allignment of structure

[Anthony]

Hi,
I've got a question about the allignment of data in a structure.
What happens in memory when i declare the following

struct A
{
int x;
}
stuct B : public A
{
int y;
}

Is it compiler specific how the memory is alligned when I instance B?
Or can do something like this:

B b;
int* z = &(reinterpret_cast<int>(b)); //z point to x
z++; //z points to y

Or does the VTABLE pointer cause problems here?

Thanks in regard,
Anthony Lansbergen

 

[Victor Bazarov]

I've got a question about the allignment of data in a structure.
What happens in memory when i declare the following

struct A
{
int x;
}
stuct B : public A
{
int y;
}

Is it compiler specific how the memory is alligned when I instance B?
Yes.

Or can do something like this:

B b;
int* z = &(reinterpret_cast<int>(b)); //z point to x
z++; //z points to y

Most likely you can't. The Standard imposes no requirement on
the behaviour of such code. It's called "undefined behaviour".

Or does the VTABLE pointer cause problems here?

There is no such thing in the language as "VTABLE pointer". If
you're talking of a very common way to implement virtual function
mechanism in the language, then what does it matter here? Your
structs have no virtual functions.

Victor