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

[Daniel Jacobowitz <drow@mvista.com>]

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.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer