Re: c/4784: Anonymous structs issues

["Joseph S. Myers" <jsm28@cam.ac.uk>]

The following reply was made to PR c/4784; it has been noted by GNATS.

From: "Joseph S. Myers" <jsm28@cam.ac.uk>
To: <bangerth@dealii.org>,  <gcc-bugs@gcc.gnu.org>, 
    Joseph Myers <jsm28@cam.ac.uk>,  <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: Re: c/4784: Anonymous structs issues
Date: Fri, 7 Mar 2003 09:51:25 +0000 (GMT)

 On 7 Mar 2003 bangerth@dealii.org wrote:
 
 >     Hm, with 3.3 and present mainline, we get on this code
 >     -----------------------
 >     struct s {
 >         int x;
 >         struct { int x; };
 >     };
 >     ------------------
 >     the following message:
 >     g/x> /home/bangerth/bin/gcc-3.4-pre/bin/gcc -W -Wall -std=c99 -c x.c
 >     x.c:3: warning: declaration does not declare anything
 
 What's relevant is -std=gnu99 and -std=gnu89, as this is a GNU extension.
 That warning hardly diagnoses what the problem is; the point of the 
 extension is that certain declarations that don't declare anything do, in 
 fact, declare nested anonymous struct elements.  The PR asks for a hard 
 error (with a more sensible error message).  What about more complicated 
 cases, such as:
 
 struct s {
   struct {
     int a;
     struct {
       int b;
     };
   };
   struct {
     int b;
     int c;
   };
 };
 
 (where the duplicate "b" elements should be diagnosed)?
 
 >     gcc3.2 is quiet. If compiled in C++ mode, we get this:
 >     g/x> /home/bangerth/bin/gcc-3.4-pre/bin/gcc -W -Wall -c x.cc
 >     x.cc:3: error: declaration of `int s::<anonymous struct>::x'
 >     x.cc:2: error: conflicts with previous declaration `int s::x'
 >     x.cc:3: error: duplicate member `s::<anonymous struct>::x'
 >     
 >     Joseph, is this approximately what you wanted gcc to
 >     tell us?
 
 What the C++ compiler does isn't part of the PR (C++ has its own rules;  
 this is a C extension), but those error messages are the sort of error I
 think the C front end ought to be giving: they accurately diagnose what
 the problem in the example code is.
 
 -- 
 Joseph S. Myers
 jsm28@cam.ac.uk