From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeroen Dobbelaere <Jeroen.Dobbelaere@tvd.be>
To: Aurel Balmosan <ab@orga.com>
Cc: egcs-bugs <egcs-bugs@cygnus.com>
Subject: Re: Initialising an union.
Date: Wed, 19 Aug 1998 10:03:00 -0000
Message-id: <35DB0717.430E5814@tvd.be>
References: <35D842BF.93D35CB8@orga.com> <35D9C176.873FB5F6@tvd.be> <35DAB938.618E3FFE@orga.com>
X-SW-Source: 1998-08/msg00386.html
List-Id: <gcc-bugs.sourceware.org>

Yes, I forgot to say that this is only true for C++

(See http://www.cs.sbcc.net/~shouk/cppdraft/cd2/ for a copy
of the working paper)

(maybe something to add to the faq, although it is not the definitive
standard :( )

I don't know what it should be for C++.

Also note that in your example, you are using an **auto-variable** :

void test() 
{       union x X = { 0 }; 
        for(;;); 
        X.a++; 
} 

It also seems that I mixed up static/global variables and auto :

This is the relevant section for this problem :

 8.5.1  Aggregates                                      [dcl.init.aggr]
[..]

15When  a  union  is  initialized with a brace-enclosed initializer, the
  braces shall only contain an initializer for the first member  of  the
  union.  [Example:
          union u { int a; char* b; };

          u a = { 1 };
          u b = a;
          u c = 1;              // error
          u d = { 0, "asdf" };  // error
          u e = { "asdf" };     // error
    --end example] [Note: as described above, the braces around the ini-
  tializer for a union member can be omitted if the union is a member of
  another aggregate.  ]


It seems not to say anything about the initialization of remaining
bytes. Because those are on the stack, those (probably) wont be
initialized -> so you should explicitly initialize the member you need.


Aurel Balmosan wrote:
> 
[..]
> 
> Well in the ANSI-C books I have this is not defined in this way. It is only
> said that unions can now be initialised (ANSI-C version 2)
> 
> So it seems to not a bug in egcs-1.0.3a but what draft is it? C++ or ANSI-C?
> 
> Bye,
> 
>         Aurel.
> 
> --
> Aurel Balmosan           | Department SE-SW
> ORGA Kartensysteme GmbH  | phone: +49 5254 991 824
> An der Kapelle 2         | fax  : +49 5254 991 749
> 33104 Paderborn, Germany | mailto:ab@orga.com