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

[Christoph Jaeschke <cjaeschke@onlinehome.de>]

Daniel Jacobowitz wrote:
> 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.
> 

Sure, I'm interested in contributing. But, because I'm not very familiar 
with the command interface (that's why ptype was re-used), I would be 
happy if someone else create a new command and just call the processing 
func.

If Jim or Andrew send me the forms, you will get the patch.