Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!ukma!xanth!mcnc!ecsvax!uncw!session
From: session@uncw.UUCP (Zack Sessions)
Newsgroups: comp.lang.c
Subject: Re: VMS extensions
Keywords: VMS C
Message-ID: <334@uncw.UUCP>
Date: 6 Apr 89 14:50:39 GMT
References: <1321@Portia.Stanford.EDU>
Reply-To: session@uncw.UUCP (Zack Sessions)
Distribution: na
Organization: Math/Computer Science Department
Lines: 51

Quoting the VAX-C manual:

To illustrate the use of variant aggregates, consider the following code
example which doe not use variant aggregates:

/* the number on the right represents offsets */
struct TAG_1
{
	int a;		/* 0 */
	char *b;	/* 4 */
	union TAG_2	/* 8 */
	{
		int c;		/* 0 */
		struct TAG_3
		{
			int d;		/* 0 */
			int e;		/* 4 */
		} nested_struct;
	} nested_union;
} enclosing_struct;

To access nested member d you would have to use:

enclosing_struct.nested_union.nessted_struct.d

Using variant aggregates:

struct TAG_1
{
	int a;
	char *b;
	variant_union
	{
		int c;
		variant_struct
		{
			int d;
			int e;
		} nested_struct;
	} nested_union;
} enclosing_struct;

Here to access d you would use:

enclosing_struct.d

To convert to non-variant aggregates it would seem like you
would have to expand all references to any member in a variant
aggregate to the full reference and use non-variant aggregates.

Zack Sessions