, so the test in C would
hide the test in A. And as neither objects contains any data then there
is no real difference between them. If I had more time I would try out a
few things, like making the methods virtual and adding variables to the
objects, i.e. private: int data; initialised differently in each object,
with a getter function the same in each class.
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When multiple instances of an object is created there is still only one
method in memory, which is passed a this pointer to the object it is
operating on. So in the case of this example there are two methods
defined, and when you cast into the C type the compiler directs to the C
method as opposed to the A method. If you tried to access data that
existed in C but not A then you would get errors.
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I hope I have explained that OK. I'm rushing a little as I'm going out
in a minute.
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Jason.

----- Original Message -----=20
From: Ioannis Vranos <mailto:no...@ya...> =20
To: Dev-C++ <mailto:dev...@li...> =20
Sent: Saturday, October 20, 2001 6:24 PM
Subject: [Dev-C++] Strange effect

Strange effect. Consider the code:=20
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#include <iostream>
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class A
{
public:
void test() { std::cout<<"A!\n"; }
};
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class C: public A
{
public:
void test() { std::cout<<"C!\n"; }
};
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int main()
{
 using namespace std;
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  A a;
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  C *cp=3Dstatic_cast<C *>(&a);
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  cp->test();
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}
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It produces
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C:\c>temp
C!
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Isn't this wrong? I expected either a GPF or garbage, or even "A!" but
not "C!".
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Ioannis
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* Ioannis Vranos
* Programming pages: http://www.noicys.f2s.com
<http://www.noicys.f2s.com/>=20
* Alternative URL: http://run.to/noicys
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