Subj : Re: Why not unions
To   : comp.programming
From : Alex Fraser
Date : Thu Jul 28 2005 12:26 am

"Rob Thorpe" <robert.thorpe@antenova.com> wrote in message
news:1122490853.570267.241310@f14g2000cwb.googlegroups.com...
[snip]
> In C there are two main uses of unions:
> 1. To save space by using a single location to store many types of
> data.
[snip]
> union bar {
>   int x;
>   double y;
> }
> struct foo {
>   enum thing what_it_is;
>   union bar b;
> }
>
> foo.what_it_is describes what is in the union b, it could have values
> DOUBLE  or INT for example.
>
> It's only worth making this a union if we need the space.  If we don't
> then we could use:
>
> struct foo {
>   enum thing what_it_is;
>   int x;
>   double y;
>   char *z;
> }
>
> Which is simpler and easier to check.

Why do you think that?

FWIW, I would generally use an "unnamed" (not sure if that is the correct
term) union type declared inside the struct:

struct foo {
    enum thing what_it_is;
    union {
        int x;
        /* etc */
    } b;
};

Alex

.