unions and pointers

[sans-hubris]

I was trying to do some funky coding with unions just for fun when I found out that if you have a pointer in the union and you try to assign a pointer to an instance of the union, the compiler errs out (in particular, I'm using gcc 2.95.3, fyi.)

E.g.:

union {
int * x;
int y;
}z;
z = (int)malloc(5*sizeof(int));
/* This does not seem to be legal. */


Is there a way around this?

[l01yuk]

I haven't tried this but

union a { /* Give yourself the choice. */
int * x;
int y;
} *z; /* Make this a pointer. */

z = malloc(5*sizeof(*z));


Don't cast malloc, #include <stdlib.h> instead. :)

[Strike]

Well, first of all, you are assigning an int to something that isn't an int. Secondly, why are you casting the result of malloc (a void *) to an int? And lastly, why are you malloc'ing space for int's and not for the union. l01yuk has the right idea, it seems to me.

[PrBacterio]

umm wtf? Its not really clear what you're trying to do here, but what you posted showed a severe lack of understanding of how pointers, unions and C in general work.

But I think you meant to do

z.x = malloc(sizeof(int) * 5);

or something along those lines...

[sans-hubris]

Strike was right, I made the cast incorrectly.

While l01yuk's code works, it defeats the purpose of what I was trying to do.

PrBacterio, I never use unions for normal coding (I find them dangerous.) As I said in my first post, this was just for something fun. I wasn't exactly sure how unions could work.

[jemfinch]

Originally posted by sans-hubris
PrBacterio, I never use unions for normal coding (I find them dangerous.) As I said in my first post, this was just for something fun. I wasn't exactly sure how unions could work.

They're not dangerous, you just gotta tag'em.

Jeremy