This is a very early version of a patch I'm working on for 
http://sourceware.org/bugzilla/show_bug.cgi?id=9065 to provide a typeid 
capability in gdb.  It's nowhere near done, but I'd like to put it out 
there in case anyone objects wildly to what I'm doing or how I'm doing it.

What it does:

If you have some code from the source:

    #include <iostream>
    #include <typeinfo>
    using namespace std;

    struct A { virtual ~A() { } };
    struct B : A { };

    struct C { };
    struct D : C { };

    int main() {
       B bobj;
       A* ap = &bobj;
       A& ar = bobj;
       cout << "ap: " << typeid(*ap).name() << endl;
       cout << "ar: " << typeid(ar).name() << endl;

       D dobj;
       C* cp = &dobj;
       C& cr = dobj;
       cout << "cp: " << typeid(*cp).name() << endl;
       cout << "cr: " << typeid(cr).name() << endl;
    }

this patch will let you do stuff like:

    (gdb) p typeid(dobj)
    $1 = "D"
    (gdb) p typeid(dobj).name()
    $2 = "D"
    (gdb) p typeid(*ap).name()
    $3 = "A"
    (gdb)

In C++, typeid returns a reference to a class type_info, which contains 
a member ".name()."  Just for consistency with that, I've made this 
implementation accept both a complete C++-like form of 
typeid(<whatever>).name(), or the abbreviated form of typeid(<whatever>).

[Question: Internally, this patch is based on "sizeof" which actually 
creates an int type that, in addition to just being printed, can be used 
for stuff like "set <var> = sizeof(<whatever>)".  The gdb typeid doesn't 
even try to create an analogue to a type_info class, it just extracts 
the name from the appropriate type struct and creates a cstring type 
from it.  Would it be good/essential for the implementation to 
instantiate a real type_info class?  (That, I suspect, will be a lot 
more work...)]

Anyway, feedback welcome.

Chris