🚀 go-pugleaf

"John Harrison" <john_andronicus@hotmail.com> wrote in message
news:bgvm8q$smqin$1@ID-196037.news.uni-berlin.de...
>
> "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

Thanks John! I'll look into that.

Cheers,
Michael