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From: rmasters@bbn.COM (Bob Masters)
Newsgroups: comp.lang.c
Subject: Re: initialization of unions
Message-ID: <4237@ccv.bbn.COM>
Date: Tue, 27-Oct-87 10:16:36 EST
Article-I.D.: ccv.4237
Posted: Tue Oct 27 10:16:36 1987
Date-Received: Thu, 29-Oct-87 22:15:42 EST
References: <165600017@uiucdcsb>
Reply-To: kgregory@ccy.bbn.com (Keith D Gregory)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 41
Summary: They may be initialized

In article <165600017@uiucdcsb> wsmith@uiucdcsb.cs.uiuc.edu writes:
>
>I have a question about initialization of variables in C.
>Kernighan & Ritchie do not speak of what happens when a union is
>attempted to be initialized.  The 4 compilers available to me disagree on 
>what is legal.
 
ANSI C has a specific way of initializing unions, which, as I recall is so
ambiguously worded as to be almost useless (allow 20 minutes to decipher :-)

As I recall (this was from several months ago, when I was writing a book on
Turbo-C . . . they didn't follow the standard . . .), unions are initialized
as if you were initializing their first element.  So . . .

union u1 {
    long   along;
    int    anint[2];
  } myunion = { 0x012345678L };
  
union u2 {
    int    anint[2];
    long   along;
  } yourunion = { 0x5678, 0x1234 };


. . . are both valid declarations, and (on a small-endian machine, such as an
'86) are pretty much equivalent.

>
>struct foo  {
>	union {
>		char * pch;
>		int a;
>		} j;
>	int l;
>	} unionvar = { "hello\n", 37 };
>

I believe that this should work on an ANSI-compatible compiler

-kdg