22/02/2008, 06h49
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#5
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Re: how do I know where "this" pointer is?
Thank you for your post.
jason.cipriani@gmail.com wrote:
> On Feb 21, 9:13 pm, jameschen <wengerm...@gmail.com> wrote:
> > The question is that why ebp-12 is the "this" pointer, how to how?
>
> Like Red said it's implementation-specific. However, many compilers
> that I've seen implement class member functions by passing a pointer
> to the instance data ("this") to the member functions as a "hidden"
> parameter. Similar (sort of) to doing, say, this:
>
> struct Something {
> int data;
> };
>
> void SomeMemberFunction (Something *s, int param) {
> s->data = param;
> }
>
> In order to emulate this:
>
> class Something {
> int data;
> void SomeMemberFunction (int param) {
> data = param;
> }
> };
>
> And so the "this" pointer is passed as a parameter to the member
> function on the stack; since that info needs to be available inside
> the member function.
>
> Again, that's implementation specific, that's only a general summary,
> AFAIK there's nothing standardized about that. I wouldn't rely on it
> being at EBP-12 even with the same compiler. It may also depend on
> compiler options used, the number of other parameters the function
> takes, the calling convention, and many other things that you can't
> rely on.
>
> Red Floyd wrote:
> > Why do you want to know?
>
> Yes; unless you are just trying to satisfy your curiosity, if you are
> considering doing something strange you may want to consider other
> simpler methods before doing whatever it is you are doing.
>
> Jason
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