🚀 go-pugleaf

"Michael" <mstauff@bellatlantic.net> wrote in message
news:r1BYa.1145$014.1012@nwrdny02.gnilink.net...
> Hi,
>
> I'm dev'ing in C++ using Codewarrior 8.3, on OS 9.2 & X.
>
> I'm trying to find out if there's a way to preserve the order of class
> member variables, ie the order in which they are listed in the class
> declaration. I'm hoping to be able to reference a class member indirectly
by
> deref'ing another class member that is a known distance away. I've done
this
> before on Windows (VC++) and it works nicely, but the same approach
doesn't
> seem to work in OS 9 (or maybe because of the CW compiler?). I haven't
tried
> yet on OS X but I imagine it might be the same on OS 9?
>
> A simple example is below. This simple example might work, but I've been
> trying to get it to work in a much larger class. I haven't tested
> extensively, thinking that someone might have a quick answer for me.
>
> class MyClass{
>     char interestingValue;
>     char placeHolder;
> }
>
> MyClass obj;
>
> char val = *(&(obj.placeHolder)-1);
>
> I was thinking there might be a compiler option or pragma I could use to
fix
> the order of the members during compilation. Does anyone have any
> suggestions?
>
> Many thanks,
> Michael
>

I don't think you need any pragmas or compiler options.

#include <stddef.h>

char val = *(&(obj.placeHolder) - (offsetof(MyClass, placeHolder) -
offsetof(MyClass, interestingValue)));

offsetof is a macro defined in <stddef.h>.There are some restrictions on
what sort of class you can use offsetof with.

john