[Bug c++/12620] New: compatibility issue with anonymous struct/union support

[Bug c++/12620] New: compatibility issue with anonymous struct/union support

[jbeulich at novell dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12620

           Summary: compatibility issue with anonymous struct/union support
           Product: gcc
           Version: 3.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jbeulich at novell dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu

In

class ccc {
public:
	union {
		int i;
	};
};

all other compilers I can check with (Intel, Microsoft, Borland, MetroWerks)
treat i as a member of ccc. Since the feature is documented to exist for
compatibility reasons, the behavior should be compatible, too.

This can easily be tested with above declaration and the code

template<typename T> void test(T p);

void test() {
	test(&ccc::i);
}

by observing what template instantiation is selected by the compiler.

[Bug c++/12620] compatibility issue with anonymous struct/union support

[jbeulich at novell dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12620



------- Additional Comments From jbeulich at novell dot com  2003-10-15 12:23 -------
gcc 2.96, btw., also behaves the requested/expected way.

[Bug c++/12620] compatibility issue with anonymous struct/union support

[jbeulich at novell dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12620



------- Additional Comments From jbeulich at novell dot com  2003-10-15 12:25 -------
... to some degree: for the example given, &ccc::i evaluates to the offset based
from the starting address of ccc, not (as 3.3.1 does) from the start of the
union. For naming purposes, the anonymous union is still considered.

[Bug c++/12620] compatibility issue with anonymous struct/union support

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12620


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-10-15 17:52 -------
Can you give a full example of what is wrong?

[Bug c++/12620] compatibility issue with anonymous struct/union support

[jbeulich at novell dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12620



------- Additional Comments From jbeulich at novell dot com  2003-10-16 07:46 -------
What is wrong is that
a) the template gets instantiated with T = int ccc::{anonymous}::* rather than T
= int ccc::* and
b) &ccc::i is calculated relative to the union base address rather than the
classes one, so if there are class members preceding the union (or base
classes), then this still continues to be zero (note that I understand that the
actual value of the member pointer should not be used, but in a debugging
context it may be of actual use).

[Bug c++/12620] compatibility issue with anonymous struct/union support

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-28 21:39 -------
This is done this way because it is the right thing to do as members of the anonymous union are 
not really members of the ccc but they only act as members just for name lookup reasons.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12620