Re: [patch] ptype: show members of an unnamed struct inside an union

[Daniel Jacobowitz <drow@false.org>]

On Tue, Aug 28, 2007 at 09:36:33PM -0700, Joel Brobecker wrote:
> > > Does this case actually make any sense? I don't think you can access
> > > this union in your C program either, or can you?
> > 
> > GCC supports anonymous unions.  There's a test for it in the GDB
> > testsuite, too.
> 
> But how can you access this union if the field doesn't have a name?
> More precisely, using the example that Carlos sent:
> 
>    struct my_page {
>      union {
>        struct { int mapping; };
>      };
>    };
> 
> How do you access the union?

In C, it would be "my_page_var.mapping".  The union is transparent.
I think GDB has some failures for anon-union.exp with recent GCC
related to this...

More interesting example.  First you have:

struct s {
  int x;
  int y;
};

Later you switch to:

struct s {
  int x;
  union {
    int y;
    void *z;
  };
};

The anonymous union lets s.y keep working.

-- 
Daniel Jacobowitz
CodeSourcery