Accessing child variables through higher level structures

Question

If I have these structures:

typedef struct { int x; } foo;
typedef struct { foo f; } bar;

Normally you would access x through

Answer 1

In C++, it is possible in two ways. The first is to use inheritence. The second is for bar to contain a reference member named x (int &x), and constructors that initialise x to refer to f.x.

In C, it is not possible.

Answer 2

In C (99 and onward) you can access the common initial sub-sequence of union members, even if they weren't the last member written to¹.

In C11, you can have anonymous union members. So:

typedef struct { int x; } foo;
typedef struct {
  union {
    foo f;
    int x;
  };
} bar;

---

1. Yes, that applies to structures. But according to the standard:
   • A structure pointer, suitably converted, points to the first member.
   • A union pointer, suitably converted, points to any union member.
   • So their location in memory is the same.