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From: wsmith@uiucdcsb.cs.uiuc.edu
Newsgroups: comp.lang.c
Subject: initialization of unions
Message-ID: <165600017@uiucdcsb>
Date: Sun, 25-Oct-87 18:10:00 EST
Article-I.D.: uiucdcsb.165600017
Posted: Sun Oct 25 18:10:00 1987
Date-Received: Wed, 28-Oct-87 20:45:50 EST
Lines: 39
Nf-ID: #N:uiucdcsb:165600017:000:1096
Nf-From: uiucdcsb.cs.uiuc.edu!wsmith    Oct 25 17:10:00 1987


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.

K&R say that if an initialization list is incomplete, the remaining fields
are initialized to zero, which works on all 4 compilers, if for example the
union is the last element of a structure and I do not leave a value for
that place. The difference occurs when I try to place a value into the
union field.  2 consider this to be an error, one bluntly saying: "unions
can not be initialized".  The other two allow the initialization to take
place if the first option of the union matches the value being placed in.

Which two are correct according to the new standard?

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

This ^^^  works on two and not on the other two.

struct foo2 {
	int l;
	union {
		char * pch;
		int a;
		} j;
	} unionvar = { 37 };

This ^^^  works on all four.

Bill Smith
ihnp4!uiucdcs!wsmith
wsmith@a.cs.uiuc.edu