Anonymous Union Member Access

[Michael B Allen]

Consider the following structure with a union:

struct shape {
int type;
union {
struct circle c;
struct square s;
struct polydoodle p;
} u;
};

To access the circle member c one would do:

struct circle *c = &sh.u.c;

But is it legit to access union members through the union rather than
through the arm explicitly like:

struct circle *c = &s.u;

?

Mike

 

[xarax]

Consider the following structure with a union:

struct shape {
int type;
union {
struct circle c;
struct square s;
struct polydoodle p;
} u;
};

To access the circle member c one would do:

struct circle *c = &sh.u.c;

But is it legit to access union members through the union rather than
through the arm explicitly like:

struct circle *c = &s.u;

You'll need a cast, but otherwise it looks alright.
All union members are guaranteed to start at offset
zero.

struct circle *c = (struct circle *) &s.u;