c - Access to the actual member of a union by address

Question

I was wondering if can be posible to access the actual member of a union by the union address and not by the -> & . operators. If that is posible, is that allowed?

Answer 1

you can access the memory of the union using the addressof operation &(union)

e.g.

union foo {
  int32_t bar;
  int64_t baz;
} afoo;

void * address = &afoo;

But the point of a union is to allow transparent access to a 'shared' region of data that composed of different types; if you wanted char * access to the data, then you can use a char * member, and access the data in that manner.

pretending that the *address is a different type, we can use:

int64_t *abar = (int64_t*)address;
printf("%llu\n", *abar);