struct/union/pointer query- A Summary

[Ron Widell]

My thanks to one and all who responded to my previous query re. structures
in unions, and for patiently pointing out what should have been obvious (I
used to think that I had a keen eye for the obvious :-)).

In article <1298 at motmpl.UUCP> I wrote that I couldn't understand why this
wouldn't work:
> main()
> {
> 	union {
> 		unsigned short foo;
> #ifdef BURP
> 		struct burp {
> #else
> 		struct {
> #endif
> 			unsigned char fuz;
> 			unsigned char bar;
> 			} baz, *sptr;
> 	} glorp, *uptr;
> #ifdef BURP
> 	struct burp  baz, *sptr;
> #endif
> 	uptr = &glorp;
> 	sptr = &glorp.baz;
        ^^^^

The answer, to quote tim at crackle (Tim Olson):

|Without BURP defined, sptr is declared as an element of the union glorp
|(just like baz) -- it is not a "top-level" structure definition. 
|Therefore, you must access it like:
|
|	glorp.sptr = &glorp.baz;

or, as others mentioned (after uptr has been assigned):

	uptr->sptr = &glorp.baz;

So, when I wrote:
> BTW #2- What I *think* I'm defining is a union with three members: 1) an
> unsigned short (on the target machine it's an int). 2) a structure of 2
> unsigned chars. 3) a pointer to a structure of 2 unsigned chars.

schaefer at cse.ogc.edu (Bart Schaefer) pointed out:

|That's exactly what you did, but that isn't how you used it.

Once again my profound thanks to the following people:

arnor!freimer (Robert Freimer)
dfmeyer at cbnewsc.ATT.COM (dennis.f.meyer)
crackle!tim (Tim Olson)
"Jeremy A. Siegel" <bridge2.ESD.3Com.COM!jzs>
"Stuart R. Kemp" <cs.umn.edu!kemp>
math.rutgers.edu!bumby (Richard Bumby)
cse.ogc.edu!schaefer (Barton E. Schaefer)
Walter Murray <hpda!walter>
arnor!uri (Uri Blumenthal)
nluug.nl!nlgvax!smak!suhas
SSD.HARRIS.COM!shirono (Roberto Shironoshita)

Thanks, as well for being gentle with me (you must have known I'm a hardware
type who's trying to learn).

Regards,
-- 
Ron Widell, Field Applications Eng.	|UUCP: {...}mcdchg!motmpl!ron
Motorola Semiconductor Products, Inc.,	|Voice:(612)941-6800
9600 W. 76th St., Suite G		| I'm from Silicon Tundra,
Eden Prairie, Mn. 55344 -3718		| what could I know?