__VFPTR as a member

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Hi,
I'm relatively new to C++ (like 6 months exp).
I was reading about the vtables for Virtual Functions.

I created a class with a member as:

C++

int *__vfptr; // 2 underscores

Surprisingly, when I debug the app, it gets linked to the vtable pointer!
PS: We need to have at least one virtual function in the class.

But, its like an array of function pointers and it's const.

If I use const_cast on this - it doesn't seem to work :(
Is there anyway I could remove this constness?

Just imagine the possibilities.. ;P

Me using VS2008 on XP.

Posted 30-Nov-10 23:50pm

maQueueBex

Updated 1-Dec-10 0:13am

Sauro Viti

v2

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CPallini 1-Dec-10 6:01am

Pardon the silly question, but: "why should you give such a name to the data member?"

Sauro Viti 1-Dec-10 6:16am

Why do you want to modify the vtable of an object? Sincerely, I'm not able to imagine what does the possibilities are...

maQueueBex 1-Dec-10 6:37am

@CPallini - I did that on purpose.

@Sauro Viti -
Redirecting (the already redirected)virtual function calls at run time?

CPallini 1-Dec-10 15:35pm

Still I cannot see the usefulness of fooling the compiler this way.

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Electron Shepherd · Accepted Answer · 2010-12-01T05:49:00

Solution 1

The C and C++ language standards reserve identifiers starting with either two underscores or an underscore followed by an upper-case letter for the compiler implementation.

Therefore __vfptr won't be subject to the "normal" rules for variables.

Posted 1-Dec-10 5:49am

Electron Shepherd

Comments

maQueueBex 1-Dec-10 22:45pm

#include <iostream>

int main()
{
int __ = 1;
__ = 5;
}

I tried this, and it seems to work like a normal var! Even __a or anything.
Is it like undefined behavior when we use this? Compiler may or may not mess it up?