Re: [Dev-C++] Strange effect

[Jason H. <jas...@bt...>]

MessageAFAICT 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.

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.

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.

I hope I have explained that OK. I'm rushing a little as I'm going out =
in a minute.

Jason.
  ----- Original Message -----=20
  From: Ioannis Vranos=20
  To: Dev-C++=20
  Sent: Saturday, October 20, 2001 6:24 PM
  Subject: [Dev-C++] Strange effect


  Strange effect. Consider the code:=20

  #include <iostream>

  class A
  {
  public:
  void test() { std::cout<<"A!\n"; }
  };

  class C: public A
  {
  public:
  void test() { std::cout<<"C!\n"; }
  };



  int main()
  {
   using namespace std;
  =20
    A a;
   =20
    C *cp=3Dstatic_cast<C *>(&a);
   =20
    cp->test();

  }


  It produces

  C:\c>temp
  C!

  Isn't this wrong? I expected either a GPF or garbage, or even "A!" but =
not "C!".


  Ioannis

  * Ioannis Vranos
  * Programming pages: http://www.noicys.f2s.com
  * Alternative URL: http://run.to/noicys