[Bug c/58303] New: C99 union initializers new union members clobber earlier data

[Bug c/58303] New: C99 union initializers new union members clobber earlier data

[darrenrjenkins at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58303

            Bug ID: 58303
           Summary: C99 union initializers new union members clobber
                    earlier data
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: darrenrjenkins at gmail dot com

If using C99 initializers on a union, and using different union members.
The later members seem to clobber the previous members data.
I haven't looked at the standards with respect to this, but it seems wrong.

#include <stdio.h>

typedef struct
{
    int a;
    int b;
} a_t;

typedef struct
{
    int c;
    int d;
} b_t;

typedef union
{
    a_t a;
    b_t b;

} c_t;

void main( int argc, char *argv[] )
{
    c_t var = { .a.a = 4, .b.d = 7 };

    printf( ".a.a = %d .b.d = %d\n", var.a.a, var.b.d );
}

[Bug c/58303] C99 union initializers new union members clobber earlier data

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58303

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
In C99, only one union member may be active at a time, assignment to one of
union members invalidates all the others.  So I don't see anything wrong on
this.

[Bug c/58303] C99 union initializers new union members clobber earlier data

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58303

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |mpolacek at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
An initializer for an union is a single value.  In C89, only the first member
of a union can be initialized; in C99/C11 you can use the designated
initializers to specify which member to initialize, but still only a single
member of an union can be initialized.