Re: RTTI working for G++

[Jimmy Guo <guo at cup dot hp dot com>]

Daniel,

I recently looked into rtti print support and fixed several bugs in that
area.  Also I've created a test case under gdb.hp/gdb.aCC/.  Looks like
what I changed might work with G++ as well now that you're adding
support to it.  The fix is against HP WDB source, which is based on
sourceware's as of 1/10/00, so I'm not ready to submit against
sourceware's tree yet.  However, one of the fixes was that when print
object is on, and one wants to print member / methods of the derived
type, you can now do so.  Besides, there're some fixes to handle pointer
to a derived type and explicit casting of a pointer to a base to a
derived type.  I feel that these fixes will complement yours.  If
possible I want to send the diffs of the fixes to you to see if that
would make it into your patch.  Also I can look at your patches as well.

- Jimmy Guo, guo@cup.hp.com


On Mon, 13 Mar 2000, Daniel Berlin wrote:

>Okay, i have RTTI working for g++.
>Well, all except for multiple inheritance.
>
>Scratch that last part, i just made it offset properly if you have >1
>baseclass, so al is good.
>
>If i could have one or two volunteers to make sure it's not just my setup,
>and that all is well, before i post the patches asking for comments, i'd
>appreciate it.
>In any case, let me know what you guys think of it so far.
>If you look at the output, you'll notice that while for printing, it will
>print the object as if it was it's derived type, when it comes to
>accessing members/methods, just like in C++, you can't access the members,
>unless you specifically cast it to that derived type.
>
> For those wondering what the patch will do, check this out:
>
>The inheritance on these classes in the example looks like this
>
>fred is a base
>dan and bob both inherit directly from fred.
>george is another base.
>george2 inherits from george and bob (public george, public bob)
>
>I'll rename them so they make more sense as i work up testcases.
>
>But anyway, here's some output:
>
>GNU gdb 20000204
>Copyright 1998 Free Software Foundation, Inc.
>GDB is free software, covered by the GNU General Public License, and you are
>welcome to change it and/or distribute copies of it under certain conditions.
>Type "show copying" to see the conditions.
>There is absolutely no warranty for GDB.  Type "show warranty" for details.
>This GDB was configured as "i386-unknown-freebsdelf4.0".
>Setting up the environment for debugging gdb.
>.gdbinit:5: Error in sourced command file:
>No symbol table is loaded.  Use the "file" command.
>(gdb) file a.out
>Reading symbols from a.out...done.
>(gdb) b main
>Breakpoint 1 at 0x8048918: file a.cc, line 29.
>(gdb) set print object on
>(gdb) set print pretty on
>(gdb) set print vtbl on
>(gdb) set print array on
>(gdb) r
>Starting program: /usr/local/gdb/src/gdb/a.out 
>
>Breakpoint 1, 0x8048918 in main () at a.cc:29
>
>29	{
>(gdb) n
>31		dan=new daniel();
>(gdb) n
>32		cout <<typeid(*dan).name()<<endl;
>(gdb) p dan
>$1 = (daniel *) 0x8051030
>(gdb) p dan[0]
>$2 = (daniel) {
>  <fred> = {
>    a = 0, 
>    _vptr$ = 0x804f390
>  }, 
>  members of daniel: 
>  b = 0
>}
>(gdb) ptype dan
>type = class fred {
>  public:
>    int a;
>
>    fred & operator=(fred const &);
>    fred(fred const &);
>    fred(void);
>    virtual int ab(void);
>} *
>(gdb) p dan[0]->b
>There is no member or method named b.
>(gdb) n
>6daniel
>33		dan=new bob();
>(gdb) 
>34		dan=new george2();
>(gdb) p dan
>$3 = (bob *) 0x8051040
>(gdb) p dan[0]
>$4 = (bob) {
>  <fred> = {
>    a = 0, 
>    _vptr$ = 0x804f378
>  }, 
>  members of bob: 
>  c = 0
>}
>(gdb) p dan[0].c
>There is no member or method named c.
>(gdb) n
>35		dan->a=55;
>(gdb) p dan[0]
>$5 = (george2 [incomplete object]) {
>  <george> = {
>    d = 0
>  }, 
>  <bob> = {
>    <fred> = {
>      a = 0, 
>      _vptr$ = 0x804f360
>    }, 
>    members of bob: 
>    c = 0
>  }, 
>  members of george2: 
>  e = 0
>}
>(gdb) l
>30		fred *dan;
>31		dan=new daniel();
>32		cout <<typeid(*dan).name()<<endl;
>33		dan=new bob();
>34		dan=new george2();
>35		dan->a=55;
>36		cout <<typeid(*dan).name()<<endl;
>37	}
>38	
>(gdb) n
>36		cout <<typeid(*dan).name()<<endl;
>(gdb) p dan
>$7 = (suspicious *) 0x8050064
>(gdb) p dan[0]
>$8 = (george2 [incomplete object]) {
>  <george> = {
>    d = 0
>  }, 
>  <bob> = {
>    <fred> = {
>      a = 55, 
>      _vptr$ = 0x804f360
>    }, 
>    members of bob: 
>    c = 0
>  }, 
>  members of george2: 
>  e = 0
>}
>(gdb) c
>Continuing.
>7george2
>
>Program exited normally.
>(gdb) q
>
>Script done on Mon Mar 13 19:34:51 2000