Re: Proposal: offset based member name (or type) lookup

[Daniel Jacobowitz <drow@mvista.com>]

On Sun, Jan 04, 2004 at 12:25:37PM -0500, Daniel Jacobowitz wrote:
> On Sun, Jan 04, 2004 at 06:56:05PM +0100, Christoph Jaeschke wrote:
> > Hi,
> > 
> > I would like to propose a offset based member name lookup of
> > structs/classes. Assume:
> > 
> >     struct X {
> >         int a;
> >         int b;
> >     };
> > 
> >     struct Y {
> >         struct X x[4];
> >         int c;
> >     };
> > 
> >     struct Z {
> >         Y  y;
> >     };
> > 
> > If you apply a patch for gdb 6.0 I've prepared, you can ask gdb by
> > 
> >     ptype Z + 28
> > 
> > about Z's relative name at offset 28
> > 
> >     .y.x[3].b
> > 
> > using
> > 
> >     ptype Z+28, typechain
> > 
> > gdb will append also the typechain
> > 
> >     .y.x[3].b, typechain = ::Y::X[4]::int
> > 
> > 
> > There may be a better suited command than 'ptype' for it, it was choosen 
> > just because it was the simplest way to add it.
> > 
> > The patch contains also a caching mechanism, speeding up a lot if you do 
> > many lookups in big nested structures. It has a minimal memory 
> > requirement and will not hurt for single lookups.
> > 
> > The patch can be send if you are interested in.
> 
> Well, I don't like the syntax, but I think this is a wonderful idea.
> The other feature I've been meaning to add since forever is a variant
> of ptype which shows byte offsets for every field.
> 
> The problem with using ptype is that "Z+28" already has a meaning; gdb
> will try to add the two, or call an overloaded + operator in C++, et
> cetera.  This should probably be a new command; that'll be more useful
> for MI anyway.

Oh, and I forgot the obligatory followup to this: if you are
interested in contributing this patch, and I hope you are, then please
file an FSF copyright assignment.  Jim or Andrew can send you the
appropriate forms to get the process started.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer